Integrating Molecules and Morphology: Consensus or Conflict in the Symbiotic Copepods?
Department of Zoology, NHM
TUESDAY 17th April, 12pm
Neil Chalmers Science Seminar Room (DC.LG16)
No group of plants or animals on Earth exhibits the range of morphological diversity as seen among the extant Crustacea. This structural disparity is best demonstrated by the symbiotic Copepoda. Given their moderately high host specificity in conjunction with the incredible spectrum of potential marine hosts, it is highly conceivable that parasitic copepods significantly outnumber their free-living counterparts in species diversity. Their successful colonization or utilization of virtually every metazoan phylum has generated a great diversity in copepod body morphology, which is arguably unparalleled among the Crustacea. For example, some highly modified copepods such as the polychaete-associated Herpyllobiidae and Melinnacheridae lack any external trace that could positively identify their crustacean affinity and their divergent body plans defy any attempts to place them in a higher level classification on morphological grounds alone. Other families such as the Monstrillidae and Thaumatopsyllidae demonstrate how extremely powerful natural selection can be in shaping morphology to meet functional needs so that distantly related taxa may appear uncannily similar. Small subunit ribosomal sequence data (18S rDNA) can help resolving some of the controversial issues that had reached a temporary impasse in the phylogeny and classification of the symbiotic copepods, such as the placement of the Monstrillidae and Thaumatopsyllidae, the paraphyly of the Cyclopoida and the origin of parasitism in the freshwater environment. Examples will be given that demonstrate the usefulness of such data in the classification of highly transformed and morphologically reduced taxa, the inference of colonization events and the placement of incertae sedis known exclusively from juvenile stages. I will present evidence that illustrates how the use of 18S sequence data can lead to the discovery of previously overlooked morphological characters and how they can potentially impact on the ordinal level classification of the Copepoda.
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