Showing papers in "Evolution in 1970"

Evolutionary strategies in lizard reproduction.

Abstract: Several investigators have dealt in a theoretical way with the evolution of reproductive rates and attendant life history phenomena (Cole, 1954; Lack, 1954, 1966, 1968; Murphy, 1968; Svardson, 1949; Williams, 1966a, 1966b). Tinkle (1969a) has applied evolutionary principles in an attempt to construct a general theory of the evolution of single-broodedness and iteroparity, of viviparity, and of clutch size and clutch number in lizards. Most of the data presented by him were qualitative. In this paper we pose a series of questions concerning reproductive strategies which have evolved among one group of vertebrates (the lizards), and provide quantitative data to answer them. We further present comparable data from birds, the vertebrate group most thoroughly studied in this respect. Finally, we suggest the weaknesses in studies of reptilian reproduction in the hope of stimulating future workers to collect data that are essential to answer these specific questions.

Convergent evolution of mediterranean-climate evergreen sclerophyll shrubs.

Abstract: It has been long noted that in areas of climatic similarity throughout the world the aspect, or physiognomy, of the vegetation is also similar (Humboldt, 1806; Griesebach, 1872). This relationship of climate to vegetation forms the very foundation of ecologicalplant geography. There has been a long history of attempts to utilize various nonfloristic, physiognomic characterizations of vegetation and to relate these to regional, local, and microclimate (DuRietz, 1931; Raunkiaer, 1934; Adamson, 1939; Cain, 1950; Cooper, 1961; Knight, 1965; Knight and Loucks, 1969). Although the details of the different research approaches have been subject to a certain amount of controversy the broad generalities are above dispute. Environmental similarity can produce growth form similarity no matter what the evolutionary history of the flora in question. In California, for example, within the chaparral vegetation, the dominant plants belong to such diverse families as the Ericaceae, Rhamaceae, and Rosaceae, yet all possess a large degree of growth-form similarity, i.e., deep-rooted, evergreen, sclerophyllous shrubs (Fig. 1) . Even more striking than this within-vegetation type homology is the homology found between vegetation growing in similar but disjunct climates. The mediterranean climatic type (summer drought, winter rain) occurs in California, South Africa, central Chile, southern Australia, as well as in the Mediterranean region. In all five of these areas the native vegetation has a similar appearance: a dense scrub dominated by woody evergreen sclerophyllous species. The isolation of these geographic areas and the almost complete taxonomic dissimilarity between their resident floras indicates that they have had distinct evolutionary histories (Table 1). The general life strategies of plants found in representative mediterranean climatic areas are similar (Table 2) . Droughtevading annuals predominate. Herbaceous perennials, which die back to the ground surface during the drought period, are also common. Similar proportions of these life forms are characteristic of the desert. The dominant life forms of the mediterranean climatic regions are evergreen trees and shrubs which tolerate the drought period. In deserts the tree form is generally absent and the shrubs, for the most part, lose all or a portion of their leaves during the summer drought. The severity of the mediterranean climate is apparent when the details of the seasonal climatic regime are examined. The seasonal course of temperature and soil moisture are shown for a representative Californian region (Fig. 2). During the summer months when temperatures are generally favorable for growth, moisture is limiting and atmospheric and soil drought prevails. When the rain returns in the winter and the soil moisture profile is recharged, temperatures are low and growth is further limited. Annuals germinate following the first winter rains but growth is very slow while temperatures remain cold. As temperatures increase in late winter and early spring, and while moisture is still available, growth greatly accelerates. As the upper soil profile dries out the annuals complete their life cycle. They survive the drought period as seeds. Thus there is but a brief period when conditions are favorable for vigorous plant growth (Major,

A model for the evolution of pinniped polygyny.

Abstract: Most persons who study the breeding behavior of seals and sea lions yield to the temptation to theorize about the evolution of the remarkable polygyny and impressive sexual dimorphism shown by these animals. I recently participated (Peterson and Bartholomew, 1967) in this long-standing and highly inferential tradition by helping to outline a verbal model based on ideas first suggested by Nutting (1891) and extended by Bertram (1940) and by Bartholomew (1952). The present paper undertakes to elaborate this model and to place it more firmly in a documentable behavioral context.1 The model has some general properties but in its present form it is applicable only to pinnipeds. Patterns of polygyny are too diverse to have a single evolutionary explanation. For example, sexual dimorphism is central to our pinniped model, but it has been apparent for many years (Huxley, 1938) that the functional role of sexual dimorphism varies markedly between different taxa.

Genetic variation in the horseshoe crab (limulus polyphemus), a phylogenetic "relic".

Abstract: To many early evolutionists, particularly those of the mutationist school, the existence of evolutionarily stable forms ("living fossils" or phylogenetic "relics") posed a difficult problem, and, even among contemporary biologists, the feeling that "a long-standing stability of organization seems antithetical to the concept of evolution" may persist (Volpe, 1967:140). In the early part of this century, it was popularly believed that stable or slowly evolving (bradytelic) lines lacked the genetic variation necessary for more rapid evolution as a result of having abnormally low mutation rates; as Mayr (1963) puts it, a lack of variation in time and space was interpreted as a reflection of genotypic stability. Largely because of the influence of Simpson (1944), Stebbins (1944), Schmalhausen (1949), and Dobzhansky (1951), the mutationists' interpretation of bradytely has now been all but abandoned by evolutionists in favor of the view that the principal factors controlling rates of evolution are to be found in the organism-environment relationship. Additionally, Mayr (1963 :304) has suggested that phenotypic "uniformity in space and time is due to a highly perfected 'buffering system,' in other words, to genetic homeostasis." The ecological hypothesis is well expressed in Simpson's (1944:141) conclusions that "the final and probably the most fundamental factor in the relationship is that bradytelic groups are so well adapted to a particular, continuously available environment that almost any mutation occurring in them must be disadvantageous" and that "bradytely results from the equilibrium of large breeding populations of animals specifically adapted to a continuously available environment that is relatively invariable . . . ." Yet, as Mayr (1963) notes, there is no evidence to refute (or to support) the hypothesis that bradytely results from loss of mutability. The recent development of electrophoretic techniques for demonstrating allelic variation at loci controlling enzymes and other proteins in natural populations (Hubby and Lewontin, 1966; Lewontin and Hubby, 1966) permits a test of the mutationists' thesis. The purpose of this study is to compare degrees of protein polymorphism and underlying genic heterozygosity in a classic phylogenetic "relic," the horseshoe or king crab (Limulus polyphemus), and in several representatives of horotelic lines (those evolving at standard rates) for which data are already available. Evidence of a level of genetic variation in Limulus similar to that in horotelic forms will support the modern ecological and homeostatic interpretations of bradytely. But if the mutationists' thesis is valid, Limulus should show an unusually low degree of polymorphism at its genetic loci. Limulus polyphemus is one of five living species of the Subclass Xiphosura, a group of marine arthropods usually placed with the Subclass Eurypterida (extinct giant water scorpions) in the Class Merostomata of the Subphylum Chelicerata. Following a period of adaptive radiation in the early and middle Paleozoic, the Merostomata became much less prominent after the Permian. Several Mesozoic forms are known in the Family Mesolimulidae, but by the Tertiary the fossil record is all but absent. There are presently three living genera, all belonging to the Family Limulidae, only one of which, Tachypleus, is known from the fossil record (Stormer,

Host specificity of fig wasps (agaonidae).

Abstract: For the development of seeds, the figs (Ficus spp.) are dependent upon small chalcidoid wasps of the family Agaonidae. No other means of pollination of fig flowers is available to the plant, and the wasps cannot develop anywhere except in the gall flowers of the fig.2 There has been considerable difference of opinion as to the degree of host specificity of the fig pollinators. For example, Baker (1961) did not fully accept the specificity of fig wasps, but in a later publication Baker and Hurd (1968) said that in the enormous genus Ficus a unique situation prevails in which almost every species of fig has a recognizably different wasp as a pollinator. The present paper evaluates the evidence concerning such specificity and its occasional breakdown. The female agaonids carrying pollen enter the young receptacles at the time the female flowers are ready for pollination (female phase). Wasps probably first pollinate all the female flowers (shortand long-styled) and next lay eggs in the short-styled ones. The flowers which are only pollinated develop normally and each produces a seed, while the pollinated flowers which also received agaonid eggs become "gall flowers," each nourishing a single wasp larva. The agaonid wasps reach maturity in a male-phase fig. Copulation takes place before the females escape from the galls inside the fig. After copulation, the females emerge from the galls and immediately go to the anthers, which become ripe synchronously with the softening of the fig and the emergence of the wasps inside of it. There is a difference in the way the wasps pick up the pollen from the anthers in the two subgenera of figs that reach the New World, Urostigma and Pharmacosycea. In Urostigma, exclusively pollinated by Blastophaga (Pegoscapus), the females emerge from their galls and at once go to the dehisced anthers. They pick out the pollen from the anthers using the mandibles and front legs, and move it to corbiculae or concavities located in the front coxae and in the mesosternum (Ramirez, 1969; see also Galil and Eisikowitch, 1968b and Galil and Snitzer-Pasternak, in press, for Ficus religiosa). Once the corbiculae are filled, the wasps go to exits made by the males through the fig wall and fly away. The pollen of most New World Urostigma is not shed from the anthers without wasp activity because the pollen sacs do not open sufficiently. In Pharmacosycea figs of the New World, which are exclusively pollinated by species of Tetrapus, the anthers dehisce and shed the pollen naturally and apparently without the help of the wasps; the wasps which are emerging from the galls inside the fig become completely dusted with it. They also eat it before leaving the fig. Once the newly emerged female wasps, dusted with pollen or carrying it in the corbiculae, escape from their ripe figs, they fly to another fig tree of the same species in which they developed and which pos1 Contribution number 1451 from the Department of Entomology, University of Kansas, Lawrence, Kansas. 2 Galil and Eisikowitch (1968a) divide the developmental phases of a syconium in a way which I have followed, thus: Phase A (Prefemale): young syconium prior to the opening of the ostiole. Phase B (Female): ostiolar scales loosen, female flowers ripen, agaonid and other sycophilous wasps penetrate into the syconium and oviposit into the ovaries. Phase C (Interfloral): wasp larvae and fig embryos develop. Ovaries occupied by the larvae are transformed into galls. Phase D (Male): male flowers mature, wasps reach the adult stage, fertilized female wasps leave the syconia via channels bored by the males. Phase E (Post-floral): both the syconia and the seeds inside them ripen.

Taxonomic diversity of island biotas.

Abstract: Students of biogeography since Darwin have focused disproportionately on oceanic islands. The prime bases for this interest have been the distinct forms which have evolved in the genetic isolation provided by islands and the ecological situation pertaining because the species successfully colonizing any island are but a small subset of the mainland species pool. One aspect of the latter effect which has received attention is that, within any higher taxon, the mean number of species per genus (S/G) on an island is usually lower than S/G for its presumed source area (MacArthur and Wilson, 1967). If it is assumed that congeneric species tend to resemble one another more in any measurable biological characteristic than do less closely related species, then the lower S/G on an island implies a more "diverse" biota on the island than on the source area. Although Williams (1964) pointed out that a random subset of any species pool has an expected S/G lower than that of the entire pool, Moreau (1966) and Grant (1966) attach significance to the lower S/G per se on islands, without regard for whether this S/G is lower or higher than expected, and attribute the lower insular value to ecological and/or evolutionary phenomena. In this paper I will first treat qualitatively the general distribution of the S/G ratio for random subsets of any species pool, then analyze the data for a series of well-studied island groups, and finally reassess the ecological and evolutionary ideas formulated on this subject in the light of the statistical treatment. THEORETICAL CONSIDERATIONS

Rapid population differentiation in a mosaic environment. i. the response of anthoxanthum odoratum populations to soils.

Abstract: Most environments are variable in both space and time. Plant species may cope with this variability by restricted microdistribution (Snaydon, 1962a), by wide adaptability of individual genotypes (Bjorkman and Holmgren, 1963; Bradshaw, 1965; Cook and Johnson, 1968), or by population differentiation and polymorphism (HeslopHarrison, 1964). Population differentiation is more likely to occur where environmental factors are stable in time but vary in space (Levins, 1962,1963; Maynard Smith, 1966). Soil factors have this type of variability (Beckett, 1967), but by contrast climatic factors are highly variable in time, and less variable over short distances. Localized population differentiation should therefore occur in response to the spatial heterogeneity of soil factors, provided that genetically determined intraspecific variation is available, and is responsive to selection. Intraspecific variation in response to soil nutrient factors has been found in a wide range of plant species (Vose, 1963; Epstein and Jefferies, 1964). Natural populations within plant species, collected from contrasting soil types, also frequently differ in their response to those soil types (Kruckeberg, 1951, 1967; Snaydon, 1962b; Nixon and McMillan, 1964; Ramakrishnan, 1965; Hutchinson, 1967), and the response of natural populations to specific nutrient or toxic elements in the soil is often correlated with the level of those elements in their native soils (Melchers, 1939; Jowett, 1958; Snaydon and Bradshaw, 1962, 1969; Antonovics et al., 1967; Hutchinson, 1968). It seems therefore that the necessary intraspecific variation exists, and has been subject to selection. Population differentiation over short distances, within both plant and animal species, has recently attracted attention (Jain and Bradshaw, 1966); selection experiments (Thoday and Boam, 1959; Streams and Pimental, 1961) and field studies (Creed et al., 1959; Briggs, 1962; Snaydon, 1963; Aston and Bradshaw, 1966; McNeilly, 1968) indicate that geographical isolation is not essential for population differentiation to occur. The rate of change of population structure has also been extensively studied. Population structure may change rapidly in response to contrasting environmental conditions, especially within relatively shortlived animal species (e.g. Dobzhansky, 1947, 1963; Kettlewell, 1961; Clark and Murray, 1962). Rapid changes in the population structure of plant species have also

Potential extinction through competition between two species of terrestrial salamanders.

Abstract: The research presented here concerns the relationship between the distributions of the plethodontid salamanders Plethodon cinereus cinereus (Green) and P. richmondi shenandoah Highton and Worthington. The purpose of this study is to present evidence that interspecific competition and microclimatic conditions may interact in these salamanders to limit the distributions of the species and that extinction may become a potential threat to one of the species when the other is more adept at exploiting these conditions. This paper describes the microgeographic distributions of the two species. Subsequent papers will give experimental data on interspecific competition and microclimatic conditions as factors limiting distributions. The distributions of closely related animal species often present difficult problems for interpretation. Lack (1944) felt that when two such species come into contact, interspecific competition has the potential to force them to one of four stable states: (1) one species will eliminate the other, (2) the two may occupy allopatric, but often contiguous, geographic regions, (3) they may live in sympatry but occupy different habitats or (4) they may occupy the same habitat but differ in food, or other resource, utilization. That any such arrangements do evolve through interspecific competition is poorly documented, although often inferred from indirect evidence (Miller, 1967). Indeed, Andrewartha and Birch (1954) question the biological importance of interspecific competition itself. Studies on the distributions of salamanders have been particularly unrevealing, and only two have critically attempted to define the factors influencing the interactions of related species-pairs. Hairston (1949, 1951) described the altitudinal separation of Plethodon jordani and P. glutinosus. The former usually occurs at high altitudes and the latter at lower elevations in the southern Appalachian Mountains, although there are areas where altitudinal separation breaks down and the two species occur sympatrically. P. jordani is apparently limited in distribution by moisture, since it fails to drop to the drier low elevations even in the absence of P. glutinosus. The distribution of P. glutinosus is possibly limited in some areas by competition, since it is able to exist at high elevations in the absence of P. jordani but often not in its presence. Hairston felt that there is geographic variation in the interspecific competition of these two species. Dumas (1956), from his study of two sympatric species of Plethodon from western North America (P. vehiculum and P. dunni), arrived at a conclusion somewhat different than that of Hairston. Dumas felt that the two species he studied are sympatric in geographic distribution with little or no competition for food due to the adverse physical environment limiting population size. There is, however, competition on a microgeographic scale for sites that are favorable with respect to moisture, with P. dunni displacing P. vehiculum from preferred sites. Hairston's study exemplifies state (2) and Dumas' study illustrates state (3) in Lack's system, although it is not clear whether or not these states are stable or are transitory indications of impending competitive exclusion. State (4) of Lack's system is demonstrated by two studies on populations of salamanders. Worthington (1968, 1969) showed that three species of eastern North American salamanders lay their eggs in the

Analysis of simple cave communities i. caves as islands

Abstract: Cave animals have fascinated evolutionary biologists since Darwin primarily because of their eye and pigment degeneration, and the extensive speciation they exhibit (Eigenmann, 1909; Valentine, 1945; Barr, 1968). On the other hand, ecological studies in caves have been few, and these have been for the most part descriptive in nature. In recent years several excellent reviews of cave ecology have appeared (Barr, 1967; Poulson and White, 1969). I will not attempt to summarize recent progress except to note that many investigators have concluded that cave populations are foodlimited. The stable cave environment has existed for relatively long periods of time. One of the important problems in stable environments is what are the major factors that influence diversity and structure of such communities (Sanders, 1968; Brooks, 1950; Lloyd et al., 1968; Poulson and White, 1969). Caves are a good place to study this question because caves contain simple communities, thus allowing investigation of all species except those that are very rare and difficult to find. In a series of three papers, I hope to shed light on certain aspects of the problem of control of species diversity in caves, both in terms of the number of species and their abundances.

Further genetic studies of the south amherst population of drosophila melanogaster.

Abstract: The genetic structure of the natural population of Dr-osophila melanogaster found in South Amherst, Massachusetts, was first outlined in a report by Ives (1945) based on studies which were initiated in 1931 and which became quantified in 1938. Changes in the structure of this population have been reported and discussed in Ives (1954) and in Band and Ives (1961, 1963, 1968). In the 1938-1946 period a high frequency of lethal chromosomes was found in early fall collections from this population together with a very low rate of allelism between the lethal chromosomes. It seemed probable then that only by selection against these recessive lethals when they were in heterozygous condition was their frequency kept from reaching substantially higher levels. At no time in the 1938-1958 period was there a high enough rate of allelism to enable one to observe if homozygosis might also act as an appreciable restraining factor in this population. In the joint studies of Band and Ives a significant correlation was found with certain weather factors and it was suggested that to some extent summer rainfall and, even more, the average daily temperature range during the week before the flies are collected have a strong influence on the frequency of lethal and semilethal chromosomes found in a given collection. Experimental studies by Band (1963) have in fact demonstrated just such a selective effect by temperature range. The continuity of the South Amherst population has been indicated by the recurrent appearance of the uncommon eye color mutant, cardinal-3. That mutant was found in the offspring of the first (1931) South Amherst collection, which was from a very large population growing on the fermenting corn silage in a silo on a small dairy farm owned by the author's father, and was reported in Plough and Ives (1934). It has appeared in a low proportion of the third chromosomes from the South Amherst population in nearly every year that second chromosomes from that population have been analysed for lethals, including 1969. These observations suggest that the fall population, which is sampled by collections from the author's porch, is a consistently large breeding unit of a continuous population. That population may, however, consist of several much smaller breeding units early in the summer when flies do not always come to the porch site in numbers sufficient for a meaningful quantitative test. Late in 1965, a search was initiated by Dr. James E. Carver, Jr., working on a N.I.H. postdoctoral fellowship, for a place in South Amherst where flies could be collected routinely in quantity early in the growing season. He found such a place at the Markert apple storage, about 5 km (3 miles) from the author's residence. Close to the storage is a large, continuous pile of rotten apples, which appears from Dr. Carver's ecological observations (to be published separately), and from the genetic data to be reported here, to be a major source of the South Amherst population. During the 1966-1969 period, collections have been made from at least the first and the last flies appearing each year in the 'Supported in part by contract number AT (30-1)2467 with the United States Atomic Energy Commission and in part by grant number GB-5680 from the National Science Foundation. 2 This paper is dedicated to Professor Th. Dobzhansky on the occasion of his 70th birthday.

Microevolutionary sequences as a fundamental concept in macroevolutionary models.

Abstract: Mechanisms of major evolutionary change have remained one of the more vexing problems in evolutionary biology. The long time periods associated with their operation precludes the use of experiments and direct observations for the elucidation of the mechanisms underlying transspecific changes. Paleontologists have supplied most of the direct observations of major phyletic evolution in plants and animals, but they have been severely limited in their efforts to clarify the associated evolutionary mechanisms because of the nature of the fossil record. Evolutionists are restricted to analogies and assumptions as the main bases for the formulation of theories explaining large evolutionary changes. Most earlier students assumed that evolution of new taxa or of new complex adaptive features resulted from some type of saltation; hence they believed that the mechanisms of transspecific evolution differed from those acting at the species level. They also believed that the known methods of microevolution could not explain the "fundamental differences" associated with the origin of a new complex adaptation or the rise of a new major taxon. These views mirrored the large gaps in the known fossil record at that time and still undiscovered or inadequately studied adaptations among living organisms. With the development of the synthetic theory of evolution beginning in the 1930's, many workers claimed that major evolutionary change occurred by the same mechanisms

Apomixis, polyploidy, and speciation in dichanthium.

Abstract: The grass genera Bothriochloa O. Kuntze, Capillipedium Stapf, and Dichanthium Willemet are united across the bridging compilospecies B. intermedia (Harlan and de Wet, 1963a; de Wet and Harlan, 1966). They include sexually reproducing diploids and apomictic polyploids, and Bothriochloa is further characterized by sexually reproducing polyploid species (de Wet et al., 1963). The sexual and asexual polyploid species are in a very active stage of evolution (de Wet, 1968a, b; Harlan and de Wet, 1963b). Mechanisms that contribute towards rapid speciation among the agamospecies will be discussed.

The population biology of annual grassland hemiparasites. i. the host environment

Abstract: Two traits are common to all hemiparasitic plants: the ability to form root grafts with other plants via haustoria, and the presence of functional chlorophyll. Beyond this, further generalizations are not easily made. Hemiparasites grow as annuals, biennials, perennials, woody shrubs, vines and trees in a variety of habitats ranging from equatorial to polar latitudes. The functional nature of each kind of host-parasite relationship will be related to many parameters, among which life form, physical habitat, breeding system, and host characteristics are important. In this continuing series, annual grassland hemiparasites have been singled out for study because of the interesting characteristics of the grassland environment. In California, annual grasslands range from coastal bluffs to hot inland valleys and montane foothills. Most of the species making up this community are alien; it is a new flora not more than 200 years old (Wells, 1964). Species diversity is usually high within and between hemiparasite sites (Thurman, 1966), however, dominance diversity is usually low within a site during any one year (McNaughton, 1968; Heady, 1958) and there can be great variability in the dominant species from year to year. Members of the genus Orthocarpus (Scrophulariaceae) are the most common hemiparasites in California grasslands. These herbaceous flowering plants gain water, minerals, and organic compounds from host plants via haustorial root connections. Haustoria are small, hemispherical, lateral swellings on the parasite roots which penetrate the host root cortex and connect the two vascular systems. Under laboratory conditions of ample water and nutrients, a majority of individuals in most population samples can complete their life cycles without depending upon a host, though they may remain quite small in some species. In nature seedlings may be free-living for up to several weeks in a continually moist soil. Eventually, most population members indiscriminately form haustoria with one or more adjacent plants, and the increased supply of water, minerals, and organic compounds produces the rapid growth phase characteristic of annual hemiparasites. Orthocarpus species and most of their hosts are annuals; consequently, the members of each Orthocarpus population must annually reestablish a successful relationship with one or more individuals from among many potential hosts. Dispersal is normally independent of host plants and their seeds, but exceptions have been noted (Atsatt, 1965). Germination as well is not dependent upon the presence of host plants as has been shown for the genus Striga (Saunders, 1933). Consequently, the annual reassociation of Orthocarpus individuals and their hosts is a random process. The purpose of this continuing investigation is to describe the functional nature of this facultative heterotrophism. We wish to reveal the selective pressures operating upon annual hemiparasite populations and the specific responses to these pressures.

On the maintenance of a shell pattern and behavior polymorphism in acmaea digitalis, a limpet.

Abstract: Crypsis is a common phenomenon in many animal groups and, with its attendant selective pressures, has been the subject of considerable discussion. It has been studied intensively in the snails Cepaea nemoralis and C. hortensis (Lamotte, 1959; Carter, 1967; Clarke, 1962; Cain and Sheppard, 1950, 1952, 1961; Owen, 1965; Sheppard, 1951). Briefly, Cepaea exhibit several colors and patterns which often match the habitat of the animal. Sheppard (1951) found that the thrush, Turdus ericetorum, selectively preys on color morphs of the snail, and Owen (1965) and Clarke (1962) report that the selection is frequency dependent or apostatic. This type of selection allows a highly diverse polymorphism to be maintained. Moths such as Biston betularia are also selectively preyed on by birds (Kettlewell, 1955) and the moths appear to actively select a matching background, enhancing their effective crypsis (Kettlewell, 1955; Sargeant, 1966). Colton (1916) described a polymorphism in Thais lapillus, the dog whelk, correlated it subjectively with background, and invoked weak natural selection as being responsible for reducing natural variety to a complex of inconspicuous forms. Moore (1936) found that the color of these whelks is a function of pigment quality of their food. In the limpet, Acmaea digitalis, two form complexes exist. The one, subjectively, is characteristic of beds of the gooseneck barnacle, Pollicipes polymerus

Evolution of pair cooperation in a tropical hummingbird.

Abstract: In contrast with the many species of birds that form pairs during the breeding season, hummingbirds, in general, have a promiscuous mating system. The male mates with the female, and the female carries out the remainder of the reproductive effort, including nest-building, incubating the eggs and caring for the young, unaided by the male. The only reports to the contrary are for Colibri coruscans, the Sparkling Violet-ear of the Andes of South America, in which the male may aid in incubating the eggs and caring for the young (Moore, 1947; Schafer, 1954). However, Ruschi (1965) reported that only females attended the six nests of this species he studied, one in the wild and five in captivity. A pair bond in most hummingbirds, then, is limited to the short time during which a male and a female must cooperate to insure successful copulation. During the breeding season, the typical situation in hummingbirds is for males to hold mating and feeding territories at flowering plants, from which they attempt to exclude all other hummingbirds. In many cases, the female is treated aggressively by the male, both before and after mating, in a manner similar to the treatment accorded other conspecific intruders into his territory. The present report discusses pair relations of Panterpe insignis, the Fierythroated Hummingbird, during the breeding season. In this species a longer-term pair bond is apparently formed. The male still does not participate in the actual nesting effort, but indirectly does aid the female in

Respiration in early tetrapods-the frog is a red herring.

Abstract: The key feature of the fish-tetrapod transition is the invasion of the land. Utilization of the resources there available requires solution of four special problems: locomotion, control of the milieu interieur, internal fertilization, and the use of gaseous rather than liquid sources and sinks for the respiratory gases. The last problem will be dealt with here. It may most simply be stated as "How did the earliest tetrapods breathe?" The recent literature contains two views regarding the breathing methods of the earliest amphibians, namely (1) that cutaneous respiration must have been important during the transition period (Szarski, 1962; Hughes, 1966; Rahn, 1966) and (2) that these animals had lungs that were filled by a quick pulsatile contraction of the buccal cavity, often described as air swallowing or pulse pumping, rather than by an aspiration mechanism (Cox, 1967; McMahon, 1969). There are certain obvious objections to these views. Cutaneous respiration seems inherently implausible as a breathing method for the earliest amphibians such as Ichthyostega (Romer, 1966). These fossils appear (1) to have been of very large size, i.e., 3 to 4 feet long, and (2) to have lived in coal swamps which presumably indicated a fairly warm climate; (3) many such forms, furthermore, show ossification on the flanks and belly and the epidermis of larger specimens was probably thicker and more keratinized. Pulse pumping as a method for replenishing the contents of the lungs is also unlikely because of the stiff flanks, containing solid, well-articulated ribs and often a sheathing of bony scales; Willem (1931) has already argued from similar evidence that stegocephalians used aspiration plus pulse pumping. The statements in the literature apparently represent an extrapolation from frog physiology rather than a response to observations of the fossil record. Do Recent frogs represent a red herring? Under the circumstances, it seems most appropriate to review the mechanisms of gas exchange, the options available to the transitional forms, and the probability and sequence for the changes that actually occurred. Such a review, within the framework of recent electromyographical analyses of air-pumping mechanics in the breathing of fishes, frogs, turtles, and crocodilians, is here offered. It suggests that the classical observations on frogs do not by themselves furnish a suitable base for speculations about the behavior and physiology of the earliest amphibians.

The reproductive behavior and the nature of sexual selection in scatophaga stercoraria l. (diptera: scatophagidae). vii. the origin and evolution of the passive phase.

Abstract: The reproductive behavior of the dung fly, Scatophaga stercoraria L, has been divided into a series of separate phases; eg searching, genital contact, etc (Parker, 1970b) These are mostly self-explanatory and occur in many animal species An exception, however, is the post-copulatory passive phase oif the male In S stercoraria the average density of males searching around fresh cattle droppings (the site of mating and oviposition) is very high, especially during the population peaks (Parker, 1970a) Females lay several successive batches of eggs and visit the fresh dung only to mate and oviposit (Parker, 1970e) Genital contact begins immediately after a female arriving at the dung is captured by a searching male After copulation the male adopts the passive behavior phase by raising his abdomen away from that of the female but otherwise retaining the same mount posture The female has considerable freedoim of movement and is quite free to oviposit; the only contact maintained by the male is the grasp of his front tarsi around the junction between her thoirax and abdomen The male's middle and hind legs rest on the dung surface Ovipositing pairs are attacked repeatedly by searching males and "take-overs" (where the attacker displaces the original male and takes possession of the female) are not infrequent (Parker, 1970d) The female initiates separation after oviposition, and her behavior also determines whether or not a passive phase is adopted by the male (Parker, 1970e) Females remain quiescent only when both fresh dung is present and they still have mature eggs to lay Otherwise they show "swaying" reactions during copula and immediately after which cause the males to separate without a passive phase These reactions resemble the rejection reactions shown by many unreceptive female Diptera The term "passive phase" may be defined as a stage of the male's reproductive behavior during which he remains mounted on or otherwise attached to the female but without true genital contact between the two sexes "Copula" or "copulation" is regarded as synonymous with true genital contact Sometimes the terms "amplexus" (literally, an embrace) and "tandem behavior" have been used loosely for situations resembling passive phases "Passive phase" is used because it cointra-sts, with the phase of active sperm transfer; it is not intended to imply general inactivity of the male Passive phase males often show vigoirous rejection reactions when attacked by single males, Passive phases occur infrequently in widely separated groups, of animals, though their adaptive significance has attracted little speculation and apparently no quantitative analysis The aim of the present paper is to investigate the possible selective values of the passive phase in S stercoraria, and to consider its origin and the method by which it may have evolved

Introgression across isolating barriers in wild and cultivated oryza species.

Abstract: Cultivated rice species and their wild relatives are differentiated into several groups mutually isolated by various types of reproductive barriers (Chu et al., 1969a). Their natural hybrids occur across the barriers. In West Africa, two cultivated species, Oryza sativa L. and O. glaberrima Steud. are often in mixed culture, while their respective wild relatives, O. perennis Moench subsp. barthii and O. breviligulata Chev. et Roehr. grow sympatrically as weeds. Hybrid swarms between glaberrima and breviligulata are frequently found, but natural hybrids of other species are rare (Oka and Chang, 1964). O. sativa is isolated from O. glaberrima and O. breviligulata by an F1 sterility barrier. O. perennis subsp. barthii is isolated from others by a crossing barrier and partly by F1 weakness and sterility (Chu and Oka, 1970). However, some barthii populations in West Africa were found to be contaminated by introgression. The junior author formerly reported that \"the African forms of perennis are of two types, one with a small number of panicles per plant, a small number of spikelets per panicle and high pollen fertility, and the other with the same characters in opposite\" (Oka, 1964, p. 86). Jachuck and Sampath (1967) also pointed out that some barthii strains varied widely in fertility and other characters and might be highly heterozygous. We often found off-types (or the second type mentioned above) of barthii among plants raised from seeds collected in natural

Comparative studies of seed proteins of species of gossypium by gel electrophoresis.

Abstract: Polyacrylamide gel electrophoresisof seed proteins offers a biochemical approach to the evolutionary aspects of plant speciation. The background and theory of polyacrylamide gel electrophoresis were thoroughly discussed by Ornstein (1964), and the method and application of the technique to analyze and compare human serum proteins were presented by Davis (1964). Amino acid changes within a protein, due to mutational changes, can result in altered protein migration rates when the proteins are compared in the matrix system of polyacrylamide. Therefore, since species differ genetically at many loci, the individuality of each plant species can usually be expressed according to its protein banding pattern. Steward et al. (1965), Boulter et al. (1966), and Sastry and Virupaksha (1967) modified the polyacrylamide gel electrophoretic technique so as to detect protein changes in developing and differentiating plant seedlings and to examine protein content of seeds. Many workers believe proteins from seed or other dormant tissue from plants represent a more stable reflection of the genomic state in a given species than that obtained from developing seedlings. Subsequently, their electrophoretic work further elucidated or confirmed taxonomic relations between species obtained previously by well known classical methods of geographical, morphological, cytological, and hybridization analyses. For example, Fox et al. (1964) with Leguminoseae, Vaughan

Sexual selection for size differences in two species of sandpipers

Abstract: The usual pattern of sexual dimorphism in birds is for males to be larger and more brightly colored than females. In a few families the opposite is true, and often correlated with the "reversed dimorphism" is a reversal of the roles of the sexes with respect to much of the reproductive behavior. Usually the kind of dimorphism present in a group, normal or reversed, is characteristic of all its members. In the sandpipers (Scolopacidae), however, "all stages of incipient reversal may be observed, but without providing a clue as to the selective advantages. Indeed, the shore birds are perhaps the most interesting family of birds as regards sexual size dimorphism ranging, as they do, from species in which the female is dominant and larger to others . . . in which the male is much the larger" (Amadon, 1959: p. 533). Recent discussions (e.g., Selander, 1966) of sexual size dimorphism in birds have emphasized its potential ecological advantages. This study is an attempt to determine the selective advantage of sexual size differences in two species of sandpipers, the Stilt Sandpiper (Micropalama himantopus) and the Least Sandpiper (Calidris minutilla). In these species females average slightly larger than males both in body measurements (Table 1) and weight, but there are no consistent sexual plumage differences. Both species arrive unpaired on their breeding grounds at Churchill, Manitoba, but begin nesting within a few days of arrival (Jehl, in prep.). Thus, there is selection for rapid pair formation. Courtship patterns are similar in the two species. Briefly, a male attracts a female to his territory through persistent flight singing, which is followed by ground displays associated with the choice of a nest site. As in virtually all other species of birds (Verner, 1964), the proximate basis for mate selection is unknown. One may hypothesize, however, that over-all size, or the size of a particular body part, might act as a secondary sex character to influence mate selection. If so, sexual size differences in these species could be ascribed to sexual selection. Because females average larger than males, one would predict that small males and/or large females would be among the earliest to pair; one might also expect size differences to be greater among early-nesting pairs. The possibility of nonrandom mating with respect to size can be investigated by testing for correlations between size and time of pairing.

Evolution of dioecy from gynodioecy.

Abstract: sions do not bear directly on the truth or falsity of my hypothesis concerning the relationship between conservatism and variation Long's citation of Bader's conclusions as a criticism of my weighting procedure appears to depend tacitly on an assumption fairly widely made by biologists: that the coefficient of variation is the only meaningful way to measure variability in organisms Since we know what selection operates ultimately on genetic variances and not on genetic coefficients of variation and since we are now faced with the case of a data set in which different ways of measuring "variability" lead to different and seemingly paradoxical conclusions, it would seem the coefficient of variation should be used somewhat more cautiously in biological investigations LITERATURE CITED

Self-fertility in maritime and zinc mine populations of armeria maritima (mill.) willd.

Abstract: There is evidence for considerable variability in breeding systems of plants. This variability can be seen in many ways: closely related species often differ from each other in their breeding systems; cultivated plants may differ from their wild ancestors; differences have been recorded between individuals within populations; selection for change in breeding systems has been successful on many occasions (Stebbins, 1957; Antonovics, 1968a). All this is powerful evidence for the idea that in plants the breeding system of a species is not a fixed and rigid characteristic but is capable of change under the influence of selective processes. If this is so we could expect to see evidence of this, particularly within a species which occupies a range of habitats, where particular environments or situations may evoke genetical modifications to the breeding system. Support for these arguments has been given by many people (e.g. Darlington and Mather, 1949). Recently Antonovics (1968a) has shown a high level of self-fertility in populations of two grass species inhabiting toxic waste heaps which he suggests has arisen as a result of selection for reduced gene flow. The present paper reports the situation to be found in Armeria maritima (Mill.) Willd., a species complex found in maritime areas and in inland zinc contaminated calamine areas of Europe.

Cynodont postcranial anatomy and the "prototherian" level of mammalian organization.

Abstract: The origin of mammals from synapsid reptiles occurred during the Late Triassic. Although evolutionary events both preceding and following that time were important to the ultimate development of living mammals, certain Late Triassic forms possess such an even balance of reptilian and mammalian characters that they are truly transitional between the two classes. It should be emphasized that this transition comprised a biological series of events, and that these are meaningful only when interpreted in biological terms. However, the usual techniques of direct observation and experimentation on living animals are unavailable for these unique biological events. Instead, investigations of mammal origins must utilize indirect means, viz., functional interpretations of transitional forms and comparative studies of primitive living mammals. This paper uses both approaches to evaluate the question of the kind of biological organization that characterized the transitional forms on or near the reptilemammal boundary. Some authors (e.g., Winge, 1941; Kermack, 1963; MacIntyre, 1967) have implied or overtly claimed that Mesozoic mammals were advanced little toward a mammalian level of organization, and that it was only in late Mesozoic or early Tertiary times that taxonomic Mammalia underwent the transition from a basically reptilian to a mammalian level of biological organization. Bakker (1968) claimed that advanced mammal-like reptiles and Jurassic mammals were no more mammalian in posture and locomotion than modern lizards. New evidence bearing on the origin of mammalian characters is here Dresented through (1) a functional interpretation of the postcranial anatomy of certain advanced mammal-like reptiles and (2) through the phylogenetic implications of monotreme biology. Cynodonts, a diverse group of PermoTriassic therapsids (mammal-like reptiles), possess a suite of cranial features indicative of a probable ancestral relationship to mammals. Among these features are ethmoturbinals, double occipital condyles, secondary palate (cf. Brink, 1956), jaw structure (Barghusen, 1968), and dentition (Crompton and Jenkins, 1968). Previously, the origin of mammals was obscured by an apparent hiatus in the paleontological record between the last major therapsid faunas of the early Triassic and the earliest Mesozoic mammalian faunas of the middle Jurassic. Recently, however, the remains of Late Triassic mammals have been recovered in relative abundance (Kermack, 1967a; Parrington, 1967); this new evidence now provides a more substantial basis for deductions on the derivation and initial radiation of Mesozoic mammalian orders. Crompton and Jenkins (1968) concluded that cynodonts are the most likely ancestors of mammals on the basis of similarities in dentition; the same conclusion was reached by Barghusen (1968) on evidence of the jaw apparatus. With a few exceptions (Gregory and Camp, 1918; Romer, 1922; Simpson, 1928, 1929; Brink, 1956; Parrington, 1961), students of early mammalian evolution have generally neglected the postcranial skeleton-primarily because postcranial material of Mesozoic mammals is relatively scarce or, when available, is

Genetics of lupinus. ii. the selective disadvantage of the pink flower color mutant in lupinus nanus.

Abstract: The flower color of Lupinus nanus Dougl. is normally blue except for the white area in the center of the banner. Burlingame (19 21) reported the occurrence of pink-flowered variants which Harding and Mankinen (1967) found to be Mendelian recessives (pp). Their frequency is low, generally less than 10-3, but a few populations have been observed with as many as 1 or 2% pink-flowered plants. These frequencies are characteristic of several flower color mutants and suggest a selective disadvantage of variant flower color. The purpose of the present study is to compare relative fitness values and two fitness components, viability and reproductive fertility, of the pink and wildtype genotypes in natural populations. In order to obtain estimates of relative fitness values, outcrossing rates and genotypic frequencies are estimated.

Experimental introgression in the genus phaseolus. i. effect of mating systems on interspecific gene flow.

Abstract: MATERIALS AND METHODS gested the use of at least one and preferably four sibbed generations to hasten the breakup of linkage groups. Stephens (1961) also recognized the possible importance of mating systems in determining the rate and extent of introgression. In this paper, the effects of three mating systems upon interspecific gene flow between two partially isolated diploid species are reported. Evidence is also presented for the rapid release of genetic variability in advanced backcross populations subjected to a single generation of self-fertilization. A preliminary report of this work has been published previously (Wall, 1966).

Measurements by dna renaturation of the genetic basis of parasitic reduction.

Abstract: It has been suggested that parasitic organisms have a simpler genome than their free-living counterparts. Measurements by reciprocal DNA hybridizations in vitro have shown that the parasitic plant Cuscuta californica has a smaller genome than several closely related autotrophic plants (Searcy, 1970). These studies have the shortcoming of detecting only the hybridization of the highly repetitive sequences of DNA; the non-repetitive sequences react too slowly to hybridize significantly under the conditions used (Melli and Bishop, 1969; Britten and Kohne, 1968). The size of the genome may also be determined by DNA renaturation. Denatured DNA fragments can be made to renature in vitro, forming a specifically base-paired structure as in native DNA (Marmur and Doty, 1961). As predicted theoretically, and as confirmed empirically, the rate of renaturation is inversely related to the molecular weight of the entire DNA molecule of phages and bacteria (Marmur and Doty, 1961; Bolton et al., 1965; Britten and Kohne, 1968; Wetmur and Davidson, 1968). The DNA of higher organisms renatures faster than would be predicted from the haploid complement of DNA because of the presence of highly repetitive DNA sequences (Waring and Britten, 1966; Britten and Kohne, 1968). However, the rate of renaturation of the slowest reacting components can be used to measure the "kinetic complexity" of an organism, which is a measure of the total number of different sequences in the DNA of an organism (Wetmur and Davidson, 1968).

The b-chromosome system of myrmeleotettix maculatus (thunb). iv. the dynamics.

Abstract: A necessary first step in the analysis oJ the population genetics of a given species is the adequate description, both in space and in time, of the genetic variation present in different populations of that species. Such variation may be studied in terms of two principal differences. First, allelic variation at individual loci, and second. variation in the structure and/or the number of chromosomes. Both, in fact, frequently lead to the development of polymorphic facies. Those associated with allelic variation are now relatively well understood for they have pronounced, often dramatic, effects on the exophenotype, effects which greatly facilitate an analysis of their adaptive roles. Thus allelic polymorphism is associated with mimicry in butterflies, with camouflage in moths and snails, with resistance to malarial parasites in man, and with floral biology in primroses (Sheppard, 1967). By contrast, most of the known chromosome polymorphisms are exophenotypically cryptic in character. It is often assumed that such polymorphisms are concerned, in some undefined way, with biochemical effects (see for example Wallace, 196,8), but the balance of evidence to date is that chromosome polymorphisms are expressed initially in the endophenotype rather than the exophenotype (John and Lewis, 1966). Coupled with this, the endophenotypic effects they promote can be either supplemented or counteracted by other components of the genetic system. Their study and their analysis is thus both more complex and more exacting than that of the conventional allelic nolvmornhisms. It comes as no surprise, therefore, to find that in very few instances have we any real appreciation of the factors which govern the presence or the frequency of particular chromosome polymorphisms in particular populations. British populations of the mottled or club-horned grasshopper, Myrmeleotettix maculatus, are polymorphic with respect to the presence of supernumerary or Bchromosomes (Barker, 1960; John and Hewitt, 1965a, b). These extra elements have no obvious immediate effect on exophenotype, as has been demonstrated by a study of five populations with from 10% to 40% B-chromosomes, in which five morphological characters were scored for each individual. The characters were (1) the number of stridulatory pegs per hind leg, (2) average length of tibiae (3) average length of femurs, (4) average length of wings, and (5) number of segments per antenna. These particular characters were chosen since they are important in a range of functions, from courtship and species recognition to movement and dispersal, and are probably influenced by a variety of developmental pathways. Table 1 contains a brief summary of the results from these five populations, all of which occur in a parkland about 3 miles across. There is no consistent picture with regard to differences between non-B and B-containing individuals within or between populations. The reason for considering the between-individual and within-individual variances, is because of the established effect of B-chromosomes on the chiasma frequency. Individuals with such supernumeraries have higher mean cell chiasma

The genetic basis of crossing barriers between oryza perennis subsp. barthii and its related taxa.

Abstract: Oryza perennis Moench, distributed throughout the humid tropics, comprises four main geographical forms, Asian, African, American, and Oceanian (Morishima, 1969). The African form was considered by Tateoka (1963) to be O. barthii, but the present writers take it as a subspecies of O. perennis (d. Chandler, 1964, p. 251-2). For convenience, it is simply called barthii in this paper. In West Africa, four species having the so-called A genome often grow sympatrically, i.e., O. perennis (barthii), O. sativa (introduced from Asia), O. breviligulata, and O. glaberrima. Natural hybrids between them are rare, however, except between breviligulata and glaberrima (Oka and Chang, 1964). As reported in this paper, barthii was found to be isolated from its related taxa by a crossing barrier. To estimate the genetic basis of the crossing barrier, histological and genetic investigations were made in crosses with barthii.

Natural crossing between apis mellifera adansonii and apis mellifera ligustica.

Abstract: One of the reasons advanced for the extraordinary success of the African bee Apis mellifera adansonii in its new environment in South America is the supposed mating advantage of the African drones. On the other hand, another factor may be involved. Some researchers have proposed the hypothesis that a sort of sexual isolation might have evolved between A. m. adansonii Latr. and Italian bees, A. m. ligustica Fab. The experiments reported here were done in order to provide an evaluation of these hypotheses. A total of 41 nuclei, with three combs and about 2 kg of bees in each, were utilized. Each of 20 nuclei had one African virgin queen; each of the other 21 had one Italian virgin queen. One very strong hive harbored 1000 drones, 500 of which were Italian and 500 African. Queens were raised by the Doolittle method. Drones were raised from unfertilized eggs laid in a comb drawn from drone foundation. The rearing schedules were planned in such a way that the queens were 4 to 5 days old (nuptial flight age) when the drones were 11 to 14 days old (completely matured). The nuclei, complete with three combs, bees, and one virgin queen each, were put in an opening in a Eucalyptus forest (Rio Claro, Brazil), about 5-6 km from the next bee yard. They were distributed in a circle of 10meters radius around the hive with the drones. Each nucleus entrance was provided with a queen excluder which was

The genetics of dacus oleae. iv. relation between adult esterase genotypes and survival to organophosphate insecticides.

Abstract: The main bulk of adult esterases in the olive fruit fly Dacus oleae (Gmel) is controlled by two autosomal and independent genes, gene A and gene B. Gene A synthesizes an acetylcholinesterase and gene B a pseudocholinesterase or a lipase. Both genes are highly polymorphic in natural populations. More than 15 active alleles plus one silent allele have been found for gene A; more than 10 active alleles plus one silent in gene B. (Zouros et al., 1968; Zouros and Krimbas, in press; Krimbas and Tsakas, in press.) Most of the Dacus populations in olive orchards in Greece have been under control for the last few years with an organophosphate insecticide, dimethoate. It is generally accepted that organophosphate esters kill insects by inhibition of their cholinesterases (for a review of the "cholinesterase hypothesis" see O'Brien, 1960). Since both esterase enzymes controlled by genes A and B are cholinesterases or related to them it seemed interesting to investigate the action of dimethoate, acting as a selective agent, on genes A and B polymorphisms. Laboratory experiments dealing with this question are reported below.