Evolution's Rainbow. Joan Roughgarden

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СКАЧАТЬ lead to widespread participation in breeding and a concentrated distribution of resources lead to power hierarchies, family feuds, and labor strife. We see economic markets for transactions of reproductive opportunity.

      As we now move to social systems featuring multiple genders, the language biologists use to describe how animals behave becomes particularly loaded. The language always lauds the individuals who hold territories and possess mates, as though each male were biologically entitled to a castle of his own, complete with princess. Words like stealing, parasitism, deceit, and mimicry dominate the discussion and distort the sophisticated reality of what really happens in societies that contain a biological diversity of participants. Instead, the theory of transactions of reproductive opportunity seems to extend nicely to family organizations with multiple genders.

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      Multiple-Gender Families

      The social roles of multiply gendered animals are indicated by their bodies. Males or females in a species may come in two or more sizes or colors. The morphological differences are the tip of the iceberg. The two morphs approach courtship differently, have different numbers of mates, have different arrangements of between-sex and same-sex relationships, live different life spans, prefer different types of real estate for their homes, exercise different degrees of parental care, and so on. Because body shape, color, and posture—the important modes of communication in fish and lizards—are so easily visible to biologists, multigender societies are better described in these groups than in groups that communicate more by sound and scent.

      Biologists have struggled with naming these within-sex polymorphisms. They may be called alternative mating strategies to emphasize the different approach of each morph to courtship. Or they may be called alternative life histories to emphasize the different life path each morph takes. Previously, I suggested that we call these different expressions of how to live “genders.” I feel this word best captures the totality of the differences between the morphs, extending from mating, through lifestyle, to length of life.

      Phrases like “alternative” mating strategy or “alternative” life history are especially poor names for multiple genders because the “alternative” strategy is usually the most common strategy. Singling out a minority strategy as “normal” and labeling the rest “alternative” is simply prejudice. Societies with multiple genders are not easy to describe because we’re not prepared to find what we actually see. But let’s wade in.

      TWO MALE, ONE FEMALE

      The first step beyond one-male one-female two-gender societies are those with two male genders and one female gender, making three altogether. Here’s a sample.

      Bullfrogs (Rana catesbeiana) have two male genders: large males who call at night, giving bullfrogs their name, and small males who are silent.¹ Both are reproductively competent, and females mate with both. Silent males turn into calling males as they grow older. Male frogs in other species² and males in many vertebrate groups also have to decide when to begin breeding—whether to wait until established enough to flaunt wealth and power, or to begin sooner with fewer resources but lots of charm. Perhaps silent males should not be considered a different gender from calling males, but rather an early developmental stage of the same gender. Compare this case with others, though, and you may agree that it makes more sense to view males who mature from a silent stage into a calling stage as changing genders.

      Did you know a fish could sing? There is a fish in the bays and estuaries of the Pacific coast, including San Francisco Bay, called the plainfin midshipman (Porichthys notatus) because of its bioluminescent spots, which resemble rows of buttons on a Navy uniform. These fish are also known as the California singing fish or canary-bird fish. The species has two male genders who behave somewhat like bullfrogs. The large male gender consists of fish who defend territories and guard the eggs laid in them. To signal readiness to mate, a large male emits a low humming sound for as long as fifteen minutes, and a female may respond by entering the territory and laying eggs there. Females lay only one batch of eggs. A large male guards a big collection of eggs laid by five or six females. The small male gender consists of fish that mature at a younger age and are silent, like the silent bullfrogs. They don’t defend territories. Instead, they mate by darting in to fertilize eggs being laid in a large male’s territory.

      

      This fish is but one of hundreds of known species where males come in two or more genders. This species is unusual because its habit of singing has allowed biologists to determine how deeply the anatomy of the two male genders differs. For biology wonks, here are the technical details: The large male gender relative to the small male gender has a relative sixfold advantage in the mass of sound-producing muscles, a three-to fivefold increase in the number and diameter of sound-producing muscle fibers, a cellular ultrastructure with enlarged zones densely filled with mitochondria, a more branched endoplastic reticulum, larger sarcomeres, and Z-lines that are twenty times wider. Motoneurons and pacemaker neurons are also three times larger, as well as sonic axons with terminal boutons two to three times larger. And so on. Even without being a biology wonk, the large male and small male genders clearly represent deeply different developmental programs, involving different expressions of entire suites of genes.³

      Thus, both the bullfrog and plainfin midshipman have a calling large male gender and a silent small male gender. A bullfrog male changes from the small gender to the large gender as he ages, whereas a male plainfin midshipman is locked into one of these genders for life.

      In the Pacific, coho salmon (Oncorhynchus kisutch) have two types of males. A “jack” spends two years in the ocean before returning to streams to breed, and a “hooknose” spends three years in the ocean before returning to breed. The female spends three years in the ocean too. All three types die after breeding. A jack is small and cryptically colored, and a hooknose is big, has a pronounced snout (hence its name), and is brightly colored.

      The females excavate a nest in the gravel in which they lay their eggs. When they do, the closest male fertilizes the most eggs. Hooknose males are better than jacks at fighting for position near a female and wind up with the most fertilizations. The jacks obtain some fertilizations by darting in under the female while she is laying eggs. The benefit for the jack of being able to breed one year earlier and avoiding the hazard of living another year at sea compensates for its relative disadvantage in fertilizations compared with the hooknose. Jack and hooknose coho salmon appear to have equally successful strategies of life.⁴

      In the Atlantic, salmon (Salmo salar) have some males that migrate from rivers to the sea as smolts and return after about five years as large anadromous males about 75 centimeters in length. Other males, called parr, don’t bother journeying to the sea. They remain in the streams and mature in about three years at near 50 centimeters. The females also migrate to the sea and return. At spawning, a large anadromous male defends access to a female, while the parr hang out downstream. When the anadromous male and female are mating, the parr dart in and obtain some fertilizations. These two male life strategies work out to have about the same overall success when survival and mating access are factored in.

      Male red deer (Cervus elaphus, also called elk) who don’t have antlers probably are counterparts of the silent male frogs.⁵ Called hummels (or notts), these deer are in better physical condition than males with antlers, and may at times be more successful at mating.⁶

      THREE MALE, ONE FEMALE-SUNFISH

      Now to species with three male genders. The females here have one gender, making four genders in total. A good example is the sunfish, a deep-bodied fish averaging about 10 centimeters in length and exceedingly common in North American lakes. When I was in high school in New Jersey, I remember seeing sunfish underwater. Every time I went snorkeling in one of the nearby lakes, I would see them through my face mask. If I went fishing, all I would catch were СКАЧАТЬ