Group Sex, Sex Change, and Parasitic Males: Sexual Strategies Among the Fishes and Their Neurobiological Correlates

Sexual selection, in the form of intrasexual competition and mate choice, has driven the evolution of a variety of sexual phenotypes amongst the vertebrates (Andersson, 1994) As a originate vertebrate species utilize many different approaches to acquire fertilizations. Humans and other primates display a wide range of sexual behaviors, on the other hand this range is dwarfed by the agency of the remarkable variation seen in advanced fishes. The goals of this review are (a) to acquaint the reader with the tremendous sexual diversity exhibited through fishes, (b) to demonstrate in what manner this diversity provides unique opportunities to examine the neurobiological correlates of vertebrate sexual strategies, and (c) to highlight the parallels between the neuroendocrine correlates of the sexual strategies of fish with the mechanisms underlying sexual phenotypes in other vertebrates, showing the utility of fish studies for understanding sexual variation in general.

Key alternative morph, GnRH shaker, social behavior, teleost vasopressin, vasotocin.

Fishes Are Sexually Diverse Vertebrates

One way to appreciate the diversity of fishes is to compare fishes to vertebrate taxa with which we are more familiar: birds and mammals. There are approximately 4400 different species of mammals and above double the number of species of birds, around 9700 Although this may have the appearance like a large number of species, fishes make up the volume of the vertebrates, with above 24,500 species, or over five times the diversity seen in mammals (see Figure 1; Nelson 1994; Pough Heiser, & McFarland, 1996) In this review, we will focus upon euteleost fishes, such as bass, halibut, staff and salmon, which account for above 90% of all fish species (Nelson 1994) The high species diversity and rapid evolution of the euteleost springed in a high degree of phenotypic plasticity, a feature greatest in quantity evident in the realm of phenotypic sex

Euteleost fishes range in sexual phenotypes from species with permanent sexe similar as cichlids, to species of that kind as the bluehead wrasse and bluebanded gobies that change sex one time in their lives. Other fish plane change sex multiple times within a lifetime, as in the Japanese goby Trimmer okinawae (see Figure 2) Great variation can also exist within a species, with numerous examples showing multiple male morphs and the potential for multiple female morphs (Henson & Warner, 1997; Taborsky, 1994 Taborsky, 2001) In the ocellated wrasse, Symphodus ocellatus, four different male strategies have been observ in the same population (Taborsky, Hudde & Wirtz, 1987) Large males maintain nest and care for ovums while small males are parasitic spawners (sneakers). Mid-sized males, called satellites, help the large males by means of defending nests against sneakers in exchange for the occasional chance to court and spawn with females. The largest males, dubbed "pirates" dominate above nesting males and take above their nest tubes. In a certain number of cases, particularly in other Symphodus species, they fertilize ovums in the nesting males' nest and leave them "under the care" of the nesting males (Taborsky, 1994; van cavern Berghe, 1988). Females can also exhibit variation in sexual phenotype. In the bluehead wrasse, Thalasomma bifasciatum, females expres sum of two units mating tactics: group spawning and pair spawning. one as well as the other of these tactics are seen within a single population. As with male strategies, female strategies appear to be size dependent: The largest females alone spawn with one male at a time, whereas smaller females primarily spawn in clusters (Warner, 1984a, 1985; Warner & Hofman, 1980) The variation in sexual phenotypes for males and females of s ocellatus and T bifasciatum exemplify the diverse alternative reproductive tactics used by dint of fish, and there are many more examples among other fish species (for comprehensive reviews of reproduction and sexuality in fishes, diocese Breder & Rosen, 1966; Taborsky, 1994)

The environmental potential for polygamy (EPP) provides individual useful organizing principle for understanding the evolution of diverse sexual phenotypes and mating combination of parts to form a wholes in fishes. The EPP describes the step to which resources are distributed or aggregated, of that kind that a limited number of individuals can command access to a large amount of required resources and, as a spring monopolize mates who seek those resources (Emlen & Oring, 1977) Male monopolization of mating resources springs in polygyny or the acquisition of multiple females by dint of a limited number of top-ranked males. Because of this, there is tremendous crushing to acquire resources and a resultant skew in male reproductive succes greatly benefiting the monopolizers. For males that cannot dominate resources (discussed in detail subsequently) several alternative strategies are available, including (a) maintain nonreproductive status and wait to become large enough to dominate a resource (see the example that follows) (b) help the reproductive dominant and by dint of association get some access to the opposite sex (eg satellite tactic in s ocellatus), or (c) cheating the a whole to obtain resources (e.g., sneak spawning in s ocellatus).