Academic journal article The Psychological Record

THE EFFECT OF MALE FAMILIARITY ON PROXIMITY TIME IN FEMALE EASTERN MOSQUITOFISH (Gambusia Holbrooki)

Academic journal article The Psychological Record

THE EFFECT OF MALE FAMILIARITY ON PROXIMITY TIME IN FEMALE EASTERN MOSQUITOFISH (Gambusia Holbrooki)

Article excerpt

Among live-bearing fish, females often prefer larger or more colorful males, or males engaging in ritualized courtship. However, in eastern mosquitofish, Gambusia holbrooki, the factors affecting females' choice of males are unclear. We tested whether female Gambusia prefer to spend time near unfamiliar males over males with whom they have prior experience, expecting that females would prefer unfamiliar males. We examined both visual/olfactory and full exposure experience with males. As a control, we tested females with pairs of unfamiliar males. Control females showed no preferences between males. Females in the visual/olfactory experiment spent more time with males in general following 30-minute exposure, compared to 24-hour exposure. In the full exposure experiment, females spent more time with unfamiliar males only after 24 hours of previous exposure to the familiar male. We discuss the data in the context of mate choice, familiarity, female deprivation, and sexual satiation.

In female mate choice, females prefer characteristics of certain males over others and males who exhibit a preferred characteristic will have a reproductive advantage over those who do not. Because female live-bearing fish show considerable parental investment, intersexual selection probably influences their mate selection. In fact, intersexual selection has been documented in a variety of Poeciliid fish, including mosquitofish, Gambusia spp.; guppies, Poecilia reticulata; swordtails, Xiphophorus spp.; and mollies, P. shenops. Typically such research is conducted using indirect measures of mate choice-that is, measuring the time females spend in proximity to males with particular characteristics (see Houde, 1997, for discussion of methods for testing mate choice). This is done primarily so that female choice can be distinguished from the male's behavior. Choice tests may or may not be followed by actual mating tests, but typically correlate with male reproductive success when it can be directly measured.

A series of studies by Houde and colleagues (Houde, 1988; Long & Houde, 1989) has confirmed that the degree of orange pigment in male guppies influences female choice. In addition, Bischoff, Gould, and Rubenstein (1985) found that female guppies, when presented large-tailed and short-tailed males, spent more time with large-tailed males. Basolo (1990) reported that female swordtails, X. helleri, spent a greater amount of time with males who had long swords than those with short swords, and that the time increased with the length of the sword.

The Poeciliid fish used in the present study were Gambusia holbrooki, or eastern mosquitofish. They are found primarily in the southeastern United States, but have been introduced all over the world (Courtenay, 1984). Adult females average 30 mm in length and can be identified by an egg spot on the lower abdomen that darkens and swells when the female is pregnant. Adult males average 25 mm in length and can be identified by a gonopodium, a modified anal fin that acts as an intromittive organ. Mating occurs when the male swims up to the female from behind, swings his gonopodium down and onto the female's egg spot, and delivers sperm. Both sexes are grayish in color and neither seems to have any striking coloration or ornamentation. An exception is the presence of melanism in a small percentage ([less than] 3%) of the male Gambusia population which is dark and mottled in appearance and easily distinguished from normally pigmented males (Martin, 1986).

Intersexual selection has been studied in Gambusia, including whether females prefer males based on size, ornamentation, or courtship display. Bisazza and Marin (1991) found no female preference for large or small males in groups of adult females that had been (a) housed with males, (b) male deprived for 30 days, (c) male deprived for 4 months, or (d) were virgin. Across female groups, females showed no preference for spending time with either large or small males during dichotomous choice tests when males differed in size by at least 5 mm. …

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