Comparative phylogeography of West African amphibians and reptiles

Abstract

Comparative phylogeographic studies often support shared divergence times for co‐distributed species with similar life histories and habitat specializations. During the late Holocene, West Africa experienced aridification and the turnover of rain forest habitats into savannas. These fragmented rain forests harbor impressive numbers of endemic and threatened species. In this setting, populations of co‐distributed rain forest species are expected to have diverged simultaneously, whereas divergence events for species adapted to savanna and forest‐edge habitats should be absent or idiosyncratic. We conducted a Bayesian analysis of shared evolutionary events to test models of population divergence for 20 species of anurans (frogs) and squamates (lizards and snakes) that are distributed across the Dahomey Gap, a climate change‐induced savanna barrier responsible for fragmenting previously contiguous rain forests of Ghana into two regions: the Togo‐Volta Hills and the Southwestern Forests. A model of asynchronous diversification is supported for anurans and squamates, suggesting that drivers of diversification are not specifically related to ecological and life history associations with habitat types. Instead, the wide variability of genetic divergence histories exhibited by these species suggests that biodiversity in this region has been shaped by diversification events that extend beyond the Holocene. Comparisons of the genealogical divergence index, a measure of the genetic divergence between populations due to the combined effects of genetic isolation and gene flow, illustrate that these populations represent a broad sampling of the speciation continuum.

Evolution of the African slippery frogs (Anura: Conraua), including the world’s largest living frog

“…This bears similarities to phylogenetic patterns among genera of African dwarf toads with the divergence of Altiphrynoides , which is endemic to the Ethiopian Highlands, from a clade containing Central and West African genera occurring in the earliest Miocene (Liedtke et al, 2016), as well as divergences between rainforest trees from eastern and West and Central Africa (Couvreur et al, 2008). More recent divergences within species that may represent undescribed lineages, including C. alleni and C. crassipes , appear to have occurred during the Pliocene and Pleistocene, which is similar to other recent studies of forest‐restricted tropical anurans in this region (Bell et al, 2017; Leaché et al, 2019, 2020).…”

“…The Bayesian species delimitation analyses supported either 9, 11 or 12 ‘species’ based on the combination of priors. As also recovered by Leaché et al (2020), the population of C. derooi from the Atewa Range of south‐central Ghana (Kouamé et al, 2007; Hillers et al, 2009; Lindsell et al, 2019) likely corresponds to an undescribed species; note that the location indicated in Leaché et al (2020) is incorrect as it is in south‐western Ghana which is well outside the recognized range for this species (Channing & Rödel, 2019; Hillers et al, 2009). Substructure within C. alleni was well supported in all analyses, although further splitting of subclades 1 (in the Fouta Djallon highlands) and 2 (Figure 1b, ) varies based on the configuration of priors used.…”

“…This also rejects our hypothesis that the Central African species form a clade exclusive of those species in West and East Africa. However, there is evidence for regional in situ speciation in West Africa both because C. alleni and C. derooi are sister taxa and because both taxa possibly comprise at least two distinct species each (Figure 1d; compare Hillers et al, 2008 and Leaché et al, 2020, respectively).…”

Impacts of the Toba eruption and montane forest expansion on diversification in Sumatran parachuting frogs (Rhacophorus)

“…Our study highlights the difficulties of unravelling diversification histories in a region subjected to complex historical processes (Lohman et al, 2011; Frantz et al., 2013; Leaché, Oaks, Ofori‐Boateng, & Fujita, 2020). One limitation of current models is that they are restricted to testing fairly simple demographic histories (Oaks, Siler, & Brown, 2019; Terhorst & Song, 2015), which approximate diversification processes of taxa subjected to complex events such as glacial cycles or repeated volcanic events (Lohman et al, 2011).…”

Taxonomic hypotheses and the biogeography of speciation in the Tiger Whiptail complex (Aspidoscelis tigris: Squamata, Teiidae)

“…Speciation processes have often been inferred from relationships between genealogical and geographical patterns (e.g., Camargo et al 2010), with 'phylogeography' now a burgeoning discipline uniting intraspecific (i.e., population-level) and macroevolutionary perspectives (Avise 2009). Comparative analysis of intra-and inter-specific patterns has revealed spatial features driving diversification and lineage reticulation at continental scales (Burbrink et al 2018, Wollenberg Valero et al 2019, Leaché et al 2020). Yet relating spatial and temporal patterns is not always straightforward, with juxtaposition of contemporary geographics with aspects of modern biodiversity sometimes yielding contradictory patterns.…”