Fitness Implications of the Mating System and Reproductive Ecology of Tuatara
Sexual selection and reproductive strategies affect individual fitness and population genetic diversity. Long-standing paradigms in sexual selection and mating system theory have been overturned with the recent integration of behavioural and genetic techniques. Much of this theory is based on avian systems, where a distinction has now been made between social and genetic partners. Reptiles provide contrast to well-understood avian systems because they are ectothermic, and phylogenetic comparisons are not hindered by complicated patterns of parental care. I investigate the implications of the mating system and reproductive ecology on individual fitness and population genetic diversity of tuatara, the sole extant representative of the archaic reptilian order Sphenodontia. Long-term data on individual size of Stephens Island tuatara revealed a density-dependent decline in body condition driven by an apparently high population growth rate resulting from past habitat modification. Spatial, behavioural, and genetic data from Stephens Island tuatara were analysed to assess territory structure, the mating system, and variation in male fitness. Large male body size was the primary predictor of 1) physical access to females, 2) competitive ability, and 3) mating and paternity success. Seasonal monogamy predominates, with probable long-term polygyny and polyandry. Annually, male reproduction is highly skewed in the wild and in captivity. Over 80% of offspring from a captive population on Little Barrier Island were sired by one male and multiple paternity was found in approximately 18% of these clutches, although it was not detected in any wild clutch. The dominance structure has lead to reduced genetic variation in the recovering Little Barrier Island population. Stephens Island tuatara show fine-scale population genetic structuring that appears to be driven by past habitat modification and a sedentary lifestyle in the absence of sex-biased dispersal or migration. These results will improve conservation management of tuatara by providing guidelines for maximising genetic diversity of small and captive populations and will aid in selecting founders for translocated populations. Because of the archaic phylogenetic position of tuatara, this study provides a baseline for comparisons of mating system evolution in reptiles.