Reproductive asynchrony and population divergence between two tropical bird populations

High-latitude vertebrates generally breed seasonally and synchronouslyas the primary environmental cue used to time seasonal processesis photoperiod. Investigations of tropical vertebrates havealso documented seasonal reproduction, but it is unclear howsynchronous reproduction is, both within and between populations.In this study, we investigated whether seasonal reproductionin a tropical species is synchronous between two populationsin close proximity and, if not, whether asynchrony is correlatedwith genetic and cultural differentiation. We describe two equatorialpopulations of rufous-collared sparrows (Zonotrichia capensis),at the same latitude and separated by 25 km, that each breedseasonally but out of phase with each other. This asynchronousreproductive phenology is associated with local weather patternsand is independent of photoperiod. At a finer scale, reproductivetiming is more highly synchronized within monogamous pairs thanwithin the population as a whole. Associated with the differencein reproductive phenologies, we document that males in eachpopulation sing different song dialects. Using microsatelliteDNA analysis, we found limited gene flow and significant geneticdifferentiation between the two populations. From these resultswe hypothesize that cultural and genetic differentiation betweenpopulations, which can be greater in tropical populations thantemperate ones, can be associated with locally adapted reproductivephenologies.