Drivers of unique and asynchronous population dynamics in Malagasy herpetofauna

Abstract

Aim: A long history of isolation coupled with complex landscapes makes Madagascar ideal for exploring the historical factors that have shaped patterns of population diversity and endemism. Many species-level studies have suggested Late Quaternary climate change may have influenced population dynamics in the tropics, but unique biomes and individual species properties may have driven idiosyncratic responses to these shifts. Here, we use community-scale population genetic data to investigate the impact of Quaternary climate cycles on shared demographic response and investigate the contributions of both biotic and abiotic factors which shape these demographic trajectories. Location: Madagascar.Taxon: Reptiles and Amphibians.Methods: Using community-scale population genetic data, we implement a hierarchical approximate Bayesian computation approach to evaluate the degree of synchronous population expansion during glacial cycles across herpetofaunal assemblages both within and across discrete biomes and taxonomic groups. We use Bayesian model averaging to identify intrinsic and extrinsic conditions predictive of individualistic demographic change. Results:We find that demographic responses are not uniform across groups, with more than 50% of all populations showing signal of recent expansion. Our explanatory models indicate species occupying narrow elevational ranges had a higher probability of expansion, while amphibian assemblages showed higher genetic diversity and greater departures from population neutrality. Expansion events were largely asynchronous, with coexpansion found in less than half of all populations. Exceptionally, 69%-74% of all humid-restricted populations coexpanded during the start of the Last Glacial Period at around 100 kya, supporting the hypothesis of a more extensive humid forest cover for Madagascar during this time. Main conclusions:We show that differences in life history and regional biogeography have contributed to patterns of richness and endemism found across Madagascar, and historical connectivity across humid forests has been an important factor in shaping present-day diversity and endemism on Madagascar, particularly for amphibians.

Repeated divergence of amphibians and reptiles across an elevational gradient in northern Madagascar

“…Madagascar has served as model to develop numerous hypotheses of diversification mechanisms (e.g. Colwell & Lees, 2000; Craul et al, 2007; Dewar & Richard, 2007; Goodman & Ganzhorn, 2004; Kuhn et al, 2022; Lees et al, 1999; Raxworthy & Nussbaum, 1995; Wilmé et al, 2006; Wollenberg Valero, 2015), as partially summarized in Vences et al (2009) and Brown et al (2014). Most of these studies were based on either patterns of species distributions, phylogenies, or both.…”

Coalescent simulations indicate that the São Francisco River is a biogeographic barrier for six vertebrates in a seasonally dry South American forest

“…Body size is often used as a proxy of dispersal capability, with small bodied-animals presenting stronger responses to vicariant barriers (Wollenberg et al, 2011;Arteaga et al, 2016). Species-specific traits other than body size, such as habitat use, may also affect dispersal (Zamudio et al, 2016;Reid et al, 2019;Kuhn et al, 2021). For example, phylogenetic studies indicate a strong vicariant effect of the SFR on several species of limbless (or reduced-limb) fossorial squamate (Rodrigues, 1996;Rodrigues and Juncá, 2002; 10.3389/fevo.2022.983134 Siedchlag et al, 2010;Almeida et al, 2020), which likely have limited river-crossing abilities due to their underground lifestyles.…”

Speciation rates are unrelated to the formation of population structure in Malagasy gemsnakes

“…A previous study found that rates of diversification in the gemsnakes declined significantly over the entire tree during the Pleistocene (Kuhn et al, 2022 ). Since then, Louca and Pennell ( 2020 ) demonstrated that rates of speciation estimated from molecular phylogenies may be congruent with a wide range of diversification scenarios.…”