Hermaphrodite mature sex dating
The polychaete worm provides one of the best model systems through which to test the mechanisms underlying sex allocation adjustment in outcrossing hermaphrodites.
In this species, sex allocation is not complicated by gender-specific supporting structures (such as reproductive organs, genitalia, etc.).
To face ensuing sperm competition (Parker 1998), hermaphrodites are predicted to allocate proportionally more resources to the male function and fewer resources to the female function as mating group size increases.
Charnov (1982) and Fischer (1984) derived these theoretical predictions from the Hamilton's (1967) theory of Local Mate Competition (LMC).
In the protandric and then simultaneously hermaphroditic polychaete worm reproductive resources are flexibly allocated in the protandrous and the hermaphroditic phase.
The cost of male reproduction during adolescence is spread over the whole energy budget of the animal as shown by the shortening of lifespan and the lowering of growth rate in individuals with enhanced male expenditure during the protandrous phase.
Although these findings confirm that hermaphrodites adjust their sex allocation flexibly in relation to population size, the direction and the amount of the adjustment follow different patterns in the different species studied.
Locher and Baur (2002) observed a shift in the same direction after reared in large groups, an unexpected increase in egg production was observed (compared to that of isolated individuals) and it occurred at the expense of body growth (Koene and ter Maat 2004).Tan and others (2004) documented that in the leech sp., although in the latter a trade-off between sexual functions is revealed under specific conditions (Schärer and others 2005).In gastropods, evidence for a trade-off between sexes was found only after considerable experimental manipulations.According to LMC theory, in separate sex organisms, when populations are structured in such a way that mating group sizes are small and related males compete for fertilization, females are expected to bias the sex ratio of their offspring towards daughters (that is, the sex which suffers less competition) and produce the minimum number of sons which can ensure fertilization of all their daughters.As the number of females in a patch increases, their progeny will mix.