Cryptic Species in Putative Ancient Asexual Darwinulids (Crustacea, Ostracoda)

Abstract

BackgroundFully asexually reproducing taxa lack outcrossing. Hence, the classic Biological Species Concept cannot be applied.Methodology/Principal FindingsWe used DNA sequences from the mitochondrial COI gene and the nuclear ITS2 region to check species boundaries according to the evolutionary genetic (EG) species concept in five morphospecies in the putative ancient asexual ostracod genera, Penthesilenula and Darwinula, from different continents. We applied two methods for detecting cryptic species, namely the K/θ method and the General Mixed Yule Coalescent model (GMYC). We could confirm the existence of species in all five darwinulid morphospecies and additional cryptic diversity in three morphospecies, namely in Penthesilenula brasiliensis, Darwinula stevensoni and in P. aotearoa. The number of cryptic species within one morphospecies varied between seven (P. brasiliensis), five to six (D. stevensoni) and two (P. aotearoa), respectively, depending on the method used. Cryptic species mainly followed continental distributions. We also found evidence for coexistence at the local scale for Brazilian cryptic species of P. brasiliensis and P. aotearoa. Our ITS2 data confirmed that species exist in darwinulids but detected far less EG species, namely two to three cryptic species in P. brasiliensis and no cryptic species at all in the other darwinulid morphospecies.Conclusions/SignificanceOur results clearly demonstrate that both species and cryptic diversity can be recognized in putative ancient asexual ostracods using the EG species concept, and that COI data are more suitable than ITS2 for this purpose. The discovery of up to eight cryptic species within a single morphospecies will significantly increase estimates of biodiversity in this asexual ostracod group. Which factors, other than long-term geographic isolation, are important for speciation processes in these ancient asexuals remains to be investigated.

Artificial dam lakes as suitable habitats for exotic invertebrates: Ostracoda ecology and distribution in reservoirs of the Eastern Iberian Peninsula

“…It can be argued that the on-going global warming could facilitate colonization of northern habitats by non-indigenous species coming mainly from Africa, through migratory birds stopping at the Iberian Peninsula in their routes. Among the most common ostracods in the studied reservoirs, we found D. stevensoni, a species with cosmopolitan distribution (Sohn, 1987;Karanovic, 2012), but see Schön et al (2012) for a discussion of Darwinulidae cryptic species. Despite we found a relative high number of species in the studied reservoirs, it must be noticed that about half of the samples did not contain living specimens.…”

On the Strandesia obtusata/elliptica lineage (Ostracoda, Cyprididae) in the alluvial valley of the upper Paraná River (Brazil), with the description of three new species

“…For example. Bode et al (2010) found close to 40 cryptic species in a single ostracod morphospecies Eucypris virens Jurine, 1820, while Schön et al (2012) identified several cryptic species in the putative ancient asexual darwinulid ostracods using molecular markers. Whereas previously several ostracod workers correctiy wamed for significant variability in valve morphology of ostracods as a consequence of different water chemistries (see, for example, Finston, 2000), present day research detects cryptic and discrete genetic clusters ('species') that are often unidentifiable based on morphology.…”

“…This method identifies discrete clusters in molecular phylogenies as "phylogenetic species", comparing the genetic distances within and between the clusters. This method has already been applied successfully to ostracod phylogenies, e.g., for Eucypris virens by Bode et al (2010), for Bennelongia by Martens et al (2012) and for darwinulids by Schön et al (2012).…”

On the modern distribution of the euryhaline speciesCyprideis torosa(Jones, 1850) (Crustacea, Ostracoda)

“…In Eucypris virens (Jurine), close to 40 cryptic species have been described from Europe and North Africa (Bode et al 2010), while Schön et al (2012) found three cryptic species in Darwinula stevensoni (Brady & Robertson) and eight in Penthesilenula brasiliensis (Pinto & Kotzian). Analysis of DNA sequence data of Romecytheridea species of Lake Tanganyika, revealed a high cryptic diversity with allopatric distribution.…”