A Molecular Phylogeny of Warbling-Finches (Poospiza): Paraphyly in a Neotropical Emberizid Genus

We investigated the phylogenetic relationships of 12 species within a single genus of neotropical passerine (Poospiza) using 849 bp (283 codons) of the cytochrome b mitochondrial gene. We further explored evolutionary affinities of these taxa using sequence from an additional 47 thraupine (tanagers) and 7 emberizine (sparrows and buntings) genera, members of the predominantly New World family Emberizidae. Poospiza have traditionally been considered part of the emberizine radiation. However, our analyses suggest that members of this genus are more closely related to some thraupine lineages than they are to the other neotropical emberizine genera included in our study (Atlapetes, Embernagra, Melopyrrha, Phrygilus, Saltatricula, Tiaris). Although member taxa are closely related, the genus Poospiza appears to be paraphyletic with representatives of 6 thraupine genera (Cnemoscopus, Cypsnagra, Hemispingus, Nephelornis, Pyrrhocoma, Thylpopsis) interspersed among four well-supported Poospiza clades. The majority of species within this Poospiza–thraupine clade have geographic ranges that are exclusive to, or partially overlap with, the Andes Mountains. It is probable that these mountains have played an important role in driving cladogenesis within this group. Sequence divergence (transversions only; mean 4.7 ± 1.3%) within the clade suggests that much of this diversification occurred within the late Miocene and Pliocene, a period coincident with major orogenic activity in central-western South America.     

Patterns of Genetic Population Differentiation in Four Species of Amazonian Frogs: A Test of the Riverine Barrier Hypothesis1

Patterns and levels of allozyme variation among populations of Amazonian frogs were used to test the riverine barrier hypothesis of species differentiation. Two frog species were sampled from each of the two main forest habitats on both banks of the Juruá River in the southwestern Brazilian Amazon Basin at various points along its course to contrast different barrier strengths. Scarthyla ostinodactyla and Scinax rubra were sampled from flooded forest (varzea), and Physalaemus petersi and Epipedobates femoralis from non-flooded forest (terra firme). All species showed high levels of within-population genetic variation. Average Nei's (1978) and Rogers’ (1972) genetic distances between sampled sites for all species were high indicating substantial among-population differentiation. The observation of low gene flow between sampled sites within species was further substantiated with Slatkin's (1993) M? analyses. Randomization tests suggested that there was some population structure at a few assayed polymorphic loci that was consistent with the riverine barrier hypothesis. However, it was apparent from the raw allozyme frequency data that these results were largely driven by substantial differentiation at one or a few collecting localities rather than by basin-wide patterns of riverine differentiation. Phenograms using genetic distance matrices supported this interpretation. Patterns of geographic variation are probably more consistent with the idea of this region being a zone of secondary contact.     

Genetic population structure of the sagebrush Brewer’s sparrow, <Emphasis Type="Italic">Spizella breweri breweri</Emphasis>, in a fragmented landscape at the northern range periphery

Assessing the genetic consequences of habitat fragmentation is a crucial step in conservation planning for species in endangered habitats. We tested for the impact of natural habitat fragmentation on gene flow and genetic diversity in seven northern breeding locations of the sagebrush Brewer’s sparrow, Spizella breweri breweri. Genetic analyses using five highly variable DNA microsatellite loci suggested that individuals sampled within a sagebrush landscape fragmented by natural elements such as coniferous forest, comprise a single genetic population and that gene flow among them is unimpeded. We posit that juvenile dispersal links seemingly isolated breeding locales of this species, and discuss implications of our findings for conservation of migratory songbirds in the northern portion of their ranges in light of potential shifts in distribution due to climate change.     

Genetic diversity across the range of a temperate lizard

Aim  To examine range-wide patterns of genetic diversity in association with range limits in a broadly distributed temperate lizard, and to identify the contributions of a series of environmental, geographical and historical variables to the observed patterns. Reduced genetic diversity may limit local adaptation in peripheral populations, thereby limiting their ability to adapt to marginal environmental conditions, possibly explaining the existence of temporally stable range limits.
Location  Various sampling locales throughout eastern and central USA and southern Ontario, Canada.
Methods  Genetic diversity of nuclear DNA microsatellites was estimated for each of 38 populations from across the range of eastern North America's most broadly distributed lizard, the five-lined skink, Plestiodon fasciatus (Linnaeus, 1758).
Results  Local climatic conditions and an interaction between distance from range border and glaciation history best predicted a population's present-day genetic diversity. Overall, peripheral populations had reduced genetic diversity relative to that of central populations, but this difference was attributable to the reduced genetic diversity in peripheral populations to the north and west that are not bordered by any obvious physical boundaries.
Main conclusions  Some, but not all, peripheral populations had reduced genetic diversity relative to that of more central populations, which probably arose through an interaction of ecological and historical factors. Peripheral populations that were bordered by an obvious boundary (e.g. an ocean) had higher diversity than peripheral populations that were not bordered by an obvious physical barrier to range expansion, suggesting that reduced intrapopulation genetic diversity is associated with range limits in the five-lined skink.