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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.
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.
Charnov (1982) and Fischer (1984) derived these theoretical predictions from the Hamilton's (1967) theory of Local Mate Competition (LMC).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.Moreover, complex trade-offs may occur between resources allocated to reproduction and those devoted to growth and maintenance.In a growing number of hermaphroditic species sex allocation is reported to be also size dependent (Petersen and Fischer 1996; Trouvè and others 1999; Schärer and others 2001; Angeloni 2003; Tan and others 2004).