Evolutionary history of Scinax treefrogs on land‐bridge islands in south‐eastern Brazil

Abstract

Aim We investigated how Pleistocene refugia and recent (c. 12,000 years ago) sea level incursions shaped genetic differentiation in mainland and island populations of the Scinax perpusillus treefrog group. Location Brazilian Atlantic Forest, São Paulo state, south‐eastern Brazil. Methods Using mitochondrial and microsatellite loci, we examined population structure and genetic diversity in three species from the S. perpusillus group, sampled from three land‐bridge islands and five mainland populations, in order to understand the roles of Pleistocene forest fragmentation and sea level incursions on genetic differentiation. We calculated metrics of relatedness and genetic diversity to assess whether island populations exhibit signatures of genetic drift and isolation. Two of the three island populations in this study have previously been described as new species based on a combination of distinct morphological and behavioural characters, thus we used the molecular datasets to determine whether phenotypic change is consistent with genetic differentiation. Results Our analyses recovered three distinct lineages or demes composed of northern mainland São Paulo populations, southern mainland São Paulo populations, and one divergent island population. The two remaining island populations clustered with samples from adjacent mainland populations. Estimates of allelic richness were significantly lower, and estimates of relatedness were significantly higher, in island populations relative to their mainland counterparts. Main conclusions Fine‐scale genetic structure across mainland populations indicates the possible existence of local refugia within São Paulo state, underscoring the small geographic scale at which populations diverge in this species‐rich region of the Atlantic Coastal Forest. Variation in genetic signatures across the three islands indicates that the populations experienced different demographic processes after marine incursions fragmented the distribution of the S. perpusillus group. Genetic signatures of inbreeding and drift in some island populations indicate that small population sizes, coupled with strong ecological selection, may be important evolutionary forces driving speciation on land‐bridge islands.

Population structuring of the ubiquitous stingless bee Tetragonisca angustula in southern Brazil as revealed by microsatellite and mitochondrial markers

“…Indeed, the characteristic star shape of the T. angustula haplotype network provides evidence of relatively recent local extinction, recolonization, and population expansion. Several phylogeographic studies of vertebrate and invertebrate populations, conducted in some of the areas that we studied, have also found low mtDNA nucleotide diversity (Cabanne et al ., ; Carnaval et al ., ; Batalha‐Filho et al ., ; Brito & Arias, ; Francisco & Arias, ; D'Horta et al ., ; Bell et al ., ). As argued in these papers, changes in climate during the Pleistocene generated population bottlenecks followed by species expansion, and this is reflected in localized low nucleotide diversity to this day.…”

Vicariance and marine migration in continental island populations of a frog endemic to the Atlantic Coastal forest

“…This incursion isolated present-day continental islands and likely fragmented the ranges of several Atlantic Coastal Forest species, including our focal species. Studies of other species endemic to this region show a reduction of genetic diversity in island species or populations relative to those on the mainland (Grazziotin et al, 2006;Bell et al, 2012). Here, we build on these studies by investigating fine-scale genetic diversity in an organism that exhibits tolerance to saltwater and thus may be capable of dispersing to continental islands.…”

Insular Anurans (Amphibia: Anura) of the coast of Rio de Janeiro, Southeast, Brazil

“…Different species of the bromeliad dwelling frogs of the Scinax perpusillus group (sensu Peixoto 1987) are present on four of the studied islands. Species of this group also occur on islands off the coast of São Paulo State (Brasileiro et al 2007a, b; AlvesSilva and Silva 2009), where Bell et al (2012) founded molecular evidence of significant genetic differentiation between insular and mainland populations exclusively for Scinax faivovichi. The other two insular populations included on their study, from Mar Virado and Queimada Grande, were not genetically differentiated from mainland populations, even though the latter shows a considerable differentiation in call.…”

“…The other two insular populations included on their study, from Mar Virado and Queimada Grande, were not genetically differentiated from mainland populations, even though the latter shows a considerable differentiation in call. Cases of amphibian genetic divergence on land-bridge islands have been attributed to genetic drift before the formation of the islands (VeloAntón et al 2011;Bell et al 2012).…”