Alternative Reproductive Behaviors: Three Discrete Male Morphs in Paracerceis sculpta, an Intertidal Isopod from the Northern Gulf of California

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Abstract
Paracerceis sculpta breeds in intertidal sponges, Leucetta losangelensis, where males employ 1 of 3 discrete alternative reproductive behaviors. Elaborate alpha-males attract females to spongocoels where mating and brooding of young by females occurs. Variance in the number of females per alpha-male is high (N = 0-11). Smaller beta-males, resembling females, and tiny gamma-males, resembling juveniles, invade spongocoels containing alpha-males and sexually receptive females. Alpha-, beta-, and gamma-males maintained in the laboratory do not molt or grow, and the 3 morphs differ in the relative amounts of energy they invest in somatic versus gonadal tissue (gamma > beta > alpha). Alternative male reproductive behaviors may have evolved in P. sculpta, since intensifying sexual selection on alpha-males allowed only the most competitive alphas to mate. Males that obtained mates by avoiding direct competition with alphas (e.g., mimicking females or stealing mates) may have persisted, despite their reduced fitness, because they experienced greater fitness than competitively inferior alphas. Similar selective pressures and thus similar male polymorphisms probably exist in other Crustacea.