Promote Gene Flow Research Articles

Pollination biology ofImpatiens hainanensis(Balsaminaceae) populations at different altitudes

The genus Impatiens, known as “dicotyledonous orchids”, is of great interest to pollination biologists because of its extremely wide diversity and different types of specialized pollinators. In this study, populations of Impatiens hananensis, endemic to Hainan Island, distributed at three different altitudes were studied. Floral phenology, floral structure, pollen viability and stigma activity, floral visitors and their behavior, and the breeding system were determined. Results showed that the average life span of a single flower was 4.10 ± 0.46 d; the male and female flowers lasted 3.15 ± 0.24 d and 0.95 ± 0.36 d, respectively. The species’ flowering peak was in early August, and the high altitude population flowered the latest. The pollen viability of a single flower appears in the trend of first increased then decreased with the flowering time went on, and reached to the highest on the second flowering day in low and middle altitude populations, and which declined gradually with the flowering time went on in high altitude population. Stigma activity generally rose as flowering time went on, but this measure was lower in high altitude population on different flowering days. The main pollinators were Amegilla leptocoma and A. zonata; A. leptocoma was the main visitor in low and middle altitude populations while A. zonata was in the high altitude population. We observed no automatic self-pollination or apomixis in I. hainanensis, and hand-pollination increased the fruit set (75–90%), 468 生 物 多 样 性 Biodiversity Science 第 22卷 compared to the natural situation (40–60%). This lower natural pollination success rate was especially true in the high altitude population where pollination was most limited. Therefore, conservation work with Impatiens hainanensis should protect both habitats and effective pollinators of I. hainanensis in order to promote gene flow via pollinators and seed movement among populations at different altitude via pollinators, and maintain the population genetic diversity and effective population size of Impatiens hainanensis.

Seascape analysis reveals regional gene flow patterns among populations of a marine planktonic diatom.

We investigated the gene flow of the common marine diatom, Skeletonema marinoi, in Scandinavian waters and tested the null hypothesis of panmixia. Sediment samples were collected from the Danish Straits, Kattegat and Skagerrak. Individual strains were established from germinated resting stages. A total of 350 individuals were genotyped by eight microsatellite markers. Conventional F-statistics showed significant differentiation between the samples. We therefore investigated whether the genetic structure could be explained using genetic models based on isolation by distance (IBD) or by oceanographic connectivity. Patterns of oceanographic circulation are seasonally dependent and therefore we estimated how well local oceanographic connectivity explains gene flow month by month. We found no significant relationship between genetic differentiation and geographical distance. Instead, the genetic structure of this dominant marine primary producer is best explained by local oceanographic connectivity promoting gene flow in a primarily south to north direction throughout the year. Oceanographic data were consistent with the significant FST values between several pairs of samples. Because even a small amount of genetic exchange prevents the accumulation of genetic differences in F-statistics, we hypothesize that local retention at each sample site, possibly as resting stages, is an important component in explaining the observed genetic structure.

Variable salinity tolerance in ascidian larvae is primarily a plastic response to the parental environment

Both phenotypic plasticity and local genetic adaptation may contribute to a species’ ability to inhabit different environmental conditions. While phenotypic plasticity is usually considered costly, local adaptation takes generations to respond to environmental change and may be constrained by strong gene flow. The majority of marine species have complex life-cycles with pelagic stages that might be expected to promote gene flow and plastic responses, and yet several notable examples of local adaptation have been found in species with broadcast larvae. In the ascidian, Ciona intestinalis (Linnaeus, 1767),—a common marine species with broadcast spawning and a short larval stage—previous studies have found marked differences in salinity tolerance of early life-history stages among populations from different salinity regimes. We used common-garden experiments to test whether observed differences in salinity tolerance could be explained by phenotypic plasticity. Adult ascidians from two low salinity populations [2–5 m depth, ~25 practical salinity units (PSU)], and two full salinity populations (25–27 m depth, ~31 PSU) were acclimated for 2–4 weeks at both 25 and 31 PSU. Gametes were fertilized at the acclimation salinities, and the newly formed embryos were transferred to 10 different salinities (21–39 PSU) and cultured to metamorphosis. Adult acclimation salinity had an overriding and significant effect on larval metamorphic success: tolerance norms for larvae almost fully matched the acclimation salinity of the parents, independent of parental origin (deep or shallow). However we also detected minor population differences that could be attributed to either local adaptation or persistent environmental effects. We conclude that differences in salinity tolerance of C. intestinalis larvae from different populations are driven primarily by transgenerational phenotypic plasticity, a strategy that seems particularly favourable for an organism living in coastal waters where salinity is less readily predicted than in the open oceans.

The spatio-temporal colonization and diversification across the Indo-Pacific by a ‘great speciator’ (Aves,Erythropitta erythrogaster)

The Indo-Pacific region has arguably been the most important area for the formulation of theories about biogeography and speciation, but modern studies of the tempo, mode and magnitude of diversification across this region are scarce. We study the biogeographic history and characterize levels of diversification in the wide-ranging passerine bird Erythropitta erythrogaster using molecular, phylogeographic and population genetics methods, as well as morphometric and plumage analyses. Our results suggest that E. erythrogaster colonized the Indo-Pacific during the Pleistocene in an eastward direction following a stepping stone pathway, and that sea-level fluctuations during the Pleistocene may have promoted gene flow only locally. A molecular species delimitation test suggests that several allopatric island populations of E. erythrogaster may be regarded as species. Most of these putative new species are further characterized by diagnostic differences in plumage. Our study reconfirms the E. erythrogaster complex as a 'great speciator': it represents a complex of up to 17 allopatrically distributed, reciprocally monophyletic and/or morphologically diagnosable species that originated during the Pleistocene. Our results support the view that observed latitudinal gradients of genetic divergence among avian sister species may have been affected by incomplete knowledge of taxonomic limits in tropical bird species.

Testing the Role of Meander Cutoff in Promoting Gene Flow across a Riverine Barrier in Ground Skinks (Scincella lateralis)

Despite considerable attention, the long-term impact of rivers on species diversification remains uncertain. Meander loop cutoff (MLC) is one river phenomenon that may compromise a river’s diversifying effects by passively transferring organisms from one side of the river to the other. However, the ability of MLC to promote gene flow across rivers has not been demonstrated empirically. Here, we test several predictions of MLC-mediated gene flow in populations of North American ground skinks (Scincella lateralis) separated by a well-established riverine barrier, the Mississippi River: 1) individuals collected from within meander cutoffs should be more closely related to individuals across the river than on the same side, 2) individuals within meander cutoffs should contain more immigrants than individuals away from meander cutoffs, 3) immigration rates estimated across the river should be highest in the direction of the cutoff event, and 4) the distribution of alleles native to one side of the river should be better predicted by the historical rather than current path of the river. To test these predictions we sampled 13 microsatellite loci and mitochondrial DNA from ground skinks collected near three ancient meander loops. These predictions were generally supported by genetic data, although support was stronger for mtDNA than for microsatellite data. Partial support for genetic divergence of samples within ancient meander loops also provides evidence for the MLC hypothesis. Although a role for MLC-mediated gene flow was supported here for ground skinks, the transient nature of river channels and morphologies may limit the long-term importance of MLC in stemming population divergence across major rivers.

Coupling genetic and species distribution models to examine the response of the Hainan Partridge (Arborophila ardens) to late quaternary climate.

Understanding the historical dynamics of animal species is critical for accurate prediction of their response to climate changes. During the late Quaternary period, Southeast Asia had a larger land area than today due to lower sea levels, and its terrestrial landscape was covered by extensive forests and savanna. To date, however, the distribution fluctuation of vegetation and its impacts on genetic structure and demographic history of local animals during the Last Glacial Maximum (LGM) are still disputed. In addition, the responses of animal species on Hainan Island, located in northern Southeast Asia, to climate changes during the LGM are poorly understood. Here, we combined phylogeographic analysis, paleoclimatic evidence, and species distribution models to examine the response of the flightless Hainan Partridge (Arborophila ardens) to climate change. We concluded that A. ardens survived through LGM climate changes, and its current distribution on Hainan Island was its in situ refuge. Range model results indicated that A. ardens once covered a much larger area than its current distribution. Demographic history described a relatively stable pattern during and following the LGM. In addition, weak population genetic structure suggests a role in promoting gene flow between populations with climate-induced elevation shifts. Human activities must be considered in conservation planning due to their impact on fragmented habitats. These first combined data for Hainan Partridge demonstrate the value of paired genetic and SDMs study. More related works that might deepen our understanding of the responses of the species in Southeast Asia to late Quaternary Climate are needed.

Will arboreal mammals use rope-bridges across a highway in eastern Australia?

Artificial structures designed to promote road-crossing by arboreal mammals are increasingly being installed in Australia but there is a limited understanding of their usefulness. We studied five 50–70-m-long rope-bridges (encompassing three designs) erected across the Pacific Highway, a major freeway in eastern Australia. Native arboreal mammals showed a willingness to explore these structures, being detected by camera traps on four rope-bridges. The vulnerable squirrel glider (Petaurus norfolcensis) crossed on one rope-bridge at least once every 4.5 weeks over a 32-week period. The feathertail glider (Acrobates pygmaeus), common ringtail possum (Pseudocheirus peregrinus) and the common brushtail possum (Trichosurus vulpecula) were detected on one of two rope-bridges that extended under the freeway at creek crossings. The feathertail glider was detected on all three rope-bridge designs. Our results suggest that rope-bridges have the potential to restore habitat connectivity disrupted by roads for some arboreal mammals. Further research is needed to refine the design and placement of rope-bridges as well as to determine whether these structures promote gene flow.

Pleistocene and ecological effects on continental‐scale genetic differentiation in the bobcat (Lynx rufus)

The potential for widespread, mobile species to exhibit genetic structure without clear geographic barriers is a topic of growing interest. Yet the patterns and mechanisms of structure--particularly over broad spatial scales--remain largely unexplored for these species. Bobcats occur across North America and possess many characteristics expected to promote gene flow. To test whether historical, topographic or ecological factors have influenced genetic differentiation in this species, we analysed 1 kb mtDNA sequence and 15 microsatellite loci from over 1700 samples collected across its range. The primary signature in both marker types involved a longitudinal cline with a sharp transition, or suture zone, occurring along the Great Plains. Thus, the data distinguished bobcats in the eastern USA from those in the western half, with no obvious physical barrier to gene flow. Demographic analyses supported a scenario of expansion from separate Pleistocene refugia, with the Great Plains representing a zone of secondary contact. Substructure within the two main lineages likely reflected founder effects, ecological factors, anthropogenic/topographic effects or a combination of these forces. Two prominent topographic features, the Mississippi River and Rocky Mountains, were not supported as significant genetic barriers. Ecological regions and environmental correlates explained a small but significant proportion of genetic variation. Overall, results implicate historical processes as the primary cause of broad-scale genetic differentiation, but contemporary forces seem to also play a role in promoting and maintaining structure. Despite the bobcat's mobility and broad niche, large-scale landscape changes have contributed to significant and complex patterns of genetic structure.

Climate induced changes in matrix suitability explain gene flow in a fragmented landscape – the effect of interannual rainfall variability

In fragmented landscapes, the survival of species and the maintenance of populations with healthy genetic structures will largely depend on movement/dispersal of organisms across matrix areas. In this article, we highlight that effects of fragmentation and climate change occur simultaneously and may enhance or mitigate each other. We systematically analyzed the effect of increasing interannual variation in rainfall on the genetic structure of two neighbouring small mammal subpopulations in a fragmented savanna landscape. The effect of interannual rainfall variation is analyzed for two contrasting scenarios that differ in mean annual rainfall and are both close to a dispersal threshold. Scenario 1 (low mean annual rainfall) lies slightly below this threshold and scenario 2 (high mean annual rainfall) slightly above, i.e. the amount of rainfall in an average rainfall year prevents dispersal in scenario 1, but promotes gene flow in scenario 2. We show that the temporal dynamics of the matrix was crucial for gene flow and the genetic structure of the neighbouring small mammal subpopulations. The most important result is that the increase in rainfall variability could both increase and decrease the genetic difference between the subpopulations in a complex pattern, depending on the scenario and on the amount of variation in rainfall. Finally, we discuss that the relevance of the matrix as temporarily suitable habitat may become a key aspect for biodiversity conservation. We conclude to incorporate temporal changes in matrix suitability in metapopulation theory since local extinctions, gene flow and re‐colonization are likely to be affected in fragmented landscapes with such dynamic matrix areas.

Phylogeography of Steller sea lions: relationships among climate change, effective population size, and genetic diversity

The biology of the Steller sea lion (Eumetopias jubatus) has been the subject of intense scientific investigation. This is primarily due to the rapid decline of population size in the western part of the species' range since the 1970s and the subsequent Threatened and Endangered species listings that had direct impact on the management of one of the world's largest fisheries. The Steller sea lion has emerged as an indicator species representing the environmental health of the North Pacific Ocean and Bering Sea. In this study, to better understand the historical processes that have culminated in the extant populations of E. jubatus, a large genetic data set consisting of 3 mitochondrial regions for > 1,000 individuals was analyzed from multiple phylogeographic and demographic perspectives. The results describe the role of climate change in shaping the population structure of E. jubatus. Climatically associated historical processes apparently involved differential demographic responses to ice ages (and putative glacial vicariance) dependent on population size. Ice ages during times of small effective population size promoted restricted gene flow and fragmentation, and ice ages occurring during times of large population size promoted gene flow and dispersal. These results illustrate that effective population size has a profound effect on how species respond to climate change, an observation with obvious implications for large mammals and endangered species under the present conditions of imminent anthropogenically caused climate change. In addition, the results confirm previous observations of strongly biased historic and contemporary gene flow involving dispersal from west to east. Furthermore, phylogenetic patterns in combination with available fossil data suggest the potential of an Asian origin of E. jubatus. The results of this study provide a detailed scenario for the history that has shaped contemporary populations of E. jubatus

A Comparison of Frugivory and Scatter-Hoarding Seed-Dispersal Syndromes

Frugivory (animals ingest all or part of fleshy-fruits and defecate or regurgitate seeds) and scatter-hoarding (animals store seeds in small caches in soil) are two important vertebrate-mediated seed dispersal syndromes. In both instances, there is an exchange of food for seed transport, but there are many important differences. For example, the seeds of frugivore-dispersed plants are often clumped in feces or under roosts and the microsite of depostion is often unsuitable for seedling establishment. However, frugivores can transport seeds long distances allowing plants to colonize new areas and promoting gene flow between populations. Scatter-hoarding animals, on the other hand, actively space seeds in microsites that often favor seedling establishment, but don’t move seeds very far. Both modes of seed dispersal can be very effective, but in different way. Some species of plants have evolved propagules that take advantage of both modes of dispersal in two separate phases (i.e., diplochory), apparently to obtain both types of benefits.

Female “dispersal” in hamadryas baboons: Transfer among social units in a multilevel society

Unlike most cercopithecines, hamadryas baboons (Papio hamadryas hamadryas) are characterized by female-biased dispersal. To clarify this pattern within the context of their hierarchical social system (comprising one-male units, clans, bands, and troops), we report here 7 years of data on female transfers among social units in wild hamadryas baboons in Ethiopia. Female tenure in one-male units (OMUs) ranged from 1 to 2,556 days (N = 208) and survival analysis revealed a median tenure length of 1,217 days (40 months). Changes in OMU membership consisted almost exclusively of takeovers by males, not voluntary transfer. Of 130 takeovers, 67% occurred within the band and 33% across bands, and, of the 22 takeovers for which we have clan membership data, 77% occurred within, not between, clans. These results reinforce the notion that hamadryas female dispersal is not analogous to sex-biased dispersal in other taxa, because (1) at least in Ethiopian populations, females do not disperse voluntarily but are transferred, often forcibly, by males; (2) only dispersal between bands will promote gene flow, whereas females are most often rearranged within bands; (3) hamadryas females undergo social dispersal but not usually locational dispersal; and (4) while male hamadryas are far more philopatric than females, they have been observed to disperse. It thus appears that the ancestral baboon pattern of female philopatry and male dispersal has evolved into a system in which neither sex is motivated to disperse, but females are forcibly transferred by males, leading to female-mediated gene flow, and males more rarely disperse to find females.

Strategies for conserving forest genetic resources in the face of climate change

Conservation of genetic diversity is important for continued evolution of populations to new environments, as well as continued availability of traits of interest in genetic improvement programs. Rapidly changing climates present new threats to the conservation of forest genetic resources. We can no longer assume that in situ reserves will continue to preserve existing genetic diversity. Management of reserves should become more active. In some reserves, existing genetic diversity should be preserved by creating stands that are more resistant to threats using silvicultural treatments such as thinning and prescribed burning. In other reserves, natural selection and adaptation to changed environments should be promoted by increasing within population genetic diversity and promoting gene flow. This may be done by locating reserves in areas of high environmental heterogeneity, minimizing fragmentation, and using assisted colonization to increase genetic diversity by establishing populations adapted to future climates within or adjacent to reserves. Threats to native stands from climate change and other interacting threats should bring a renewed importance to ex situ collections, particularly for rare and disjunct populations and those at the warmer and drier edges of a species range. Assisted colonization to move threatened populations to new environments must be considered as an additional conservation measure.

Phylogeography of the sea star Marthasterias glacialis (Asteroidea, Echinodermata): deep genetic divergence between mitochondrial lineages in the north-western mediterranean

We explore the phylogeography of the broadcast spawner Marthasterias glacialis along south Europe and Azores. Sequences of the cytochrome c oxidase gene from 225 specimens, belonging to 10 localities, were analysed. We found 73 haplotypes grouped within two lineages (divergence 2.9%). One lineage was Atlanto–Mediterranean, whereas another one was exclusively Mediterranean. Estimation of lineages split goes back to 830,000–580,000 (±120,000) years ago. This suggests that sea-level oscillations during the Pleistocene glaciations promoted gene flow interruption, lineage divergence between basins and cryptic speciation. Secondary contact between populations allowed a recolonization of the Mediterranean by the Atlantic lineage. When animals of the Atlanto–Mediterranean lineage were considered separately, F st index and AMOVA did not show significant differences between populations along either the Iberian Peninsula or basins. Isolation by distance between populations was not detected, and only populations of Plymouth and Azores showed significant differences to all the others. The remoteness of Azores islands might explain the structure of this population. Haphazard arrival of larvae and local extinctions rather than contemporary restricted gene flow might be responsible for the distinctive population structure of Plymouth.

Population differentiation of the shore crab <i>Carcinus maenas</i> (Brachyura: Portunidae) on the southwest English coast based on genetic and morphometric analyses

Carcinus maenas has a planktonic larval phase which can potentially disperse over large distances. Consequently, larval transport is expected to play an important role in promoting gene flow and determining population structure. In the present study, population structuring on the southwest coast of England was analysed using molecular and morphometric approaches. Variation at eight microsatellite loci suggested that the individuals sampled within this region comprise a single genetic population and that gene flow among them is not restricted. Nevertheless, the FST values estimated across loci for all populations suggested that the Tamar population was significantly different from the Exe, Camel and Torridge populations. This differentiation is not explained by isolation by distance, and coastal hydrological events that are apparently influencing larval flux might be the cause of this pattern. Morphometric analysis was also performed. Analysis of carapace and chela shape variation using landmark-based geometric morphometrics revealed extensive morphological variability, as the multivariate analysis of variance showed significant morphometric differences among geographic groups for both sexes. Thus, the morphological differentiation found may be a plastic response to habitat-specific selection pressures.

Consequences of near and far between‐population crosses for offspring fitness in a rare herb

Crosses between plants from different populations may result in heterosis or outbreeding depression. However, despite its importance for conservation, little is known about the spatial scale over which these effects may arise. To investigate the consequences of between-population crosses at two distinct spatial scales, we conducted reciprocal crosses between four populations from two regions in the rare perennial herb Aster amellus. We assessed seed set and offspring fitness in a common garden experiment. Overall, between-population crosses within regions (10 km) resulted in 8% lower seed set than within-population crosses, while between-region crosses (70 km) resulted in 17% higher seed set than within-population crosses. Moreover, offspring from between-population crosses produced 18% more flower heads than offspring from within-population crosses. We conclude that hybridisation between A. amellus plants from different populations did not lead to immediate outbreeding depression and, thus, could represent a valid conservation option to increase genetic diversity. Moreover, our results suggest that the distance between populations affects the outputs of between-population crosses and therefore needs to be taken into account when promoting gene flow between populations.

WHEN COLD IS BETTER: CLIMATE-DRIVEN ELEVATION SHIFTS YIELD COMPLEX PATTERNS OF DIVERSIFICATION AND DEMOGRAPHY IN AN ALPINE SPECIALIST (AMERICAN PIKA,OCHOTONA PRINCEPS)

The genetic consequences of climate-driven range fluctuation during the Pleistocene have been well studied for temperate species, but cold-adapted (e.g., alpine, arctic) species that may have responded uniquely to past climatic events have received less attention. In particular, we have no a priori expectation for long-term evolutionary consequences of elevation shifts into and out of sky islands by species adapted to alpine habitats. Here, we examined the influence of elevation shifts on genetic differentiation and historical demography in an alpine specialist, the American pika (Ochotona princeps). Pika populations are divided into five genetic lineages that evolved in association with separate mountain systems, rather than lineages that reflect individual sky islands. This suggests a role for glacial-period elevation shifts in promoting gene flow among high-elevation populations and maintaining regional cohesion of genetic lineages. We detected a signature of recent demographic decline in all lineages, consistent with the expectation that Holocene climate warming has driven range retraction in southern lineages, but unexpected for northern populations that presumably represent postglacial expansion. An ecological niche model of past and future pika distributions highlights the influence of climate on species range and indicates that the distribution of genetic diversity may change dramatically with continued climate warming.

Phylogeographic patterns and demographic history ofSchiedea globosa(Caryophyllaceae) on the Hawaiian Islands

Geomorphological changes have been demonstrated to have had profound impacts on biodiversity, often leading to demographic expansions and contractions and allopatric divergence of taxa. We examined DNA sequence variation at two nuclear and one maternally inherited plastid locus among 10 populations of Schiedea globosa on the Hawaiian Islands to assess the primary factors shaping genetic structure, phylogeographic patterns, and the importance of geographic isolation to population divergence. Schiedea globosa has characteristics that may promote gene flow, including wind pollination and rafting of plants in ocean currents. However, we detected significant differentiation among populations on all islands except Hawaii, with the maternally inherited plastid locus having the greatest genetic structure (F(ST) = 0.81). Migration rates across all loci are less than one migrant per generation. We found evidence of growth in several populations and on the islands of Molokai and Maui, which supports population expansion associated with the formation of Maui Nui during the last glacial maximum. Similar to data for many other Hawaiian taxa, these data suggest S. globosa originated on Oahu and subsequently colonized Molokai, Maui, and Hawaii in progression. Given the high level of genetic structure, allopatric divergence will likely contribute to further divergence of populations.

Insect pollination and self-planting seed dispersal strategy in the true viviparous mangrove tree species Ceriops tagal (Perr.) C.B. Robinson (Rhizophoraceae)

Ceriops tagal is a seaward and high salt-tolerant specialist mangrove species. It flowers during the winter season. The flowers have an explosive pollen release mechanism and are adapted for tripping by flies and honey bees. The tripped flowers achieve self or cross-pollination. High winds can also trip flowers, but this only contributes to autogamy. The plant is viviparous; most propagules fall off and settle near the mother plant. We have observed that such propagules do not show healthy growth, hence the establishment of successive offspring in the same habitat is doubtful. These results suggest that C. tagal requires introduction of propagules from other mangrove forests to promote gene flow and maintain sufficient genetic diversity for the successful establishment and expansion of populations.

Comparative phylogeography of two endemic birds of the Tibetan plateau, the white-rumped snow finch ( Onychostruthus taczanowskii) and the Hume’s ground tit ( Pseudopodoces humilis)

Postglacial colonization has created the main phylogeographical structures in the endemic species of the Tibetan plateau; however, patterns of diversification are species idiosyncratic and indicative of variations in geographic divergence. Here we compare the phylogeographical structures of two endemic birds of the Tibetan plateau, the white-rumped snow finch ( Onychostruthus taczanowskii) and the Hume’s ground tit ( Pseudopodoces humilis), both of which are commonly associated with alpine meadow habitats. Our results suggested that these two species experienced rapid population expansion at times estimated as 0.05–0.16 million years ago (Ma). These expansion periods were congruent with the retreat of the last extensive glacial period (0.5–0.175 Ma). Whereas O. taczanowskii populations were derived from a single more widely distributed refugium that existed along the east margin of the Tibetan plateau, P. humilis expanded from independent refugia that were located within both the northeast and southeast margin of the Tibetan plateau. While both birds experienced similar colonization events, their phylogeographical structures are quite contrasting. No trace of geographical divergence is found in O. taczanowskii, suggesting that considerable gene flow occurred after the postglacial colonization. In contrast, a geographic separation can be detected between two refugia populations of P. humilis, specifically the higher altitude platform and lower altitude edge regional groups. The gene flow between these two regions is restricted ( M = 0.43). We estimate the divergence time as approximately 0.361 Ma, dating to the extensive glacial period. Potential explanations for the different phylogeographical structures of these two sympatric birds may include variance in dispersal ability, altitude specific and independent or semicontinuous refugia. While a combination of high flight ability and semicontinuous refugium may have promoted gene flow in O. taczanowskii populations, weak dispersal coupled with separated refugia may have sufficiently isolated populations such to facilitate genetic divergence in P. humilis.