Lockhart, S. J. 2006. Molecular evolution, phylogenetics, and parasitism in Antarctic cidaroid echinoids. unpublished Ph.D. thesis, University of California, Santa Cruz, 151 pp.

149063

Publication

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The cidaroid echinoids of Antarctica are used as a model to test the proposal that the Antarctic Circumpolar Current (ACC) has acted as primary trigger in the unusual radiation of this region's brood-protecting invertebrate clades. An unexpected discovery of extreme mitochondrial substitution rate heterogeneity among Cidaridae lineages was revealed by initial analyses. A rate of 4.2 ± 0.4% sequence divergence per million years for tropical Eucidaris species separated by the Isthmus of Panama contrasts with a fossil-calibrated rate of 0.18 ± 0.02% is calculated for the lineage that includes the Antarctic Ctenocidarinae and related subfamilies, Stereocidarinae and Goniocidarinae.The causes of this exceptional evolutionary rate variation are unknown. A mixed-model partition Bayesian analysis of molecular data produced a phylogenetic tree the calibration of which is achieved utilizing fossil data in a penalized likelihood analysis. Substantial divergence is shown to originate during the Oligocene subsequent to an 'early' initiation of the ACC by ~34 Ma at which time successively shorter periods separate splits between major lineages within a 'core' clade of Aporocidaris, Ctenocidaris, Notocidaris and Rhynchocidaris . The ACC, by mediating rare dispersal events to suitable new habitat where speciation can proceed in isolation is concluded herein to be the primary force initiating and driving radiation in at least this clade of brooding cidaroids. Echinophyces mirabilis Mortensen, 1909 has been reported to parasitize some oral-brooding Antarctic cidaroid species. For the past century, this unknown parasite has been attributed the remarkable capability of inverting the reproductive system of its echinoid host. The echinoid species previously thought parasitized are shown by phylogenetic analysis not to be closely related to either each other or to (apparently) infected specimens. The latter form a previously unrecognized reciprocally monophyletic clade. A new genus--- Miracidaris ---is proposed for this clade and the enigmatic Aporocidaris incerta (Koehler, 1902) is designated as type species. The recognition of Miracidaris necessitates a reevaluation of E. mirabilis parasitism and it is concluded that a low level of impact to host is the most parsimonious scenario. Evidence is unearthed in support of a taxonomic affiliation of this parasite with the Orthonectida.

Antarctic

Echinoidea

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