Abstract. The study of the patterns of reproductive isolation in relation to species divergence is critical for the understanding of the process of speciation. Comparative analyses of this kind were previously conducted in Drosophila, Lepidoptera, frogs, ducks, and birds in general. In the present study, we used information from the literature to analyze hybrid inviability in relation to species divergence in pigeons and doves. Four main patterns arose from this analysis:(1) as in the other groups studied, F 1 hybrid inviability gradually increases as species diverge, the time needed to reach total inviability being higher in birds than in the other groups; (2) as expected, the presence of geographic overlap does not influence the evolution of postzygotic isolation; (3) the percentage of unhatched eggs does not differ between hybrids of the first generation and the backcrosses, but it increases in the second hybrid generation; and (4) pigeons and doves follow Haldane's rule, as found in the other groups studied so far. The similarity between the results of this and previous studies contributes to the growing evidence suggesting that the patterns of the evolution of postzygotic isolation, and the process of speciation in general, are shared among animal groups.

No abstract

SummaryThe Yellow Cardinal Gubernatrix cristata is a globally endangered passerine endemic to southern South America. Although the conservation status of this species is alarming, there is no information about factors that affect its reproductive success. We studied the breeding biology of a Yellow Cardinal population in Corrientes province in north-east Argentina and report reproductive parameters, such as timing of breeding, clutch size, hatching success and chick survival and analyse factors influencing nest survival. The breeding season lasted from October to December with most nesting attempts occurring during the second half of November. Re-nesting after nest failure occurred in approximately 35% of pairs but we did not observe re-nesting after successful attempts. Modal clutch size was three eggs and successful nests fledged on average 1.6 chicks. We observed brood parasitism by Shiny Cowbirds Molothrus bonariensis in 33% of the nests. The main cost of brood parasitism was the puncture of cardinal eggs by cowbird females, which very often resulted in nest abandonment. Another factor reducing reproductive success was parasitism by botflies Philornis sp., which occurred in 22% of the nests and reduced chick survival. We determined daily nest survival rate with MARK software and found that during the egg stage, it decreased with time of breeding and brood parasitism by Shiny Cowbirds. Our results indicate that Shiny Cowbird and botfly parasitism represent a threat for Yellow Cardinals. Conservation actions to protect the remaining populations of Yellow Cardinals should consider the impact of Shiny Cowbird parasitism.