Abstract
With 104 endemic species family Candonidae is one of the most diverse crustacean groups in Lake Baikal, yet their phylogenetic relationships and position in the family have not been addressed so far. Here, we study the phylogenetic position of Baikal candonids within the family and their evolutionary history using molecular markers for the first time since their original description. We choose 10 Baikal and 28 species from around the world, and three ribosomal RNA‐s (18S, 28S, and 16S), and analyze individual and concatenated datasets using Bayesian Inference in MrBayes and BEAST. For molecular divergence time estimates, four fossil records are used to calibrate the root and three internal nodes. The 28S dataset is tested under the strict molecular clock, while for other data we use relaxed clocks. Resulting trees show incongruence between molecular and fossil divergence time estimates, with the former suggesting older ages. Strict molecular clock analysis results in narrower node age confidence intervals and younger time estimates than other analysis. All trees support at least two candonid lineages in Baikal, with two independent colonization events, and 28S suggests a major radiation between 12 and 5 Mya. This divergence time estimate mostly agrees with another, unrelated, ostracod group in the lake and other lake animals as well. Baikal candonid clades show a close phylogenetic relationship with Palearctic lineages, but their deep divergence is indicative of separate genera. Results also suggest a monophyly of tribes that today live exclusively in subterranean waters, and we offer several hypotheses of their evolutionary history.
Highlights
From dinoflagellates (Annenkova, 2013) to seals (Palo & Väinölä, 2006), Lake Baikal is a place of exceptional biodiversity
Samples were taken from 11–15 m depths by SCUBA diving from the shore of Lake Baikal at Listvyanka (51°51′51.3′′N 104°50′37.8′′E) on September 12, 2015
Due to the very limited 16S dataset, the resulting tree did not support partition of Candonidae into two clades, and positioned Trapezicandonini as a sister taxon to Baikal and some other non-Baikal candonids, but as the Trapezicandonini branch was very long, this union might be a result of the long branch attraction
Summary
From dinoflagellates (Annenkova, 2013) to seals (Palo & Väinölä, 2006), Lake Baikal is a place of exceptional biodiversity. Lake Tanganyika, in comparison, has 64 ostracod species and subspecies, but a slightly higher endemicity (94%) (Martens, 1994), and far more endemic genera than Baikal The latter is a matter of the current systematics and previous taxonomic decisions, and does not necessarily reflect phylogeny of the group (Martens et al, 1994). The aim of this research was to study evolutionary history and phylogeny of Baikal candonid ostracods, which has not been done so far To address this problem, we use three molecular markers (18S rRNA, 28S rRNA, and 16S rRNA) and 38 Candonidae species, of which 10 are from Lake Baikal and include representatives of all three genera. Our results will test if the divergence time estimates based on slowly evolving nuclear markers (such as 18S and 28S) are comparable to those based on COI (Schön & Martens, 2012)
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