Gametic incompatibility between species of the sea urchin Echinometra on the two sides of the Isthmus of Panama

The genus Echinometra has E. vanbrunti in the E Pacific, and E. lucunter and E. viridis in the Caribbean. E. viridis is morphologically distinct from the other two species, leading to the conclusion that E. lucunter and E. vanbrunti constitute a geminate pair. Allozyme data, on the other hand, place the speciation event of the 2 currently sympatric species after the Pliocene rise of the Isthmus. Crosses between E. viridis and E. vanbrunti produce rates of fertilization almost equal to those manifested in homogamic crosses. Sperm of E. lucunter can fertilize eggs of the other two species, but few of its eggs permit fertilization by heterospecific sperm. Contrary to the predictions of the "speciation by reinforcement' hypothesis, degree of incompatibility between the allopatric E. lucunter and E. vanbrunti is higher than between the sympatric E. lucunter and E. viridis. Despite the incomplete and unidirectional nature of their gametic isolation, E. lucunter and E. viridis maintain their genetic integrities. Incompatibility of E. lucunter eggs with heterospecific sperm has evolved in the last 3.5 Myr, after the rise of the Isthmus. -from Authors

Duke Scholars

Author Clifford W. Cunningham Biology