The role of interspecific competition and hybridization in phenotipic evolution of Passer sparrows

Abstract

Interactions between closely related species, including resource competition and hybridization, might influence phenotypic evolution and play a significant role in evolutionary diversification. There may be different outcomes of such interactions on phenotypic evolution. In sympatry, traits may diverge to diminish interspecific competition or maladaptive hybridization, a process known as character displacement, or they may convergence for instance due to gene flow. I studied phenotypic evolution in three taxa of Passer sparrows by comparing trait values of several morphological characters (beak height, beak length, tarsus length, wing length and bib size) in sympatric and allopatric populations of the Spanish sparrow (Passer hispanoliensis), Italian sparrow (Passer italiae) and house sparrow (Passer domesticus). The Italian sparrow has a hybrid origin and is intermediate between its two parental species, the house and Spanish sparrow both genetically and phenotypically. I looked for patterns of convergence or divergence in sympatry and inferred these patterns in light of evolutionary processes. I found a complex pattern of sympatric convergence, divergence and parallel shifts in the different traits and species. This complexity may be a result of the interplay between gene flow and divergent and convergent natural selection affecting the traits. However, the Spanish sparrow stood out as one showing more consistent patterns of trait divergence in sympatry with either of the two other species. The Spanish sparrow also appear to occupy a broader niche when in allopatry than in sympatry, suggesting that interspecific competition may have played a significant role in shaping its ecologically relevant traits.