Abstract
BackgroundUncovering how populations of a species differ genetically and ecologically is important for understanding evolutionary processes. Here we combine population genetic methods (microsatellites) with phylogenetic information (mtDNA) to define genetic population clusters of the wide-spread Neotropical túngara frog (Physalaemus pustulosus). We measure gene flow and migration within and between population clusters and compare genetic diversity between population clusters. By applying ecological niche modeling we determine whether the two most divergent genetic groups of the túngara frog (1) inhabit different habitats, and (2) are separated geographically by unsuitable habitat across a gap in the distribution.ResultsMost population structure is captured by dividing all sample localities into two allopatric genetic lineages. The Northern genetic lineage (NW Costa Rica) is genetically homogenous while the Southern lineage (SW Costa Rica and Panama) is sub-divided into three population clusters by both microsatellite and mtDNA analyses. Gene flow is higher within the Northern lineage than within the Southern lineage, perhaps due to increased landscape heterogeneity in the South. Niche modeling reveals differences in suitable habitat between the Northern and Southern lineages: the Northern lineage inhabits dry/pine-oak forests, while the Southern lineage is confined to tropical moist forests. Both lineages seem to have had little movement across the distribution gap, which persisted during the last glacial maximum. The lack of movement was more pronounced for the Southern lineage than for the Northern lineage.ConclusionsThis study confirms the finding of previous studies that túngara frogs diverged into two allopatric genetic lineages north and south of the gap in the distribution in central Costa Rica several million years ago. The allopatric distribution is attributed to unsuitable habitat and probably other unknown ecological factors present across the distribution gap. Niche conservatism possibly contributes to preventing movements across the gap and gene flow between both groups. Genetic and ecological data indicate that there is the potential for ecological divergence in allopatry between lineages. In this context we discuss whether the Northern and Southern lineages should be recognized as separate species, and we conclude that further studies of pre- and post-zygotic isolation are needed for a final assessment. Identified population clusters should motivate future behavioral and ecological research regarding within-species biodiversity and speciation mechanisms.
Highlights
Uncovering how populations of a species differ genetically and ecologically is important for understanding evolutionary processes
Microsatellites Population structure: Most population structure was captured by dividing all sample localities in two genetic lineages (Figure 1, Figure 2a) The southern lineage, was further subdivided in two or three sub-clusters (Figure 2b, c), while the Northern lineage remained undivided even by increasing K to 10
Conducting the analysis separately for the Northern and Southern lineage resulted in the same geographic-genetic pattern, i.e. by analyzing the Southern lineage alone ΔKsouth was highest for Ksouth = 3
Summary
Uncovering how populations of a species differ genetically and ecologically is important for understanding evolutionary processes. By applying ecological niche modeling we determine whether the two most divergent genetic groups of the túngara frog (1) inhabit different habitats, and (2) are separated geographically by unsuitable habitat across a gap in the distribution. A central goal of evolutionary ecology is to understand processes that determine the distribution of genetic diversity and population connectivity through gene flow. Most studies of genetic population structure of amphibian show little or no genetic differentiation with moderate to high gene flow and dispersal rates at the local scale (1520 km) [8,12,13]. Less common are pattern of panmixia among distant localities (Bufo marinus, [14]) or strong genetic differentiation across very small geographic distances (Bufo calamita, [9])
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