Meeting Abstract
55.3 Thursday, Jan. 6 The role of postmating isolating barriers in the hybridization of Orangethroat Darters. BOSSU, Christen M.*; NEAR, Thomas J.; Yale University; Yale University christen.bossu@yale.edu
Understanding the maintenance and dissolution of reproductive isolating barriers between species is essential to the study of how biodiversity originates. Yet, the completeness of species reproductive barriers may not be uniform across a species’ geographic range, resulting in a mosaic of hybridization. Asymmetric introgressive hybridization has played a substantial role in the evolution of the Orangethroat darter species complex, or Etheostoma spectabile species clade. The ranges of E. spectabile species and the mitochondrial donor, E. caeruleum, overlap extensively, yet the introgression is not widespread; the movement of E. caeruleum haplotypes into E. spectabile seems to be limited to the Ozarks and the Buffalo River system in the Eastern Highlands. This variation in hybridization rates across different geographic areas suggests that reproductive isolation is not equivalent everywhere this set of species co-occur. Comparing reproductive isolating barriers between areas with and without mitochondrial introgression will decipher which barriers are not complete, allowing for the initial formation hybrids. My objectives are to determine whether asymmetric postmating isolation barriers can explain the asymmetric mitochondrial introgression pattern. Postmating isolation includes mechanisms that restrict fertilization after mating, reduce hybrid fitness after fertilization (hybrid inviability and hybrid sterility), and reduce the mating success or survivorship of hybrids. Noncompetitive experimental crosses within and between these darter species determined that postmating barriers (e.g. fertilization success and hybrid viability) are incomplete but not localized. Additional competitive crosses were conducted and paternity analyses completed to test whether there is a conspecific sperm bias, or whether E. spectabile sperm has a competitive advantage.
