The complex study of complexes: The first well-supported phylogeny of two species complexes within genus Caridina (Decapoda: Caridea: Atyidae) sheds light on evolution, biogeography, and habitat

Atyid shrimps, a key component of tropical freshwater ecosystems, face multiple anthropogenic threats and thus

need special attention. With more than 300 described species, the genus Caridina is the most speciose of all the

Caridea infra-order. Caridina spp. occupy diverse habitats in tropical freshwaters of the Indo-West Pacific region.

Several species complexes have been recognized, based on common morphological features, but little is known

about how well these morphological characteristics align with phylogenetic characteristics. Furthermore, no

phylogeny of the genus Caridina published so far has provided well-resolved and supported relationships among

different species, thus impeding the possibility of proposing evolutionary hypotheses. In this study we used next

generation sequencing (NGS) to provide new insights into the phylogenetic relationships among the genus

Caridina, focusing on two complexes: ‘Caridina nilotica’ and ‘Caridina weberi’. We collected 92 specimens belonging

to these two groups from most of their known geographical range, representing 50 species, for which we

sequenced seven mitochondrial genes and two nuclear markers using ion torrent NGS. We performed a phylogenetic

analysis, which yielded the first well-supported tree for the genus Caridina. On this tree were mapped the

geographic ranges and the habitats used by the different species, and a time calibration was tested. We found the

driving factors that most likely account for separation of clades are differences in habitat and to a lesser extent

geography. This work provides new insights into the taxonomy of this group and identifies opportunities for

further studies in order to fill knowledge gaps that currently impede the management and conservation of atyid

species.

1. Introduction