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| Nectophryne afra and N. batesii in Liedtke, Soler-Navarro, Gomez-Mestre, Loader & Rödel, 2021. |
Highlights:
• The Nectophryne tree toads harbour cryptic genetic diversity.
• Despite occuring in sympatry, little morphological disparity is observed.
• Rivers and forest fragmentation are consistent with phylogenetic diversification patterns.
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.
Keywords: Central Africa, Amphibia, Diversity hotspot, Phylogeography, Lower Guinea forests, Guineo-Congolian forest, Sympatry, Character displacement
Conclusion:
We show that substantial genetic divergence exists within the genus Nectophryne, with both currently described species warranting taxonomic revision since both contain distinct evolutionary lineages within them. Morphological variation is minimal among species and genetic clades despite the genetic divergence observed. The distinct genetic clades in both N. afra and N. batesii are geographically isolated and, interestingly, show near parallel phylogeographic histories. In both cases, the geographic divisions of clades correspond to the three proposed biogeographic scenarios described for this region, but based on the available data, it is difficult to distinguish between these.
How N. afra and N. batesii lineages themselves have diverged remains uncertain. Both show centres of genetic diversity in the same geographic regions, highly sympatric distributions and relatively few external morphological differences. To understand how these toads evolved, we suggest further investigations into their life history, more fine scaled characterization of their microhabitat use and studies on their trophic ecology. This would shed light on prezygotic isolation mechanisms that may have driven the speciation of these curious amphibians and has allowed them to largely coexist with no evidence of hybridization.
H. Christoph Liedtke, Diego J. Soler-Navarro, Ivan Gomez-Mestre, Simon P. Loader and Mark-Oliver Rödel. 2021. Parallel Diversification of the African Tree Toad Genus Nectophryne (Bufonidae). Molecular Phylogenetics and Evolution. 162, 107184. DOI: 10.1016/j.ympev.2021.107184
