Showing papers in "Evolution in 1968"

Adaptive significance of pigment polymorphisms in colias butterflies. i. variation of melanin pigment in relation to thermoregulation.

Abstract: The identification of the selective forces acting on natural variation in a population of organisms may be a formidable task. Only a few such identifications have been made, as in the studies of Cain and Sheppard (1954 et seq., summarized by Ford, 1964) and others on polymorphism in Cepaea snails, or the studies of Kettlewell (summary: Kettlewell, 1961) on industrial melanism in moths. The wing pigmentation of pierid butterflies presents many opportunities for this sort of analysis. Much natural variation in this system has been noted in the genera Pieris and Colias (Bowden, 1961, 1963; Gerould, 1923; Remington, 1954). These insects deposite two kinds of pigment in their wing scales: melanin, which is black, and pteridines, which may be white, yellow, orange, or red. The wings of different Colias species may possess any of the latter shades as

Pollination by Euglossine Bees

Abstract: The relationships between some orchid flowers and male euglossine bees were first observed in Darwin's time (Criiger, 1865), but the peculiarities of these interactions have been recognized only within the last decade. Our knowledge of the relationships has increased greatly in recent years, especially through the efforts of Dodson (Dodson and Frymire, 1961, etc.). While our understanding is still quite imperfect, its botanical aspects are relatively clear, and a discussion of euglossine pollination from this viewpoint may be of value. The tribe Euglossini includes six genera; the males of the four non-parasitic genera, Eufriesea, Euglossa, Eulaema and Euplusia, show a characteristic behavior pattern on many flowers. The bees are attracted primarily by odor. When they visit an euglossine flower, they brush on the surface of the flower with pads of hair on the forefeet. The bees characteristically brush for a short time and then hover near the flower while scrubbing their legs together and evidently placing some substance in their inflated hind tibiae. The bees usually repeat this behavior several or many times, sometimes remaining as long as 90 minutes at one inflorescence. Dodson and Frymire ( 1961 ) suggest that the bees become somewhat inebriated during their visits at orchid flowers. Vogel (1963, see also Dressler, 1967) has suggested that the bees are gathering a terpenoid "Duftstoff," or odor substance, from the surface of the flower and placing this in their tibiae, but the nature of the substance and its role in the biology of the bee are both problematical at present. The flowers which are visited only by males usually lack nectar, but are very fragrant. The females, of course, visit and pollinate many nectarand pollen-producing flowers, but I will use the phrase "euglossine pollination" only for the special relationship which involves the male bees. Some 30 genera of orchids (including relatively unrelated groups) show this relationship with the euglossine bees, as do some species of Anthurium and Spathiphyllum (Araceae) and Drymonia and Gloxinia (Gesneriaceae). It should be emphasized that the euglossine bees do not obtain their food from these flowers, but visit a variety of other flowers which produce nectar, especially Apocynaceae, Marantaceae and some Rubiaceae. SPECIFICITY

EVOLUTIONARY PROCESSES IN POPULATIONS OF COPPER TOLERANT AGROSTIS TENUIS Sibth.

Abstract: A considerable number of genecological studies on many plant species have described differentiation into local populations, amongst which those of Turesson, Gregor, and Clausen Keck and Hiesey are of note. These, and the majority of subsequent works on this subject assumed the paramount importance of natural selection in the evolutionary process. Because differences in morphology, physiology, etc., could be found between populations, natural selection was assumed to have brought about such differences; evidence for the occurrence of natural selection was indirect. In the plant kingdom direct evidence in the form of data showing changes in gene frequencies between generations is scant. The studies of Kemp (1937), Sylven (1937), Charles (1964), Barber (1966), and Aston and Bradshaw (1966), are exceptions. In the animal kingdom by contrast, the early work of Bumpus (1898), and di Cesnola (1907) on the snail Helix abustorum showed the occurrence of such changes. In more recent years, the role of natural selection in animal populations has received considerable attention, of which the works of Kettlewell (1961) on Lepidoptera, Sheppard (1958) on Cepea nemoralis, and Kurten (1964) on Ursus spelaeus are notable examples. The adult plants found in any natural population represent the resultant of the interaction of natural variation, gene flow, and natural selection, in otlier words, the status quo. Plants raised from seed produced by such populations, by contrast, show the potential variability of the population before the operation of selection. A

Adaptation to heterogeneous environments. i. variation in heterophylly in ranunculus flammula l.

Abstract: A population of organisms is adapted for existence in a constant environment when its individuals are adequately equipped both physiologically and morphologically for maintenance, growth and reproduction. The population then has what is called immediate fitness. But, of course, no environment is constant; all organisms must cope with change or heterogeneity both within and between generations. This they do through individual and population adaptability. Individual adaptability has been referred to in many ways, for example, as individual ecological amplitude, plasticity, phenotypic flexibility (Thoday, 1953), individual homeostasis (Lewontin, 1957) and buffering (Allard and Bradshaw, 1964). It depends basically on the physiological capabilities of the organism and is manifest as conformance or its obverse regulation (homeostasis) in morphogenesis, physiological maintenance, procreation and behavior. Whether conformance (plasticity) or regulation (stability) is the more adaptive solution for an organism faced with environmental heterogeneity depends on the peculiarities of the organ systems affected and the extent of the environmental change. Constancy can be preserved in critical attributes such as temperature, moisture, or photosynthesis only by changing some other component or attribute of the system. Sometimes the change is rapidly reversible (homeostasis in the sense of Cannon, 1932), sometimes slowly reversible (acclimation) and sometimes irreversible. The change may not show outwardly, in which case it is purely physiological, or the physiological response may have a morphological effect, in which case it is morphological as well.

Local gene dispersal in phlox.

Abstract: The local population ideally is composed of an aggregation of organisms sharing in a common gene pool and exchanging genes freely (Wright, 1931, 1943a, 1949). Such freedom, however, rarely is achieved in nature, for the dispersal of genes is highly leptokurtic (Dobzhansky and Wright, 1943, 1947; Bateman, 1947a, 1950; Griffiths, 1950; Colwell, 1951). Within a local population of outbreeding organisms, this form of gene dispersal leads to the formation of a series of overlapping panmictic units referred to as "neighborhoods" (Wright, 1940, 1943a, 1946). Knowledge of the neighborhood structure of plant and animal populations is meager. In animals, neighborhood studies have been conducted only on Drosophila (Dobzhansky and Wright, 1941, 1943, 1947), Cepaea (Lamotte, 1951) and Sceloporus (Kerster, 1964). In plants neighborhood investigations have dealt almost exclusively with wind-pollinated trees including Fraxinus, Pseudotsuga, Populus, Ulmus, Picea, Cedrus (J. Wright, 1953) and Pinus (Bannister, 1965); a notable exception is the work on the entomophilous, annual herb, Linanthus parryae (Wright, 1943b). To the authors' knowledge, the neighborhood structure of populations of perennial herbs has never been determined. The work discussed below was undertaken to fill this void. The purpose of this paper is to consider intrapopulation gene dispersal and the type of neighborhood engendered by the dispersal pattern in the self-incompatible, perennial herb, Phlox pilosa L. Phlox pilosa is one of the most highly diversified species in the genus, and has evolved a series of subspecies and races fitting its ecologically diversified area (Wherry, 1930, 1955; Levin and Smith, 1965). The species is a conspicuous element of the spring flora of mesic prairies and open woodlands throughout much' of the eastern United States. Colonies of P. pilosa contain from tens to thousands of individuals, and often display marked exomorphic variation. Pollination is performed by an array of insects, the Lepidoptera being especially suited for the task (Grant and Grant, 1965). Seed-set in natural populations is about 40%, i.e., the triovulate capsule yields an average of 1.2 seeds (Levin and Kerster, 1967a). Seeds are ripened during the early summer and scattered by the force of the dehiscing capsule; there are no special mechanisms for longdistance dispersal. Neighborhood determinations were made on three colonies in Cook County, Illinois. The colonies inhabited undisturbed sand prairies, and each was composed of several thousand plants which occupied an area in excess of 1000 M2. Colony designation (I, II, III) is assigned on the basis of density, colony I being the most dense. Data on pollen and seed dispersal and density were collected from each colony, and synthesized for neighborhood calculations.

Studies on competition in rice. iii. the mechanism of competition among phenotypes.

Abstract: The previous papers in this series (Jennings and de Jesus, Jr., 1968; Jennings and Herrera, 1968) concerned the magnitude and direction of interphenotypic competition in varietal mixtures and hybrid populations of contrasting plant types of rice (Oryza sativa L.). Relative yielding ability of the components of the mixtures was established from long-term yield trials of material grown in pure stand. It was concluded that competitive ability and agronomic worth were negatively associated in the materials studied under the agronomic and environmental variables provided. There are many basic implications and consequences of these findings to plant breeders, geneticists, and students of evolution. Their universality depends, in part, on a fuller understanding of the mechanism of competition and competitive ability. The literature contains many descriptions of the effect of competition on reproductive rates of organisms. Comparable attention, however, has not been given to such critical questions as: (1) What are the effects of competition on plant development? (2) At what growth stage does competition begin? (3) What are the plant characters that confer competitive ability? (4) What is the factor for which rice plants compete? Answers to these questions are required to increase understanding of the phenomenon of competition. This paper treats these aspects.

The role of competition in the evolution of migration

Abstract: One of the major objectives of modern ecology is analysis of the role of ecological processes in the evolutionary origin of adaptations. The problem of the origin of migration, however, has received little attention from this standpoint. Even for birds, in which the phenomenon of migration has been a major focus of research, most attention has been directed to the study of proximate factors important in initiating migration and the physiological processes and orientation mechanisms involved in the actual movements. Few studies have concentrated on the ultimate factors responsible for the origin of these complex mechanisms. General theories of the evolutionary origin of bird migration have been in existence for a long time. Thomson (1926) and Lincoln (1939) have summarized early theories, which' tend to fall into two main groups: (1) northern ancestral home theories, and (2) southern ancestral home theories. Northern ancestral home theories assume that most presently migratory forms were permanent residents in preglacial northern areas corresponding approximately to their present breeding ranges. With advance of continental glaciers and attendant climatic changes these birds were forced southward, from where they either attempted to return yearly to breed as close to their ancestral home as possible, or in some way retained a racial memory of the ancestral home, to which they were able to return seasonally following glacial retreat. It is often suggested that the stimulus for these return movements is the crowded conditions created in tropical and subtropical areas due to the northern birds being forced south. Southern ancentral home theories assume that most present migrants were originally permanent residents in southern areas, possibly corresponding to their present winter ranges. Following glacial retreat these species began to invade seasonally favorable northern areas for breeding as a result of competition for food or breeding sites in southern areas. Some authors (Berlioz, 1950; Dorst, 1961) have suggested the operation of both of the above patterns. Although these ideas have received extensive criticism (Mayr and Meise, 1930; Wolfson, 1948; Moreau, 1951) they have found their way in almost unmodified form into some recent textbooks of ornithology (Wallace, 1955; Welty, 1963). Mayr and Meise (1930) have suggested that the existence of areas with seasonally favorable and unfavorable conditions, rather than the occurrence of glaciation, is the condition required for the evolution of migration. They suggest that the normal reproductive excess, primarily through competition for food, is the factor favoring development of mechanisms allowing seasonal occupation of such areas. Although recognizing that migration must thus have existed in preglacial times, they conclude that, due to the great restriction of migration routes which must have occurred during glacial maxima, modern migration route patterns are almost entirely post-glacial in origin. They show that extreme crowding of birds in tropical and subtropical areas during glacial maxima is unlikely, and hypothesize that changes in distribution patterns and migration routes during glacial advances and retreats are the results of extinction of local populations and dispersal resulting from normal reproductive excess. Intraspecific competition and intensification of migratory drive are suggested as factors important in the elongation of migration routes and the origin of "leapfrog" patterns in which races breeding farthest north winter

Social mimicry; character convergence versus character displacement.

Abstract: In an earlier discussion of social behavior (Moynihan, 1960), it was suggested that there will usually be very strong selection pressure for or against the development, or maintenance, of similarities between any two species which come into contact with one another. Or-and this is not quite the same thing-for or against the development or maintenance of conspicuous differences. The term "social" is used in the broadest possible sense here, to include all reactions, even hostile or sexual, between two or more individuals. See also below, p. 321. These selection pressures probably are correlated with, and actually causally related to, another general aspect of social behavior. It usually will be advantageous for any reaction between individuals, of the same or different species, to be as "definite" (usually overt) as possible. If only because definite patterns usually are more rapid than inconclusive or highly ambivalent reactions. The importance of "saving time" has been stressed by a number of students of animal behavior (see, for instance, the comments by Marler, in Blair, 1961:86); but it has been frequently overlooked in actual practice. Most species of animals are preyed upon by something; and almost all kinds of social activity may render an individual conspicuous to predators. It obviously may be advantageous to keep periods of conspicuousness as brief as possible. The time saved by abbreviating a social reaction can also be devoted to useful "maintenance" activities such as feeding or drinking or resting. The following paper will be primarily a review of some of the different factors favoring divergence or convergence among species. Special attention will be paid to certain types of convergence (based on new information obtained by recent studies of neotropical species). This will be supplemented by a somewhat speculative attempt to determine the "typical" temporal relationship, i.e. the usual sequence, of divergence and convergence among species which show (or have shown) both tendencies at different stages of their history.

Size-fecundity relationships and their evolutionary implications in five desmognathine salamanders.

Abstract: The plethodontid salamander genus Desmognathus comprises seven species according to current taxonomy, of which six occur in, and four are endemic to the Appalachian Mountain system of eastern North America. Over most of the southern Blue Ridge Physiographic Province several of these forms may exist sympatrically. An apparent maximum of sympatry occurs in the Balsam Mountains of southwestern Virginia, where five species, D. quadramaculatus, D. monticola, D. fuscus, D. ochrophaeus, and D. wrighti occur in abundance. Organ (1961) studied the ecological relationships and population dynamics of these species at Whitetop Mountain and Mt. Rogers in the Balsam Mountains. Hairston (1949) compared the ecologies of D. quadramaculatus, D. monticola, D. ochrophaeus, and D. wrighti in the Black Mountains of North Carolina where those four forms occur sympatrically. Both authors found that, in the order given above, these species form a series in which decreasing size is paralleled by an increasing tendency toward terrestrial habits. Organ further found that the trend is also paralleled by increasing juvenile survivorship. He concluded that heavier juvenile mortality is associated with aquatic sites, and that D. quadrarnaculatus, D. monticola, D. fuscus, D. ochrophaeus, and D. wrighti represent an evolutionary trend in which selection has favored progressively more terrestrial habits. Size and egg production are positively correlated in the genus Desmognathus, as they are in many animals. Organ (1961) also emphasized that the larger species lay larger clutches than the smaller ones, and that the evolutionary trend within the genus has been "the gradual transformation of a population with a high egg production and low survival into a population with low egg production and a high survival to maturity." He found no differences in number of clutches per year or age at maturity that might compensate for differences in clutch size. This paper attempts to further explore and compare the relationships between size and fecundity among the five sympatric species of Desmognathus and to elaborate on the hypotheses drawn by Organ relative to evolutionary trends in reproductive habits. In particular I have sought to determine whether fecundity differences among the five species are explained simply by differences in their sizes, or whether sizefecundity relationships are more complex.

Studies on competition in rice i. competition in mixtures of varieties.

Abstract: Cultivated rice (Oryza sativa L.) may be loosely differentiated into tropical and temperate variety groups separated geographically, morphologically in vegetative character associations, and yielding potential. The thousands of tropical varieties are distinct in having vigorous seedling and early vegetative growth; large, pale-green, and lax leaves; tall, weak culms; sensitivity to photoperiod and/or late maturity; profuse tillering; strong grain dormancy; appreciable grain shattering; low yield response to nitrogen; and low to, moderate yield potential (Jennings, 1966b). This tropical plant type is well adapted to a monsoonal climate and relatively primitive cultural practices, but fails to respond to improved agronomic practice. Improved spacing procedures, fertilization, and water and weed control do not increase yields of the tropical plant types to levels comparable with those grown in temperate countries. Varietal improvement in tropical Asia has been confined largely to selection within, and hybridization among, local varieties, and little improvement in yielding ability has been realized. A concerted effort has been made in several countries, however, to increase variability by hybridization of local varieties with temperate types, mostly japonica varieties from Japan. But again, despite considerable international effort, little success has been achieved. Although such indica X japonica crosses show considerable hybrid sterility, and there is a progressive increase in indica characters from generation to, generation (Oka, 1957, 1958), a recent review of the subject (Jennings, 1966a) contended that early generation sterility is not a prime cause of breeding failure. Most breeders in the tropics have concluded that the bulk breeding method used in the plant improvement programs has given particularly discouraging results. Bulk breeding, especially with progenies of crosses involving contrasting plant types, results in a progressive loss from generation to generation of desired intermediate recombinants and types resembling the introduced parental plant types. Breeding materials, objectives, and procedures followed at The International Rice Research Institute are determined by the principle that certain morphological and physiological characters determine grain yield potential (Tsunoda, 1965; Tanaka et al., 1966). This concept of plant type involves strict selection for specific combinations of leaf dimensions, leaf color and arrangement, culm height and tillering (vigor and arrangement), early maturity and insensitivity to photoperiod, as traits associated with productivity, nitrogen responsiveness and lodging resistance (Jennings, 1964; Jennings and Beachell, 1965). As the fundamental objective of the program is to, increase yield of tropical varieties by 100 to 300%, it follows that existing tropical types must be drastically modified in gross morphology (Beachell and Jennings, 1965). The breeding program based on these principles has resulted in rapid and dramatic progress. Experimental and farm yields of fixed lines of tropical indicas crossed with temperate indicas and japonicas, grown in several countries under careful management, have exceeded 10 ton/ha and averaged from 5 to 9 tons compared with 2 to, 4 tons for local varieties grown under the same conditions (International Rice Research Institute, 1967). This rapid progress is in contrast to the situation that has prevailed throughout tropical Asia for so long and questions the

The beginnings of primates.

Abstract: When and from what mammalian group did primates originate? This question cannot yet be answered as accurately as students of Cretaceous and early Tertiary mammals would like. Although the evidence is still fragmentary and meager, however, the beginnings of primate radiation and their origin can be relatively well recognized. The insectivore-primate transition and the taxonomic boundary have been referred to, mentioned, and occasionally briefly and vaguely discussed in the literature. In discussing the insectivore-primate boundary, one is restricted mostly to known changes and inferred adaptations of dentitions, and to the sparse evidence offered from the pertinent cranial anatomy. Many teeth, dentitions, and a few skulls of Cretaceous and early Tertiary insectivores, condylarths, and primates are the only facts that serve as the basis of the present evaluation. The only inferred evidence that is used relates to dietary habits of some of the fossil forms. This inference is largely based on the vaguely consistent dietary habits of recent primates, that is, on sound behavioral and physiological facts. It was clearly recognized by Simpson (1959:268) that the most primitive known prosimians ". . . had acquired a rather vague but real grade distinction from the primitive insectivores." McKenna (1963), in spite of the title of his fine study of Paleocene and Eocene apatemyids, did not specifically discuss the primate-insectivore boundary. The same author in his 1966 paper on the origin of the primates, however, gave a very penetrating, accurate, and relatively detailed examination of some characters (with emphasis on the origin of the bulla and changes in the carotid circulation) of practically all known groups of mammals that have immediate bearing on the nonprimateprimate boundary. An attempt will be made in the following discussion to delineate the earliest known primates from their taxonomically and presumably adaptively different insectivore ancestors. The very first major grade of primate evolution, which probably incorporates all known Cretaceous, Paleocene, some Eocene, and several recent groups, will be referred to as the prosimian grade, briefly sketched by Simpson (1959:268). Before the question of the nature of the insectivore-primate transition is pursued further, several of the pertinent early insectivore families will be briefly examined. In addition, some recognizable important differences and similarities of certain aspects of the dentition and its occlusion will be assessed. It is disputable which of the known Cretaceous or early Tertiary eutherians is most primitive. Although it is not doubted among specialists that the Insectivora and the primitive families of Deltatheridia of the Cretaceous and Paleocene are the two most primitive orders of eutherian mammals, some of the genera must be examined for a more detailed analysis. It appears most probable that a long, roughly transversely running preparacrista and postmetacrista are primitive in the Metatheria and Eutheria. In the recently published lower Cretaceous therian Pappotherium (Slaughter, 1965) and in the Lance marsupials these features are obvious. These long and necessarily transverse preparacrista and postmetacrista are closely correlated with a very efficient transverse shear. Correlated with the noted feature of the upper molars is a rather transverse trigonid, relatively more so than

An experimental evaluation of premating isolation in the hyla ewingi complex (anura : hylidae).

Abstract: Littlejohn (1965) investigated geographic variation in male mating call structure in two closely related southeastern Australian tree frogs: Hyla ewingi and H. verreauxi. The geographic ranges of these species are such that there is an extensive, linear zone of sympatry with adjacent areas of allopatry (see map in Littlejohn, 1965). It was found that whereas the calls of allopatric populations of the two species were remarkably similar, those of sympatric populations were quite distinctive, differing especially in pulse repetition rate (no overlap in ranges of variation). Other differences were also noted, their nature depending on the locations of the samples in the elongated zone of sympatry; i.e., whether they were from "deep" or "shallow" sympatry. Thus deep sympatric H. verreauxi differed further from shallow sympatric H. ewingi in having a lower carrier (dominant) frequency and reduced amplitude modulation; while deep sympatric H. ewingi differed further from shallow sympatric H. verreauxi in having a shorter note duration. In both species the shallow sympatric populations differed from the adjacent allopatric populations to a lesser extent. This pattern of geographic variation, particularly in pulse repetition rate, was interpreted as resulting from reinforcing selection for efficient premating reproductive isolation. Female response characteristics were presumed to follow the trends in male mating call divergence. Two predictions were made concerning potential premating isolation between allopatric populations. Firstly, since calls of remote allopatric populations of H. ewingi and H. verreauxi were so similar, it was suggested that this ethological character would not be effective as an isolating mechanism. Secondly, since the range of variation of pulse repetition rate in deep sympatric H. verreauxi did not overlap that of allopatric H. verreauxi (a difference comparable with that seen in the heterospecific sympatric populations), premating reproductive isolation of these populations was predicted. Although differences in mating calls have been shown to operate as important premating isolating mechanisms in other species of hylid frogs (Blair and Littlejohn, 1960; Littlejohn, 1960, 1961; Littlejohn, Fouquette, and Johnson, 1960; Littlejohn and Michaud, 1959; Michaud, 1962; Snyder and Jameson, 1965), direct experimental evidence was lacking in the H. ewingi complex. Accordingly, a program of call discrimination trials was arranged in order to test the assumption that the mating call differences were operating as premating isolating mechanisms. Since the calls of shallow sympatric H. ewingi are similar to those of adjacent allopatric H. ewingi, the predictions about the degree of premating isolation present between the two allopatric populations could also be tested. For practical reasons it was possible to test female H. ewingi and H. verreauxi from only one area-western sympatry. Even so, the results of the trials are convincing, allowing some conclusions and further predictions to be made.

Metachromism or the principle of evolutionary change in mammalian tegumentary colors.

Abstract: A study of geographic variation in marmosets, a family of small, New World Primates, reveals with unusual clarity a principle of chromatic variation in mammals only vaguely suspected or dimly visualized before. Races of the common marmoset of upper Amazonia, the saddleback tamarin, Saguinus [uscicollis, exhibit virtually every nuance of mammalian coat colors from primitive agouti to practically colorless, or albinotic. Chromatic variation, in a given race, begins with agouti in some part, or chromogenetic field, of the pelage. In successive steps, or races, the agouti color progresses to blackish or brown, then through tones of red, orange, yellow and cream, to white. In other chromogenetic fields, the sequence may be from agouti to blackish or dark brown as in the first, then through successively paler tones of brown to drab, gray and white. Ultimately, all color fields fade into a more or less uniformly whitish coat. The chromatic succession is geographic and phylogenetic. Rivers form the boundaries between each of the thirteen well-differentiated races of Saguinus [uscicollis. Populations of different races within sight and call of each other on opposite banks of meandering streams, live within the same wide range of arboreal habitats. They are exposed to the same sun, moon, winds, rains, enemies, diseases and competition. They consort with the same organisms, use the same kinds of shelters and eat the same foods the same days. Each race, nevertheless, remains sharply defined by color, or color pattern throughout a geographic range which may cover tens of thousands of square miles (Fig. 3). Tegumentary differences between races and between related species living in separate parts of the same environment, as in the case of Saguinus [uscicollis, are apparently non-adaptive. Nevertheless, the same color and pelage characters may seem to be adaptive in other species where geographic variation is correlated with environmental differences. The common eastern Brazilian marmoset, Callithrix jacchus, for example, occupies a greater and more diversified range than that of any other marmoset. Differences between the five recognized races (d. p. 567, Figs. 10, 12) are expressed in coloration, and in the disposition and development of aural and circumaural tufts. Forms of tufts vary independently of environment. Overall color differences, however, are for the most part clinal and roughly correlated with geographic variation in rainfall. Dark races of Callithrix jacchus live in areas of heavy rainfall, pale races in less humid zones with the nearly white or albinotic populations occupying the driest part of the range. Geographic variation in the Amazonian Callithrix argentata is also clinal but with the relationship of coloration to humidity precisely the reverse of that in Callithrix jacchus. The southernmost and darkest race, the brown-furred black-faced Callithrix argentata melanura, occupies the relatively cool dry scrublands of the Mato Grosso,while the completely albinotic (and black-eyed) C. a. leudppe, is confined to the hot, humid rain forests at the mouth of the Rio Tapaj6z (Figs. 8, 9). The albinotic race of Saguinus fuscicollis registers still another contradictory note. This form of the saddle-back tamarin lives in a small interfluvial basin where humidity and all other environmental factors are the

Origin and early evolution of marsupials.

Abstract: Today marsupials inhabit the Australian region and most of the New World, their range extending as far north as Canada and reaching southward almost to Tierra del Fuego. Until a few year ago the fossil record of marsupials contained evidence of only a small number of genera from European Tertiary strata; a dozen or so from North American Mesozoic and Cenozoic deposits; and a larger number from South America, some from the Tertiary resembling modern Australian marsupials. Only a few fossils of pre-Pleistocene age were known from Australia and marsupials were-and still are-unknown in the fossil record of continental Asia and Africa. The area of origin of the Marsupialia and the times and routes by which marsupials moved between North America, Australia, and Europe were matters of speculation. The intriguing zoogeographic problems were not the only reason for focusing scientific attention on the Marsupialia. Recent marsupials exhibit a variety of structures and systems suggesting inheritance with little change from the earliest mammals. The fossil record available 20 years ago did not contain any evidence directly documenting the origin and interrelations of marsupials and placentals. It only sug-

Cumulative parental age effects in drosophila subobscura.

Abstract: Many investigators have studied parental age effects (Strong, 1954). These are physiological (Simmonds, 1948; David, 1961; Rockstein, 1957; Rockstein and Gutfreund, 1961; Rockstein and Brandt, 1963), morphological (Wattiaux and Heuts, 1963) or genetic like cross-over frequency (Bridges, 1927), sex ratio (Heuts, unpublished) and oligogene segregation ratios (Heuts, 1956). These facts concern only the first generation. Several authors tried to, prove a cumulation of parental age effects, using young versus old individuals; for instance, rotifers (Lansing, 1954), Drosophila (Comfort, 1953), house fly (Rockstein, 1959) and mouse (Johnson and Strong, 1963). A similar experiment was started with Drosophila subobscura for the study of the possible cumulative parental age effects on sexual behavior, fertility, longevity and chromosomal polymorphism. MATERIALS

Monophyly or diphyly in the origin of whales.

Abstract: The phyletic unity of the Cetacea is still a matter of dispute. Recently Yablokov (1964; see also Kleinenberg, 1958, 1959) has given well-reasoned arguments that much of the aquatic adaptation of the two recent suborders was evolved separately, from an ancestor without these adaptations. Although not always compelling and sometimes overstated, these arguments are persuasive and they may in general be accepted. For a review of the earlier literature on this subject see Kellogg (1936). Yablokov and Kleinenberg further conclude, in agreement with several previous authors, that the Odontoceti and Mysticeti originated separately from terrestrial animals. Granting that much of the evolution of whales is homoplastic, as is true for probably all other mammalian orders except the least diverse, it is still legitimate to ask whether the latest common ancestor of the recent suborders was sufficiently specialized to be called a whale. The evidence from recent forms is of little help here, but the earliest fossil whales are more promising. It is immediately obvious that the better-known families of archaeocetes, the Basilosauridae and Dorudontidae, could not have given rise to any recent whale, but it is not so obvious that the Protocetidae could not have done so.

Selection mechanisms associated with intraspecific shell variation in littorina picta (prosobranchia: mesogastropoda).

Abstract: Many species of the well-known genus Littorina exhibit considerable variation in size, shape, shell color, color pattern and external sculpture. For example, variations in color pattern and sculpture in Littorina ziezae (Bequaert, 1943), L. saxatilis (Dautzenbergand Fischer, 1912; Bequaert, 1943) and L. obtusata (Dautzenberg and Fischer, 1914; Barkman, 1955) have been described. Of the three species of Littorina in the Hawaiian Islands, the greatest shell variation occurs in the endemic L. picta Philippi. The shells of this species display a wide range of variation in color pattern, sculpture, and size (Whipple, 1965). The purpose of this work was to clarify the origin of intraspecific shell variation in L. pieta. The following objectives were outlined: (1) to study the distributional pattern of the shell sculpture variation; (2) to determine the environmental factors which may affect the distribution of morphological and physiological variations in L. picta; (3) to rear larvae from several types of adult populations; and (4) to ascertain the probable selection mechanisms determining the distribution of the shell sculpture variation. The two extremes in sculpture of L. pieta are a smooth shell with faint or no spiral ribs and tubercles and a heavily sculptured shell with raised spiral ribs bearing many regularly-spaced tubercles (Figs. 1, 2). The extreme variations were distinguished by Philippi in 1845 and 1847 (Whipple, 1965) who named the sculptured type, L. picta (Fig. 1: F, G), and the smooth type, L. pieta var. marmorata (Fig. 1: A, B). Intergradations between the extremes in

Diploid-tetraploid-haploid cycles and the origin of variability in dichanthium agamospecies.

Abstract: It is generally accepted that most natural polyploids fall somewhere in between the classically recognized autoand alloploid in genome constitution (Stebbins, 1947; LOve, 1964). Although probably rare, genomic true alloploids are recognized to have played a major role in speciation, whereas true autoploids are usually assumed to have contributed relatively little towards the origin of variation in plants. No new genes are added to the population through autoploidy, the expression of mutations are successfully masked, the autoploid is often largely sterile, and is probably soon eliminated from the population in competition with the ancestral diploids. However, in tetraploid agamospecies with sexually reproducing diploid races, even partially sterile but fully sexual autotetraploids may provide a temporary genetic bridge between apomictic biotypes. Such a system, associated with possible haploidy, to insure continuous contact with sexuality, was observed in Dichanthium (Gramineae).

Genotype frequency and mating success in the willistoni species group of drosophila.

Abstract: Petit (1951, 1954, 1958) observed in Drosophila melanogaster that the mating success of mutant and wild type flies is a function of the relative frequencies of the two types in cultures. Usually the less frequent males achieve mating more frequently than do males of the same genotype when it is a majority. In one case (that of the mutant, white), the mating success was, however, highest both when white was rare and when it was frequent, while at intermediate frequencies it was at a disadvantage in mating. Ehrman, Spassky, Pavlovsky, and Dobzhansky (1965) and Ehrman (1966, 1968) observed apparently the same phenomenon in D. pseudoobscura. Here the mating advantage of rare genotypes was found not only for mutants but also for carriers of different gene arrangements, strains of different geographic origin, and even for flies of the same strain grown at two different temperatures. Spiess (in Ehrman, 1966, and 1968a) found mating advantages of rare types also in D. persimilis. Both D. pseudoobscura and D. persimilis exhibit the mating advantages of

THE EFFECT OF DIFFERENTIAL VIABILITY ON THE POPULATION DYNAMICS OF t ALLELES IN THE HOUSE MOUSE.

Abstract: The remarkable polymorphism at the T locus in natural populations of the house mouse, Mus musculus, has been shown by Dunn and his collaborators (Dunn, 1953, 1957, 1960; Dunn and Suckling, 1956) to be maintained by a balance between selection and an abnormal segregation mechanism. Homozygotes for various mutant alleles (designated as tw) found in wild populations are either unconditional lethals or male sterile. The effective sperm pool of heterozygous males, however, contains between 85% and 99% t bearing sperm so that the loss of the mutant t alleles in homozygotes is counter-balanced by their increase from the segregation in heterozygous males. Bruck (1957) and Dunn and Levene (1961) gave the theoretical equilibrium frequency of mutant t alleles for the lethal and male-sterile case, respectively, as functions of the intensity of the distortion of genetic ratios in the sperm pool. In particular, if q is the equilibrium frequency of the t allele and m is the proportion of t bearing sperm in the genetic pool of heterozygous males

The population biology of the butterfly, euphydryas editha. viii. oviposition and its relation to patterns of oviposition in other butterflies.

Abstract: This paper is one of a continuing series investigating the population biology of Euphydryas editha (Nymphalidae: Nymphalinae). The life history and general biology of this butterfly have been described in preceding papers that have dealt with aspects of its ecology, phenetics, and reproductive biology (Labine, 1964; Ehrlich, 1965; Ehrlich and Mason, 1966; Labine, 1966a; Mason, Ehrlich, and Emmel, 1967, 1968; Johnson, Keith, and Ehrlich, 1968). The present paper is concerned with oviposition and its ecological consequences. "Oviposition" is used here in a broad sense and is meant to include oviposition behavior, egg number, egg size, rate of oviposition, etc. Attempts to interpret the oviposition pattern of Euphydryas editha led to comparisons with what is known of oviposition patterns in other butterflies.

Considerations on speciation in chalcidoidea (hymenoptera).

Abstract: Among sexually reproducing organisms, speciation involves the division of a species by the appearance of reproductive barriers which isolate a part of its population. Such barriers prevent, or at least greatly retard, the exchange of genetic material between the separated populations so that they are able to diverge genetically under the influences of natural selection, or genetic drift in small populations. If one accepts the argument of most evolutionists that the reproductive barriers operating in animal speciation must be of a geographical nature (e.g. Mayr, 1963), and that speciation must always be allopatric, then one is confronted with something of a paradox by a group of parasitic wasps, the Chalcidoidea. Chalcids are very numerous in species, well over 2000 being described from the nearctic region (Peck, 1963) and in the British Isles alone there are at least 1000 species. The superfamily is probably in a state of active evolution at the present time, a fact suggested by several assemblages of closely allied or sibling species occurring in most families. However, many species, including groups of sibling species, extend over large geographical areas. Boucek (1965) writes \"... the Chalcidoidea are poor subjects for zoogeographic conclusions. Most of the species have very wide distribution areas, which may be said almost certainly even about the lesser-known species.\" Associated with this wide geographical distribution of chalcids is a ready dispersal of adults into many different habitats within the range of the species. They may be found in habitats far from the nearest host; examples are certain Mesopalobus, Torymus and Olynx species parasitic in oak galls but sometimes found on sand-dunes or moorland, miles from the nearest oak tree. No doubt adult dispersal is an adaptation to meet the situation of a scattered host distribution, and its efficacy is shown by the parasitization of small, isolated host populations. Being small insects, usually only 2 or 3 mm long, chalcids can be readily carried in air currents. Accidental transportation by man must also occur frequently. As a consequence of ready dispersion, both across geographical obstacles and into a variety of habitats, prolonged geographical isolation of populations is probably less frequent than in most other groups of animals. How can this be reconciled with the apparently rapid evolutionary rate in the Chalcidoidea? A possible answer to this question has emerged

Competitive interactions and the evolution of ecological niches as illustrated by the australian honeyeater genus melithreptus (meliphagidae).

Abstract: An important consequence of the numerical impoverishment of isolated, and especially insular, faunas is that the component species, as a result of new opportunities, may show shifts in body form, way of life, and basic ecology. Classic cases of structural change and radiation into vacant niches occur in the Hawaiian (Amadon, 1950), and Galapagos (Lack, 1947) avifaunas. Alternatively, there may be a simple broadening or shift in feeding zones, as described by Crowell (1962) in the birds of Bermuda. Just how interactions between species help in the molding of individual "niches" in these faunas has not been completely resolved. Evolutionists, noting that a considerable level of "ecological exclusion" is the end result, see interspecific competition as a major force. This attitude has been challenged by ecologists like Andrewartha and Birch (1954), and Birch and Ehrlich (1967) on the grounds that, since the intermediate steps cannot be observed, it involves unjustified assumptions. They see the need for studies of contemporary situations where selective pressures of all kinds can be weighed. The present paper reviews a case where it is possible to correlate body morphology and ecology in a variety of situations and to interpret these against changed backgrounds of "competitor" species. It concerns Australian honeyeaters (Meliphagidae) of the genus Melithreptus. Four species show no geographic variation over extensive continental ranges but significant structural changes when they enter isolated, faunistically impoverished, areas. The study also throws light on one of the puzzling features of island avifaunas, the tendency of insular species to have longer bills and legs. METHODS

Studies on competition in rice ii. competition in segregating populations.

Abstract: The initial paper of this series (Jennings and de Jesus, Jr., 1968) reported a pronounced negative association between competitive ability in varietal mixtures and yield capacity in pure stands in distinct plant types of rice (Oryza sativa L.). Tall, leafy, spreading, tropical types were more competitive but yielded less than short-statured, small-leaved, erect, agronomically desirable types of temperate origin. This paper describes studies of the comparative competitive and yielding abilities of tall and dwarf segregates from a hybrid between the tall, leafy, lodging-susceptible Philippine variety, Peta, and the erect, Taiwanese indica dwarf, Taichung Native 1. Height in this hybrid is conditioned monogenically, with tallness being completely dominant to dwarfism (Aquino and Jennings, 1966). Derivatives of hybrids between Taichung Native 1 and Peta or other typical tropical varieties have yielded consistently between 5 and 9 ton/ha on experimental and farmers' fields in Southeast Asia (International Rice Research Institute, 1967).

Reproductive isolating mechanisms in the blue-winged warbler - golden-winged warbler complex.

Abstract: Speciation phenomena have received considerable attention from geneticists, taxonomists, and evolutionary theorists. A primary impasse to our knowledge has been the paucity of field studies employing direct observations of species in some critical stage of this process. The birds chosen for this study, Blue-winged Warblers (Vermivora pinus) and Golden-winged Warblers (V. chrysoptera), are at a critical point; the parental phenotypes continue to occur although fertile hybrids are produced. We deal with the reproductive relationships of the two species and hybrids. Data from field studies and the literature lead to conclusions about pairing mechanisms, the success of hybrids vs. parental types, and possible factors promoting reproductive isolation as well as those increasing interbreeding. This species complex is ideal for investigations of speciation for several reasons: (1) the zone of sympatry and hybridization is extensive, (2) their history of contact is reasonably well-documented, (3) there are many accounts in the literature of mixed pairs in different areas of sympatry, and (4) field observations are not difficult early in the season since the birds are conspicuous and have rather small territories. The Blue-wing, formerly the more southern species, has expanded its range northward in the last hundred years and is now extensively sympatric with the Golden-wing (Short, 1963; Berger, 1958). When birds intermediate in plumage were discovered in the late 1800's, there was much speculation concerning their origin. Finally Faxon (1913) carefully followed a mixed pair and found that progeny resembling the "Brewster's Warbler," one of the intermediate types, resulted from this mating. Unfortunately, the great interest in these species then waned, since the origin of intermediate specimens was no longer a mystery. Only recently have ornithologists begun detailed investigations. Parkes (1951) proposed an interpretation of the inheritance of plumage color and pattern supported by observations of the progeny of mixed pairings. Berger (1958) outlined historical changes and the ecological status of the two species and hybrids in the Great Lakes states. More recently, Short (1962, 1963), studying the two species and hybrids in several areas of sympatry by detailed analyses of specimens, showed that introgression has taken place. The present study is based mainly on investigations in two areas, but is far from definitive because the situation is complex and ever-changing throughout the area of sympatry. There is great need for more intensive studies in many different areas and over a long period of time; only then will all of the complex processes become clear. This paper is one of a series on song, courtship, ecology and territory in Blue-winged Warblers, Golden-winged Warblers and their hybrids (Ficken and Ficken, 1966 in press a, b, c.)

Mimetic versus disruptive coloration in intergrading populations of limenitis arthemis and astyanax butterflies.

Abstract: The occurrence of variability and intermediate forms in areas of geographic overlap between populations which elsewhere are distinct and relatively homogeneousis a situation of great interest. Such phenotypic intergradation often indicates interspecific or inter-racial hybridization and is therefore one key to understanding the process of the origin of species. Numerous instances of this phenomenon are known (see Remington, 1968, for a recent review). One of the most historically significant concerns two North American nymphaline butterflies of the genus Limenitis, L. arthemis Drury and L. astyanax Fabricius. Fisher (1930) regarded the available data on these butterflies as evidence for their being incipient species on the verge of attaining complete genetic isolation. This example proved important to understanding not only the role of sexual selection in interspecies evolution (Huxley, 1938a, b) but also laid the foundation for Dobzhansky's (1937) theory that, following allopatric separation and divergence, speciation can be completed by selection in the zone of secondary overlap. Notwithstanding the absence of subsequent substantiating data, this interpretation of the arthemis-astyanax complex was accepted by Hovanitz (1949), reasserted by Fisher (1958), and again put forward by Mayr (1963). The major reasons that these insects have been considered on the verge of becoming separate species are as follows: (1) the two are strikingly different in several aspects of their adult color-pattern; (2) they have nearly exclusive geographic

Island patterns in the solomon islands bird fauna.

Abstract: Galbraith and Galbraith, 1962). Distribution patterns of this type have recently been discussed in the Solomons for certain insects (Greenslade, 1968) and a similar analysis is carried out here for birds in greater detail permitted by the more extensive knowledge of their island distribution. In addition to supporting the conclusions reached from insect distributions it shows that the results of recent zoogeographical studies by other workers on a much larger scale can be used to explain complex local patterns within an archipelago. Two assumptions are made. The first is that distributions can be considered in terms of the present island pattern (Fig. 1) since this has probably persisted since some period in the Pleistocene (Greenslade and Peake, in preparation) providing adequate time for subspeciation (Moreau, 1966). Secondly, it is assumed that expanding taxa tend to move from large to small islands, most easily across narrower water gaps; there is also an overall W to E movement from source areas, primarily New Guinea and the Bismarck archipelago and secondarily Bougainville, through the Solomons. Further discussion of this assumption is given by Greenslade (1968), and routes of immigration and dispersal derived on this basis are shown by arrows in Figure 1. Island distribution and habitat data are

The genetics of polymorphism in the goose anser caerulescens.

Abstract: Although the most recent A.O.U. checklist of North American Birds (1957) records the Blue Goose and the Lesser Snow Goose as distinct species (Chen caerulescens [= Anser caerulescens] and C. hyperborea [= A. hyperborea] respectively), many ornithologists today agree with the conclusion of Cooch (1961) that the smaller subspecies of the Snow Goose Anser caerulescens caerulescens is polymorphic and has two clearly defined color phases, a blue phase and a white phase. Some authors, e.g. Manning et al. (1956) prefer to regard the Blue Goose and the Lesser Snow Goose as conspecific but consisting of two subspecies. Polymorphism is well known in birds and has been well documented by Mayr (1942) and Huxley (1955). In only a few cases, however, has it been possible to infer the genetic basis of the polymorphism. O'Donald and Davis (1959) have studied the genetics of the color phases of the Parasitic Jaeger (Stercorarius parasiticus) . Meyerriecks ( 1957) has some observations on genetics of polymorphism in the Great Blue-Great White Heron complex. Williamson (1957) reported on the genetic basis for the dimorphism found in the goslings of the Ross's Goose, and Ryder (1967) extended these observations. Lowther (1961) recorded an interesting case of polymorphism in the White-throated Sparrow and Thorneycroft (1966) presented cytological evidence for the genetic basis of this polymorphism. Most observers, however, have had either to ignore the genetic basis or to suggest a genetic basis with no genetic evidence on which to base their speculations. Genetic data of this nature are not easy to obtain in non-domesticated birds. Many birds will not breed in captivity. In the wild it is possible to gain meaningful genetic evidence only if a large number of families is studied and if the polymorphism is detectable in nestling stage, or alternatively if the nestling can be kept in captivity, or can be marked for individual recognition until the adult plumage appears. The polymorphism of Anser caerulescens is in many ways ideal for study. Large colonies, where the different morphs interbreed, can be found. The polymorphism is detectable in both adult and gosling plumages and is observable in both sexes. Most species of birds produce too few offspring in anyone season for a genetic study based on individual families to be feasible, but when a large population can be examined, some pooling of data allows conclusions about the genetic basis to be drawn. This paper is an attempt to analyze the genetic basis for the polymorphism in this dimorphic species, by investigating a sample of the large colony at Boas River, Southampton Island, North West Territories, Canada. Although there are indications that color differences lead to differences in choice of nest sites and time of breeding, these attributes of the polymorphism have been ignored in the present study. In the course of this analysis, observations on the assortative mating behavior were made. These observations, which are described in detail below, led to the conclusion that some form of imprinting, as suggested by Huxley (1955), was operating. This in turn suggested that such imprinting, if complete, could lead in a few generations