Male mate choice and the potential for complex mating dynamics in the tree lizard (Urosaurus ornatus)

A growing body of literature is recognizing that males may also play a role in the mating process by behaving non‐randomly toward potential female mates during courtship. In numerous species, discrete color polymorphisms in males are inferred to represent alternative mating tactics, which often correspond with concomitant asymmetries in ecology and behavior. In terms of their mating behavior, these ecological outcomes of a color polymorphism should affect a morph's likelihood and frequency of encountering females in a population, possibly favoring the evolution of morph‐specific mating preferences. Knowledge of how male morphs contribute to a species’ overall mating dynamics will improve our understanding of how sexual selection shapes phenotypic diversity in color polymorphic systems. We conducted a mate choice experiment to evaluate the extent and morph specificity of non‐random mating preferences by male ornate tree lizards, Urosaurus ornatus. We observed the behavior of blue and yellow males in an experimental arena in response to a choice between an orange or yellow female. We found that blue males preferred yellow females over orange females, and although yellow males visited females more often than blue males overall, their attention was not morph‐specific. Given male morph differences in choosiness, and their differences in social dominance, we conclude that female throat color may be partly under sexual selection in U. ornatus. However, a lack of concordance between male and female mating preferences (drawn from an earlier study) suggests that overall mating dynamics may serve to maintain, rather than enhance, color morph differences in this species.     

Differences in Mating Propensity Between Immature Female Color Morphs in the Damselfly Ischnura elegans (Insecta: Odonata)

Female-limited color polymorphisms occur in a variety of animal taxa where excessive male sexual harassment may explain the coexistence of multiple female color morphs. In the color polymorphic damselfly Ischnura elegans, mature and immature female color morphs coexist at the mating site where males are in search for suitable mating partners. Here, we study male preference and female mating propensity for the two immature female morphs. As would be expected, compared to mature morphs, both immature female morphs mate much less. Within immature females, one morph consistently mates more frequently compared to the other morph, a pattern that is similar for the ontogenetically corresponding mature female morphs. Preference experiments with the two differently colored immature female morphs, however, did not indicate male mate preference for either morph. Low mating frequencies of immature females at natural sites in combination with relatively high attractiveness of immature models in terms of male preference indicate that female behavior influences female mating success.     

Male dimorphism, territoriality and mating success in the tropical damselfly, Paraphlebia zoe Selys (Odonata: Megapodagrionidae)

The tropical damselfly Paraphlebia zoe has two male morphs: a black-winged (BW) male which is associated with territorial defense of oviposition sites; and a hyaline-winged (HW) male similar in appearance to females, and, compared to the black morph, less frequently found defending territories. In a wild population of this species, we first assessed the relationship between phenotypic traits [male morph, size and territorial status (being territorial or non-territorial)], their role on mating success, and the degree to which a particular territory may contribute to male mating success. Second, to relate a physiological basis of being territorial we compared both morphs in terms of muscular fat reserves and thoracic muscle, two key traits related to territory defense ability. Males of both morphs defended territories although the BW males were more commonly found doing this. BW males were larger than HW males and size predicted being territorial but only within HW males (territorial males were larger) but not in BW males. Male mating success was related to territorial status (territorial males achieved a higher mating success), but not to morph or size. Furthermore, territory identity also explained mating success with some territories producing more matings than others. The BW morph stored more fat reserves which may explain why this morph was more likely to secure and defend a place than the HW morph. However, the HW morph showed higher relative muscle mass which we have interpreted as a flexible strategy to enable males to defend a territory. These results are distant to what has been found in another male dimorphic damselfly, Mnais pruinosa, where the advantage of the non-territorial morph relies on its longevity to compensate in mating benefits compared to the territorial morph.     

Boldness,Dominance, and Territoriality in the Color Polymorphic Tree Lizard,Urosaurus ornatus

Social dynamics in territorial species often reflect underlying variation in aggression and other aspects of social dominance among individuals. In ornate tree lizards (Urosaurus ornatus), males differing in dewlap color differ in social dominance: while blue males are the dominant, aggressive morph and always territorial, yellow males tend to exhibit a less‐aggressive satellite behavioral tactic. However, in habitats with fewer available territorial resources, yellow males defend territories and increase in relative abundance. These observations suggest that consideration of social dominance alone may be insufficient to explain U. ornatus' territorial dynamics in the wild. Here, we tested how both dominance and another important behavioral trait, boldness, contribute to the outcome of territorial disputes in tree lizards. We recorded the territorial behavior of blue and yellow male tree lizards (entered in pairs) in an experimental arena. At the end of each trial, we then approached each male and recorded whether it fled (shy) or not (bold) in response to our approach. As expected, dominant blue males exploited the higher quality perch more often than yellow males. However, when approached by a simulated predator, blue males were more likely to flee than yellow males. Thus, while blue males are more dominant, yellow is likely the bolder morph. As a result, this morph may be better equipped to defend territories in riskier environments. We conclude that although dominance asymmetries may predictably drive initial territorial interactions among competing males, variation in other behaviors (like boldness) may perturb the long‐term outcome of these interactions across variable environments.     

Male mate preference as an agent of fecundity selection in a polymorphic salamander

Color polymorphisms are associated with variation in other traits which may affect individual fitness, and these color‐trait associations are expected to contribute to nonrandom mating in polymorphic species. The red‐backed salamander (Plethodon cinereus) exhibits a polymorphism in dorsal pattern: striped and unstriped, and previous studies have suggested that they may mate nonrandomly. However, the mechanism(s) contributing to this behavior remain unclear. Here we consider the role that male preference may have in driving mating behavior in P. cinereus. We limit our focus to striped individuals because this morph is most likely to be choosy given their dominant, aggressive behavioral profiles relative to unstriped males. Specifically, we evaluated (a) whether striped males preferentially associate with females with respect to her dorsum color, size, and body condition and (b) if so, whether female traits are evaluated via visual or chemical cues. We also considered whether the frequency of another male social behavior, nose taps, was associated with mate preferences. We found that striped male P. cinereus nose tapped more often to preferred females. However, males only assessed potential mates via chemical cues, preferring larger females overall. Reproductive phenology data on a sample of gravid females drawn from the same population indicated that the color morphs do not differ in reproductive traits, but larger females have greater fecundity. Given our findings, we conclude that female P. cinereus are under fecundity selection, mediated by male preference. In this manner, male mating behavior contributes to observations of nonrandom mate associations in this population of P. cinereus.     

Pollinator Competition as a Driver of Floral Divergence: An Experimental Test

Optimal foraging models of floral divergence predict that competition between two different types of pollinators will result in partitioning, increased assortative mating, and divergence of two floral phenotypes. We tested these predictions in a tropical plant-pollinator system using sexes of purple-throated carib hummingbirds (Anthracothorax jugularis) as the pollinators, red and yellow inflorescence morphs of Heliconia caribaea as the plants, and fluorescent dyes as pollen analogs in an enclosed outdoor garden. When foraging alone, males exhibited a significant preference for the yellow morph of H. caribaea, whereas females exhibited no preference. In competition, males maintained their preference for the yellow morph and through aggression caused females to over-visit the red morph, resulting in resource partitioning. Competition significantly increased within-morph dye transfer (assortative mating) relative to non-competitive environments. Competition and partitioning of color morphs by sexes of purple-throated caribs also resulted in selection for floral divergence as measured by dye deposition on stigmas. Red and yellow morphs did not differ significantly in dye deposition in the competition trials, but differences in dye deposition and preferences for morphs when sexes of purple-throated caribs foraged alone implied fixation of one or the other color morph in the absence of competition. Competition also resulted in selection for divergence in corolla length, with the red morph experiencing directional selection for longer corollas and the yellow morph experiencing stabilizing selection on corolla length. Our results thus support predictions of foraging models of floral divergence and indicate that pollinator competition is a viable mechanism for divergence in floral traits of plants.     

Diurnal changes and frequency dependence in male mating preference for female morphs in the damselfly Ischnura senegalensis (Rambur) (Odonata: Coenagrionidae)

Ischnura senegalensis females exhibit color dimorphism, consisting of an andromorph and a gynomorph, which might be maintained under a frequency-dependent process of mating harassment by mate-searching males. Males change their mating preference for female morph depending on prior copulation experience. Binary choice experiments between two female morphs were carried out in four local populations in the early morning (07.00–09.00 hours) and the afternoon (12.00–14.00 hours), times which mark the onset and the end of diurnal mating activity, respectively. According to the line census along the water's edge, the proportion of andromorphs in the female population varied from 21 to 67% throughout the survey period for four local populations. Males showed non-biased preference for female morphs in the early morning in each local population, while they chose the common morph in the afternoon. Male mating preference for female morphs was positively correlated to the proportion of female morphs in the population. If the selective mating attacks on the common female morphs inhibit their foraging and/or oviposition behavior, frequency-dependent male mating attacks might provide a selective force for maintaining the female color dimorphism in I. senegalensis .     

Reflectance spectra and mating patterns support intraspecific mimicry in the colour polymorphic damselfly <Emphasis Type="Italic">Ischnura elegans</Emphasis>

Coexistence of female colour morphs in animal populations is often considered the result of sexual conflict, where polymorphic females benefit from reduced male sexual harassment. Mate-searching males easily detect suitable partners when only one type of female is present, but become challenged when multiple female morphs coexist, which may result in frequency-dependent mate preferences. Intriguingly, in damselflies, one female morph often closely resembles the conspecific male in body coloration, which has lead to hypotheses regarding intra-specific male-mimicry. However, few studies have quantitatively evaluated the correspondence between colour reflectance spectra from males and male-like females, relying instead on qualitative visual assessments of coloration. Using colour analyses of reflectance spectra, we compared characteristics of the body coloration of ontogenetic male and female colour morphs of the damselfly Ischnura elegans. In addition, we evaluated whether males appear to (1) discriminate between immature and mature female colour morphs, and (2) whether male-like females experience reduced male mating attention and low mating frequencies as predicted from male-mimicry. Spectral reflectance data show that immature female morphs differ substantially in coloration from mature individuals. Mating frequencies were much lower for immature than mature female morphs. For the male-like female morph, measures of colour were statistically indistinguishable from that of both immature and mature conspecific males. Mating frequencies of male-like females were lower than those of other mature female morphs under field and experimental conditions. Together, our results indicate that males may use the observed spectral differences in mate choice decisions. Furthermore, male-like females may be regarded as functional mimics that have reduced attractiveness and lowered rates of sexual harassment by mate-searching males.     

Supplementation of male pheromone on rock substrates attracts female rock lizards to the territories of males: a field experiment

Background

Many animals produce elaborated sexual signals to attract mates, among them are common chemical sexual signals (pheromones) with an attracting function. Lizards produce chemical secretions for scent marking that may have a role in sexual selection. In the laboratory, female rock lizards (Iberolacerta cyreni) prefer the scent of males with more ergosterol in their femoral secretions. However, it is not known whether the scent-marks of male rock lizards may actually attract females to male territories in the field.

Methodology/Principal Findings

In the field, we added ergosterol to rocks inside the territories of male lizards, and found that this manipulation resulted in increased relative densities of females in these territories. Furthermore, a higher number of females were observed associated to males in manipulated plots, which probably increased mating opportunities for males in these areas.

Conclusions/Significance

These and previous laboratory results suggest that female rock lizards may select to settle in home ranges based on the characteristics of scent-marks from conspecific males. Therefore, male rock lizards might attract more females and obtain more matings by increasing the proportion of ergosterol when scent-marking their territories. However, previous studies suggest that the allocation of ergosterol to secretions may be costly and only high quality males could afford it, thus, allowing the evolution of scent-marks as an honest sexual display.     

MAPPING INDIVIDUAL VARIATION IN MALE MATING PREFERENCE SPACE: MULTIPLE CHOICE IN A COLOR POLYMORPHIC CICHLID FISH

Sexual selection theory largely rests on the assumption that populations contain individual variation in mating preferences and that individuals are consistent in their preferences. However, there are few empirical studies of within-population variation and even fewer have examined individual male mating preferences. Here, we studied a color polymorphic population of the Lake Victoria cichlid fish Neochromis omnicaeruleus , a species in which color morphs are associated with different sex-determining factors. Wild-caught males were tested in three-way choice trials with multiple combinations of different females belonging to the three color morphs. Compositional log-ratio techniques were applied to analyze individual male mating preferences. Large individual variation in consistency, strength, and direction of male mating preferences for female color morphs was found and hierarchical clustering of the compositional data revealed the presence of four distinct preference groups corresponding to the three color morphs in addition to a no-preference class. Consistency of individual male mating preferences was higher in males with strongest preferences. We discuss the implications of these findings for our understanding of the mechanisms underlying polymorphism in mating preferences.     

The evolution of wing color: male mate choice opposes adaptive wing color divergence in Colias butterflies

Abstract Correlated evolution of mate signals and mate preference may be constrained if selection pressures acting on mate preference differ from those acting on mate signals. In particular, opposing selection pressures may act on mate preference and signals when traits have sexual as well as nonsexual functions. In the butterfly Colias philodice eriphyle , divergent selection on wing color across an elevational gradient in response to the thermal environment has led to increasing wing melanization at higher elevations. Wing color is also a long-range signal used by males in mate searching. We conducted experiments to test whether sexual selection on wing melanization via male mate choice acts in the same direction as natural selection on mate signals due to the thermal environment. We performed controlled mate choice experiments in the field over an elevational range of 1500 meters using decoy butterflies with different melanization levels. Also, we obtained a more direct estimate of the relation between wing color and sexual selection by measuring mating success in wild-caught females. Both our experiments showed that wing melanization is an important determinant of female mating success in C. p. eriphyle . However, a lack of elevational variation in male mate preference prevents coevolution of mate signals and mate preference, as males at all elevations prefer less-melanized females. We suggest that this apparently maladaptive mate choice may be maintained by differences in detectability between the morphs or by preservation of species recognition.     

Female lizards ignore the sweet scent of success: Male characteristics implicated in female mate preference

Sexual selection molds the morphology, physiology and behavior of males in many animals. At first glance, it seems reasonable to assume that females would use the same male traits and signals in mate choice as males do during male-male competition. However, intra- and intersexual competition may affect traits in the same or the opposite direction, with differing strength. We investigated which color, morphometric and performance traits are selected for through male-male competition and whether female mate preference is based on these same traits and/or dominance status in the three male color morphs of the lizard Podarcis melisellensis. Males with relatively bigger heads and relatively higher bite forces were more likely to win fights and orange males were always dominant over the other morphs. Females, however, preferred scents of bigger males that were in better body condition, and surprisingly had lower bite force capacities. They did not show a preference for scents of any particular color morph or for scents of the more dominant males. These results indicate that intra- and intersexual competition may result in selection for different secondary sexual traits in P. melisellensis.     

Colour Polymorphism and Alternative Breeding Strategies: Effects of Parent’s Colour Morph on Fitness Traits in the Common Wall Lizard

Colour polymorphism (CP) is widespread in animals, but mechanisms underlying morph evolution and maintenance are not completely resolved. In reptiles, CP is often genetically based and associated with alternative behavioural strategies, mainly in males for most cases. However, female colour morphs also display alternative reproductive strategies associated with behavioural and physiological traits, which may contribute to maintain CP in the population. Both sexes of the common wall lizard (Podarcis muralis) show three pure colour morphs, white, yellow and red. Here, we looked for the effects of male and female colour morphs on fitness traits of captive-breeding pairs. All yellow-throated females laid clutches of many small eggs and produced many light offspring, behaving as r-strategists, whereas white-throated females laid clutches of few large eggs and produced few heavy offspring, behaving as K-strategists. Red-throated females adopted a conditional Kr-strategy depending on their size/age. These basic female strategies were modulated in relation to mate morph: white females had the best fitness gain in terms of viable offspring when mated to red males; mating between yellow morphs yielded a greater breeding success than all other morph crosses, but also lighter offspring; finally, red females produced heavy progeny when paired with red or white males, and light offspring in pair with yellow males. Thus, correlation between CP and traits relevant to fitness combined with non-random mating, either assortative or disassortative, could increase the potential for CP to contribute to divergent evolution in the common wall lizard.     

Mate Preference for Novel Phenotypes: A Fresh Face Matters

Conspicuous polymorphism in sexually selected traits is usually attributed to processes such as frequency‐dependent selection that can maintain genetic variation. Recent evidence indicates that dramatic variation of male coloration in guppies (Poecilia reticulata) is promoted by a form of frequency‐dependent selection in which males bearing rare or novel color patterns achieve higher mating success than males bearing common patterns. Active female preference for unfamiliar or rare color patterns has been implicated in generating this rare‐phenotype advantage, but the behavioral processes responsible for the preference remain unclear. To determine whether familiarity that is developed over a very short timescale can lead to a rare‐male mating advantage, we measured female response to courtship by males with color patterns that were the same as or different from that of the previous male to court. Females showed two types of short‐term preference variation in this experiment. On the first trial day, females shifted their preferences on a timescale of minutes, showing strong preference for males bearing a color pattern different from that of the immediately previous male to court. Twenty‐four hours later, females were less responsive to male courtship overall, and there was no difference in females’ response to different‐ and same‐morph males. Females also preferred males with more orange coloration on both trial days, but this color preference was independent of the preference for ‘different’ color patterns. These data suggest that the behavioral process underlying rare‐male advantage in guppies is that females prefer males bearing unfamiliar color patterns and that familiarity is determined over a very short timescale.     

Variation between and within the sexes in body size preferences

Although it is often assumed that males and females have mating preferences for larger individuals of the other sex, potential underlying differences between male and female preferences for body size are not commonly investigated. Here, sexual differences in body size preferences are examined in the poeciliid fish, Brachyrhaphis rhabdophora. Females preferred larger males to smaller males, but preference did not appear to be affected by female size. One population-level analysis for males did not indicate an overall preference for larger females. A closer examination, however, revealed an effect of male size on preference; larger males preferred larger females, while smaller males preferred smaller females. It appears then that females, regardless of size, share a preference for large males, but males differ in their behaviour, depending on their body size. In addition, while the degree of difference in size between paired females did not appear to affect male preference, the degree of difference in size between paired males strongly affected female preference; the greater the difference, the more strongly females preferred the larger male. Thus, intersexual selection is found to operate in both sexes, but how it operates appears to differ. Intrasexual and intersexual differences in mating behaviour may be missed when evaluating population-wide preferences. That is, there can be underlying differences in how the sexes respond and the consequences of such differences should be considered when investigating mate choice. The results are considered in terms of the evolution of mating preferences, alternative mating strategies, assortative mating, the maintenance of trait variation in a population, and current methods to evaluate mating preferences.     

Do Displays Send Information about Ornament Structure and Male Quality in the Ornate Tree Lizard,Urosaurus ornatus?

Displays can transmit information about ornament or male quality; however, few studies have simultaneously explored the relationship between displays, ornament and male quality within a single species. We quantified ornament morphology (five throat color morphs, throat area, and belly area), male quality (bite force, sprint speed, body condition, and body mass), display behavior [percent time displaying (PTD), number of pushups per display, and display duration], and movement behavior among males in a population of the ornate tree lizard, Urosaurus ornatus. Previous studies have shown that male U. ornatus are polymorphic in throat coloration and that morphs differ in behavioral aggression. Our study shows that blue throat morphs use 1.5 more pushups per display than other male color morphs, which suggests that throat color and display behavior act as backup signals for aggression. However, other data support the multiple messages hypothesis, and overall our data do not provide conclusive evidence for any one hypothesis. In addition, we show that body mass is positively related to both PTD and percent time moving and this relationship is independent of color morph. We also found that throat area, belly area, bite force, sprint speed, and body condition are unrelated to display behavior. This result highlights at least some discordance between display behavior, ornaments, and performance in U. ornatus and suggests that these traits may be evolving independently.     

Mating system in a population of the wasp <Emphasis Type="Italic">Polistes dominulus</Emphasis> (Christ) (Hymenoptera,Vespidae)

The specific features of mating females and males of different morphs collected from a population of the wasp P. dominulus in Southern Ukraine were studied. Data analysis of mating individuals in experiments indicated a random mate choice by size and assortative mating by coloration. The most actively copulating males in the experiments had light-colored mesopleuron, sternite, and fore and middle coxae. They were similar in the color pattern and size to resident males, which defend their territories in the habitat. Most P. dominulus females mated only once. In their coloration, those females represented the majority of the individuals in the population. The color variability of the foundresses was shown to change in a cyclic pattern. The possibility that such variability may result from selective or assortative mating is discussed. The color and pattern traits of P. dominulus females and males could serve as markers of their reproductive strategies and their reproductive success on the whole.     

Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated males assiduously mate guard females on their territory. Yellow-throated males do not defend a territory, but patrol a large home range. They obtain secretive copulations from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, activity, and home range size and concomitantly gained greater control over female home ranges than blue- or yellow-throated males. Experimentally elevating plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels that were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is not without costs. Orange-throated males had low survival compared to the other morphs. Finally, some yellow-throated males transformed to a partial blue morphology late in the season and the endurance of these transforming yellow-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly higher plasma T late in the season compared to the plasma T earlier in the season. T appears to play an important role in the physiological changes that all three color morphs undergo during the process of maturation. In some yellow males, T plays an additional role in plastic changes in behavior and physiology late in the reproductive season. We discuss natural and sexual selection on physiological and behavioral traits that leads to the evolution of steroid regulation in the context of alternative male strategies.     

Asymmetric dominance and asymmetric mate choice oppose premating isolation after allopatric divergence

Assortative mating promotes reproductive isolation and allows allopatric speciation processes to continue in secondary contact. As mating patterns are determined by mate preferences and intrasexual competition, we investigated male–male competition and behavioral isolation in simulated secondary contact among allopatric populations. Three allopatric color morphs of the cichlid fish Tropheus were tested against each other. Dyadic male–male contests revealed dominance of red males over bluish and yellow‐blotch males. Reproductive isolation in the presence of male–male competition was assessed from genetic parentage in experimental ponds and was highly asymmetric among pairs of color morphs. Red females mated only with red males, whereas the other females performed variable degrees of heteromorphic mating. Discrepancies between mating patterns in ponds and female preferences in a competition‐free, two‐way choice paradigm suggested that the dominance of red males interfered with positive assortative mating of females of the subordinate morphs and provoked asymmetric hybridization. Between the nonred morphs, a significant excess of negative assortative mating by yellow‐blotch females with bluish males did not coincide with asymmetric dominance among males. Hence, both negative assortative mating preferences and interference of male–male competition with positive assortative preferences forestall premating isolation, the latter especially in environments unsupportive of competition‐driven spatial segregation.     

Female Preference for Sympatric vs. Allopatric Male Throat Color Morphs in the Mesquite Lizard (Sceloporus grammicus) Species Complex

Color polymorphic sexual signals are often associated with alternative reproductive behaviors within populations, and the number, frequency, or type of morphs present often vary among populations. When these differences lead to assortative mating by population, the study of such polymorphic taxa may shed light on speciation mechanisms. We studied two populations of a lizard with polymorphic throat color, an important sexual signal. Males in one population exhibit orange, yellow, or blue throats; whereas males in the other exhibit orange, yellow, or white throats. We assessed female behavior when choosing between allopatric and sympatric males. We asked whether females discriminated more when the allopatric male was of an unfamiliar morph than when the allopatric male was similar in coloration to the sympatric male. We found that female rejection of allopatric males relative to sympatric males was more pronounced when males in a pair were more different in throat color. Our findings may help illuminate how behavioral responses to color morph differences between populations with polymorphic sexual signals contribute to reproductive isolation.