An integrative approach to the taxonomy of the pigmented European Pseudomonocelis Meixner, 1943 (Platyhelminthes: Proseriata)

Abstract

Only a few species belonging to the Proseriata (Platyhelminthes) show a parenchymatic pigmentation, which may aid identification. Among these, Pseudomonocelis agilis has a yellowish body and is provided with a reddish-brown girdle in front of the statocyst. The species is known for limited areas of northern Europe and the Mediterranean. The present study was conducted to assess both the taxonomic status of populations attributed to the species across the unusually wide range for an interstitial flatworm, which lacks an obvious means of dispersal, and the levels of genetic variability within and among populations, by employing an integrative approach that included the analyses, on six populations, of three molecular markers (small subunit ribosomal 18S-like gene, inter-simple sequence repeat, allozymes), karyotypes, and 11 morphological characters. Furthermore, crossbreeding experiments were carried out on the Mediterranean populations. The results obtained revealed the existence of four highly divergent genotypic clusters, accompanied by karyological differences, with complete intersterility among the clusters tested. The combination of approaches adopted strongly supports the conclusion that the wide-ranging European pigmented species P. agilis is actually composed of four species: P. agilis in the Baltic area; Pseudomonocelis cetinae in the Adriatic; and Pseudomonocelis sp. nov. A and Pseudomonocelis sp. nov. B in the western and eastern Mediterranean, respectively. The latter two species are morphologically indistinguishable for the parameters essayed. Reconstruction of the phylogenetic relationships of these taxa, including congeneric and consubfamilial outgroups, showed that pigmentation is a plesiomorphic condition for the genus Pseudomonocelis and that Pseudomonocelis sp. nov. A shares a previously undetected, sister-group relationship with species of the unpigmented P. ophiocephala complex. The present study thus depicts complex speciation processes in a mesopsammic species, which involves allopatric divergence operating on different scales and ecological shifts, and highlights that the contribution of microturbellarians to marine biodiversity may be seriously underestimated.

COI sequencing as tool for the taxonomic attribution ofPatellaspp. (Gastropoda): the case of morphologically undistinguishable juveniles settled on aPatella ferrugineaadult

“…This practice has been recently advocated as the best way to overcome potential caveats of species' delimitation methods (Padial et al, 2009;Casu et al, 2009).…”

Phylogeography of the marine interstitial nemertean Ototyphlonemertes parmula (Nemertea, Hoplonemertea) reveals cryptic diversity and high dispersal potential

“…Molecular studies of marine meiofauna have shown that wide distributions often consist of multiple cryptic species (e.g., Rocha-Olivares et al 2001;Casu and Curini-Galletti 2004;Derycke et al 2008;Casu et al 2009), a pattern seen in many marine organisms, including those with planktonic larvae (Knowlton 2000). In addition, meiofaunal species exhibit phylogeographic breaks-boundaries between intra-specinc lineages-where no obvious barriers to dispersal exist, suggesting restricted gene flow (Derycke et al 2008).…”

“…Nonetheless, individuals may be eroded from the sediment by wave or current action or dispersed with suspended sediment (Palmer 1988) as well as on macroalgae and other substrata (Thiel and Gutow 2005;Derycke et al 2008). Relatively few phylogeographic studies of meiofauna exist (see Todaro et al 1996;von Soosten et al 1998;Rocha-Olivares et al 2001;Westheide et al 2003;Castro-Longoria et al 2003;Casu and Curini-Galletti 2004;Derycke et al 2005Derycke et al , 2007Derycke et al , 2008Derycke et al , 2010Casu et al 2009Casu et al , 2011Andrade et al 2011), and fewer still across the otherwise well-studied southeastern US phylogeographic boundary (Schizas et al 1999(Schizas et al , 2002. As a result, we lack a good general understanding of population differentiation in the environment occupied by these organisms.…”

Masters of miniaturization: Convergent evolution among interstitial eukaryotes

“…[20,21] Nonetheless, it is likely that most meiofaunal species still await discovery and form cryptic species complexes within geographically restricted areas. [2,[22][23][24][25] Widespread convergence and extreme morphological reduction among meiofaunal species present a massive challenge for accurate phylogenetic reconstruction, because morphological and reproductive evidence on their own can mislead inferences of meiofaunal interrelationships and evolutionary history. [24,25] Molecular phylogenetic approaches provide great potential to circumvent these issues and help avoid the circularity intrinsic to using the same morphological and reproductive characters one is trying to understand.…”

“…[2,[22][23][24][25] Widespread convergence and extreme morphological reduction among meiofaunal species present a massive challenge for accurate phylogenetic reconstruction, because morphological and reproductive evidence on their own can mislead inferences of meiofaunal interrelationships and evolutionary history. [24,25] Molecular phylogenetic approaches provide great potential to circumvent these issues and help avoid the circularity intrinsic to using the same morphological and reproductive characters one is trying to understand. [26] We anticipate that improved understanding of meiofaunal diversity will provide important insights into (i) the origin and early evolutionary stages of metazoans, (ii) the origins of miniaturization through heterochronic developmental mechanisms, and (iii) the patterns and causes of convergent evolution at both organismal and community levels.…”