| Summary: | The study of breeding system evolution has been prolific given the broad subjects that it embraces, from the social environment and sexual selection to courtship behaviour and parental care. The general objective of this dissertation was to test empirically ideas shown in recent models of breeding system evolution. Using plovers Charadrius spp. as model organisms, which show remarkable variation in breeding systems, I investigate how adult sex ratio (ASR) and operational sex ratio (OSR) are linked together and relate to two major components of breeding systems: courtship behaviour and parental care. Experimental studies have led to equate ASR and OSR, but they are not necessarily the same and the way they correlate in nature is unknown. Here I show that in a wild polygamous plover population these ratios seem to be uncorrelated (Chapter 2). Differences in the social environment and the degree of mating competition between monogamous and polygamous populations could also be reflected in their courtship behaviour; higher courtship rates in a polygamous plover than in a monogamous closely-related plover support this prediction (Chapter 3). OSR may be more variable throughout time than ASR, and therefore be less reliable as a cue to the social environment. In support of this prediction ASR was better than OSR at predicting the duration of female brood care in a polygamous plover where females have variable care (Chapter 4). Sex-specific timing of breeding could differ according to the social environment and the level of mating competition in a population, I compared six populations of five closely-related plover species with varying breeding systems (Chapter 5); only one polygamous population showed sex-specific differences in arrival date and the length of time spent in the breeding grounds. Finally, I discuss the contribution of these results to the understanding of breeding system evolution and suggest potential future lines of research.
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