Ultraviolet vision and mate choice in the guppy (Poecilia reticulata)

Ultraviolet (UV) vision is well documented for many speciesof vertebrates. UV cues are known to be used in foraging, navigationand in mate choice. We conducted a series of behavioral experimentsto investigate the role of UV perception in mate choice inboth female and male guppies (Poecilia reticulata). In ourexperiments the visual appearance of potential mates was manipulatedusing either UV transmitting (UV+) or UV blocking (UV-) filters.Female guppies significantly preferred UV+ males. Male guppiestended to prefer UV- females, but their preferences were marginallynonsignificant. Further experiments investigating the roleof luminance, indicate that UV wavelengths are probably beingused for color discrimination rather than for detecting differencesin brightness. These experiments raise the possibility thatUV is used in mate assessment in different ways by male andfemale guppies. This may reflect the different strategies thatthe two sexes have in order to maximize reproductive success.To our knowledge, these are the first data showing that UVis used by any fish species in mate selection.     

Female mate copying in the guppy {Poecilia reticulata): age-dependent effects

Virtually all studies of mate choice to date have assumed thatfemales choose mates independent of one another. Social cues,however, such as the mate choice of conspecifics, may also playan important role in such decisions. Previous work has shownthat female guppies of similar age copy each other's choiceof mates. Here we examine the effect of relative age on matechoice copying in the guppy, Poecilia reticulata, and examinewhether younger individuals are more likely to copy the matechoice of older conspecifics than vice versa. Results indicatethat younger females copy the mate choice of older females,but older individuals do not appear to be influenced by themate choice of younger individuals.     

Mate-choice copying under predation risk in the Trinigadian guppy (Poecilia reticulata)

Although females of numerous species possess genetically-basedpreferences for certain male trails and male preferentiallywith males possessing these traits, recent theoretical and experimentalevidence indicates that they may also copy (imitate) the matechoices of other females under certain circumstances. Such mate-choicecopying is expected to be most prevalent when females have theopportunity to observe the mate choices of others and when matechoice is costly to females. One potential direct fitness costof mate choice is increased individual risk of mortality dueto predation. Here, we investigate for the first time the effectof increasing the apparent risk of predation on the tendencyof females to copy the experimentally staged mate choice ofanother female. Using adult female guppies (Poecilia reticulata)originating from a Trinidadian population that experiences arelatively high fish predation pressure, we first establishthat they possess a preference for the more brighdy coloredof two simultaneously presented males in the absence of bothmate-copying opportunity and an immediate threat of predation.However, most females reversed their initial mate preferencewhen given an opportunity to copy the mate preference of anotherfemale in the absence of predation threat The proportion offemales reversing their preference when given the opportunityto do so was not affected by increasing the apparent risk of(fish) predation. This result may be owing either to femaleguppies tending to copy the mate choice of others whenever theopportunity arises because the benefits of doing so accrue irrespectiveof the ambient risk of predation or to females choosing randomlybetween males with respect to their color pattern in the presenceof the predator irrespective of mate-copying opportunity. Thesetwo explanations for the apparent lack of an effect of predationrisk on mate-choice copying per se are both plausible but unfortunatelycould not be easily distinguished here. It may thus be possible,and interesting, that individual female guppies chose randomlybetween the available males in the presence of the predatorbut otherwise copied the choice of others when given the opportunityto do so.     

Genes, copying, and female mate choice: shifting thresholds

Recent experimental work on guppies (Poecilia reticulata) hasexamined the strength of genetic and cultural (copying) factorsin determining female mate choice. Using females from a populationwith a heritable preference for the amount of orange body colorpossessed by males, prior work discovered that a threshold differencein orange color among males existed below which females wouldchoose a less orange male if they observed another female choosethat male, but above which they consistently preferred the moreorange of the males, regardless of whether they viewed anotherfemale prefer the less orange male. I tested whether this thresholdcan be shifted by increasing the amount of mate-copying informationavailable to a female. I demonstrate that when a female hasthe opportunity to see two different model females independentlyprefer the less orange of two males or a single female neara drab male for a longer period of time (twice as long as inprior work), the observer female prefers this drab male evenwhen males dramatically differ in orange coloration.     

Intrinsic reproductive isolation between Trinidadian populations of the guppy, Poecilia reticulata

Although Trinidadian populations of the guppy, Poecilia reticulata, show considerable adaptive genetic differentiation, they have been assumed to show little or no reproductive isolation. We tested this assumption by crossing Caroni (Tacarigua River) and Oropuche (Oropuche R.) drainage populations from Trinidad's Northern Range, and by examining multiple aspects of reproductive compatibility in the F1, F2 and BC1 generations. In open-aquarium experiments, F1 males performed fewer numbers of mating behaviours relative to parental population controls. This is the first documentation of hybrid behavioural sterility within a species, and it suggests that such sterility may feasibly be involved in causing speciation. The crosses also uncovered hybrid breakdown for embryo viability, brood size and sperm counts. In contrast, no reductions in female fertility were detected, indicating that guppies obey Haldane's rule for sterility. Intrinsic isolation currently presents a much stronger obstacle to gene flow than behavioural isolation, and our results indicate that Trinidadian populations constitute a useful model for investigating incipient speciation.     

Female mate preference explains countergradient variation in the sexual coloration of guppies (Poecilia reticulata)

We tested the hypothesis that mate choice is responsible for countergradient variation in the sexual coloration of Trinidadian guppies (Poecilia reticulata). The nature of the countergradient pattern is that geographical variation in the carotenoid content of the orange spots of males is counterbalanced by genetic variation in drosopterin production, resulting in a relatively uniform pigment ratio. A female hue preference could produce this pattern, because hue is the axis of colour variation most directly affected by the pigment ratio. To test this hypothesis, we crossed two populations differing in drosopterin production and produced an F(2) generation with variable drosopterin levels. When the carotenoid content of the orange spots was held constant, female guppies preferred males with intermediate drosopterin levels. This shows that females do not simply prefer males with greater orange spot pigment content; instead, the ratio of the pigments also affects male attractiveness. To our knowledge, this is the first direct evidence for a hypothesized agent of countergradient sexual selection.     

Repeatability of mate choice in female red jungle fowl

We staged female mate choice trials between pairs of males andrepeated the process for each female to determine the repeatabilityof female preference for males in red jungle fowl (Gallus gallus)in the first and second half of the breeding season. We measuredmale morphological traits (the size and color of the comb andthe brightness of the hackle feathers) that females are knownto use in choosing a mate. In the first half of the breedingseason, females showed repeatability in their choices of matewith respect to the male's comb characters. Females did notshow a repeatable preference with respect to male hackle feathers,and we found no repeatability of mate choice in the second halfof the season. Females seem to primarily look at the male'scomb when choosing a mate, and other ornaments seem only ofsecondary importance.[Behav Ecol 7: 243-246 (1996)]     

The influence of water velocity on the display behavior of male guppies, Poecilia reticulata

The objective of this experiment was to determine if differentwater velocities during ontogeny affect male physical condition,male signal intensity, and female mating preferences in theguppy (Poecilia reticulata). Guppies were raised in aquariain either high or low water velocities and fed in excess. Analysisof 72 males from four replicates indicated that high velocitymales had longer mean displays and spent more total time displayingthan low velocity males. These males also had significantlyfaster swimming speeds, wider caudal peduncles, and were moreattractive to females than low velocity males. There were nodifferences in display rates, body widths, standard lengths,or copulation attempts between high and low velocity males.These results indicate that water velocity conditions duringontogeny act as a proximal factor that influences the displaybehavior of guppies. Water velocity caused an indirect increasein the power of the male display to produce a female sexualresponse. The morpho-metric measurements suggest that the proximalmechanism behind the increased display intensity was the increasedmuscle development of males raised in high water velocities,which resulted in longer prolonged swimming speeds and moreintense displays. Therefore, display behavior of guppies maybe a general indicator of overall male physical condition.[BehavEcol07: 272–278 (1996)]     

Sequential mate encounters: female but not male body size influences female remating behavior

Whether and how individuals choose sequentially among matesis an important but largely neglected aspect in sexual selectionstudies. Here, we explore female remating behavior in the cellarspider Pholcus phalangioides. We focus on body size as one ofthe most important traits involved in mate choice. Large andsmall females (n = 216) were double mated with large or smallmales in all eight possible combinations. All females copulatedwhen virgin, but only 82% accepted a second male. The chanceof a female remating was not significantly predicted by thebody size of the second or first male or by the size differencebetween the two. In contrast, a previous study demonstrateda male size effect in that larger males monopolized femalesuntil egg laying when two males of different sizes were present.We suggest that sequential encounters are more common undernatural conditions than male monopolization of females becauseestimates of concurrent multiple paternity together with observationsin a natural population do not favor mate guarding as the predominantmating strategy in this species. It follows from our study thatthe intensity of sexual selection on male size may be greatlyoverestimated when using a competitive laboratory setting fora species in which females generally encounter mates in a sequentialfashion. Female remating probability was significantly predictedby female size, with large females remating with higher probabilitythan small females. Thus, when mating with large females, malesmay gain higher fertilization success through increased femalefecundity but also face a higher sperm competition risk.     

No female mate choice in Mallee dragon lizards, Ctenophorus fordi

Aspects of sexual selection were studied in a sexually monomorphic Australian agamid lizard (Ctenophorus fordi), in particular with respect to the sensory exploitation hypothesis. In enclosure trials, females were offered the choice between large vs. small males and, in a different experiment, males with blue vs. normal head color. The rationale for these experiments was: firstly, to establish if females actively solicit copulations; secondly, if so, do females solicit copulations non-randomly with respect to male size (because large males may have access to food resources); thirdly, if male coloration is manipulated to match traits of congeneric, conspicuous and sexually dimorphic species, do females show preference for this novel trait (in accordance with the sensory exploitation hypothesis). The corresponding manipulations were also made in a free-living population where the distribution of females on the home ranges of color-manipulated males were monitored. Blue-headed males were accepted as mating partners both in the staged mating trials and in the natural population. Females appeared not to express any kind of active or passive mate choice (rejection); in only one out of 62 trials did a female approach a male herself rather than being approached by the male(s). There was no discrimination against any male category regardless of size or color within a female's receptive period and the manipulation of male head color in the natural population did not result in spatial re-distribution of females. Thus, a female appears to mate unselectively within her receptive period. Rejection behaviors were used only outside of the receptive period to communicate, to all males, that the female is not receptive.     

Familiarity adds to attractiveness in matters of siskin mate choice

There is currently considerable controversy in evolutionary ecology revolving around whether social familiarity brings attraction when a female chooses a mate. The topic of familiarity is significant because by avoiding or preferring familiar individuals as mates, the potential for local adaptation may be reduced or favoured. The topic becomes even more interesting if we simultaneously analyse preferences for familiarity and sexual ornaments, because when familiarity influences female mating preferences, this could very significantly affect the strength of sexual selection on male ornamentation. Here, we have used mate-choice experiments in siskins Carduelis spinus to analyse how familiarity and patterns of ornamentation (i.e. the size of wing patches) interact to influence mating success. Our results show that females clearly prefer familiar individuals when choosing between familiar and unfamiliar males with similar-sized wing patches. Furthermore, when females were given the choice between a highly ornamented unfamiliar male and a less ornamented familiar male, half of the females still preferred the socially familiar birds as mates. Our finding suggests that male familiarity may be as important as sexual ornaments in affecting female behaviour in mate choice. Given that the potential for local adaptation may be favoured by preferring familiar individuals as mates, social familiarity as a mate-choice criterion may become a potential area of fruitful research on sympatric speciation processes.     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death

Male-biased dimorphism in body size is usually attributed tosexual selection acting on males, through either male competitionor female choice. Brown antechinuses (Antechinus stuartii) aresexually dimorphic in size, and heavier males are known to siremore offspring in the wild. We investigated four possible mechanismsthat might explain this large-male reproductive advantage. Wetested if there is a female preference for large males, a femalepreference for dominant males, if larger males compete moreeffectively for mates, and if there is a survival advantagefor large males during the mating season. We established nestinggroups of males in captivity and conducted mate choice trialsin which males from nesting groups either could or could notinteract. We assessed male dominance rank and recorded survivaltimes after mating. Females did not prefer larger males directly.The results suggest that the other three mechanisms of sexualselection tested account for the large-male advantage: largemales competed more successfully for mates, so were sociallydominant; females rejected subordinates (males they saw losingtwice in contests to previous mates); and dominant males survivedfor longer after their first mating. Females judged male rankbased on direct observation of male competitive interactionsat the time of mating and apparently could not distinguish rankfrom male scent. Effects of size and dominance on male reproductivesuccess are not confounded by age because male antechinusesare semelparous.     

Use of digitally modified videos to examine female mate preference for orange spot coloration of males in the guppy, Poecilia reticulata

Digitally modified video techniques may provide some advantages for the behavioral study of animals, including fishes. However, the validity of the experiments that are conducted using digitally modified videos should be verified. In the present study, we examined female mate preference in the guppy, Poecilia reticulata in a Japanese population by exploring an appropriate method involving the use of digitally modified video playbacks. For the male stimulus, two video images were produced by digital modification of a video recording of a male; the brightness of the orange spot coloration of the male was enhanced (bright male) in one video and decreased (dull male) in the other video. In experiment 1, female choice was examined according to the method described in previous studies, i.e., two monitors were set on opposite sides of the test aquarium to simultaneously present two stimulus male images to the females. However, in this experiment, the stimulus male images did not attract the females to a greater extent than the blank aquarium images. In addition, although the first trial showed a female preference for bright males, in the second trial, in which each stimulus male image was shown from the monitor opposite to that used in the first trial, a significant preference for bright males could not be detected. In experiment 2, a monitor was placed on one side of the aquarium and the left and right sides of the monitor showed the two stimulus male images simultaneously. In addition, a 24-h time interval was set between the first and second trials. Females spent more time in the proximity of the male images than that of the blank images, and a female preference for bright males was observed in both trials. The results of this study clearly indicate the female preference for males possessing bright coloration of orange spots. These results also suggest that the one-sided monitor system adopted in experiment 2 is a more appropriate method than the two-sided monitor system to examine female mate preferences by using digitally modified video playbacks.     

Phenotypic correlates of spermatozoon quality in the guppy, Poecilia reticulata

The phenotype-linked fertility hypothesis suggests that a femalecan benefit directly from mate choice when the cues she usesindicate the quantity and/or quality of his spermatozoa. Wetested the link between sperm quality and male body size andcoloration in the resource-free mating system of the guppy,a tropical fish characterized by strong female choice. Largermales possessed larger testes and are therefore predicted toproduce larger numbers of spermatozoa than smaller males. Largermale guppies also produced longer spermatozoa than smaller males.Degree of carotenoid coloration did not predict either the quantityor the quality of a male's spermatozoa. These results are consistentwith a previous study that showed that female guppies in thestudy population prefer larger males to brightly colored males.The male-size directed increase in spermatozoon size may bethe result of interplay between sperm competition and the coevolutionof spermatozoon traits with the female reproductive tract.     

Variation in female mate choice within guppy populations: population divergence,multiple ornaments and the maintenance of polymorphism

The evolutionary significance of variation in mate choice behaviour is currently a subject of some debate and considerable empirical study. Here, I review recent work on variation within and among guppy (Poecilia reticulata) populations in female mate choice and mating preferences. Empirical results demonstrate that there is substantial variation within and among populations in female responsiveness and choosiness, and much of this variation is genetic. Evidence for variation in preference functions also exists, but this appears to be more equivocal and the relative importance of genetic variation is less clear cut. In the second half of this review I discuss the potential significance of this variation to three important evolutionary issues: the presence of multiple male ornaments, the maintenance of polymorphism and divergence in mate recognition among populations. Studies of genetic variation in mate choice within populations indicate that females have complex, multivariate preferences that are able to evolve independently to some extent. These findings suggest that the presence of multiple male ornaments may be due to multiple female mating preferences. The extreme polymorphism in male guppy colour patterns demands explanation, yet no single satisfactory explanation has yet emerged. I review several old ideas and a few new ones in order to identify the most promising potential explanations for future empirical testing. Among these are negative frequency dependent selection, environmental heterogeneity coupled with gene flow, and genetic constraints. Last, I review the relative extent of within and among-population variation in mate choice and mating preferences in order to assess why guppies have not speciated despite a history of isolation and divergence. I argue that variation within guppy populations in mate choice and enhanced mating success of new immigrants to a pool are major impediments to population divergence of the magnitude that would be required for speciation to occur.     

The effects of familiarity and group size on mating preferences in the guppy,Poecilia reticulata

Abstract In recent years, it has become evident that frequency dependence in the attractiveness of a particular phenotype to mates can contribute to the maintenance of polymorphism. However, these preferences for rare and unfamiliar male phenotypes have only been demonstrated in small, controlled experiments. Here, we tested the preference for unfamiliar mates in groups of six to 96 individuals over 13 days, in the guppy (Poecilia reticulata). We observed individual behaviour in situ to test whether fish discriminate two unfamiliar individuals among many familiar ones. We found that unfamiliar males and females were preferred over the familiar fishes in all groups and that this effect decayed over time. Increasing group sizes and levels of sexual activity did not hamper the preference for unfamiliar mates, providing further support for the role of frequency dependent mate choice in the maintenance of trait polymorphism in natural populations.     

Female mate choice across mating stages and between sequential mates in flour beetles

Few studies have examined how female premating choice correlates with the outcome of copulatory and post-copulatory processes. It has been shown that polyandrous Tribolium castaneum females discriminate among males before mating based on olfactory cues, and also exert cryptic choice during mating through several mechanisms. This study tested whether a male's relative attractiveness predicted his insemination success during copulation. Bioassays with male olfactory cues were used to rank two males as more and less attractive to females; each female was then mated to either her more attractive male followed by less attractive male, or vice versa. Dissections immediately after second copulations revealed a significantly higher percent of successful inseminations for females that remated with more attractive males compared with those that remated with less attractive males. These results indicate that cryptic female choice during copulation reinforces precopulatory female choice in T. castaneum, and suggest that females could use cryptic choice to trade up to more attractive males, possibly gaining better phenotypic or genetic quality of sires.