Saturday, June 30, 2018

[Herpetology • 2018] Sky, Sea, and Forest Islands: Diversification in the African Leaf‐folding Frog Afrixalus paradorsalis (Anura: Hyperoliidae) of the Lower Guineo‐Congolian Rain Forest

Afrixalus paradorsalis  Perret, 1960

in Charles, Bell, Blackburn, et al., 2018. 
photo: Daniel M. Portik

To investigate how putative barriers, forest refugia, and ecological gradients across the lower Guineo‐Congolian rain forest shape genetic and phenotypic divergence in the leaf‐folding frog Afrixalus paradorsalis, and examine the role of adjacent land bridge and sky‐islands in diversification.

Location: The Lower Guineo‐Congolian Forest, the Cameroonian Volcanic Line (CVL), and Bioko Island, Central Africa.

Taxon: Afrixalus paradorsalis (Family: Hyperoliidae), an African leaf‐folding frog.

We used molecular and phenotypic data to investigate diversity and divergence among the A. paradorsalis species complex distributed across lowland rain forests, a land bridge island, and mountains in Central Africa. We examined the coincidence of population boundaries, landscape features, divergence times, and spatial patterns of connectivity and diversity, and subsequently performed demographic modelling using genome‐wide SNP variation to distinguish among divergence mechanisms in mainland (riverine barriers, forest refugia, ecological gradients) and land bridge island populations (vicariance, overwater dispersal).

We detected four genetically distinct allopatric populations corresponding to Bioko Island, the CVL, and two lowland rain forest populations split by the Sanaga River. Although lowland populations are phenotypically indistinguishable, pronounced body size evolution occurs at high elevation, and the timing of the formation of the high elevation population coincides with mountain uplift in the CVL. Spatial analyses and demographic modelling revealed population divergence across mainland Lower Guinea is best explained by forest refugia rather than riverine barriers or ecological gradients, and that the Bioko Island population divergence is best explained by vicariance (marine incursion) rather than overseas dispersal.

Main conclusions: 
We provide growing support for the important role of forest refugia in driving intraspecific divergences in the Guineo‐Congolian rain forest. In A. paradorsalis, sky‐islands in the CVL have resulted in greater genetic and phenotypic divergences than marine incursions of the land bridge Bioko Island, highlighting important differences in patterns of island‐driven diversification in Lower Guinea.

Keywords: Africa amphibian, historical demography, land bridge island, Lower Guinea, phylogeography

Figure 1: Sampling localities of Afrixalus paradorsalis paradorsalis (circles) and A. p. manengubensis (triangles) in the Lower Guinean forests of continental Central Africa and Bioko Island. Sampling localities are coloured according to the mitochondrial (mtDNA) haplotype groups and distinct genetic lineages identified in analyses of the ddRADseq (nuDNA) dataset (Figure 2). Symbols with white borders reflect localities with only mtDNA sequence data and symbols with no border reflect localities with only morphological data. The right panel depicts the locations of key mountains along the Cameroon Volcanic Line

Kristin L. Charles, Rayna C. Bell, David C. Blackburn, Marius Burger, Matthew K. Fujita, Václav Gvoždík, Gregory F.M. Jongsma, Marcel Talla Kouete, Adam D. Leaché and Daniel M. Portik. 2018. Sky, Sea, and Forest Islands: Diversification in the African Leaf‐folding Frog Afrixalus paradorsalis (Anura: Hyperoliidae) of the Lower Guineo‐Congolian Rain Forest. Journal of Biogeography. DOI: 10.1111/jbi.13365

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