Sperm-limited fecundity and polyandry-induced mortality in female nematodes Caenorhabditis remanei

Abstract

In many sexually reproducing species, females are sperm limited and actively mate more than once which can lead to sperm competition between males. However, the costs and benefits of multiple matings may differ for males and females leading to different optimal mating frequencies and consequent sexual conflict. Under these circumstances, male traits that reduce females' re-mating rates are likely to evolve. However, the same traits can also reduce, directly or indirectly, female survival and/or manipulate female fecundity. Evidence of this sexual conflict is common across several taxa. Here, we examine the evidence for this form of conflict in the free-living nematodes of the Caenorhabditis genus. Members of this group are extensively used to describe developmental and physiological processes. Despite this, we understand little about the evolution of selfing, maintenance of males and sexual conflict in these species, particularly those with gonochoristic mating strategies. In this study, we demonstrate experimentally sexual conflict in the gonochoristic of C. remanei cultured under laboratory conditions. In our first experiment, we found that female fecundity increased with the number of males present which suggests that females' reproduction may be sperm limited. However, increasing the number of males present also reduced female survival. A second experiment ruled out the alternative explanation of density-dependent reduction in female survival when more males were present as increasing female density correspondingly did not affect female survival.

Insights Into Species Divergence and the Evolution of Hermaphroditism From Fertile Interspecies Hybrids of Caenorhabditis Nematodes

“…9 females cannot take full advantage of abundant sperm. This may be a general feature of the species, for example as a consequence of female spermatheca size, barriers to remating, male effects on female fecundity (Diaz et al 2010), or as a consequence of unintended inbreeding in our laboratory stocks. Additionally, the reduction of C. briggsae hermaphrodite brood size by C. sp.…”

Female, but not male, nematodes evolve under experimental sexual coevolution

“…Caenorhabditis remanei female fitness decreases with the number of mating partners and therefore represents a perfect fit for our experiment [32]. We intensified sexual conflict to females above the laboratory baseline (1 : 1 sex ratio) for 20 generations by imposing a 1 : 5 (polyandry, PA) sex ratio and relaxed it using a 5 : 1 (polygyny, PG) sex ratio.…”

Determinants of female fecundity in a simultaneous hermaphrodite: the role of polyandry and food availability

“…Furthermore, the receipt of sperm can represent a material benefit, if female reproductive success is limited by the number of sperm that is available to fertilize all the eggs (e.g., Pitnick 1993; Levitan and Petersen 1995;Fjerdingstad and Boomsma 1998;Diaz et al 2010). Several empirical studies across a wide range of taxa have demonstrated that repeated matings are advantageous to females (e.g., Wagner et al 2001;Fedorka and Mousseau 2002;Schwartz and Peterson 2006;Klemme et al 2007), which suggests that direct benefits may promote the evolution of multiple mating.…”