Paternity share predicts sons' fetal testosterone

Abstract

Multiple paternity is common in many species. While its benefits for males are obvious, for females they are less clear. Female indirect benefits may include acquiring 'good genes' for offspring or increasing litter genetic diversity. The nutria (Myocastor coypus) is a successful invasive species. In its native habitat, it is polygynous, with larger and more aggressive males monopolizing paternity. Here, using culled nutria we genetically examined multiple paternity in-utero and found a high incidence of multiple paternity and maintenance of the number of fathers throughout gestation. Moreover, male fetuses sired by the prominent male have higher testosterone levels. Despite being retained, male fetuses of 'rare' fathers, siring commonly only one of the fetuses in the litter, have lower testosterone levels. Considering the reproductive skew of nutria males, if females are selected for sons with higher future reproductive success, low testosterone male fetuses are expected to be selected against. A possible ultimate explanation for maintaining multiple paternity could be that nutria females select for litter genetic diversity e.g., a bet-hedging strategy, even at the possible cost of reducing the reproductive success of some of their sons. Reproductive strategies that maintain genetic diversity may be especially beneficial for invasive species, as they often invade through a genetic bottleneck.

Figure 1

Male fetal T levels: (a, b) T levels of male fetuses of M. coypus. (a) Male fetuses’ T levels in relation to their father’s proportion in the litter, this relationship is significant (P = 0.0054). (b) Box plot of male fetuses' T levels in relation to their assignment to rare father versus main and single fathers (grouped into main fathers group); the two groups are significantly different (P = 0.0005). The mother's identity was incorporated as a random factor in the statistical model (see text for detailed statistics).

Figure 2

T levels of adult males and females: (a–f) T levels determined from caracasses of adult males and females of M. coypus. (a) Adult males' T levels in relation to weight (P = 0.0015). (b) Adult males' T levels in relation to total length (P = 0.04). (c) Adult males' T levels in relation to skull width (P = 0.015). (d) Adult females' T levels in relation to weight corrected for gestational age and litter size, no significant relationship was detected. (e) Adult females' T levels in relation to total length, no significant relationship was detected. (f) Adult females' T levels in relation to skull width, no significant relationship was detected.