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Back to the odd assortment of animal species in which some males gain a reproductive advantage from their resemblance, temporary or permanent, to the females of their species. Giant cuttlefish alter their color patterns and shapes to mimic females; red-sided garden snakes do it with pheromones. In a number of fish, including our own plainfin midshipman, smaller males exploit their deceptive appearance to gain acesss to spawning sites guarded by larger territorial males. (Some commentators on this phenomenon have evoked the movie Some Like it Hot. Bear in mind, however, that Tony Curtis and Jack Lemmon were on the run from the mob when they joined the all-girl orchestra. Proximity to Marilyn Monroe was an unexpected benefit. Call it an exaptation.) 

As if two male morphs weren’t enough, a handful of creatures have evolved a three-morph system. About the last place you would expect to find a complex polymorphism would be among the isopods, mostly small marine crustaceans. Meet Paracerceis sculpta, an inhabitant of the intertidal zone from Southern California to Mexico. (At this point, visualize David Attenborough turning over a rock in a tide pool.) As described in 1987 by Stephen Schuster, then at UC Berkeley and now at Northern Arizona University, P. sculpta has alpha, beta, and gamma males. Alphas guard harems of females in the cavities of sponges, where they lay their eggs. Betas are the size and shape of females; like Type II midshipman fish, they sneak past the alphas and mate with his females. Gammas, which mimic juvenile isopods, also follow a sneaker strategy. It’s interesting that gammas invest the most energy in sperm production, followed by betas then alphas. (The testes of Type II midshipmen are much larger in proportion than those of the territorial Type I. This seems to be a pattern among polymorphic males.) 

Bony fish, which appear to have tried everything at least once during their evolutionary history, have also developed three-morph variations. Bluegill sunfish (Lepomis macrochirus), native to the eastern North America, have been stocked in California lakes and reservoirs as sport fish. I remember them fondly, dredged in cornmeal and deep fried, with a side of hushpuppies and maybe some coleslaw. Anyway, parental bluegills, like Type I midshipmen, hold territories where females lay eggs. Satellite males mimic females in size, color, and behavior, swimming under the parental’s radar. There is also a smaller sneaker morph, analogous to salmon jacks. Satellites and sneakers spawn at younger ages than parentals, but don’t live as long. 

Then we have the side-blotched lizard (Uta stansburiana), common in western scrublands. UC Santa Cruz biologist Barry Sinervo has studied this species since 1989. Male lizards, he reports, are color-coded, with either orange, blue, or yellow throats, and each color morph has a different reproductive strategy. Orange-throats defend large territories which are home to several females and are prone to usurp the territories of other males. Blue-throats have smaller territories and are often mongamous. They team up with fellow blue-throats against the more aggressive orange-throats. Sinervo calls them “the sensitive male lizards of the new millennium.” Yellow-throats, which resemble (some) females, are sneakers. 

Depending on the circumstances, each type can outcompete one of the others, in a kind of rock-scissors-paper game, and the numbers of each cycle over time. (I note that someone has elaborated the game into rock-scissors-paper-Spock-lizard, for which I can think of no analogues in the natural world.) Orange-throats dominate blue-throats, blue-throats deter yellow-throats, yellow-throats cuckold orange-throats. The frequency of each morph in a local population cycles from year to year, depending on the success of each of the three strategies. 

Female side-blotched lizards, it turns out, are playing a game of their own. Orange-throated females are more aggressive and lay large clutches of small eggs. Yellow-throated females produce smaller clutches of larger eggs. In the language of population biology, orange-throats are “r strategists,” as are codfish, spiders, and lemmings; yellow-throats are “K strategists,” like condors, elephants, and humans. Blue-throats are apparently rare among females, and orange-throats and yellow-throats exhibit a two-year cycle. 

I’ll save another well-known case of alternative male reproductive strategies, the bizarre shorebird called the ruff, for next week. Before that, though, a response to a reader’s comment that male polymorphism might be a relatively recent artifact of environmental pollutants. All the varieties of sneaker males among fish, reptiles, and birds appear to be anatomically normal and fully functional males. Typically fish exposed to hormone mimics show intersex traits, with both male and female reproductive organs. It seems clear that polymorphisms in the isopods, salmon, sunfish, lizards, harriers, and ruffs represent genetically-determined evolutionarily stable strategies, not aberrant responses to exotic chemicals.