Role of spawning synchrony on hybridization barriers in sympatric intertidal fucoid algae - when and why

Tese de Doutoramento, Ciências do Mar, da Terra e do Ambiente, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2016In sympatric assemblages of congeners with incomplete reproductive barriers, the synchrony within species and asynchrony between species may be under strong selection, reinforcing prezygotic reproductive isolation and reducing hybridization. Interspecific asynchrony and gametic incompatibility are considered the two most important prezygotic mechanisms reinforcing assortative mating and acting against hybridization. However, divergence of reproductive strategies in closely related species might also contribute to reproductive isolation. The main goal of this thesis was to investigate hypotheses concerning the mechanisms that act against hybridization in sympatric species with external fertilization, including the asynchrony of gamete release, mating system variations and gametic incompatibility. As a model we used sympatric Fucus species with different reproductive modes, hermaphroditic (selfing) and dioecious (obligate outcrossing). The results show a clear relationship between patterns of gamete release and tidal/circadian cycles that contributes to interspecific variation in spawning time between hermaphroditic and dioecious species. The data support the hypothesis that asynchronous egg release acts as a prezygotic barrier to hybridization between hermaphroditic and dioecious species, and therefore, that mating system variation between congeners plays important role against hybridization. We also provide evidence that gametic incompatibility is an incomplete prezygotic barrier between Fucus species. Results show the potential of interspecific fertilization, and the potential growth and survival of hybrids relative to the parental lineage