Factors affecting gestation periods in elasmobranch fishes

Abstract

Gestation periods vary greatly across elasmobranch species. Differences in body size and body temperature (i.e. major determinants of metabolic rates) might explain such variation. Although temperature effects have been demonstrated for captive animals, body size effects remain undocumented. Moreover, whether metabolic rates of mothers or those of embryos affect gestation periods remains unclear. Because biological times generally scale with mass1−β, where β is metabolic scaling exponent (0.8–0.9 in fishes), we hypothesized that elasmobranch gestation periods would scale with mass0.1–0.2. We also hypothesized that regionally endothermic species with elevated metabolic rates should have shorter gestation periods than similar-sized ectothermic species if the metabolic rates of mothers are responsible. We compiled data on gestation periods for 36 elasmobranch species to show that gestation periods scale with M0.11 and m0.17, where M and m are adult female mass and birth mass, respectively. Litter size and body temperature also affected gestation periods. Our findings suggest that the body-mass dependence of metabolic rate explains some variations in elasmobranch gestation periods. Unexpectedly, regionally endothermic sharks did not have shorter gestation periods than their ectothermic counterparts, suggesting that the metabolic rates of embryos, which are likely ectothermic in all elasmobranch species, may be responsible. This article has an associated First Person interview with the first author of the paper.

The Relevance of Time in Biological Scaling

“…Furthermore, several studies have reported scaling exponents for various biological time periods, including gestation time, lactation (weaning) time, incubation time, age at maturity (first reproduction), and life span, that are significantly different from 1/4 [ 2 , 20 , 23 , 30 , 32 , 33 , 64 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 ] or are curvilinear in log–log space [ 93 , 94 ]. In addition, mammalian life span shows a triangular pattern of covariation with body mass that is not adequately described by a single power function [ 64 , 84 , 87 , 90 ].…”

The origins and drivers of sexual size dimorphism in sharks

“…The first of these factors appears superficially similar to fecundity selection but differs in that it is the spatio‐temporal distribution of reproductive output rather than the magnitude of reproductive effort that differs between species. Selection for increased female size in matrotrophic shark species is logical given the number and size of pups produced and the extended gestation period of many sharks (Au et al., 2008 ; Tokunaga et al., 2022 ). Differences in the nature of sexual selection between oviparous and matrotrophic shark species are more problematic: in this study, we focused on testes mass—commonly used as a proxy for the intensity of post‐copulatory sexual selection, and failed to find any relationship between this variable and SSD (Tables 2 , 3 , 4 ).…”

Community science informs movement and reproductive ecology of sand tigers Carcharias taurus off North Carolina, United States of America

“…If females in NWA are copulating with multiple males to enhance offspring fitness, they may be extending individual mating windows to increase the likelihood of encountering fit males. Gestation lasts between 9-12 months and may be determined by water temperature for this species (Bennett and Bansemer, 2004;Tokunaga et al, 2022). Dispersal of pregnant females along the NC coast in varying depths likely means they may be experiencing a range of winter temperature regimes.…”