Does sexual bimaturation affect the cost of growth and the operational sex ratio in an extremely size-dimorphic reptile?

Abstract

Sexual bimaturation, an intersexual difference in age at maturity, is a consequence of sexual size dimorphism (SSD). Sexual bimaturation arises through intersexual differences in growth trajectories. In theory, differences in growth trajectories should bias the operational sex ratio in favour of the early-maturing sex. In addition, in animals with sexual bimaturation, the late-maturing sex always maintains a lower intrinsic rate of growth (k) that may be linked to the metabolic cost of growth. We studied growth, its relation to the operational sex ratio, and its metabolic cost in the extremely size-dimorphic northern map turtle. We found that females take twice as long as males to reach maturity and that females maintain higher absolute rates of growth but have a lower k. The estimated operational sex ratio was even in our study population, and estimates of annual mortality were similar between adult males and females. Based on respirometry, we found no evidence that fast-growing females incur a metabolic cost compared to non-growing males.