Partner fidelity and reciprocal investments in the mating system of a simultaneous hermaphrodite

Quantitative Matching of Clutch Size in Reciprocating Hermaphroditic Worms

“…Regular alternation between layings and fertilizations of egg clutches of variable size has been documented in several simultaneous hermaphrodites with unilateral mating (see below), such as fish (e.g., genera Hyploplectrus and Serranus [8][9][10]) and marine worms (genus Ophryotrocha [11,12]). Indeed, even if simultaneous hermaphrodites produce both sperm and eggs and reproduce via both the female and the male sexual functions, some of them must have a partner to reproduce and behave either as females or as males during a single mating event, i.e., they are outcrossers and have unilateral mating.…”

“…The femalebiased sex allocation prevents pure females from invading egg-trader populations, because the fitness of pure females should be twice as high as the fitness of trading hermaphrodites via the female role [36,37]. Experimental evidence of the central role of egg-trading in the maintenance of hermaphroditism comes from the chalk bass Serranus tortugarum, which live in relatively dense social groups, where partners of monogamous pairs regularly alternate sexual roles throughout spawning bouts [10].…”

“…Marine polychaete worms Ophryotrocha diadema, as several simultaneous hermaphrodites, do not self-fertilize and have unilateral mating (i.e., they behave either as females or as males during each mating event). They are also external fertilizers and thus cannot store allosperm, which contribute to make them ideal model organisms to investigate reciprocity, since partners usually alternate sexual roles with each other, repeatedly exchanging egg clutch of variable size [8][9][10][11][12]. However, whether the alternation of sexual roles is the result of conditional reciprocity rather than by-product reciprocity has never been tested [13].…”

“…(G)LMMs (including the ones below) were performed with the R package lme4 [47]. Following Hart and colleagues [10], we tested whether reciprocation of egg clutches within dyad occurred more often than expected by chance with runs tests performed with the R package randtests [48] and we used the Fisher's method for combining independent p values to assess whether the number of alternation of sexual roles was greater than expected in random sequences when all data were combined (R package metap [49];).…”

Resource Availability Drives Mating Role Selection in a Simultaneous HermaphroditeAplysia californica

“…One way cheating behavior may be mitigated is through successively mating, in which partners alternate roles multiple times, releasing only a small portion of their gametes in each exchange. Such cooperative “egg-trading” behavior has been observed in several serranid fish species as well as in polychaete worms (external fertilizers) (Fischer, 1980; Axelrod and Hamilton, 1981; Sella and Ramella, 1999; Sella and Lorenzi, 2000; Erisman and Allen, 2006; Crowley and Hart, 2007; Hart et al , 2016). In instances where the donor role has greater direct investment, one would expect to see reciprocal “sperm trading” instead, such as appears to be the case in several internally fertilizing gastropods (Leonard and Lukowiak, 1985; Anthes et al , 2005; Jordaens et al , 2005; Koene and Ter Maat, 2005; Facon et al , 2008)…”