Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males

Department of Biology, University of Memphis, Ellington Hall, Memphis, Tennessee 38152, USA.
Nature (Impact Factor: 42.35). 10/2004; 431(7007):446-449. DOI: 10.1038/nature02845
Source: PubMed

ABSTRACT Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.

  • [Show abstract] [Hide abstract]
    ABSTRACT: In some species, sperm is stored within the female reproductive tract for months to years, and yet remains viable to fertilize eggs and produce offspring. Female red-sided garter snakes store sperm for over 7 months of winter dormancy. In previous work, we demonstrated that these stored sperm account for an average of 25 % paternity of a litter when the female mates with a male at spring emergence. Here, we tested whether last-male sperm precedence was prevalent when a female mates with two males during the spring. On average, paternity was shared equally among the first (P-1 proportion of paternity of the first male to mate) and second males (P-2) to mate in the spring, and stored sperm (P-ss), but the variance in paternity was high. Thus, last male sperm precedence may diminish when a female has more than two mates. Male size did not affect paternity, but, as the interval between matings increased, P-1 increased at the expense of P-ss. Interestingly, as the second spring male's copulation duration increased, P-1 also increased at the expense of P-2. This result suggests that female influence over sperm and/or copulatory plug transfer during matings may also affect which male fathers her offspring in response to coercive matings as we assisted females to mate for their second mating. Finally, all females were spring "virgins"; consequently, sperm stored from autumn matings (and/or previous spring matings) remain competitive even when faced with two rivals in sperm competition and is likely the driver of the evolution of sperm longevity.
    Behavioral Ecology and Sociobiology 09/2014; 68(9):1419-1430. DOI:10.1007/s00265-014-1749-0 · 3.05 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sperm competition game theory predicts that males should respond to increasing sperm competition risk by increasing ejaculate expenditure. There is considerable support for this prediction from a diverse range of taxa. However, the cues males use to assess risk and the fitness returns for strategic ejaculation are less well understood. We explored the role of acoustic cues in the assessment of sperm competition risk by manipulating male experience of acoustically signaling conspecifics in the field cricket Teleogryllus oceanicus. Compared with males reared in acoustic isolation, males reared in song-dense environments mimicking a high sperm competition risk produced ejaculates with a greater percentage of viable sperm. However, acoustic experience had only a weak and nonsignificant effect on competitive fertilization success. We argue that female influences on paternity are likely to have a strong moderating effect on male fitness returns from prudent allocation and call for more studies that address the consequences of strategic ejaculation for male fitness.
    Behavioral Ecology 06/2013; 24(4):982-986. DOI:10.1093/beheco/art009 · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Theory assumes that postcopulatory sexual selection favours increased investment in testes size because greater numbers of sperm within the ejaculate increase the chance of success in sperm competition, and larger testes are able to produce more sperm. However, changes in the organization of the testes tissue may also affect sperm production rates. Indeed, recent comparative analyses suggest that sperm competition selects for greater proportions of sperm-producing tissue within the testes. Here, we explicitly test this hypothesis using the powerful technique of experimental evolution. We allowed house mice (Mus domesticus) to evolve via monogamy or polygamy in six replicate populations across 24 generations. We then used histology and image analysis to quantify the proportion of sperm-producing tissue (seminiferous tubules) within the testes of males. Our results show that males that had evolved with sperm competition had testes with a higher proportion of seminiferous tubules compared with males that had evolved under monogamy. Previously, it had been shown that males from the polygamous populations produced greater numbers of sperm in the absence of changes in testes size. We thus provide evidence that sperm competition selects for an increase in the density of sperm-producing tissue, and consequently increased testicular efficiency. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Evolution 01/2015; DOI:10.1111/evo.12603 · 4.66 Impact Factor