They live among other places in the waters off hawaii

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ome. When the one male wrasse dies, over the course of a few days the alpha female becomes the alpha male and takes over. From veiled damsel to bearded sheik, from a maker of eggs and a receptive mate to a sprayer of sperm and the master of all in a day or two—this is sex as a choice, sex as a consequence, sex as social order. Among clownfish—small orange- and white-striped marine fish edged in jet black—a similar transformation takes place, but with a slightly different twist. Again, these fish assemble themselves into groups made up almost entirely of females. But among clownfish, only the largest female in the group can mate with the single large alpha male. If the large female clownfish dies, the big male becomes female. After that, the largest of the young females leaves her egg-laying days behind, develops testes, and becomes the alpha female. So among clownfish, the few and the proud begin life as females, swap gonads for the grander life of the leader of the pack, and then—for the greater good—reclaim their ovaries and lay eggs as sweetly as any clownfish who’d ever graced this Earth. A tripartite tryst with a sexual subtext unlike any human ever imagined. Once more the idea of two sexes, especially two opposite sexes, seems strained by the reality of living animals. Reef gobies—lacy-finned, hand-sized fish—take an equally eclectic view toward the utility of sex. Again, when the dominant male dies, one of the females in the group will become the dominant male. But Where Our Sexes Come From 113 if a larger male should happen by and choose to take an interest in the females, the once-female-now-dominant-male fish will re-create her ovaries and live out the rest of her life as a reproductive female—unless, of course, the new male also dies. If that happens, then a whole new round of sex changes begins. And none of these changes seem to have any lasting effect on the fish. Certainly there are obvious differences between male and female gobies—color, gonads, hormones, etc.—but even repeated changes of sex do not seem to have any lasting effect. A goby that becomes a female for the first or the third time is every bit as much female. The same is true for males. The only apparent downside is that changing sexes requires a great deal of energy—lots of new proteins to be made, lots of new hormones, dramatic increases in enzyme activity, pigments to be laid down, etc. So, while the animals are changing sexes, it seems likely that they are easier targets for predators. But they do survive to offer us a whole new window into the world of sexuality—sex change as conflict resolution. And then there are species like the saddleback wrasse, midshipman fish, and some species of salmon that have two very different types of males. Saddleback wrasse are brilliant blue fish about a foot long with an orange-brown “saddle” just behind their heads. They live, among other places, in the waters off Hawaii. In schools of saddleback wrasse there are two very distinct types of males—one large, one small; one very reproductively active, one less so; one with a lot of brain cells that make arginine vasotocin (AVT) neuropeptide, and one with very few cells that make AVT. Arginine vasotocin neuropeptide stimulates mating behavior in a variety of vertebrate animals. The genetic differences (if any) between these two types of males remain unknown. But the differences between their roles in saddleback wrasse and other fish societies are obvious. One of the males spends a much larger portion of his life wooing lady wrasse and sowing his seed. The other male lives a more sedate life and knows fewer females than his more active counterpart. On the surface that would seem to be evolutionary suicide, but the less reproductive males still swim among the wrasse just as it appears they have for millennia. Both males must serve the wrasse society in important ways, because if the smaller, seemingly less repro- 114 Between XX and XY ductive wrasse were nothing more than evolutionary aberrations they would have shuffled off this mortal coil eons ago. Midshipman fish live off the west coast of the United States, and the differences between male midshipman fish further stretch our ideas about two sexes. Biologists have named the two different sorts of male midshipman fish type I and type II. Type I midshipman males take the longest to mature. During those extra days and nights, type I males grow larger and louder. Midshipman fish use a limited series of vocalizations to attract mates, so the louder a midshipman fish, the better chance he has of mating. Type II males take the energy that type Is put into size and song and use it to inflate their testes. As adults, type II males’ testes make up almost 10 percent of their body weight. That’s comparable to a 175-pound man having 17.5 pounds worth of testicles—about the weight of good-sized bowling ball. These fish have just one thing on their minds. Type I males, on the other hand, devote only about 1 percent of their total...
View Full Document

This document was uploaded on 02/04/2014.

Ask a homework question - tutors are online