A research consortium from British Columbia and Mexico establish a molecular phylogeny of 16 species of west-coast holothuroidea based on mitochondrial DNA sequences. With a few exceptions, results support the existing taxonomy, based largely on the morphology of calcareous skin ossicles. In addition to confirming that Cucumaria pseudocurata and C. curata are separate species, the researchers note that C. lubrica may actually represent 2 species, a subtidal one and an intertidal one (see differences in ossicle morphology in specimens from the Victoria, British Columbia area) and, finally, that brooding has arisen in at least 2 separate lineages within the Family Cucumariidae.
NOTE of 5 families represented in the study, F. Cucumariidae is the largest with 9 species. Of these, 7 (Cucumaria curata, C. lubrica [possibly represented by 2 species], C. pseudocurata, C. vegae, Pseudocnus astigmatus, and P. californicus) exhibit direct development
|Research study 2|
Molecular ecologists predict that marine invertebrates with widely disseminating planktonic larvae will have less genetic differentiation because of greater genetic mixing. This is tested in 2 species of sea cucumbers Cucumaria miniata and C. pseudocurata that have overlapping geographical range from southern Alaska to northern California. The first species C. miniata has a pelagic, non-feeding larva that spend about 2wk drifting before settling and metamorphosing; the second species, C. pseudocurata, broods its embryos until they hatch into crawling juveniles. The results show, as predicted, significantly greater genetic structure in the brooding species C. pseudocurata than in the species with pelagic larvae C. miniata.
A strong genetic disjunction is apparent for the brooding species C. pseudocurata between Haida Gwai (Queen Charlotte Islands) and Vancouver Island, British Columbia. A high level of genetic diversity in the northern populations suggests survival in both northern and southern refugia during the Pleistocene Glaciation, some 15-18,000 yrs B.P. In the illustration on the Right note the differences in ossicle structure between northern haplotypes (more rod- and dumbbell-shaped) and southern haplotypes (larger, perforated plates).
NOTE nucleotide sequencing data from analysis of mitochondrial DNA (mtDNA)
NOTE at least one such refugium has been identified to have existed through the last glaciation period on the east side of Graham Island in the Queen Charlotte Islands, British Columbia. The potential expansion of west-coast marine-invertebrate species from post-glaciation refugia is considered elsewhere in the ODYSSEY: LEARN ABOUT LITTORINES: REPRODUCTION & DEVELOPMENT: GENETICS and LEARN ABOUT WHELKS: DISPERSAL, HETEROZYGOSITY, & GLACIAL REFUGIA
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