Morphological and taxonomic demarcation of Brachionus asplanchnoidis Charin within the Brachionus plicatilis cryptic species complex (Rotifera, Monogononta)
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Three well-defined groups, consisting of 15 species, have recently been ascribed to organisms historically identified as the Brachionus plicatilis species complex. One of these groups, the large clade, is composed of two named species (Brachionus plicatilis s.s. and Brachionus manjavacas) and two species identifiers (B. ‘Nevada’ and B. ‘Austria’). B. ‘Austria’ has been confirmed to be B. asplanchnoidis. As no type specimen exists for this species, and the original taxonomic description is lacking in detail, we give a detailed account of this species using material from Obere Halbjochlacke in Austria where B. ‘Austria’ was first identified genetically. Our analysis of B. asplanchnoidis populations was of global scope, an approach that revealed a great degree of morphological variability. However, combining aspects of both the dorsal and ventral surfaces clearly discriminated B. asplanchnoidis from the rest of the large-type members. This approach may prove useful in taxonomic studies of other cryptic species with relatively few morphological features. We also observed a geographic pattern of genetic divergence within B. asplanchnoidis. Average uncorrected COI divergences for a 554-bp fragment of the COI gene ranged from 3.9% within species to 17.5% between species of the large clade and indicate deep divisions within the cryptic species complex.
KeywordsBrachionus plicatilis Brachionus asplanchnoidis Brachionus ‘Nevada’ Brachionus ‘Austria’ Brachionus manjavacas Rotifer Morphology Species delimitation
We would like to thank M. Serra and T.W. Snell for providing individuals and resting eggs from clones they keep in their laboratories; M. Pichler for providing technical assistance; A. Herzig for assisting in the collection of samples from Obere Halbjochlacke and Oberer Stinkersee (Austria), and C. Jersabek for the collection of sediments from which MNCHU clones were extracted and for assistance with the identification of OHJ72. This work was partially supported by an EU research project (ROTIGEN, Q5RS-2002-01302), while SP was supported by the Academy of Finland (Grant Number 258048). We gratefully acknowledge the efforts of two anonymous reviewers and D. Fontaneto whose valuable suggestions were extremely helpful to finally shape the manuscript.
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