Forest refugia and riverine barriers promote diversification in the West African pygmy shrew (Crocidura obscurior complex, Soricomorpha)

Abstract

The Crocidura obscurior or West African pygmy shrew complex is endemic to West African forests from south‐eastern Guinea, eastern Liberia, southern Côte d'Ivoire and south‐western Ghana. We explore the genetic and morphometric diversity of 239 individuals of the C. obscurior complex from 17 localities across its geographical range. Using genetic data from three mitochondrial (16S, cytochrome b and COI) and four nuclear markers (BRCA1, STAT5A, HDAC2 and RIOK3) and skull geometric morphometrics, we show that this complex is composed of two cryptic and sympatric species, C. obscurior and C. eburnea. We then test several hypotheses to infer their evolutionary history. The observed phylogeographical pattern based on cytochrome b and COI sequences fits the forest refuge theory: during arid phases of the Plio‐Pleistocene, around 3.5, 2.1, 1 and 0.5 Mya, a small number of populations survived in isolated forest patches and diverged allopatrically. During wetter climatic periods, forests expanded, leading to secondary contacts between previously isolated populations. Our results also suggest the possible contribution of episodes of isolation in subrefuges. Historical variation of the West African hydrographic network could also have contributed to the observed patterns of genetic differentiation. Rivers such as the Volta and Sassandra may act as past and/or current barriers to gene flow. Although these two species have sympatric distributions, their phylogeographical histories are somewhat dissimilar due to small differences in their dispersal abilities and ecological requirements.

Multilocus phylogeny of the Crocidura poensis species complex (Mammalia, Eulipotyphla): Influences of the palaeoclimate on its diversification and evolution

“…longipes)? A similar pattern, with several highly overlapping sister lineages, was previously observed in other Upper Guinean small mammals (Bohoussou et al, 2015;Jacquet et al, 2014;Nicolas, Bryja, et al, 2008). The…”

“…More genetic data at the genomic scale, as well as quantified morphometric data including genetically identified specimens, are necessary to further assess their taxonomical status. Several recent studies showed the power of morphometric geometric approaches to discriminate cryptic shrew species and to associate a genetic lineage to a type specimen (Jacquet et al., , ).…”

“…Several studies highlighted the difficulty to distinguish C. poensis and C. batesi based on morphological data and also raised doubts on the validity of these species Hutterer, 2005 Table S2 in Appendix S3 genetically identified specimens, are necessary to further assess their taxonomical status. Several recent studies showed the power of morphometric geometric approaches to discriminate cryptic shrew species and to associate a genetic lineage to a type specimen (Jacquet et al, 2013(Jacquet et al, , 2014.…”

Phylogeography of the heavily poached African common pangolin (Pholidota, Manis tricuspis) reveals six cryptic lineages as traceable signatures of Pleistocene diversification

“…; Jacquet et al . ), a denser sampling is required to allow the proper testing of biogeographic scenarios (including ecological and demographic data) in African common pangolins.…”

“…; Jacquet et al . ). Nevertheless, the delimitation of ‘universal’ rainforest refugia remains difficult to establish because of the cyclic, superimposed nature of rainforest contractions through time and the likely different responses of organisms to a same series of climatic changes (Lowe et al .…”