Male-male interactions and their influence on the mating behavior and success in the fountain darter, <Emphasis Type="Italic">Etheostoma fonticola</Emphasis>

Behavioral interactions between individuals of the same sex can affect the outcome of intersexual selection. For this reason, intrasexual selection is oftentimes examined independently from intersexual selection in studies aimed at understanding mating behaviors. However, a more complete understanding of sexual selection effects within a population can only come from exploring both intrasexual and intersexual selection and the potential interactions between the levels of selection. Association preferences in male and female Etheostoma fonticola do not reveal a size preference for same sex or opposite-sex individuals. However, male-male interactions may influence female choice in E. fonticola. We examined whether male E. fonticola that differ in body size exhibit differences in agonistic behaviors and mating success. Larger males do exhibit higher rates of aggressive behaviors and smaller males, in turn, exhibit more defensive behaviors. However, differences between larger and smaller males in male-male interactions did not translate into differences in spawning success. These results suggest that male size influences dominance relationships in E. fonticola but not mating success. There were also no differences between large and small males in mating attempts, which could be an outcome of the year-round breeding season found in this species, females laying eggs singly, or males fertilizing eggs individually.     

Repeatability of Male Mate Choice in the Mosquitofish, Gambusia holbrooki

Male mate choice has evolved in many species in which female fecundity increases with body size. In these species, males are thought to have been selected to favour mating with large females over smaller ones, thereby potentially increasing their reproductive success. While male mate choice is known to occur, it is less well studied than female mate choice and little is known about variation in mating preference among individual males. Here, we presented individual male eastern mosquitofish ( Gambusia holbrooki ) with paired females that differed in body size, and we quantified their mate preference on two consecutive days, allowing us to assess repeatability of preferences expressed. When males were allowed to view paired stimulus females, but not to acquire chemical or tactile cues from them, they exhibited a strong preference for large females over smaller ones. However, individual males were not consistent in the strength of their preference and repeatability was not significant. When individual males were allowed to fully interact with pairs of females, the males again exhibited a preference for large females over smaller ones, as revealed by a greater number of attempted copulations with large females than with smaller ones. In the latter social context, individual male preference was significantly repeatable. These results indicate that male eastern mosquitofish from our Florida study population possess, on average, a mating preference for larger females and that this preference is repeatable when males socially interact freely with females. The significant repeatability for mating preference, based on female body size, obtained for male mosquitofish in the current study is consistent with the presence of additive genetic variation for such preferences in our study population and thus with the opportunity for the further evolution of large body size in female mosquitofish through male mate choice.     

Validation of a Method for Quantifying Male Mating Preferences in the Guppy (Poecilia reticulata)

Male and female mating preferences are commonly inferred from association times spent with potential mates in a dichotomous‐choice test. However, this assessment method is rarely validated, particularly so for male mating preferences. Using the Trinidadian guppy (Poecilia reticulata), an important model species in the study of sexual selection, we tested whether a male’s mating preference for either of two stimulus females in a dichotomous‐choice test predicted his mating behaviours directed at the preferred female when he was allowed to swim freely with both females. First, we presented individual males with two females that differed in body length in a dichotomous‐choice apparatus in which the male could only use visual cues to assess the paired females. We quantified male mating preference as the duration of time a focal male spent associating with each female. Immediately following this test, the focal male was allowed to swim freely with both females, and we quantified the time he spent sexually pursuing each female and the number of courtship sigmoid displays and copulation attempts he directed at each female. On average, males did not significantly prefer either of the two stimulus females in either of the two tests; however, the magnitude of male preference for the larger female tended to increase as the size difference between the paired females increased. More importantly, there was a significant positive relationship between male association time in the dichotomous‐choice test and both the time spent sexually pursuing and the number of courtship sigmoid displays directed at the same female initially preferred in the dichotomous‐choice test. Collectively, these results confirm that association time measured in a dichotomous‐choice test is a reliable predictor of male mating preferences in the Trinidadian guppy.     

Independent Mating Preferences for Male Body Size and Coloration in Female Trinidadian Guppies

Although females in numerous species generally prefer males with larger, brighter and more elaborate sexual traits, there is nonetheless considerable intra‐ and interpopulation variation in mating preferences amongst females that requires explanation. Such variation exists in the Trinidadian guppy, Poecilia reticulata, an important model organism for the study of sexual selection and mate choice. While female guppies tend to prefer more ornamented males as mates, particularly those with greater amounts of orange coloration, there remains variation both in male traits and female mating preferences within and between populations. Male body size is another trait that is sexually selected through female mate choice in some species, but has not been examined as extensively as body coloration in the guppy despite known intra‐ and interpopulation variation in this trait among adult males and its importance for survivorship in this species. In this study, we used a dichotomous‐choice test to quantify the mating preferences of female guppies, originating from a low‐predation population in Trinidad, for two male traits, body length and area of the body covered with orange and black pigmentation, independently of each other. We expected strong female mating preferences for both male body length and coloration in this population, given relaxation from predation and presumably relatively low cost of choice. Females indeed exhibited a strong preference for larger males as expected, but surprisingly a weaker (but nonetheless significant) preference for orange and black coloration. Interestingly, larger females demonstrated stronger preferences for larger males than did smaller females, which could potentially lead to size‐assortative mating in nature.     

Female Size Influences Mate Preferences of Male Guppies

Guppies (Poecilia reticulata) have a promiscuous mating system in which female choice for brightly coloured males plays an important role. Consequently, much research on guppies has examined how mate choice by females has lead to the evolution of male colour patterns. Much less attention has been devoted to mate choice by males in this species. In this study, we show that male guppies are choosy when selecting a female to associate with, significantly preferring the larger female when presented with two females that differed by ≥2 mm in standard length (SL). The strength of their preference for each female increased with absolute female size. The relative sizes of the females, however, also influenced male mating preferences: males showed stronger preferences for the larger female as the difference in SL between the two females increased. Such a preference for larger females is not unexpected as fecundity generally increases with body size in female fish. Thus, males choosing to mate with the larger female should have higher reproductive success. An apparent, but non‐significant anomaly, whereby males appear to prefer the smaller of the two females when the difference between female SL was <4 mm, deserves further investigation.     

Effects of female and male size on female mating and remating decisions in a bean beetle

The body sizes of individuals of the choosing and chosen sexes in a mate choice may affect sequential mating of females. We examined the effects of the body sizes of females and their mates on attributes of female first mating, and the effects of body sizes of females and their previous and potential future mates on female remating in the adzuki bean beetle, Callosobruchus chinensis. Large- and small-sized adults were derived from larvae reared under conditions of low and high density in a bean, respectively. The speed of first mating of large females was not affected by the size of courting males, whereas small females initiated mating more rapidly when courted by small males. The remating probability of large females was not affected by first male size, whereas small females that mated first with smaller males were more likely to remate. These data suggest that pre- and post-copulatory female choices for male size depend on the female’s size, and the small females might be more willing to copulate with smaller males but prefer larger males to sire their offspring after copulation. A possible explanation for this preference is that small females may suffer greater harm from copulating with larger males.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Mating preference of female zebrafish, Danio rerio, in relation to male dominance

Mating success tends to be skewed toward dominant males, thoughfemale mate preferences may not always correlate with male dominance.In this study, we investigated the mating preferences of femalezebrafish, Danio rerio, in the absence of male–male competition.We paired females sequentially with males of known dominancerank, using a nested, repeated measures design, with egg productionas a measure of female mate preference. We predicted that femaleswould spawn more frequently and produce larger clutches whenpaired with males of higher dominance rank. We found significantdifferences among females in the size of clutches produced andamong males in the size of clutches received, but these differenceswere independent of male dominance rank. Male body size wasnot related to either dominance rank or clutch size received.These results indicate that females vary clutch size in relationto the males with which they are paired but that they do notfavor dominant males. Thus, male competition may normally overridefemale mate preference in zebrafish.     

Male size does not affect the strength of male mate choice for high-quality females in Drosophila melanogaster

Theory predicts that the strength of male mate choice should vary depending on male quality when higher-quality males receive greater fitness benefits from being choosy. This pattern extends to differences in male body size, with larger males often having stronger pre- and post-copulatory preferences than smaller males. We sought to determine whether large males and small males differ in the strength (or direction) of their preference for large, high-fecundity females using the fruit fly, Drosophila melanogaster. We measured male courtship preferences and mating duration to show that male body size had no impact on the strength of male mate choice; all males, regardless of their size, had equally strong preferences for large females. To understand the selective pressures shaping male mate choice in males of different sizes, we also measured the fitness benefits associated with preferring large females for both large and small males. Male body size did not affect the benefits that males received: large and small males were equally successful at mating with large females, received the same direct fitness benefits from mating with large females, and showed similar competitive fertilization success with large females. These findings provide insight into why the strength of male mate choice was not affected by male body size in this system. Our study highlights the importance of evaluating the benefits and costs of male mate choice across multiple males to predict when differences in male mate choice should occur.     

MATE CHOICE IN THE SAILFIN MOLLY,POECILIA LATIPINNA

We examined both female and male mate choice in the sailfín molly, Poecilia latipinna. Female mollies preferred larger males over smaller ones when comparing males from their own populations. Although the expression of this preference depends on a female's receptive state, the level of female preference does not appear to be associated with any other attribute of the female or of the males. When presented with males of the same size from different populations, females preferred native over foreign males in some but not all population combinations. These results cannot be explained by a bias for higher size-specific rates of courtship displays that is shared by all females. Males preferred larger over smaller females; larger males exhibited stronger preferences, and preference for the larger female also increased as the disparity in size between the two object females increased. We found no evidence that males preferred native over foreign females when encountered singly or in size-matched combinations. These results indicate that discrimination among populations arises because females exercise divergent directional preferences for size-specific trait values that are associated with differences among males in these values. This result implies an active role for sexual selection in contributing to the maintenance of the behavioral or morphological distinctions among males observed within and among populations.     

The effect of sex and shoal size on shoaling behaviour in Danio rerio

Male and female zebra fish Danio rerio were given choices of shoals that differed in sex and size. Male zebra fish preferred to associate with female shoals over male shoals, but had no preference when given a choice between a mixed‐sex shoal and either a male or female shoal. Female zebra fish showed no significant preference when given a choice between male and females shoals, nor between mixed‐sex shoals and either male or female shoals. When given choices between shoals of differing size, females preferred to associate with the larger shoal, whether or not they were composed of males or females. Males, however, had no preference for larger shoals over smaller shoals, whether or not they were composed of males or females. These results showed that male zebra fish were capable of distinguishing between males and females solely on the basis of visual cues. Furthermore, these results demonstrated a significant difference between the shoaling choices of male and female zebra fish, which may indicate a difference in the function of shoaling for the two sexes.     

Sexual Competition,Coercive Mating and Mate Assessment in the One‐Sided Livebearer,Jenynsia multidentata: Are They Predictive of Sexual Dimorphism?

We investigated the mechanisms of sexual selection operating on body size in the one‐sided livebearer (Jenynsia multidentata), a small fish characterized by male dwarfism. Mating in the one‐sided livebearer is coercive: males approach females from behind and try to thrust their copulatory organ at the female genital pore. Females counter males' mating attempts by either swimming away or attacking them. We tested the hypothesis that the components of sexual selection favouring small size in males (sexual coercion) were more effective than those favouring a large size (male competition and mate choice). When alone, small males had a significantly higher success in their mating attempts than large males. The proportion of successful attempts was also positively correlated with female size. When two males competed for the same female, the large male had a significant mating advantage over the small one. With a 1 : 1 sex ratio, the large‐male mating advantage vanished because each male tended to follow a different female. Large males, however, preferentially defended large females, thus compelling small males to engage with smaller, less fecund females. Males did not discriminate between gravid and non‐gravid females, but preferred mating with larger females. This preference disappeared when males were much smaller than the female, probably in relation to the risk for the male of being eaten or injured by the female. In a choice chamber, male‐deprived females that had their sperm storage depleted remained close to males and showed a preference for large individuals, a behaviour not observed in non‐deprived females. Nonetheless, when placed with males in the same aquarium, all females showed avoidance and aggression. Struggling may represent a way by which the female assesses the skill and endurance of males.     

Experience Plays a Role in Female Preference for Symmetry in the Swordtail Fish Xiphophorus malinche

Variation in female mating preferences was previously detected in wild-caught Xiphophorus cortezi and Xiphophorus malinche females: smaller (presumed younger) females preferred symmetrical males, while larger (presumed older) females preferred asymmetrical males. We examined the influence of experience on this variation in female preference by determining if X. malinche females would express a preference for symmetry as virgins, shift their preferences for bar symmetry as they got larger (older) and if experience with males of different bar number symmetry could explain the variation in female preference previously detected. Virgin females exhibited no preference for vertical bar number symmetry when tested in the young- or old-age classes. However, young virgins spent more time with the opposite treatment in the second when compared with first test, indicating an ability to detect the difference between symmetry and asymmetry, and potentially a preference to mate with multiple males. When females were reared in one of three treatments, housed with symmetrical, barless or both symmetrical and asymmetrical males, we detected both a treatment and tank effect on strength of preference for symmetry, suggesting that barring pattern and some other aspect of the social environment influenced the development of this mating preference. Finally, we detected no effect of age class on mean strength of preference for symmetry; however, there was a statistically different relationship between female size and strength of preference for symmetry across the two age classes, suggesting that the preference function for symmetry may not be linear in relation to female size.     

Pairing and insemination patterns in a giant weta (Deinacrida rugosa: Orthoptera; Anostostomatidae)

Positive size assortative mating can arise if either one or both sexes prefer bigger mates or if the success of larger males in contests for larger females leaves smaller males to mate with smaller females. Moreover, body size could not only influence pairing patterns before copulation but also the covariance between female size and size of ejaculate (number of spermatophores) transferred to a mate. In this field study, we examine the pre-copulatory mate choice, as well as insemination, patterns in the Cook Strait giant weta (Deinacrida rugosa). D. rugosa is a large orthopteran insect that exhibits strong female-biased sexual dimorphism, with females being nearly twice as heavy as males. Contrary to the general expectation of male preference for large females in insects with female-biased size dimorphism, we found only weak support for positive size assortative mating based on size (tibia length). Interestingly, although there was no correlation between male body size and the number of spermatophores transferred, we did find that males pass more spermatophores to lighter females. This pattern of sperm transfer does not appear to be a consequence of those males that mate heavier females being sperm depleted. Instead, males may provide lighter females with more spermatophores perhaps because these females pose less of a sperm competition risk to mates.     

Male Mate Choice in the Guppy (Poecilia reticulata): Do Males Prefer Larger Females as Mates?

Although females are the choosier sex in most species, male mate choice is expected to occur under certain conditions. Theoretically, males should prefer larger females as mates in species where female fecundity increases with body size. However, any fecundity‐related benefits accruing to a male that has mated with a large female may be offset by an associated fitness cost of shared paternity if large females are more likely to be multiply mated than smaller females in nature. We tested the above hypothesis and assumption using the Trinidadian guppy (Poecilia reticulata) by behaviourally testing for male mate choice in the laboratory and by ascertaining (with the use of microsatellite DNA genotyping) patterns of male paternity in wild‐caught females. We observed significant positive relationships between female body length and fecundity (brood size) and between body length and level of multiple paternity in the broods of females collected in the Quaré River, Trinidad. In laboratory tests, a preference for the larger of two simultaneously‐presented virgin females was clearly expressed only when males were exposed to the full range of natural stimuli from the females, but not when they were limited to visual stimuli alone. However, as suggested by our multiple paternity data, males that choose to mate with large females may incur a larger potential cost of sperm competition and shared paternity compared with males that mate with smaller females on average. Our results thus suggest that male guppies originating from the Quaré River possess mating preferences for relatively large females, but that such preferences are expressed only when males can accurately assess the mating status of encountered females that differ in body size.     

Does individual personality predict male mating preference for female body size in the Trinidadian guppy?

Within populations, individual animals vary considerably in their behaviour, including mate choice and personality. There is mounting interest in the potential covariation between these two behaviours within individuals, such that personality would influence mate choice. We experimentally tested this proposition under controlled laboratory conditions using male Trinidadian guppies (Poecilia reticulata) as a model study system. We assayed repeatedly the mating preference of individual males for females based on their body size. Additionally, we assayed repeatedly two ecologically relevant personality traits in males, namely exploration of a novel environment and boldness under a simulated predation threat. Finally, we analysed whether male mating preference and personality traits were repeatable, and tested whether the personality of individual males was correlated (covaried) with their mating preference scores. Although all but one of the measures of exploration and boldness behaviour were repeatable over time, male mating preference scores were not repeatable. Measures of male exploration and boldness were not inter-correlated among individuals, suggesting the absence of a behavioural syndrome between exploration and boldness. Unexpectedly, males did not exhibit on average a significant mating preference for larger females over smaller ones; they chose randomly between the paired stimulus females. Overall, we found no compelling evidence for a relationship between individual personality traits and mating preference in male guppies, suggesting that personality does not predict mate choice, at least in our study population and under our experimental conditions. We discuss potential factors, other than male personality and body length, that might maintain inter-individual variation in male mating preferences in the guppy in the wild.     

On the role of sexual selection in ecological divergence: a test of body‐size assortative mating in the eastern newt Notophthalmus viridescens

Speciation processes initiated by divergent selection often fail to complete; yet, how sexual selection is involved in the progress of ecological speciation is rarely understood. Intraspecific body‐size variation affects mate preference and male–male competition, which can consequently lead to assortative mating based on body size. In the present study, we tested the importance of body size difference in the potential of assortative mating between the two eastern newt subspecies, larger Notophthalmus viridescens viridescens and smaller Notophthalmus viridescens dorsalis. Through differential expression of life‐cycle polyphenism, these two subspecies are adapted to contrasting environments, which has likely led to the subspecific body‐size difference. We found that males of both subspecies preferred larger females of N. v. viridescens as mates presumably because of the fecundity advantage of larger females. On the other hand, no evidence of female choice was found. Larger males of N. v. viridescens exhibited greater competitive ability and gained primary access to larger females of their own kind. However, smaller males were able to overcome their inferior competitive ability by interfering with larger males' spermatophore transfer and sneakily mating with larger females. Thus, the subspecific body‐size difference importantly affected sexual selection processes, resulting in nonrandom but not completely assortative mating patterns between the larger and smaller subspecies. Although life‐cycle polyphenism facilitates the intraspecific ecological divergence within N. v. viridescens sexual selection processes, namely smaller males' mate preference for larger females and sexual interference during spermatophore transfer, may be halting completion of the ecological speciation. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 884–897.     

The effect of claw size and wave rate on female choice in a fiddler crab

How do females select a mate when they have mating preferences for multiple male traits? In experimental studies, female fiddler crabs (Uca mjoebergi) show a strong preference for males with larger claws and higher wave rates. In the field, there is no correlation between male claw size and observed wave rate. Here we document natural mating behaviour and show that females approach males who wave at a higher rate than nearby competitors. On average, an approached male had a significantly larger claw than his two nearest neighbours but did not differ in size from his two closest waving competitors. In general, smaller males were less likely to wave at approaching females. Females therefore approached mates based directly on wave rate but, because smaller males were less likely to wave, this indirectly resulted in female choice for larger than average males. Our study raises two issues. First, how do we relate the field results to previous experimental studies showing a female preference for larger claws? Second, in U. mjoebergi, males defend smaller neighbours against intruders. Our study suggests that one benefit of such defence coalitions is to decrease the number of immediate competitors present during female mate choice by retaining smaller neighbours.     

MALE DOMINANCE, FEMALE MATE CHOICE, AND INTERSEXUAL CONFLICT IN THE ROSE BITTERLING (RHODEUS OCELLATUS)

An intersexual conflict arises when males and females differ in their reproductive interests. Although experimental studies have shown that females often mate with dominant males, it may not always be in the interest of a female to do so. Here we investigated the impact of male dominance on female mate choice and offspring growth and survival in the rose bitterling ( Rhodeus ocellatus ), a freshwater fish with a resource-based mating system. Three experimental mating trials were conducted using males of known dominance rank, but with different levels of constraint on male behavior. Thus, females were able to choose among; (1) males that were isolated from each other; (2) males that could see and smell each other, but could not directly interact; (3) males that could interact fully. Using a combination of behavioral observation and parentage analyses it was shown that female preferences did not correspond with male dominance and that male aggression and dominance constrained female mate choice, resulting in a potential intersexual conflict. The survival of offspring to independence was significantly correlated with female mate preferences, but not with male dominance. A lack of strong congruence in female preference for males suggested a role for parental haplotype compatibility in mate choice.     

Linking intra‐ and interspecific assortative mating: Consequences for asymmetric sexual isolation

Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within‐species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male–male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.