Cryptic diversity and speciation in an endemic copepod crustacean Harpacticella inopinata within Lake Baikal

Ancient lakes are hotspots of species diversity, posing challenges and opportunities for exploration of the dynamics of endemic diversification. Lake Baikal in Siberia, the oldest lake in the world, hosts a particularly rich crustacean fauna, including the largest known species flock of harpacticoid copepods with some 70 species. Here, we focused on exploring the diversity and evolution within a single nominal species, Harpacticella inopinata Sars, 1908, using molecular markers (mitochondrial COI, nuclear ITS1 and 28S rRNA) and a set of qualitative and quantitative morphological traits. Five major mitochondrial lineages were recognized, with model-corrected COI distances of 0.20-0.37. A concordant pattern was seen in the nuclear data set, and qualitative morphological traits also distinguish a part of the lineages. All this suggests the presence of several hitherto unrecognized cryptic taxa within the baikalian H. inopinata, with long independent histories. The abundances, distributions and inferred demographic histories were different among taxa. Two taxa, H. inopinata CE and H. inopinata CW, were widespread on the eastern and western coasts, respectively, and were largely allopatric. Patterns in mitochondrial variation, that is, shallow star-like haplotype networks, suggest these taxa have spread through the lake relatively recently. Three other taxa, H. inopinata RE, RW and RW2, instead were rare and had more localized distributions on either coast, but showed deeper intraspecies genealogies, suggesting older regional presence. The rare taxa were often found in sympatry with the others and occasionally introgressed by mtDNA from the common ones. The mitochondrial divergence between and within the H. inopinata lineages is still unexpectedly deep, suggesting an unusually high molecular rate. The recognition of true systematic diversity in the evaluation and management of ecosystems is important in hotspots, as it is everywhere else, while the translation of the diversity into a formal taxonomy remains a challenge.

Morphological and molecular analysis of the freshwater copepod Heliodiaptomus viduus (Calanoida: Diaptomidae)

Morphological identification of the commonest Indian freshwater calanoid copepod Heliodiaptomus viduus has been facing a lot of controversies. To solve this problem, additional molecular support is needed. Hence, molecular analysis, along with morphological identification of the species using scanning electron microscopy (SEM) and optical microscopy, was carried out. The genetic distance between the intraspecific sequences in the 18SrRNA observed to be 0.000, while the interspecific distance within genus sequences varied from 0.000 to 0.002. Besides, it was noted that both the sequences (intraspecific) were present within a single clade of the phylogenetic trees with 100% bootstrap value. The genetic distance between the intraspecific sequences in the mtCOI observed to be 0.000, while the interspecific distance within genus sequences varied from 0.000 to 0.267 and lay in a separate clade in the phylogenetic tree from the within genus clade. Besides, it was noted that both the sequences (intraspecific) were present within a single clade of the phylogenetic tree with above 75% bootstrap value. Hence, the 18S rRNA (MH145356, MK457456) and mtCOI (MK621900) gene sequences of the present study are well supported the identification of H. viduus and it serves as the first molecular database besides providing morphological authentication (SEM images) of H.viduus. This combined analysis is envisioned to be helpful in selecting the ecologically and nutritionally important species for practical aquaculture.