Gonadal Dysfunction in Abnormal-Looking Anoles Is Consistent with Hybridization and Reproductive Isolation

Species-level diversification (speciation) results from the evolution of reproductive isolation. When reproductive isolation is intrinsic (independent of ecological context), speciation is thought to be irreversible. Intrinsic reproductive isolation manifests as a reduction in hybrid fitness due to Dobzhansky-Muller incompatibilities, and can render hybrids sterile or inviable. During fieldwork in western Cuba, I identified abnormal-looking individuals with small gonads within an assemblage of Anolis. I hypothesized that such individuals were interspecific hybrids and predicted a phenotypic distinctness and lower reproductive fitness. I evaluated my predictions by comparing putative hybrids with candidate parental species in external phenotypic traits and gonadal indicators of reproductive fitness. I found that putative hybrids were phenotypically distinct and did not produce sperm cells, suggesting that hybrid sterility may be important in maintaining species boundaries in this ecologically complex system.