Comparative Phylogeography of West African Rainforest Frogs Reveals Regional Variation in Refugia Dynamics

Abstract

Understanding how species responded to climatic change in the past can help predict the long-term implications of contemporary climate change. The Upper Guinean rainforests of West Africa are a global biodiversity hotspot, and it is well documented that climatic fluctuations in the Pleistocene drove the expansion and contraction of rainforest cover in this region. West African slippery frogs, genus Conraua, are rainforest specialists and present an excellent opportunity to study the effects of climate-driven landscape changes on contemporary phylogeographic patterns and population dynamics. They exclusively inhabit rainforest streams and show little morphological or ecological disparity. We generated a population-level dataset of genome-wide restriction site-associated DNA (RAD) loci for four species spread across Upper Guinea. The observed phylogeographic structure is consistent with previously postulated macro- and micro-refugia. Building on these results, we used demographic modelling to trace demographic trends over time and infer population connectivity patterns. Overall, populations in topographically complex regions, like the Fouta Djallon, showed signatures of long-term local persistence and milder changes in population size. In contrast, we found more dynamic histories of contraction and expansion in the main Upper Guinean rainforest block. Our findings provide insights into regional biodiversity patterns and show large variation in population responses to climatic fluctuations. This suggests that local environmental factors have played a key role in shaping population dynamics. Such insights are particularly relevant in relatively understudied biodiversity hotspots, such as the Upper Guinean rainforests of West Africa. Our results have implications for conservation management and prioritisation at the species, site, and ecosystem level.