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Abstract THE PRIVATE LIFE OF SHRIMPS: SEX, CONFLICT, AND SEXUAL SELECTION IN HERMAPHRODITES Juan Antonio Baeza The importance of sexual selection (e.g., selection by females
for sexual partners, pre-copulatory competition among males for
females) is widely recognized in species with separate sexes. Conversely,
sexual selection still is enigmatic in simultaneous hermaphrodites
despite more than 130 years of research since Darwin. In this talk,
I will demonstrate that sexual selection is important in the simultaneously
hermaphroditic shrimp Lysmata wurdemanni. Laboratory experiments
demonstrated that sperm competition is absent in this shrimp; female-role
hermaphrodites invariably mated only once with one other shrimp.
Also, female-role shrimps preferred small over large shrimps as
male mating partners, and the male mating ability was greater for
small compared to large hermaphrodites. The experiments above demonstrate
that sexual selection is important in this hermaphroditic species.
What are the evolutionary consequences? Using sex allocation theory
as a framework, it is possible to predict that hermaphrodites should
allocate more energy to egg than to sperm production. It should
not pay (in fitness) for hermaphrodites to produce and inseminate
female-role hermaphrodites with large amounts of sperm when full
paternity is assured in the absence of multi-male mating. Also,
small hermaphrodites should allocate proportionally more resources
to male reproduction than large hermaphrodites. This size-dependent
sex allocation permits hermaphrodites to profit from male mating
opportunities that are the greatest at small body sizes. In agreement
with the predictions above, dissections of the gonad and quantification
of ovaries versus testes mass indicated that, hermaphrodites allocated,
on average, 118 times more to the female than to the male gonad
and the proportion of resources devoted to male function was higher
in small than in large hermaphrodites. Hermaphroditism is common
in many different phyla of marine invertebrates. Studies exploring
sexual selection in hermaphrodites, which should increase our knowledge
of behavioral, physiological, and morphological diversity in the
marine environment, are in progress.
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