Ceriodaphnia smirnovi (Crustacea: Cladocera), a new species from the Mediterranean Region, and a phylogenetic analysis of the commonest species

Abstract

Species of the genus Ceriodaphnia Dana, 1853 (Crustacea: Cladocera: Daphniidae) are present in the plankton of many freshwater bodies all around the World. However, the taxonomy of the genus is still poorly developed. Most species have been described in the nineteenth century and data on their morphology and distribution should be revised according to current standards. Currently, due to lack of reliable morphological and genetic data, almost all nominal species of Ceriodaphnia are considered as species groups rather than separate biological species, complicating the detection and description of new species of the genus. Here, we redescribe the morphology of Ceriodaphnia quadrangula (O.F. Müller, 1785) based on material close to the type locality in Denmark, and describe a new species of Ceriodaphnia from the Mediterranean region. Also, we provide a phylogenetic analysis using existing and novel sequences of mitochondrial DNA of the commonest species of the genus. Ceriodaphnia smirnovi sp. nov. can be easily distinguished from C. quadrangula via presence of the head pore and the structure of the second thoracic limb, the postabdomen and the ephippium. From other species of Ceriodaphnia known to date C. smirnovi sp. nov. can also be separated on ephippium structure and some other fine morphological features. Although distribution range of C. smirnovi sp. nov. must be clarified in the future based on analysis of more sampling points, most likely, it is restricted to the Mediterranean region. The phylogenetic analyses showed high divergence among 16 different clades (mean clade separation of 13±2.3 % (mean ± SD) and 20.7±2.1% for 16S and COI respectively). These clades belonged to 11 described species and 5 undescribed. The high intraspecific variability of some species indicates the possible existence of more undescribed species within present species groups.

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“…The sequencing of 40 individuals together with 100 sequences retrieved from public databases gave rise to a phylogenetic tree based on 140 sequences, which showed the existence of 13 different clades. Twelve of these clades were already identified by Alonso et al (2021) (see Figure 15) and 10 corresponded to the currently described species. One clade ( Ceriodaphnia sp.…”

“…This is further corroborated by the ASAP analysis, which identified with a high level of confidence three putative groups within the COI dataset of C. smirnovi . Alonso et al (2021) also found large intraspecific variability (>7% for COI) in other groups of Ceriodaphnia (i.e. C. megops Sars, 1862; C. cornuta Sars, 1885 /C.…”

“…Our genetic results support the existence of a species complex containing several cryptic taxa within the C. smirnovi morphospecies. The network of haplotypes (Figure 4) and the K2P distance show a relatively high number of mutations and COI divergences of some sequences exceeding 7%, which has been used as a threshold to establish different species within cladocerans according to Alonso et al (2021) and de Almeida Castilho et al (2015). This is further corroborated by the ASAP analysis, which identified with a high level of confidence three putative groups within the COI dataset of C. smirnovi .…”

“…The C. smirnovi group is thought to be restricted to the Mediterranean region (Alonso et al, 2021), where it might occupy shallow, temporary to semipermanent ponds, with littoral vegetation and highly variable turbidity and conductivity conditions. According to our data, D. crassa and S. vetulus , which are commonly associated with vegetation and/or algal mats (Błędzki & Rybak, 2016) might be shared accompanying species.…”

“…Nowadays, the genus Ceriodaphnia is considered to contain 12 valid species but the number of species of doubtful identification that require further investigations (‘ species inquirenda ’) is almost twice (Kotov, 2013). The high number of species inquirenda has boosted in recent years molecular studies using DNA barcodes not only to find cryptic species but also to establish an accurate phylogenetic relationship between the known members of the group (Abreu et al, 2010; Alonso et al, 2021; de Waard et al, 2006; Deng et al, 2022; Jeffery et al, 2011; Sharma et al, 2014; Sharma & Kotov, 2013). However, the phylogenetic tree of Ceriodaphnia is still unresolved as well as the number of taxa within the genus.…”