Showing papers by "A. Townsend Peterson published in 1992"

Phylogeny and Rates of Molecular Evolution in the Aphelocoma Jays (Corvidae)

Abstract: -I examined hypotheses of Aphelocoma jay phylogeny derived from allozyme data. Results from various algorithms differ in details, but the overall patterns are consistent: Scrub Jays (A. coerulescens) and Unicolored Jays (A. unicolor) were derived independently from different populations of Gray-breasted Jays (A. ultramarina). Within Scrub Jays, the californica subspecies group was derived from the populations of interior North America (woodhouseii group). One Unicolored Jay population and two Scrub Jay populations, all strongly differentiated, are placed consistently at the base of the phylogeny, but phenotypic, biogeographic, and theoretical evidence suggests that these populations represent rapidly evolving populations derived from within populations of their respective species. Because analyses of rates of molecular evolution demonstrate significant rate heterogeneity, I suggest that the application of a molecular clock to date-splitting events in the Aphelocoma jays is not a valid approach. Received 18 February 1991, accepted 3 July 1991. THE THREE species of Aphelocoma jays range throughout western and southern North America and northern Central America (Fig. 1; Pitelka 1951). Scrub Jays (A. coerulescens) range from Oregon and Wyoming south to the Isthmus of Tehuantepec, with disjunct populations on Santa Cruz Island off the coast of southern California and in peninsular Florida. The 15 subspecies form five groups, each characterized by unique combinations of plumage, morphological, and behavioral characters (Fig. 1; Pitelka 1951, Peterson 1991a): (1) woodhouseii group (Wyoming and southeastern Oregon south through Great Basin and along both sides of Rocky Mountains, and then along interior slopes of Sierra Madre Oriental and Sierra Madre Occidental of northern Mexico to southern Chihuahuan Desert and vicinity of Mexico City); (2) californica group (western Oregon, California, and Baja California); (3) sumichrasti group (southern Mexico); (4) coerulescens group (peninsular Florida); and (5) insularis group (Santa Cruz Island). The Gray-breasted Jay (A. ultramarina) ranges throughout the mountains of northern and central Mexico and the southwestern United States. The seven subspecies fall into three groups characterized by unique combinations of morphological and behavioral characters (Fig. 1; Pitelka 1951): (1) potosina group (Sierra Madre Oriental); (2) wollweberi group (Si' Present address: Department of Zoology, Field Museum of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, Illinois 60605, USA. erra Madre Occidental); and (3) ultramarina group (Transvolcanic Belt). Finally, the Unicolored Jay (A. unicolor) consists of five allopatric populations, each a separate subspecies, in southern Mexico and northern Central America (Pitelka 1951). The Aphelocoma jays have been the subject of numerous comparative studies. Evaluations of social systems in the genus have led to advances in understanding ecological factors important in the evolution of sociality (Woolfenden and Fitzpatrick 1984, Fitzpatrick and Woolfenden 1986, Brown 1987, Peterson and Burt, in press). Differential habitat use in Scrub Jays (Peterson and Vargas 1992) is correlated with geographic variation in beak shape, suggesting that beak shapes have responded to natural selection (Peterson, in prep.). Integration of phylogenetic information into such investigations will allow an important new dimension of understanding (Brooks and McLennan 1990). Hence, I have attempted to estimate the phylogeny of the differentiated forms in the genus. Rates of molecular evolution. -Since the publication of the influential paper of Zuckerkandl and Pauling (1962), the idea of a "molecular clock" has been controversial in molecular biology and systematics. The clock concept is based on the assumption of a uniform rate of molecular evolution in a group. If the uniform rate assumption were correct, the accumulation of genetic differentiation between sister taxa would be time-invariant, and divergence times could be estimated from genetic distances. The clock concept is an important feature of

Genetic Variation and Differentiation in Mexican Populations of Common Bush-Tanagers and Chestnut-Capped Brush-Finches

Abstract: Genetic differentiation among four Mexican populations each of Common Bush-tanagers (Chlorospingus ophthalmicus) and Chestnut-capped Brush-finches (Atlapetes brunneinucha) was evaluated using allozyme electrophoresis. In both species, although levels of within-population variation are moderate, among-population variation is extreme, in- cluding fixed differences among populations. Genetic variation is significantly reduced in some populations on the smallest habitat islands. Differentiation is apparently unrelated to geographic distance among populations, and effects of habitat island size and isolation on genetic differentiation are not clear. Populations of the Sierra de 10s Tuxtlas in Veracruz, however, are strongly differentiated in both species.

Philopatry and genetic differentation in the Aphelocoma jays (Corvidae)

Abstract: The effects of philopatry on levels of genetic differentiation were examined in the Aphelocoma jays through comparisons of gray-breasted jays (A. ultramarina; highly philopatric) and scrub jays (A. coerulescens; dispersing). Gray-breasted jays breed cooperatively in groups of up to 25 individuals, with individuals typically breeding either on the natal territory or on adjacent territories. Western North American scrub jays breed in non-cooperative pairs, with individuals typically dispersing at least 0.5 km, and often much farther. Genetic differentiation among six populations in northern Mexico and the south-western United States in each of the species was compared using starch-gel electrophoresis of protein products of 29 presumptive genetic loci. Strong differences in levels of genetic differentiation exist between the two species, both when measured using F-statistics and in terms of the slope of the isolation by distance relationship. These results suggest that social systems involving high degrees of philopatry may lead to considerably elevated rates of genetic differentiation and speciation.