Polygynous Fish Research Articles

Sperm-limited males save ejaculates for future matings when competing with superior rivals

Adjusting ejaculates to sperm competition can lead to sperm limitation. Particularly in polygynous species, males may face a trade-off between investing sperm in current or future mating opportunities. The optimal sperm allocation decision should depend on the relative intensity of sperm competition experienced in a mating sequence. Here we asked how males respond to this trade-off in polygynous fish with alternative male mating tactics, intense sperm competition and sperm limitation. Large bourgeois males of the shell-brooding cichlid Lamprologus callipterus build nests consisting of empty snail shells, in which females spawn and raise offspring. During spawning, nest males release ejaculates into the shell opening. Genetically distinct, parasitic dwarf males enter shells during spawning to fertilize the eggs from inside the shell. These dwarf males were previously shown to be superior sperm competitors to nest males. Here we showed that when spawning with several females simultaneously, nest males reduced the spawning duration for each clutch and the number of ejaculations per female tended to decrease, reflecting sperm limitation. Experimental exposure of nest males to sperm competition with dwarf males reduced the number and duration of ejaculations by roughly half. Hence, when exposed to competition with a superior rival, nest males did not increase their sperm expenditure as predicted by sperm competition risk models, but in fact saved sperm for future mating opportunities as predicted by sperm competition intensity theory. This seems to be adaptive because of the considerable sperm demands in this species, which is partly due to their high degree of polygyny.

Female nuptial signal advertises spawning readiness in a population of Halichoeres margaritaceus on the Great Barrier Reef, Australia

Females of some polygynous fish species display female nuptial signals (FNSs), advertising spawning readiness to potential mates. Halichoeres margaritaceus, a polygynous coral reef fish, reportedly display red belly color and a unique bobbing behavior as FNSs advertising spawning readiness. In this study, I examined whether FNSs were observed in an H. margaritaceus population in Australia. Females in this study displayed red belly color as an FNS, although at a lower intensity than that reported in a Japanese population. Contrary to observations made in the Japanese population, bobbing behavior performed by females in this study showed no temporal trend as spawning approached, indicating bobbing behavior did not function as an FNS in the Australian population. The role of local selective pressures on FNS intensity and lifetime reproductive benefits H. margaritaceus may potentially gain in utilizing FNSs are briefly discussed.

Sex differences in spatial abilities and cognitive flexibility in the guppy

When males and females differ in their spatial ecology, selection is expected to promote sex differences in spatial abilities. Although this prediction applies to many species, few studies have looked at sex differences in spatial abilities outside mammals. Here, we addressed this hypothesis in the guppy, Poecilia reticulata, a polygynous fish in which males disperse more than females and inhabit more spatially complex environments. We compared the performance of male and female guppies in two spatial tasks to test whether males have been selected for enhanced spatial abilities. In a detour task (experiment 1), the two sexes showed similar ability to navigate around an obstacle to reach a target. However, males were more persistent in trying to pass through the transparent obstacle, an effect that is likely to be related to sex differences in cognitive flexibility rather than to spatial abilities. In the second experiment, with a more complex maze in which guppies had to choose between alternative routes to reach the target, males learned the task after only one presentation, whereas females did not show any evidence of learning after five trials. The direction of these differences is the same as that observed in most polygynous species investigated, suggesting a common pattern of cognitive sex differences across vertebrates.

Polygyny affects paternal care, but not survival, pair stability, and group tenure in a cooperative cichlid

It is generally assumed that there is sexual conflict over the mating system. In this view, polygyny benefits males at a cost to females, and it is hence unclear why females accept polygynous mating. However, in the facultatively polygynous fish, Neolamprologus pulcher, no costs of polygyny to females have thus far been detected. We hypothesized that the costs of polygyny remained undetected because they accrue over longer periods of time through reduced tenure and/or survival. We conducted an extended field study in which we monitored the behavior and survival of individuals breeding either monogamously or under polygynous conditions within the same natural colony. We expected that polygyny would reduce male and female survival through increased competition among males and reduced amounts of received paternal effort for females. Consequently, breeder tenure and pair stability were predicted to be lower in more polygynous groups. Our data indeed revealed costs of polygyny to both sexes. Polygynous males faced higher competition, and females paired to polygynous males received reduced paternal effort. However, this did not result in different survival rates between individuals breeding under monogamous or polygynous conditions. We conclude that in N. pulcher the fitness costs of polygyny may be either too marginal to be detected with the approaches used thus far, or that males and females in this species do not face a conflict of interest over the mating system. This raises the question which ecological factors may resolve sexual conflict, and how the accruing mating system feeds back on a species’ ecology.

Testing the low-density hypothesis for reversed sex change in polygynous fish: experiments in Labroides dimidiatus.

Hermaphroditism is ubiquitous among plants and widespread in the animal kingdom. It is an unsolved problem why reversed sex change has evolved in polygynous and protogynous reef fish. We have previously suggested that facultative monogamy occurs in low-density populations of polygynous species and that males that become single as a result of accidental mate loss may change sex when they meet larger males. In this study, to test this ‘low-density hypothesis', we conducted field experiments with the coral reef fish Labroides dimidiatus in which a portion of females were removed to create a low-density situation. The ‘widowed' males moved to search for a new mate when no male, female or juvenile fish migrated into their territories and paired with nearby single fish, whether male or female. Alternatively, males expanded their territories to take over the nearest pair whose male was much smaller. These results support our low-density hypothesis.

Do Female Three‐Spined Sticklebacks Copy the Mate Choice of Others?

1992; Kirkpatrick and Dugatkin 1994; Laland 1994; DuA common assumption in evolutionary models of female gatkin and Hoglund 1995) or indirect (Servedio and mate choice is that mating preferences are genetically Kirkpatrick 1996) selection on females. Copying, like inbased and that females choose mates independently of dependent mate choice, increases the variance of male the choices of other females in the population (reviewed mating success in a population and thus the opportunity in Andersson 1994; Ryan 1997). However, field observafor sexual selection (Wade and Pruett-Jones 1990). tions (reviewed in Hoglund and Alatalo 1995) have sugIn several species of polygynous fish (reviewed in gested and experimental studies (reviewed in Dugatkin Pruett-Jones 1992; Jamieson 1995; Dugatkin 1996a), in1996a) have confirmed that females, particularly in procluding the three-spined stickleback, Gasterosteus aculeamiscuous and lekking species, may copy the choices of tus (Ridley and Rechten 1981; Jamieson and Colgan others under certain circumstances. A female is consid1989; Belles-Isles et al. 1990; Goldschmidt et al. 1993), feered to have copied the mate choice of another female(s) males prefer to mate with males whose nests contain eggs if the probability of her choosing a specific male as a obtained from prior matings. Although previously attribmate is increased specifically as a result of her observing uted to copying (Goldschmidt et al. 1993), it remains unother females previously choosing that same male (Wade certain whether this phenomenon is due to actual mateand Pruett-Jones 1990; Pruett-Jones 1992; Dugatkin choice copying (as defined earlier), as females apparently 1996a), rather than because of any change in that male’s did not directly observe the mate choice of others in behavior due to his prior mating or proximity to females these studies. Alternatively, females may be attracted to or because of any preference by females for certain sites nests already containing eggs because the males that deirrespective of the male or to aggregate with other fefend such nests have been chosen previously by other females (Dugatkin 1992, 1996a; Pruett-Jones 1992). males (Jamieson 1995; Dugatkin 1996a), provide more Potential fitness benefits of copying accruing to feparental care (Sargent 1988), may court more vigorously males include information gained from other individuals (Jamieson and Colgan 1989), or may be more colorful that might know more about prospective mates, in(Jamieson and Colgan 1989) and/or because predation creased accuracy with which females discriminate male risk on their own eggs would be diluted by the presence quality, and reduction of the costs of mate assessment of other females’ eggs in the nest (Jamieson 1995; Forsand choice. By copying, however, an individual risks gren et al. 1996). If females prefer males with eggs almating with a recently mated male with depleted sperm ready in their nest for reasons of mate choice, then they

Female mate choice, male-male competition and parental care in the river bullhead, Cottus gobio L. (Pisces, Cottidae)

Male body size was tested for its influence on female mate choice, male-male competition and ability to defend broods in the river bullhead, Cottus gobio L., a polygynous fish with paternal care. Females presented with two potential mates of different sizes significantly preferred to spawn with the larger male. Males smaller than, or 1·5 times longer than, the female were rarely selected as mates. Larger males were more successful in defending their brood from conspecifics, which may explain female preference for them. Unmated large males displaced smaller guarding males from their nests and retained the acquired egg masses. Competition between males for nest sites with eggs can be accounted for by the preference of females for males already guarding eggs: by seizing a nest containing egg masses, a male will increase his chance of being chosen.