Spatial distributions and environmental relationships of two species complexes of freshwater atyid shrimps

Knowledge of cryptic species distributions and their relationships with environmental factors may be extremely valuable for biodiversity conservation. In freshwater ecosystems, morphologically cryptic species often have different geographic distributions that can overlap to varying extents. The importance of differential species responses to environmental conditions in determining their spatial distributions is, however, unclear. Here, we evaluated the importance of species responses to environmental drivers, in particular the physicochemical factors, in the spatial distributions and environmental relationships of two shrimp species complexes Caridina indistincta Calman, 1926 and Paratya australiensis Kemp, 1917. We analyzed shrimp specimens from 89 sites in 17 catchments across South-East Queensland by sequencing a fragment of the mitochondrial cytochrome c oxidase subunit I gene (COI) to identify individuals. Furthermore, although there is evidence that morphologically the cryptic species of these shrimps differ very little, we made detailed morphological assessments to combine with molecular data, hoping to be able to distinguish among the species more easily and cheaply for future studies. There were significant morphological differences among the three cryptic species of the C. indistincta species complex, specifically in carapace length (cl), number of dorsal teeth (nDt), number of ventral teeth (nVt), teeth posterior to orbital margin (TPOM), and the calculated ratios A/rl, and rl/cl, while the two lineages of the P. australiensis species complex differed in the number of dorsal teeth (nDt) and the calculated ratios of A/rl, rl/cl, and rh/ch. To determine the importance of species responses in explaining the spatial distribution of cryptic species based on the species-variables relationships, a redundancy analysis (RDA) was used to summarize these relationships. This ordination analysis showed distinct differences among cryptic species in their correlation with water quality variables and elevation. C. indistincta sp. B and C. indistincta sp. D were significantly associated with elevation and dissolved oxygen range, respectively. As well, P. australiensis lineages 4 and 6 were significantly correlated with elevation and conductivity, respectively. Overall, our results demonstrated the advantage of using analyses of biotic and abiotic variables as a valid approach for defining species responses to abiotic factors in cryptic species of atyid freshwater shrimps.