An experimental test to separate the effects of male age and mating history on female mate choice

Abstract

Should females prefer older males as mates? Male survival to old age might indicate the presence of fitness-enhancing genes that increase offspring fitness. However, many correlational studies show that mating with older males can lower female fecundity and even reduce offspring fitness due to epigenetic or germline mutation effects. One problem in quantifying female choice based on male age is that age is usually confounded with mating history. This begs a question: Do females choose males based on their age or their mating history? The answer requires an experimental approach, but few such studies exist. Here, we test if experimentally induced variation in the mating history of old and young males (12-week difference in postmaturity age) affects female choice in the eastern mosquitofish (Gambusia holbrooki). To vary mating history, adult males were either allowed to freely mate with females for 3 weeks or they only had visual contact with females. Immediately thereafter, we ran four-choice mating trials, using association time, to test the effects of male age and mating history (2 × 2 design) on male attractiveness. Females did not show a clear preference for males based on either characteristic. This was not due to a lack of female choice: females spent significantly more time with larger males. In addition, female choice was significantly repeatable across four trials: twice as a virgin and twice as a nonvirgin. Finally, female mating status (virgin or nonvirgin) did not affect her choice of mate, although virgin females spent significantly more time associating with test males.

Quantifying the costs of pre- and postcopulatory traits for males: Evidence that costs of ejaculation are minor relative to mating effort

“…Because female mating status does not influence her mate choice in G. holbrooki (Aich et al. 2020), we defined male attractiveness as the proportion of the total trial time the female spent within each association zone.…”

Male age alone predicts paternity success under sperm competition when effects of age and past mating effort are experimentally separated

“…To examine the effects of male age and mating history on sperm traits and reproductive success, we bred 'young' and 'old' males in the laboratory and then assigned males in each age class to one of two mating treatments (full methodological details in [33]). In brief, 'old' and 'young' males were bred from laboratory stocks in batches 12 weeks apart.…”

Combined effects of rearing and testing temperatures on sperm traits

“…Intriguingly, we found that rearing temperature altered the phenotypic correlation between body size and sperm velocity: when reared at the warmer temperature larger males had faster‐swimming sperm, but the reverse was the case for males reared at the cooler temperatures. Larger male mosquito fish are generally more attractive to females (Aich et al., 2020; Bisazza et al., 2001; Kahn et al., 2010) and have greater insemination success per mating attempt (Head et al., 2015). However, precopulatory sexual selection on male size in mosquito fish is complex and there is also evidence that smaller males are better at sneaking copulations with females (Pilastro et al., 1997) and, as a consequence, sometimes have greater reproductive success than larger males (Head et al., 2017).…”

“…There is considerable research looking at targets of precopulatory sexual selection in G. holbrooki . Several studies report that females prefer to associate with larger males (Aich et al., 2020; Bisazza & Marin, 1991; Hughes, 1985) which implies a large male mating advantage. On the other hand, some studies report that smaller males have a greater insemination success per mating attempt (Pilastro et al., 1997), whereas others find that larger males are more effective (Booksmythe et al., 2013).…”