Egg-mimicry as a mating strategy in the fantail darter,Etheostoma flabellare: females prefer males with eggs

Summary In some species of fishes with paternal care, females prefer to spawn with males already defending eggs. Such female preference appears to have resulted in adoption of unrelated eggs as a male mating strategy in several species. Page and Swofford (1984) proposed that such female preference may have also resulted in the evolution of male egg-mimics in several species of darters (Percidae); however, their hypothesis has not been tested. We examined female preference in the fantail darter (Etheostoma flabellare) and found that females preferred males with eggs over males without eggs, and males with egg-mimics over males without egg-mimics. Thus it appears that female preference for males already guarding eggs may have led to the evolution of specialized egg-mimicking morphology in males.     

Responses of female lizards,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>, to males' chemical cues reflect their mating preference for older males

Female mate choice based on visual traits appears to be rare in lizards. Field observations suggest that females of the lizard Lacerta monticola preferred to mate with larger/older males. Although older males are usually green and larger, and younger males brown and smaller, there is some overlap in size and coloration between age classes. Thus, visual cues may not always be reliable indicators of a male's age. We hypothesized that female mate-choice preferences may be based on males' pheromones, which might transmit information about characteristics such as age. In a laboratory experiment, we analyzed the effect of age of males on attractiveness of their scents to females. When we offered scents of two males of different age, females associated preferentially with scents of older males. This suggested that females were able to assess the age of males by chemical signals alone, and that females preferred to be in areas scent-marked by older males. Thus, females may increase their opportunities to mate with males of high quality, or may avoid harassment by sneaking young males. This result agreed with field observations on females mating with old males, and rejection of advances by young males. Our results also suggested that female preference for older males may depend on their own body size. Large females showed a strong preference for older males, whereas smaller females were not so selective. This, together with males' preference for large females, might lead to size-assortative matings. We suggest that the quality and/or quantity of male pheromones could communicate to the female heritable male genetic quality (i.e. age) and thereby serve as the basis of adaptive female choice in lizards.Communicated by W.E. Cooper     

Sexual selection in darkness? Female mating preferences in surface- and cave-dwelling Atlantic mollies,<Emphasis Type="Italic"> Poecilia mexicana</Emphasis> (Poeciliidae,Teleostei)

In many species, females prefer large males as mating partners. Male size can easily be determined visually. We examined how such mate choice evolves when individuals are deprived of sensory information previously used to determine male quality. Using a cave-dwelling population of Atlantic mollies, Poecilia mexicana, as a model, we asked whether the female mating preference for large male body size still occurs in this cave fish, or whether it is lacking due to the absence of visual communication in the cave environment. In simultaneous choice tests we compared the time females spent with a large or a small male. In the river-dwelling and cave-dwelling fish, as well as the population originating from the cave entrance, we found a significant preference for large males in light. Hence, the ancestral mating preference of surface-dwelling mollies has been maintained during the evolution of the cave form. However, only the cave population exhibited a mating preference in darkness. Determination of male body size appears to have been taken over by a non-visual sensory system, probably the lateral line.Communicated by K. Lindström     

Phenotypic differentiation in female preference related to geographic variation in male predation risk in the Trinidad guppy (Poecilia reticulata)

Summary Populations of the Trinidad guppy range from areas with high levels of predation by other species of fish to areas with little or no piscine predation. Previous studies have shown that variation among populations in male coloration can be explained by a balance between female preference for brighter males and natural selection against bright males. High levels of male courtship activity may also increase both predation risk and mating success. Therefore, in high-predation areas, females that mate with males that court frequently as well as those that choose bright males would presumably produce male offspring with low survivorship. Consistent with this variation in natural selection, we observed that females from high-predation populations were less likely to choose bright and frequently courting males than females from low-predation populations. This result supports the hypothesis that female preference is evolving as a character genetically correlated with the preferred male character, in which case higher levels of natural selection acting against the male character should be related to lower levels of female preference.     

Females prefer males with superior fighting abilities but avoid sexually harassing winners when eavesdropping on male fights

Selection imposed by male competition (intrasexual selection) and female choice (intersexual selection) can be con- or discordant. Specifically, females may or may not prefer mating with dominant males, and direct costs of interacting with dominant (and possibly more harassing) males have been suggested to explain avoidance of dominant males. Here, we exemplify that inter- and intrasexual selection may normally act in the same direction, but can be temporarily conflicting when social information becomes available. Using video playback techniques, we presented females of the Mexican livebearing fish Poecilia mexicana with two size-matched males and established association preferences. Half of the females could then observe the same two males fight and establish dominance, while control females saw both males side by side, but physically separated, and female preferences were subsequently re-evaluated. Females in the control group showed a significant preference for future winners in the subsequent testing, confirming an innate or acquired preference for male traits that are indicative of physical superiority, even when body size as a choice criterion is excluded. When allowed to eavesdrop on male fights, however, females did not show a preference for observed winners and even decreased time spent with them relative to the control treatment in which no fight was shown. A subsequent experiment found contest winners to show elevated levels of sexual behavior, so we argue that the temporary offset of the intrinsic female preference for dominant males after having observed a fight is indeed driven by direct costs females expect from more harassing contest winners.     

Trichinella spiralis infection in voles alters female odor preference but not partner preference

Females may choose mates based on secondary sex traits that reflect disease resistance. Accordingly, females should be able to distinguish between unparasitized and parasitized males, and should prefer to mate with unparasitized individuals. Mate and odor preferences for uninfected males or males infected with the nematode, Trichinella spiralis, were examined among prairie voles (Microtus ochrogaster) and meadow voles (M. pennsylvanicus). In a 15-min odor preference test, only female meadow voles distinguished between bedding from parasitized and unparasitized conspecific males, and preferred to spend time with bedding from unparasitized males. Although T. spiralis infection influenced odor preference in female meadow voles, there was no effect of infection status on mate preference among either species. Testosterone and corticosterone concentrations were not different between parasitized and unparasitized males. However, among prairie voles, males that spent an increased amount of time with females during the mate preference test had elevated testosterone concentrations. Taken together, these data suggest that (1) female meadow voles can discriminate between unparasitized and parasitized males, (2) the effects of infection on steroid hormone concentrations may be masked by the effects of social interactions, and (3) parasites may represent a selective constraint on partner preference in voles; however, the life cycle of parasites may influence female preference and should be considered in studies of female preference. Received: 23 April 1998 / Accepted after revision: 25 October 1998     

Male choice,fighting ability,assortative mating and the intensity of sexual selection in the milkweed longhorn beetle,Tetraopes tetraophthalmus (Coleoptera,Cerambycidae)

Summary Over five hundred adult longhorn milkweed beetles, Tetraopes tetraophthalmus, were individually marked and their copulatory success followed for one month in a pasture of Asclepias syriaca in northern Indiana, USA. Migration of beetles from the field site was greatest from areas of low population density. Dispersal was significantly greater for males experiencing low copulatory success; a similar but nonsignificant trend was observed for females. Large males, which displayed greater site tenacity than small males, copulated more frequently than small males because of their ability to displace small males from females. Both large and small males demonstrated a preference for large females in laboratory tests. Male preference in combination with aggressive displacement of small males results in size-assortative mating which was much stronger under conditions of high population density. It contributes to variance in male reproductive success since female size is known to be correlated with fecundity and offspring viability. Variance in copulatory success is similar for males and females, suggesting that both sexes experience similar intensities of sexual selection with respect to this component of reproductive success. Futhermore, comparison of this with other studies suggests that the intensity of sexual selection among males is positively correlated with the variance in body size which appears to be under both stabilizing and directional sexual selection in males but not in females.     

Polygyny in the red-winged blackbird: do females prefer monogamy or polygamy?

Five hypotheses have been proposed to explain polygyny in the red-winged blackbird (Agelaius phoeniceus). We categorized the hypotheses into three groups based on female preference for unmated versus monogamously mated males: (1) the “polygyny threshold” model, “sexy son” hypothesis and the “asynchronous settlement” model, which assume that females prefer unmated males to mated males on breeding situations of homogeneous quality; (2) the “neutral mate choice” hypothesis, which assumes that females have no preference; and (3) the “cooperative female choice” model, which assumes that females prefer monogamously mated males to unmated males. We tested the direction of female preference in two field experiments. In both experiments, newly settling females were given a choice of two adjacent territories, one defended by an unmated male and the other by a monogamously mated male. Male mating status was randomized with respect to the variation in territory quality and male quality. Early in the breeding season, significantly more females settled with the unmated males than with the mated males. Although more females settled with the unmated males than with the mated males late in the breeding season, the difference was no longer significant. Female settlement late in the season appeared to be related to the tenure of the resident females: the new females avoided territories where the resident females were in early stages of their nesting, but settled on territories where the resident females were in late stages. The pattern of female settlement shows that females prefer unmated males to mated males. The preference is consistent with the polygyny threshold model, sexy son hypothesis and the asynchronous settlement model, and inconsistent with the neutral mate choice hypothesis and the cooperative female choice model. For this reason, the latter two hypotheses are unlikely to explain the occurrence of polygyny in our population of red-winged blackbirds. Received: 1 December 1994 / Accepted after revision: 28 October 1995     

Indirect fitness benefits are not related to male dominance in a killifish

Recent theoretical and empirical studies have shown that male dominance is often at odds with female mate preference and that indirect (genetic) benefits of mate choice may not be related to male dominance. We tested whether female preference corresponded to male dominance and whether mating with dominant males conveyed benefits to offspring fitness in a small freshwater fish, the African annual killifish Nothobranchius korthausae (Cyprinodontiformes), a species without parental care. The experimental design used controlled for the effect of male age, possibility of sperm and egg depletion, and accounted for a potential that females express their preference through maternal effects by manipulation of egg mass during ovulation. By sequentially mating females with males of known dominance, we found that female N. korthausae showed no mate preference in terms of egg numbers deposited with respect to male dominance or body size and no congruent mate preference to specific males was detected. However, males sired offspring with consistently higher hatching success and the effect was repeatable across individual females. Thus, some males provided females with indirect benefits related to additive genetic quality (“good genes”) and expressed via increased hatching rate, but this benefit was not related to male dominance status or body size.     

Allopaternal care in the fathead minnow,Pimephales promelas: females prefer males with eggs

Summary Some species of fishes with exclusive male parental care exhibit the phenomenon of allopaternal care; that is, some males acquire and care for other males' eggs. We conducted a series of experiments to investigate the dynamics and evolution of allopaternal care in one such species, the fathead minnow (Pimephales promelas). In choosing a nest site, a newly reproductive male tended to take over the nest site of a parental male by evicting the resident male, rather than occupy a physically identical empty nest site. The new male generally cared for the old male's eggs, and in most cases, daily egg survival improved under the new male's care. When males were given a choice among unguarded nest sites, they preferred to occupy nest sites already containing eggs. When eggs were randomly assigned to nesting males, females preferred to spawn with males who had eggs in their nest sites. Thus, it appears that female preference for males with eggs led to the evolution of allopaternal care in the fathead minnow.     

The role of information in mate-choice copying in female sailfin mollies (Poecilia latipinna)

Female mate choice is a complex process involving both genetic and social factors. Extrinsic cues may play a role in determining how these factors interact. Mate-choice copying is a socially influenced mate-choice strategy in which females observe other females during mate choice and choose the same male as those females. Previous studies have shown that female sailfin mollies (Poecilia latipinna) prefer larger over smaller males, and this preference is assumed to be genetically based. In this study we tested, first, whether sailfin molly females changed their mate preference in favour of smaller males when they could obtain more information by observing two model females sequentially for 5 min each or one model female for 20 min next to the smaller male. Second, we tested if females that had changed their preferences in favour of smaller males maintained this learned preference afterwards. In copying experiments, females changed their preferences in favour of smaller males both when they could observe two model females each for 5 min near by a smaller male and when they could observe one model female for 20 min near the smaller male. In the latter case, females maintained this learned preference for smaller males up to 5 weeks after the copying experiment. This shows that mate-choice copying has a long-lasting effect on mate-choice decisions in sailfin molly females and that mate-choice copying can serve as a mechanism for cultural inheritance of mate preferences in females.     

Cave molly females (Poecilia mexicana, Poeciliidae, Teleostei) like well-fed males

We examined the preference of Atlantic molly females (Poecilia mexicana) to associate with a well-fed or a starved male in simultaneous choice tests. Females from three different populations were tested in three treatments: (1) the females could choose on the basis of multiple cues from the males (visual plus non-visual); (2) only non-visual cues could be perceived in darkness, (3) only visual cues were presented. The three tested populations differ clearly in their ecology: one population occurs in a typical river habitat, the second one in a milky sulfur creek outside a cave, and the third population occurs in a cave habitat (cave molly). In the river-dwelling population, females never showed a preference. In the population from the sulfur creek, females preferred to associate with the well-nourished male when visual cues from the males were available. Only cave molly females exhibited a strong preference for well-nourished males in all treatments. A morphological comparison demonstrated that wild-caught males from river habitats are typically in a good nutritional state. In the sulfur creek, males showed signs of starvation. Cave molly males were in an even worse nutritional state. In the cave population, saturated males probably indicate high fitness, thereby driving the evolution of the preference for good male nutritional state.Communicated by K. Lindström     

Symmetry, male dominance and female mate preferences in the Iberian rock lizard, Lacerta monticola

Female preference for dominant males is widespread and it is generally assumed that success in male-male competition reflects high quality. However, male dominance is not always attractive to females. Alternatively, relatively symmetric individuals may experience fitness advantages, but it remains to be determined whether males with more symmetrical secondary sexual traits experience advantages in both intra- and intersexual selection. We analysed the factors that determine dominance status in males of the lizard Lacerta monticola, and their relationship to female mate preference, estimated by the attractiveness of males' scents to females. Sexually dimorphic traits of this lizard (head size and femoral pores) appear to be advanced by different selection pressures. Males with relatively higher heads, which give them advantage in intrasexual contests, were more dominant. However, head size was unimportant to females, which preferred to be in areas marked by relatively heavier males, but also by males more symmetric in their counts of left and right femoral pores. Chemicals arising from the femoral pores and other glands might honestly indicate quality (i.e. related to the symmetry levels) of a male to females and may result from intersexual selection. Females may use this information because the only benefit of mate choice to female lizards may be genetic quality. Chemical signals may be more reliable and have a greater importance in sexual selection processes of lizards than has previously been considered.     

Female choice of large males in the treefrog Hyla chrysoscelis: the importance of identifying the scale of choice

Summary In this study, I detected the presence of female choice for larger males in the treefrog Hyla chrysoscelis. Mated males were larger than unmated males at the scales females could have assessed males: local groups (males found within 2 meters of a mated pair) and the nightly chorus. In addition, females were observed to initiate amplexus with the larger males in local groups. Mated males were larger than unmated males for two of the four seasons studied. Seasonal mating success was also analyzed with a multiple regression model that included size and chorus attendance (nights spent at the breeding site). The partial selection coefficients, which represent the relative magnitude of directional selection, were significant for size in only one season and for chorus attendance in all four seasons. Therefore, there are two possible advantages to being a large male: increased likelihood of obtaining a mate due to female preference, and increased likelihood of mating even if no female preference because of a greater number of opportunities to obtain a mating if matings occurred at random.     

Mating patterns and a test for female mate choice in Etheostoma spectabile (Pisces,Percidae)

Neither size nor breeding color correlated with spawning success of male orangethroat darters, Etheostoma spectabile (Pisces, Percidae), under natural field conditions. When females were presented experimentally with a simultaneous choice they spent no more time in proximity to large than small males, and were subsequently no more likely to spawn with large than with small males. Females also displayed no preference for bright versus dull males. Males and females did not differ significantly in size. Etheostoma spectabile may lack sexual size dimorphism as a result of the lack of female choice for size and the ineffectiveness of male attempts to monopolize females, or selection may be for increased size of females. Males are not dwarfs because of sperm competition. Contest competition among males appeared to be important in initiating spawnings but many males obtained spawnings by participating in ongoing spawning events. Etheostoma spectabile is an example of a sexually dimorphic species with no evident female preference for male size or color.     

Association patterns of sailfin mollies (Poecilia latipinna): alternative hypotheses

Individuals may associate with each other due to a variety of selective forces, such as intra- and intersexual selection, and conspecific recognition. Previous studies have concluded that mate choice governs association behavior in polygynous species of fish. I examined whether mate choice underlies the preference for larger individuals by examining preference for association (time spent in proximity to a fish) not only between opposite-sex individuals but also between same-sex individuals of the live-bearing sailfin molly (Poecilia latipinna). Males and females from three size classes were tested with a large and a small object fish of the same and opposite sex. Females preferred to associate with larger over smaller males. Males also preferred to associate with larger over smaller females, as expected. The same female and male test fish also preferred to associate with larger over smaller fish of the same sex. Moreover, females demonstrated no significant difference in their strength of preference (large–small) when offered males or females. The same held true for males. When males and females were subsequently tested with one large male and one large female, females tended to prefer large males while males showed no significant preference for association based on sex. In another experiment, females were tested with a large female and a small male, and significantly preferred the former. These findings suggest that association patterns may have arisen under a variety of conditions, such as predation pressures, shoaling behavior, and associative preference behavior. The assumption that association behavior is a uniformly sufficient predictor of mate choice in fish needs to be re-examined for P. latipinna and other species. Received: 6 November 1998 / Received in revised form: 12 May 1999 / Accepted: 12 May 1999     

Bushcricket song as a clue for spermatophore size?

Bushcricket males of Poecilimon zimmeri transfer large and protein-rich spermatophores during mating, which females directly ingest. There is correlational evidence that heavier males transfer larger nuptial gifts. In no-choice mating trials, females mated randomly with respect to male’s body weight. In contrast, in two-choice mating trials, female bushcrickets exhibit clear choice for the heavier male. This heavier male advantage was also found in pre-mating choice during phonotaxis. With manipulated mute males, females mated at random with regard to body weight of the competitors. The number of physical encounters between a female and males was low in all tests with a single male (no choice) and greater in choice-tests with two competing males. The latencies to mate also differed significantly between treatments. The time mating pairs spent in precopula was short in experiments where the males could hear rivals and significantly longer in all other tests using either a single male or mute males. Thus, acoustic signalling in male bushcrickets seems to signal male body weight. A preference for heavier males may reflect a female’s preference for a larger spermatophore and therefore a greater direct benefit.     

Variation in male sailfin molly, preference for female size: does sympatry with sexual parasites, drive preference for smaller conspecifics?

Male sailfin mollies (Poecilia latipinna) are sexually parasitized by gynogenetic Amazon mollies (Poecilia formosa). In areas of sympatry, Amazon mollies are frequently larger than female sailfin mollies. In sympatry, selection may favor males that prefer smaller conspecific mates (avoid mismating with Amazon mollies), or selection may favor males that prefer larger conspecific mates (higher fecundity). To explore this potential species and mate-quality recognition conflict, we examined male preference variation across populations. Males from one sympatric population showed stabilizing preference functions, whereas in another sympatric population, males showed directional preference functions. Variation across sympatric populations may be related to the length of time of co-evolution with Amazon mollies. In the allopatric populations, we found flat preference functions. Variation in male preferences could have important ramifications for the maintenance of Amazon mollies, as well as for the evolution of female size.     

Do sex-changing male snails use mate choice to get a jump on their “size advantage”?

Individuals of species that change sex from male to female may gain a “size advantage” from that sex change; that is, as males become larger, they become female, thus increasing their fecundity with their size. However, males could also gain an early and different reproductive size advantage by choosing large females as mates. While male preference for large females has been observed in many dioecious species, we know little about male size preference in sex-changing species. In choice experiments, we examined whether males of two congeneric species of marine sex-changing snails, Crepidula fornicata and C. convexa, chose large females over small ones as partners. We also used choice tests to see whether males of C. fornicata, a species whose members form long-term, multi-animal stacks, would choose two females in a stack over a single female. Surprisingly, males of neither species showed a preference for large females, in spite of the documented fecundity advantage associated with large female-size. Males of C. fornicata chose slightly, but not significantly, more single females than stacks, suggesting that neither number nor size drives mate choice in these animals. Key factors that may influence this lack of size preference include long association time, the likelihood of sperm competition, and the cost of extended mate search; it may also be that sex-change itself, the very factor that creates female-biased sexual size dimorphism in these species, prevents size preference, as males may gain sufficient reproductive advantage from eventually becoming large females themselves to offset any benefit of choosing large females.     

Mustached males in a tropical poeciliid fish: emerging female preference selects for a novel male trait

One possible mechanism for the (co-)evolution of seemingly novel male traits and female preferences for them is that males exploit pre-existing female biases, and livebearing fishes (Poeciliidae) have been at the forefront of this research for almost two decades. Here, using 13 poeciliid species from four different genera, we tested whether mustache-like rostral filaments found in males of some Mexican molly (Poecilia sphenops) populations could have evolved due to exploitation of a pre-existing female bias. While Mexican mollies were the only species with a significant female association preference for mustached males, we also did not find any species exhibiting significant aversion for mustached males; rather, variance in female preference scores was large throughout. For example, more than 25% of females spent twice as much time with the mustached male compared to the non-mustached male in most species, but even 31% of Mexican molly females spent more time near the non-mustached male. Hence, a comparison of the strength of preference was inconclusive. We discuss the possibility that the female preference of P. sphenops for mustached males could be due to a female pre-existing bias (sensu lato), even if population means were not significant for species other than P. sphenops. This highlights the importance of distinguishing between population means and individual preferences when interpreting mate choice, and thus, adds depth to the concept of mating preferences as a motor for evolutionary change.