Showing papers in "Evolution in 1960"

Latitudinal variations in organic diversity

Abstract: ? ? A NIMAL life is, on the whole, far more abundant and varied within -^-the tropics than in any other part of the globe, and a great num ber of peculiar groups are found there which never extend into temperate regions. Endless eccentricities of form and extreme richness of color are its most prominent features, and these are manifested in the highest de gree in those equatorial lands where the vegetation acquires its greatest beauty and its fullest development." Thus wrote A. R. Wallace (1878). His remarks apply equally to the vegetable and animal kingdoms, to the terrestrial realm, and to at least the surficial parts of the oceans. Surely this correlation of floral and faunal diversity with latitude is one of the most imposing biogeographic features on earth. On the one hand, its existence poses large-scale problems in evolution. On the other, it offers a potential tool to the geologist-paleontologist who attempts to wring patterns of earth history out of the fossil record. The following pages serve to review some previously known latitudinal gradients in organic diversity, to describe quantitatively gradients in molluscan diversity along North American shores, and to inquire into the origin of these patterns.

The evolutionary dynamics of complex polymorphisms.

Abstract: The theory of balanced polymorphism which has been elaborated by population geneticists, notably Sewall Wright and R. A. Fisher, has in the main been concerned with the effects of single loci. As theory generally goes apace with experiment, this accent on single locus polymorphisms has been due to the plethora of observational evidence relating to simple cases. It is sufficient to note the vast effort made by Dobzhansky and his co-workers in their elucidation of the inversion polymorphism of the third chromosome of Drosophila pseudoobscura. In recent years, however, a few cases have come to light of polymorphisms involving more than one Mendelian unit. Among these are the inversions on different chromosomes found in D. robustca studied by Levitan (1955 and 1958), the shell color of Cepaea nemoralis reported by Lamotte (1951) and by Cain and Sheppard (1952), the complex mimicry pattern in certain butterflies (Sheppard, 1959) and the inversions in two chromosomes of the grasshopper Moraba scurra analyzed by White (1957) and Lewontin and White (1960). The study of effects of natural selection on single locus polymorphisms must take into account only inter-allelic effects such as additivity and dominance. In multi-locus polymorphisms, however,

The ecological significance of correlation pleiades

Abstract: The concept of correlation pleiades was originally advanced by Terentjev (1931). It is based on the presence of correlations between some quantitative characteristics, e.g., between dimensions of certain parts of an organism (or between different measurements within one part) , and, at the same time, on the absence of correlations between these and other parts. The existence of correlation pleiades leads to theoretically important conclusions. The presence of correlations between, for instance, the dimensions of some parts of an organism and the absence of correlations between the dimensions of these and the other parts of the same organism indicate the independence of certain developmental processes with respect to other processes within the organism. The pleiades are thus a manifestation of differentiation. With respect to a given part, other parts of the same organism basically constitute its environment. The origin of correlation pleiades in the course of evolution is an indication of the increasing independence of certain developmental processes with respect to environmental factors, including the influences exerted by the other parts of the same organism. The study of correlations makes it possible to establish the degree of independence reached. The adoption of such a quantitative criterion provides an adequate basis for the introduction of the comparative method in the study of the process by which this independence is attained. Investigation of correlation

Interaction between inversion polymorphisms of two chromosome pairs in the grasshopper, moraba scurra.

Abstract: In studying the evolutionary dynamics of polymorphisms in natural populations, most of the work in the past has concentrated on single genetic entities. The Work of Dobzhansky and his collaborators on the inversion sequences in the third chromosome of Drosophila pseudoobscura, the studies of Lamotte (1951) on shell color and banding in the snail Cepaea nemorallis, and those of Allison (1955) on abnormal hemoglobins in man are examples of genetic studies of polymorphisms controlled by alleles at a single locus, or else by blocks of genes which act in heredity as single loci. A new order of complexity is introduced when an attempt is made to study simultaneously two or more segregating systems in the same population because of the possibility, indeed the probability, that the evolutionary fates of the different polymorphic systems are not independent. Such will be the case if there is interaction between the different loci in the determination of the fitness of various genotypes. For example, the fitness of individuals of the genetic constitution AA may be greater than those with the constitution aa if at a second locus these individuals are, let us say, BB; but this fitness relationship may be reversed in the presence of bb at the second locus. In such cases the polymorphisms A,a and B,b are not independent in their fates in the population. Levitan (1955, 1958) in his studies of the inversion polymorphisms of Drosophila robusta has evidence of a small interaction of this sort and Cain and Sheppard (1954a, 1954b) have found such interactions for shell color and banding in Cepaea nemoralis. One of the most favorable materials for the study of these interactions and their evolutionary consequences is the Australian grasshopper, Moraba scurra. In an earlier paper (White, 1957) evidence was presented that the pericentric inversions, carried on two different chromosome pairs in this species, are not combined at random in the adult male individuals of certain natural populations. The deviations from random combination were regarded as proof of a genetic interaction between the two systems of cytological polymorphism, so far as their effects on viability are concerned. The significance of this interaction effect has been discussed and a hypothesis as to how it could have arisen has been suggested (White, 1958). The present paper has two purposes. First we shall present added data on the interaction effect from recent collections. The data published previously relate to six adult male samples collected in 1955 and 1956 at various localities in South Eastern Australia. Further data on two of these populations (at Wombat, New South Wales, and Royalla "B," Australian Capital Territory) were obtained in 1958 and 1959. Statistical analysis of the more recent data provides

Allochronic Speciation In Field Crickets, And A New Species, Acheta Veletis

Abstract: McNeill (1889) was apparently the first investigator to recognize that the most abundant and widely distributed field cricket in northeastern North America is actually composed of two populations, one overwintering as a late instar nymph and maturing in spring and one overwintering in the egg stage and maturing in middle or late summer. McNeill also noted (1) that the adult males of the nymph-overwintering population more often occupy burrows and are characteristically more solitary and more aggressive than those of the egg-overwintering population, and (2) that the ovipositors of the females in the nymphoverwintering population are usually shorter in relation to the length of the body than those of the females in the eggoverwintering population. Later investigators, such as Blatchley (1903, 1920), Walker (1904), Criddle (1925), Urquhart (1941), Cantrall (1943), Fulton (1952), Alexander (1957), and Bigelow (1958) have corroborated and refined McNeill's observations on these two populations without materially altering his conclusions. It is surprising that in spite of the confusion in field cricket taxonomy, the relationships of this pair of populations have been fairly well understood by field biologists for about seventy years. Prior to Fulton's work, various names had been applied to these two forms, either as binomials or as trinomials. Fulton, Alexander, and Bigelow did not separate the two populations with formal nomenclature. Fulton remained quite uncertain as to their status, being able to deal only with the southernmost fragments of their ranges in the northwestern part of North Carolina. Alexander, puzzled by the apparent identity of the two populations in song, habitat, and distribution, noted that most females could be separated on the basis of ovipositor length, and stated (p. 592), "These two broods may interbreed in mid-summer, or possibly in fall in the southern part of their range, or it maybe that they have been isolated such a short time that no noticeable differences have yet appeared between them. Certainly more investigation is needed to, clarify their relationship." Bigelow, on the basis of differences he had discovered in the developmental rates of the two' poptulations, and the differences in diapause stage, stated (p. 147), "The distinctive differences between these two' populations are more likely to become further consolidated than they are to break down through any future gene exchange. Therefore, these two populations should be regarded as distinct species, however similar they might be morphologically." Recently, we have pooled our information on these populations and have concluded that a more detailed discussion of their relationships, and their recognition as distinct species, is in order. We believe that these species have become reproductively isolated through a seasonal' separation of adults initially imposed by'

The breeding group and seed storage: a study in population dynamics

Abstract: This is a report on the yearly frequencies since 1941 of blue and white flowered plants of Linanthus parryae, a conspicuous annual of the Mojave desert. Like most desert annuals, its abundance and dispersion varies greatly from year to year and from place to place in response to weather. The size of the breeding group would be expected to vary with these expansions and contractions. An initial survey (Epling and Dobzhansky, 1942) suggested that the inheritance of color depends on one pair of alleles. Having these natural markers, the species appeared to be a useful subject with which to study the effects of selection and genetic drift. The initial survey sampled a naturally delimited area of about 600 square miles. Linanthus was extraordinarily abundant in 1941 and the population was almost literally continuous throughout the area (fig. 1) . For the most part it consisted of white flowered plants. Three mixed areas were found, however, in which the color frequencies were locally highly variable. Only occasional blue individuals or small patches were observed in some parts of the white area. Subsequent sampling has shown that these mixed areas are persistent and that their limits have not materially changed. Four years sampling of the westernmost mixed area by the coarse method used in the initial survey also indicated that color frequencies tended to remain constant in very local populations. Permanently marked experimental plots were accordingly constructed within this area, which have permitted a systematic and detailed sampling of dispersion and flower color each year since 1944. The exact mode of inheritance of flower

Evolution of gametophytic and sporophytic systems of self-incompatibility in angiosperms.

Abstract: Self-incompatibility has been found in at least 78 angiosperm families and occurs in every major phylogenetic line (East, 1940; Fryxell, 1957; Brewbaker, 1957). It has even been discovered in at least three gymnosperm species (Pinus sylvestrisGustaffson, cited by Bateman, 1952; Larix laricina, Pseudotsuga taxifoliaFryxell, 1957), and one pteridophyte, Pteridium aquilinum (Wilkie, 1956). It occurs not only in hermaphrodite species, but also in monoecious species with unisexual flowers on the same plant (Godley, 1955). Genetically, self-incompatible species have been divided into two groups, gametophytic and sporophytic. In each of these systems there are variations particularly with regard to (i) the number of S loci and (ii) the interaction relationship between the alleles at the same or different loci (Pandey, 1957). Although there is no family yet known which has been found to contain both gametophytic and sporophytic genetic systems in the different species of the same family, this possibility is strongly suggested as will be evident from the following discussion. The evolution of the self-incompatibility phenomenon has been discussed generally by several authors (Whitehouse, 1950; Lewis, 1954; Stebbins, 1957). The present paper deals particularly with the

A functional index of hypsodonty

Abstract: GREGORY, JOSEPH T. 1950. Tetrapods of the Pennsylvanian nodules from Mazon Creek, Illinois. Amer, J. ScL, 248: 833-873. INGER, ROBERT F. 1957. Ecological aspects of the origins of the tetrapods. EVOLUTION, 11: 373-376. NOBLE, G. K. 1931. The Biology of the Amphibia. New York, McGraw-Hill, 577 pp. PEABODY, FRANK E. 1952. Petrolacosaurus kansensis Lane, a Pennsylvanian reptile from Kansas. Univ. Kans. Paleont. Contrib., Vertebrata, Art., 1: 1-41. ROMER, A. S. 1930. The Pennsylvanian tetrapods of Linton, Ohio. Amer, Mus. Nat. Hist. Bul!., 59: 77-147. 1957. Origin of the amniote egg. Sci. Monthly, 85: 57-63. SMITH, H. M. 1959. Darlington's principles of zoogeography. Turtox News, 37: 122124. WESTOLL, T. S. 1944. The Hapolepidae, a new family of late Carboniferous bony fishes. A study in taxonomy and evolution. Amer. Mus. Nat. Rist. Bull., 83: 1-121.

The endemic fish fauna of lake lanao, and the evolution of higher taxonomic categories

Abstract: La~e Lanao lies at an altitude of approximately 2,100 feet in the midst of a volcanic area in central Mindanao the largest island of the southern Philippines. Its exact area is in dispute, Herre giving it 375 square kilometers and others as m~n:y as 900. Th~ late Professor Bailey Willis, who had given much attention to Philippine geology, as well as to that of the African Rift Valley and its lakes investigated what was known of the geological history of Lake Lanao and prepared the following statement for me: \"The island of Mindanao has risen f:om the oc~an gradually and unequally since the MIOcene. It now consists of plateaus, hill country, swamps, and volcanoes. The streams were initially small and isolated from each other. The headwaters were, and are, generally swift and the lower courses estuarine. \"A north-central region was built up by basalt flows to a plateau, on which a small system of rivers developed. Some of them flowed southwesterly to Illana Bay, others northwesterly to Iligan Bay. The divide between them ranged from southwest to northeast. INTRODUCTION

The pattern of interspecific variation in the genus Oryza: its quantitative representation by statistical methods.

Abstract: Two cultivated and more than twenty wild species occur in the genus Oryza. As is well known, 0. sativa L., which comprises many varieties with different characteristics, is the most important food crop in Asian countries. 0. glaberrima Steud., another cultivated species, is grown within a rather limited area in Tropical West Africa. Among wild species, 0. perennis Moench (found in almost all tropical countries of the world),' 0. sativa f. spontanea Roschevicz (of tropical Asian countries) and 0. breviligutlata A. Cheval et Roehr. (of tropical African countries) appear to be relatively closely related to those cultivated species, in the sense that they can be easily crossed with one another and with the cultivated forms, and their chromosomes pair in the F1 almost normally. Other wild species may show a spectrum of genetic distances from the cultivated rice. The phylogenetic hierarchy of the genus, which is not yet established, attracts interest of rice students, and as a basis for approaching it, a re-evaluation of interspecific relationships is desired. The first basic taxonomic study of the genus Oryza was reported by Roschevicz

Introgressive hybridization between two southeastern treefrogs

Abstract: Natural interspecific hybridization in anuran amphibians is not rare, and a number of examples are recorded. There are, however, few conclusively proven instances of introgressive hybridization in the restricted sense of gene exchange between species. The best known case is that of the toads Bufo woodhousei fowleri and Bufo terrestris americanus (A. P. Blair, 1941; Volpe, 1952; and others). A related example is reported by A. P. Blair (1955) between Bufo w. woodhousei and Bufo microscaphus, and Wasserman (1957) provides evidence of introgression in the spadefoot toads Scaphioputs hurteri and Scaphio pus couchi. Most other presumed examples are based largely on simple identification of hybrids with no evidence for introgression, or belong to the borderline category of closely related contiguously allopatric forms that interbreed freely along a narrow zone of contact. This paper deals with a clear case of interspecific gene exchange between the green treefrog, Hyla cinerea, and the barking treefrog, Hyla gratiosa, near Auburn, Alabama. Both species are widely distributed over the southeastern coastal plain. H. gratiosa ranges from North Carolina along the coastal plain (exclusive of southern Florida) to southeastern Louisiana, extending locally above the fall line, and onto the Cumberland Plateau. H. cinerea ranges from Maryland to south-central Texas, up the Mississippi Basin to southern Illinois, and into southern Florida. The two forms are, therefore, sympatric over the greater

Meiotic drive in natural populations of drosophila melanogaster. iii. populational implications of the segregation-distorter locus,

Abstract: SD IN NATURAL POPULATIONS agreement ~ith expectations from the theory of meiotic drive; (2) to show that the results from experimental populations bear out the quantitative predictions insofar as these have been tested; (3) to present a mathematical treatment of the population consequences of some special cases of meiotic drive with special emphasis on those phenomena which bear on the behavior of SD; and (4) to consider the particular way in which one population of Drosophila has minimized the detrimental effects of the spread of SD.

Food preferences of larval and adult drosophila

Abstract: Wagner (1944) was the first to show that two species of Drosophila, D. mulleri and D. atdrichi, differ in their ability to utilize for food certain species of yeast isolated from the breeding sites of these flies. This suggested the possibility that species of Drosophila may be differentiated with respect to their food preferences. The possibility was tested experimentally by da Cunha, Dobzhansky, and Sokoloff (1955) and by Dobzhansky et at. (1956) working in California, by Dobzhansky and da Cunha (1955) and da Cunha et at. (1957) working in Brazil. In all these studies baits were exposed in the natural habitats of the flies, the baits being inoculated with different yeasts isolated chiefly from the crops of Drosophila collected in the same or different localities. The numbers of wild flies of various species which were attracted to the baits were recorded, and in many cases significant differences between the Drosophila species in the attractivity to them ,A the different yeast species were observed. Dobzhansky and Pavan (1950) and Pavan (1952) have shown that Drosophila species show also a clear differentiation with respect to the kinds of fermenting fruits and other substances which they select in their natural habitats. Dorsey and Carson (1956) attempted to discover which of the products of fermentation attract Drosophila flies. Of the several varieties of baits used, one, consisting of a molassesvinegar-water mixture, proved most attractive. A different approach was utilized by Shehata et at. (1955), Carson, Knapp, and Phaff (1956), and Phaff et at. (1956). They compared the yeast floras of the known natural breeding sites of Drosophila in California with the composition of the yeasts isolated from the crops of adult Drosophila flies captured in the same localities. They found that the adult flies feed in the main on a different range of the yeast species than their larvae do. No such differentiation was, however, discovered in Brazil (Dobzhansky, personal communication) . A still different approach has been that of Dudgeon (1954), who studied the ability of the larvae of the viritis group of species of Drosophila to develop in a wide variety of yeasts. The situation that emerges clearly from the above investigations is, first, that different yeast species are unequal in attractiveness to different species of Drosophila. Secondly, different species of yeast are not equivalent in supporting the growth of Drosophila larvae. The present investigation is primarily an attempt to study the attractivity of different species of yeast to larvae of different Drosophilae. The preference patterns discovered are then compared with the preferences exhibited by the adults of the same species of Drosophila. The only previous work dealing with larval preferences is that of Lindsay (1958), and our results are in good agreement with hers.

Isolating mechanisms in three sympatric treefrogs in the canal zone

Abstract: 484 Three species of small treefrogs, H yla microcephala Cope, H. phlebodes Stejneger, and H. ebraccata Cope, are sympatrie in the Canal Zone. They are rather similar in morphological appearance, and have similar breeding calls, and commonly call and breed in the same areas during the same periods of time. The question arises: how are these three frogs able to maintain their identities as discrete species under these conditions? Investigations were carried out in the Canal Zone during the period from April 1955 to November 1956, while stationed there with the U. S. Air Force, and during the summer months of 1958. The area studied was in the lowlands of the Pacific drainage of the Canal Zone, chiefly within a four-mile radius of the town of Pedro Miguel. All three species are of rather small body size (mean snout-vent length, millimeters-ebraccata: males 24.6, females 31.2; microcephala: males 22.8, females 27.1; phlebodes: males 22.2, females 27.4), and are quite similar in form and proportions. The basic color of all three, when active in the field (at night) is generally a rather vivid yellow with brown markings. The chief noticeable difference is in pattern, and in this characteristic ebraccata is the most distinctive. More detailed comparisons of the morphology will be presented elsewhere. Suffice it to say that the data from this source suggest that the species are quite closely related. The scheme of classification used as a guide in checking the possible types of

Therapsids as mammals

Abstract: The therapsids are usually placed in the class Reptilia as its most mammal-like representatives. This is on the basis of the now commonly accepted criteria of jaw-ear structure, where mammals are defined as having (1) a dentary-squamosal suspensorium, (2) the articularquadrate joint not a mandibular suspensorium, (3) three middle ear bones, and (4) the mandible containing only the dentary (Simpson 1959). It is the present thesis that (1) tetrapod classes should be defined on the basis of their major adaptive differences, (2) that the mammalian grade of adaptation was largely reached in the therapsids, and (3) that the therapsids should therefore be included in the Mammalia. No specific mammal or reptile need be referred to; comparison will rather be with a construct similar to the Typus of the German idealistic morphologists, whose characters are observable in most species except for obvious specializations. The Theria as a whole and the Sauropsida (of Watson 1957) as a whole are the standards of comparison. If necessary, Diadectes, Iguana, Didelphis, and Sits may be kept in mind. Much of the evidence for this view has been discussed by Brink (1957a); see also Broom (1932). The major adaptive distinctions of mammals as compared to typical reptiles will now be considered, together with any possible evidence that the therapsids had each of these characters in life. "The theoretical approach to any field of science is something of a luxury" (Burnet 1959). However, if the criteria of class placement are to be

Osteometric variation and function in bats

Abstract: Since the most extensive and direct evidence of macroevolution, the fossil record of the vertebrates, consists almost entirely of skeletal and dental remains, quantitative studies of these systems are of special interest to the evolutionist. Students of continuous variation of the skeleton have amassed an imposing quantity of data over the past several decades, much of which has been, of necessity, of a purely descriptive nature. Although a general synthesis based on studies of osteometric variation and correlation appears to lie some distance in the future, certain generalizations have emerged which consistently lead to verifiable predictions. Furthermore, there has been an ever increasing tendency to relate numerical values to relationships of genetic and functional significance. The studies of Kurten (1953, 1957) and Olson and Miller (1958) are recent examples. One of the most fundamental and readily verified generalizations in osteometrics is the circumscribed nature of the phenotypic variation within a species population in spite of the presumed great potential variability of the population. In terms of the coefficient of variation, values for groups with a definitive adult size (e.g., most mammals and birds) regularly fall within the approximate limits of 2 and 8. The concepts of developmental and genetic homeostasis as developed by Lerner (1954) and empirical data derived from wild and inbred rodent populations (Bader, 1956) suggest that groups with quite different degrees of genetic homogeneity may nonetheless manifest very similar amounts of phenotypic variation. Thus, inferences as to the relative extent of genetic heterogeneity based solely on phenotypic variation must be made with considerable caution. Consistent differences in observed variation can be demonstrated, however, both between different regions of the skeleton and between taxa of higher rank. It is with such disparities that the present study is concerned. One of the most persistent differences in magnitude of variation between higher categories of vertebrates is that which pertains to birds and mammals. In general birds exhibit a lower variation in osteometric characteristics than that shown by homologous traits of mammals. A greater intensity of centripetal selection on flyers suggests itself as a possible interpretation. With respect to differences related to position in the skeleton, several avian studies have revealed a trend of increased variation particularly in the wing, from the proximal to the distal portion of the appendage. This trend appears to be either lacking, or much less regular, in terrestrial mammals. In this context an osteometric analysis of bats should be of considerable interest. Will they exhibit magnitudes and trends of variation typical of terrestrial mammals or of birds, or, perhaps, partake of characteristics of both? Will the two appendages, which differ strikingly in morphology and function, reflect this difference in terms of quantitative variation and correlation ? The behavior of the first digit of the wing should be of particular significance. Although it is borne on the forelimb, it does not aid in support of the flight membrane (in the species studied) and resembles very closely the digits of the foot in size, shape, and function (fig. 1). No extensive osteometric study has previously been carried out in the bats.

Supernumerary Chromosomes in Haplopappus gracilis

Abstract: Since reporting the chromosome number of Haplopapputs gracilis as n=2 (Jackson, 1957), I have found other chromosome numbers in this species. In a collection of plants grown from seed obtained at Bandelier National Monument in New Mexico, chromosome numbers of n=2, n=2+1, n=3, and n=3+1 were counted. Plants having more than the normal two pairs of chromosomes were found to contain supernumerary chromosomes in the usual sense in which this term is used. In all of the New Mexican plants studied, the supernumerary chromosomes were morphologically identical. Each chromosome possessed a near-median centromere and was approximately two microns in length at mitotic metaphase. This is about one-half the length of chromosome B and one-third the length of chromosome A of H. gracilis. Studies of diakinesis failed to show any pairing of the supernumeraries with the A and B chromosomes. In the few plants grown thus far, there have been certain morphological characteristics associated with plants carrying the supernumerary chromosomes. In some plants the type of pubescence was slightly altered and the branches were thicker, especially near the tips, giving a "polyploid" appearance. In one plant, there was a greater distance between the spines on the leaves than is found in normal individuals. In typical plants of H. gracilis the achenes are brown or reddish, but in plants carrying the supernumerary chromosomes the achenes were a dark purple. It thus appears that the supernumerary chromosomes may exert a decided genetic effect, depending, perhaps, upon the genotypes with which they are associated. The characteristics associated with the supernumerary chromosomes were noticed first, and a later cytological study revealed the presence of the extra chromosomes. In addition to the supernumeraries found in plants from New Mexico, others were found recently in a population of plants from southwestern Arizona. Some plants from this population contained up to four supernumerary chromosomes that were much shorter than those in the New Mexican material. Seeds from this population are being grown in order to further analyze the material cytologically and genetically. Various explanations have been offered for the origin of supernumerary chromosomes in plants (Lewis, 1951; Swanson, 1943). In H. gracilis, I believe that two methods of origin may be possible. One would be the introduction of extra chromosomes into populations of H. gracilis as a result of hybridization and backcrossing with a species having a larger chromosome number. The second possibility might be that the extra chromosomes represent the centromeres and adj acent chromatin resulting from the aneuploid reduction process that may have given rise to the species. The mechanisms of this process have been outlined by Darlington (1937) and Stebbins (1950). It is generally assumed, however, that the centromeres and adjacent chromatin will be lost if they are genetically inert. Nevertheless, it may be possible that the centromere and adj acent chromatin are retained in some populations of the species even though they are inert and unnecessary for normal development.

Pseudogamy as an evolutionary factor in the poeciliid fish mollienisia formosa

Abstract: Pseudogamy or gynogenesis, the actiand Sanderson (1956). They have found vation of an unfertilized egg by a sperm that the ptinid beetle Ptinus lairo is an without the continuing functional particiall-female species, the members of which pation of male hereditary elements, has live normally in similar ecological situalong been known in various animals. tions with the related bisexual form P. Thus Peacock (1944) reported that eggs hirtellus. Eggs from virgin latro females of the worm Rhabditis monohystera are do not hatch, but after mating with activated by sperm of the same species hirtellus regularly produce typical latro without the participation of male chromofemales, apparently parthenogenetically. somes. The effect was experimentally Experiments with males of hirtellus sterisecured by Lillie (1912) by mixing lized by X rays have shown that viable homologous eggs and spermatozoa of sperm must participate in the activation, N ereis and separating them after a short but there is no evidence that genetic eletime, and similarly by Rothschild (1953) ments are involved. Early cytological in Paracentrotus. The same effect can work suggests that both sexes of hirtellus be achieved across species. Thus much are diploid (n = 9), whereas the latro feof the early classical work on the activamales are triploid, and latro eggs do not tion of frogs' eggs by mechanical means undergo reduction in maturation. was inspired by the observation by As far as we are aware, the only similar Bataillon in 1909 that eggs of the newt case of naturally occurring pseudogamy Pelodytes punctatus could be pseudoin a vertebrate is that first reported by gamously activated by spermatozoa of Hubbs (1932, 1933) in the viviparous Triturus alpestris, Similar observations poeciliid fish Mollienisia formosa were made on Arbacia and Chaetopterus (Girard), and since abundantly confirmed by Godlewski (1912) and on the eggs of by Meyer (1938), by Carl Hubbs (1955), the sea urchin Strongylocentrus activated by Clark Hubbs, Drewry, and Warburton by the sperm of a mollusc (Chlorostoma) (1959), and by us. Mollienisia formosa, by Loeb (1913). Summaries of the thought by Carl Hubbs to be itself of situation have been given by Hertwig hybrid origin, is found in northeastern (1936) and by Moore (1955). Mexico and southwestern Texas. In the Few cases seem to have been reported, state of Tamaulipas, Mexico, it was found however, among animals in which partheliving in fresh waters well inland, in nogenesis involving the pseudogamous company with the related M. sphenops activation of the eggs of one species by (Cuvier and Valenciennes) species comthe sperm of another constitutes the plex. Near Brownsville, Texas, it is an normal mode of reproduction. There abundant inhabitant of coastal fresh-water have been correspondingly few opporpools, living in company with another, tunities to investigate the impact of this related form, M. latipinna Le Seur. We curious reproductive mode in evolution. have since found populations of 111. One of the most interesting situations of formosa in the states of Tamaulipas and this kind in an invertebrate has been reNuevo Leon, living sympatrically with ported recently by Moore, Woodroffe, populations of the 111. sphenops complex.

Diagnosis of the classes reptilia and mammalia

Abstract: The editor has asked me to comment on two papers (Reed, 1960; Van Val en, 1960) that are published in this issue. Both those authors reach, by different paths, the conclusion that the now almost universally accepted contents of the class Mammalia should be changed to include certain extinct animals hitherto classified as reptiles (nearly but not quite the same reptiles in the two proposals). Along with a number of others who have been informed of, or who have themselves thought of, this possible change, I am opposed to it, and I have agreed to appear here as a representative of those who support the current arrangement. There is little disagreement as to the facts or as to the essential evolutionary interpretations of them. It has been known for generations that the mammal-like reptiles or the Therapsida (whose name includes the root for \"mammal\") are indeed mammal-like. Recent discoveries have added interesting details as to just what characters are mammal-like and as to approximately when they appeared, but the broad picture has not been changed. I t has been believed by some for a shorter time, but stilI for more than thirty years now, that the line between reptiles and mammals, as usually drawn, was crossed independently by more than one lineage of mammal-like reptiles whose descendants thus became, by arbitrary diagnosis, mammals. Discoveries of the last few years have strongly confirmed that conclusion, as pointed out recently in two papers (Olson, 1959; Simpson, 1959), which apparently stimulated the present exchange of views. The facts of progressive advance toward typical mammalian status and their interpretation in terms of evolutionary principles and of phylogeny are certainly of very great interest -far greater interest than the classification of the animals involved-but the present issue concerns classification, alone. Although based on scientific data, inferences, and principles, classification by its very nature involves a large, at times even a predominant, element of human judgment and ingenuity, in other words of art. The art of classification has certain canons that are so widely accepted as to restrict the play of fantasy, at least. I shall not attempt to discuss the canons in detail here (I am doing so in a book to be published by Columbia University Press), but only mention three kinds of criteria:

The Genetics of Hybrid Sterility in Drosophila paulistorum

Abstract: The willistoni species group includes five known sibling species, one of which is Drosophila paulistorutm Dobzhansky and Pavan. The morphological characteristics and the relationship of this species to D. tropicalis Burla and Da Cunha, to D. willistoni Sturtevant, and to D. equinoxialis Dobzhansky were analyzed by Burla et al. (1949). Later, a fifth sibling species, Drosophila insularis Dobzhansky, was added to the group (Dobzhansky, Ehrman, and Pavlovsky, 1957). The five sibling species can be told apart by crossability tests and by inspection of the chromosomes in the cells of the larval salivary glands; moreover, Spassky (1957) found minute differences in the structure of the genitalia, which permit him to classify living males into the five species categories. Withotit doubt, the sibling species are completely isolated reproductively. Although interspecific insemination does occasionally occur in laboratory experiments, no viable hybrids are produced except in crosses involving D. insutlaris, where the hybrids are wholly sterile. This species, D. inslcaris, is most restricted in its geographic distribution. It is known only from two islands in the Lesser Antilles, while the other four species are widespread over the American tropics. D. tropicalis, D. willistoni, D. equinoxialis, and D. paulistorum are sympatric in a region including the Amnazonian basin and the part of South America that lies north of the Equator. D. willistoni has been found to be a unified species-one not divided into subspecies showing any trace of incipient reproductive isolation. D. tropicalis includes two known subspecies which produce sterile male and fertile female hybrids (Townsend, 1954). D. equinoxialis has not yet been studied. Extensive collections of D. paulistorum from localities in Central America, the Caribbean, and South America yielded a group of geographic strains which, when brought into the laboratory and intercrossed, gave varied, and surprising, results. Not all the strains could be mated with equal ease; some matings produced no hybrids at all, while others yielded fertile female hybrids and F1 males that were completely sterile (Dobzhansky and Spassky, 1959). Thus, the species Drosophila paulistorum represents remarkably favorable material for the study of the genetics of incipient reproductive isolation. It is distributed over a vast area, it has only three pairs of chromosomes, and above all, it offers a number of the very interesting race-species "borderline cases" for analysis. We have here a series of intergrading subspecies, such that when the extremes of this series come together the reproductive isolation between them is virtually complete. Yet, gene exchange via geographically intermediate populations is possible, although it is an open question how much exchange actually does occur. The purpose of the present work is to analyze the D. paulistorum complex of nascent species with regard to the causation of the hybrid male sterility observed in crosses between the subspecies. 1 Submitted in partial fulfillment of the requiremnents for the degree of Doctor of Philosophy, in the Faculty of Pure Science, Columbia University.

Evolution of communication in bees and its role in speciation

Abstract: Several families of bees have species that are either social or subsocial. Only the subfamily Apinae, however, possesses species that are known to have reached a social level sufficiently high as to have developed some method or methods of communication among their workers. The Apinae social tribes,. in phylogenetic order, are the following: Bombini (bumblebees), Meliponini (stingless bees), and Apini (honey bees). In these bees, the evolution of communication systems is indicated by the order of their increasing complexity, and by the parallel evolution of other characters of the species in which a given system of communication is found. Ribbands (1953) suggested that exchange of food among adult bees was the first step toward communication. In fact, Bombus species neither engage in food exchange nor have a system of communication (Brian 1952, Free 1951). As far as nest structure is concerned, they are the most primitive Apinae (Kerr and Laidlaw, 1956). A first evolutionary step may have occured when foraging was so intense that a field bee gave nectar to a house bee instead of delivering it directly to the storage pots. Such house bees, when they became foragers, may have been more attracted to flowers having the same odor as the nectar they received. Indeed, workers of the most primitive Meliponini known, namely Trigona silvestrii, alert their mates to look for an artificial source of food only when a drop of scent is added to the feeder (Lindauer and Kerr, 1958). The nest structure of these bees resembles very much the one found in Bombus. The communication of the location of either a source of food or a place to live by odor is a method found in all species of Meliponini and Apini, A further step was reached when returned bees, while delivering nectar, ran excitedly in zig-zag movements knocking bees not engaged in field work with their heads or bodies. Such a method was discovered first by Lindauer (1956) in the Indian meliponid Trigona iridipennis and later by Lindauer and Kerr (1958) in ten species of Brazilian meliponids. By

Evolutionary aspects of aberrant meiosis in some pentatominae (heteroptera)

Abstract: The normal males of most animals may now and then produce a few sperms that carry an abnormal number of chromosomes. In the great majority of cases these are the result of a mitotic accident that occurred somewhere in the course of development. However, there are some species in which aberrant sperms are not accidental but are produced regularly in a certain region of all testes. Conditions such as these have been encountered in 21 species belonging to the insect Family of Pentatomidae (Heteroptera) and, more specifically, to the Subfamily Pentatominae. In most such species one entire compartment or lobe of every testis produces nothing but sperms with aberrant chromosome numbers. So bizarre are the meiotic deviations through which this is brought about that the testicular compartment in question has been called the "harlequin lobe." All the evidence indicates that such sperms very rarely produce viable offspring and they therefore play at most an indirect role in the hereditary mechanism of the species. Nevertheless they are produced in huge numbers and it is an interesting question how so wasteful a feature could have become establsihed in so many species. The cytological features of the harlequin meiosis have been treated elsewhere (Schrader, 1960) and the present account is primarily concerned with the evolutionary aspects of the harlequin lobe.

The behavior of cytoplasmic pollen sterility in populations

Abstract: Pollen sterility in plants is the most frequently observed character ~nduced by the cytoplasm. The extensive material on this subject has been thoroughly reviewed by Rhoades (1955) and by Edwardson (1956). In almost all cases, disturbances in the development of pollen arise when particular genes are located in particular cytoplasms. This occurs mostly in crosses between different species or different local strains of the same species. The same phenomenon has been frequently observed in inbred lines of cultivated plants. As an example, the classical case of pollen sterility arising in crosses between two \"strains\" of Linum, tall and procumbent, will be briefly reviewed. The case was originally described by Bateson and Gairdner (1921) and further analysed by Chittenden and Pellew (1927) and by Gairdner (1929). It appears likely that the two \"strains\" of Linum used in these experiments represent actually differ~nt species (Gajewski, 1937). If the strains tall and procumbent are crossed in both reciprocal directions, the F IS are completely fertile. If the original female parent had been tall, the F 2 is also fertile. If, however, the original female parent had been procumbent, one fourth of the F 2 plants are pollen sterile, indicating Mendelian segregation. It is concluded that the original tall strain was homozygous for a recessive gene f which, if it becomes homozygous in procumbent

Heritability of geographic variation in trunk segmentation in the red-backed salamander, plethodon cinereus

Abstract: It was recently shown by Highton and Grobman (1956) that there is geographic variation in the number of trunk vertebrae in two species of salamanders, Plethodon cinereus and P. richmondi. In the redbacked salamander, X-ray photographs of samples from New Brunswick, Indiana, New Jersey, Virginia, Tennessee and North Carolina indicated that in each area the modal number of trunk vertebrae was 20, while all of the specimens from Georgia possessed more than 20 trunk vertebrae (range, 21 to 23). On the basis of this variation, the Georgia populations were recognized as a separate subspecies, P. c. polycentratus. Highton (1957) outlined a method that made it possible to estimate, with 940/0 accuracy, the number of trunk vertebrae in Plethodon by counting the costal grooves. This method has been used to estimate the number of trunk vertebrae in available museum material from the known range of the red-backed salamander. The resulting data indicate that the amount of geographic variation in number of body segments is greater than indicated in our original report. In addition to the Georgia populations, there are a number of others which also average 21 or more trunk vertebrae. These occur in eastern Long Island, the southern portion of the Del-Mar-Va Peninsula, the southern Coastal Plain of Maryland, and parts of the Piedmont and Coastal Plain Provinces of Virginia and North Carolina. There is also a region, including the western portions of New York, Pennsylvania and Maryland, adjacent northeastern Ohio, and parts of eastern and central

Chromosomal polymorphism in egyptian populations of drosophila melanogaster

Abstract: .. D. BuseKII • 0. M£LANOGAST£R most world-wide (the former species being, however, more at home in cooler and the latter in hotter countries). Both species are \"animal weeds\" associated with man, their original distribution areas being unknown. Nevertheless, the two species contrast sharply in that D. melanogaster is very frequently chromosomally polymorphic (Dubinin, Sokolov and Tiniakov 1936, 1945; Bridges and Brehme 1944; Patterson and Stone 1952), while D. simulans has not been observed to deviate from a strict chromosomal monomorphism. The purpose of the present article is to report observations on the chromosomes of certain populations of D. melanogaster and D. simulans in Egypt. These two species constitute the bulk of the Drosophila fauna of that country, three other species (D. immigrans, D. buzzattii, and D. busckii) having been encountered only sporadically and in few locations.