In natural populations susceptible to inbreeding depression, behaviors such as female promiscuity and disassortative mating may enhance the production of outbred progeny and help maintain genetic variation at the population-level. However, empirical tests of such hypotheses have largely focused on mating systems in which female choice is known to play a large role. In insular reptile populations, cryptic choice may be important for overcoming constraints on precopulatory choice and diversifying breeder representation. We carried out pedigree reconstructions of 50 clutches of critically endangered Cyclura nubila caymanensis (Sauria: Iguanidae) to investigate the prevalence and efficacy of strategies theorized to optimize genetic compatibility among mate pairs. We found that females mating disassortatively and multiply, but not with respect to male heterozygosity, tended to produce more heterozygous offspring on average. Pair relatedness also had a negative effect on hatching success, while additional sires positively influenced clutch size. Despite evidence for direct and indirect benefits, females did not mate with more outbred or genetically dissimilar males than expected by chance. Our data imply strong reproductive skew among males, with geographic proximity and body size largely predicting siring success. Multiple-paternity occurred in a minimum of 38% of clutches. Paradoxically, females were not more promiscuous when confronted with more males, as demonstrated at a site supporting high local densities. Our data imply that while female mating behaviors have the potential to confer adaptive benefits in this small population, the trajectory of mating system evolution may be largely constrained by sexual conflict.