title: Interspecific and intraspecific variations in sibling species of sea urchin Echinometra.
abstract: Interspecific and intraspecific morphological and fertilization variations were studied in three sibling species of Echinometra (known as sp. B, C and D) found off the coast of Okinawa, Japan. Eggs from C and D were readily fertilized by sperm from all three color morphs of B when the sperm concentrations were high, but no fertilization was observed when sperm of the former were mixed with eggs from the latter. Under limiting sperm concentrations, however, both C and D were incapable to fertilize reciprocally with B. In contrast, crossing between C and D produced fertilization membrane at high and limiting sperm concentrations in both directions. Interspecific crosses between B vs. C and B vs. D clearly showed that these combinations were reproductively isolated in contrast to that observed for crossing between C and D. Interestingly, intraspecific fertilization of B showed considerable morphological variation in addition to variability in fertilization success. Intraspecific fertilization and morphological variations may occur due to a number of genetic and/or non-genetic factors. While the underlying cause(s) remain to be elucidated, the results of the present study suggest that B is now speciating very slowly.
authors.affiliation: Graduate School of Science and Engineering, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan.
authors.forename: Sk Mustafizur
authors.initials: SM
authors.lastname: Rahman
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Uehara
mesh_terms: D000818:Animals; D005260:Female; D005306:Fertilization / Q000502:physiology; D006066:Gonads / Q000033:anatomy & histology / Q000166:cytology; D007564:Japan; D008297:Male; D012617:Sea Urchins / Q000033:anatomy & histology / Q000145:classification* / Q000166:cytology / Q000502:physiology*; D035781:Siblings; D013045:Species Specificity; D013131:Spine / Q000033:anatomy & histology