Abstracts (first author)
Is hybrid speciation driven by stochastic or deterministic processes?
Natural hybridization may have a multitude of consequences for biological diversity. One possible outcome is hybrid speciation. Whether this mode of speciation is primarily driven by stochastic or deterministic processes remains an open question. Recently, it was shown that the Italian sparrow (Passer italiae) is a hybrid species formed by interbreeding between the house (P. domesticus) and Spanish sparrow (P. hispaniolensis). Today, the parent taxa occur sympatrically over large parts of their breeding range. This allows for a rare opportunity to recapitulate the processes that were involved in the formation of this hybrid species. Previous studies have shown that the Italian sparrow is fixed for house sparrow mitochondria while mito-nuclear incompatibilities appear to act as strong reproductive barriers against its other parent species, the Spanish sparrow. Further, sex-linked genes appear to be involved in reproductive barriers between the hybrid species and both parents. Studying a sympatric population of house and Spanish sparrows on the Iberian Peninsula, we recover a similar pattern. We find strong asymmetry in introgression patterns between the two parental species as well as asymmetry in introgression patterns among genomic regions. All but one of the 60 admixed individuals out of a total of 292 sampled birds had house sparrow mitochondria. Moreover, sex-linked markers in general, and those with known mitochondrial function in particular, introgressed at much lower rates into opposite mitochondrial-genetic background than did autosomal markers. These striking similarities in introgression patterns across parallel systems suggest that the formation of this hybrid species was driven by deterministic rather than by stochastic processes.