Abstract
The evolutionary history of the old, diverse freshwater shrimp genus Caridina is still poorly understood, despite its vast distribution – from Africa to Polynesia. Here, we used nuclear and mitochondrial DNA to infer the phylogeographic and evolutionary history of C. typus, which is one of only four species distributed across the entire range of the genus. Despite this species’ potential for high levels of gene flow, questions have been raised regarding its phylogeographic structure and taxonomic status. We identified three distinct lineages that likely diverged in the Miocene. Molecular dating and ancestral range reconstructions are congruent with C. typus’ early dispersal to Africa, possibly mediated by the Miocene Indian Ocean Equatorial Jet, followed by back dispersal to Australasia after the Jet’s closure. Furthermore, several different species delimitation methods indicate each lineage represents a distinct (cryptic) species, contradicting current morphospecies delimitation of a single C. typus taxon. The evolutionary history of C. typus lineages is complex, in which ancient oceanic current systems and (currently unrecognised) speciation events preceded secondary sympatry of these cryptic species.
Highlights
The Atyidae (Crustacea: Decapoda: Caridea) is a family of small freshwater shrimps that occurs across all continents, except Antarctica
C. typus is found through the Indo-Australian Archipelago, a region with a rich geological and biogeographical history
Given C. typus’ planktonic larvae and the consequent ability to disperse across oceans, two alternative scenarios can be predicted regarding this species’ genetic diversity: the first is a widespread distribution with shallow geographic structure as dispersive ability overcomes the geological history of its range; the second is a species complex, where deeper geographic structuring reveals cryptic lineages with restricted distributions
Summary
The Atyidae (Crustacea: Decapoda: Caridea) is a family of small freshwater shrimps that occurs across all continents, except Antarctica. Small eggs and planktonic larvae[4] are a feature that could contribute to C. typus’ vagility[7] Despite this widespread distribution, C. typus, like other species of Caridina[8,9,10], may comprise cryptic lineages. The opposite pattern has been found for several recently identified (previously) cryptic species of Caridina[8, 13, 14], where deep intraspecific differences have been found over very small scales. Given C. typus’ planktonic larvae and the consequent ability to disperse across oceans, two alternative scenarios can be predicted regarding this species’ genetic diversity: the first is a widespread distribution with shallow geographic structure as dispersive ability overcomes the geological history of its range; the second is a species complex, where deeper geographic structuring reveals cryptic lineages with restricted distributions. The objective of this study is to investigate C. typus species boundaries, phylogeography and the geographic distribution thereof, using multilocus molecular markers sampled from across the C. typus’ broad distribution (Fig. 1)
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