Parallel diversification of the African tree toad genus Nectophryne (Bufonidae)

H Christoph Liedtke,Diego J Soler-Navarro,Ivan Gomez-Mestre,Simon P Loader,Mark-Oliver Rödel

doi:10.1016/j.ympev.2021.107184

Abstract

African amphibian diversity remains underestimated with many cryptic lineages awaiting formal description. An important hotspot of amphibian diversification is the Guineo-Congolian rainforest in Central Africa, its richness attributable to present day and ancestral range fragmentation through geological barriers, habitat expansion and contraction, and the presence of steep ecological gradients. The charismatic Nectophryne tree toads present an interesting case study for diversification in this region. The two formally described species comprising this genus show nearly identical geographic distributions extending across most of the Guineo-Congolian rainforest, but show little morphological disparity. Both species harbour extensive genetic diversity warranting taxonomic revisions, and interestingly, when comparing the subclades within each, the two species show remarkably parallel diversification histories, both in terms of timing of phylogenetic splits and their geographic distributions. This indicates that common processes may have shaped the evolutionary history of these lineages.

Highlights

The Guineo-Congolian rainforest constitutes the second largest contiguous area of lowland tropical moist broadleaf forests after the Amazonian rainforest (Bele et al, 2015), and boasts an exceptional species richness and endemism (Myers et al, 2000; Plana, 2004; White, 1979)
The extraordinary species diversity in the Guineo-Congolian region has most frequently been attributed to three biogeographic processes: vicariance by rivers acting as either past or present barriers to gene flow, vicariance by repeated habitat fragmentation and contraction, espe cially of tropical forests, throughout the Oligocene – Miocene right up to the Pleistocene, and dispersal across pronounced ecological gradients followed by local adaptation, resulting in divergence without the need for physical barriers
The results were consistent across the different priors used, producing individual clade supports with posterior proba bilities ≥ 0.99 and an overall model with five species as performing best, with posterior probabilities ≥ 0.99 (SI 3)

Summary

Introduction

The Guineo-Congolian rainforest constitutes the second largest contiguous area of lowland tropical moist broadleaf forests after the Amazonian rainforest (Bele et al, 2015), and boasts an exceptional species richness and endemism (Myers et al, 2000; Plana, 2004; White, 1979). The extraordinary species diversity in the Guineo-Congolian region has most frequently been attributed to three biogeographic processes: vicariance by rivers acting as either past or present barriers to gene flow, vicariance by repeated habitat fragmentation and contraction, espe cially of tropical forests, throughout the Oligocene – Miocene right up to the Pleistocene, and dispersal across pronounced ecological gradients followed by local adaptation, resulting in divergence without the need for physical barriers. Evidence for these have been found in numerous taxa. A north–south seasonal inversion, often referred to as a ‘climatic hinge’ along the southern border of Cameroon as well as a coastal-inland climatic gradient, seems to have contributed to species diversification in rain forest trees (Hardy et al, 2013), primates (Mitchell et al, 2015), reptiles (Freedman et al, 2010) and amphibians (Bell et al, 2017; Jongsma et al, 2017; Leache et al, 2019)

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