Malarial parasitism and male competition for mates in the western fence lizard,Sceloporus occidentalis

Summary The effect of malarial parasitism on the ability of male western fence lizards, Sceloporus occidentalis, to compete for access to females was assessed experimentally. Pairs of male lizards, one infected with the malarial parasite, Plasmodium mexicanum, and the other not infected, were matched by size and color and placed in large seminatural outdoor enclosures along with an adult female lizard. Infected males displayed to females and to other males less often than did noninfected male lizards. Noninfected lizards were dominant in social interactions more often than malarious animals, based on duration and intensity of agonistic encounters toward the other male, and time spent with the female. Thus, malarial infection hinders the ability of male fence lizards to compete for mates.     

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.     

A further cost for the sicker sex? Evidence for male‐biased parasite‐induced vulnerability to predation

Males are typically the sicker sex. Data from multiple taxa indicate that they are more likely to be infected with parasites, and are less “tolerant,” or less able to mitigate the fitness costs of a given infection, than females. One cost of infection for many animals is an increased probability of being captured by a predator. A clear, hitherto untested, prediction is therefore that this parasite‐induced vulnerability to predation is more pronounced among males than females. We tested this prediction in the sexually size dimorphic guppy, Poecilia reticulata, in which females are typically larger than males. We either sham or experimentally infected guppies with Gyrodactylus turnbulli, elicited their escape response using an established protocol and measured the distance they covered during 60 ms. To discriminate between the effects of body size and those of other inherent sex differences, we size‐matched fish across treatment groups. Infection with G. turnbulli reduced the distance covered during the escape response of small adults by 20.1%, whereas that of large fish was unaffected. This result implies that parasite‐induced vulnerability to predation is male‐biased in the wild: although there was no difference in escape response between our experimentally size‐matched groups of males and females, males are significantly smaller across natural guppy populations. These results are consistent with Bateman's principle for immunity: Natural selection for larger body sizes and longevity in females seems to have resulted in the evolution of increased infection tolerance. We discuss the potential implications of sex‐ and size‐biased parasite‐induced vulnerability to predation for the evolutionary ecology of this host–parasite interaction in natural communities.     

Effect of parasitic infection on male color pattern and female choice in guppies

We infected male guppies Poecilia reticulata with a naturallyoccurring monogenean parasite, Gyrodactylus turnbulli, in orderto examine effects of parasitism on the expression of colorpatterns and on attractiveness to females. The color of carotenoidspots and ability to attract females were compared between experimentallyinfected fish and a control group of their fullsib brothers,which had identical color patterns and were treated identicallyexcept for actual exposure to parasites. The orange spots ofmales that had been infected for 9 days followed by treatmentwith medication to remove parasites became significandy palerand less saturated. Control males (also treated widi medication)showed no significant changes in their orange spots. Femalesin a divided aquarium choice-apparatus showed no preferencebetween control and infection-treatment males initially, butshowed significant discrimination after the infectiondisinfectiontreatment. Females spent less time near males that had beeninfected and responded to a smaller fraction of their courtshipdisplays relative to control males. There were slight differencesin courting rates of males between treatments. Parasitic infectionappears to reduce the degree of expression of carotenoid colorsin guppies, and females are able to discriminate against recentlyinfected males, probably on the basis of the color change. Byavoiding infected males, females may be able to avoid becominginfected themselves, or they may be able to identify mates basedon "good genes" for parasite resistance diat can be passed onto their offspring.     

Sexual selection versus alternative causes of sexual dimorphism in teiid lizards

Summary The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.     

Mite load predicts the quality of sexual color and locomotor performance in a sexually dichromatic lizard

Since Darwin, the maintenance of bright sexual colors has recurrently been linked to mate preference. However, the mechanisms underpinning such preferences for bright colors would not be resolved for another century. Likely, the idea of selection for colors that could decrease the chances of survival (e.g., flashy colors that can inadvertently attract predators) was perceived as counterintuitive. It is now widely accepted that these extreme colors often communicate to mates the ability to survive despite a “handicap” and act as honest signals of individual quality when they are correlated with the quality of other traits that are directly linked to individual fitness. Sexual colors in males are frequently perceived as indicators of infection resistance, in particular. Still, there remains considerable discord among studies attempting to parse the relationships between the variables associating sexual color and infection resistance, such as habitat type and body size. This discord may arise from complex interactions between these variables. Here, we ask if sexual color in male Florida scrub lizards (Sceloporus woodi) is an honest signal of resistance to chigger mite infection. To this end, we use linear modeling to explore relationships between mite load, different components of sexual color, ecological performance, body size, and habitat type. Our data show that that the brightness of sexual color in scrub lizards is negatively associated with the interaction between mite load and body size, and scrub lizards suffer decreased endurance capacity with increases in mite load. Our data also indicate that mite load, performance, and sexual color in male scrub lizards can vary between habitat types. Collectively, these results suggest that sexual color in scrub lizards is an honest indicator of individual quality and further underscore the importance of considering multiple factors when testing hypotheses related to the maintenance of sexual color.     

Parasites, male-male competition and female mate choice in the sand goby

Male sand goby Pomatoschistus minutus dominance in competition over nest sites was associated with higher body condition but not with the intensity of infection with any individual parasite of six different species, nor with an overall index combining relative levels of infection by all parasites. Body condition was not related to the intensity of infection with any individual parasite nor with the index of total relative parasite load. In trials in which females spawned, they showed a tendency to choose dominant over subordinate males as mates, but did not consistently choose less parasitized males. Variation in the relative size of the dorsal fins of males was detected, and this related to numbers of the ectoparasitic monogenean Gyrodactylus sp., suggesting that at least some infections have phenotypic effects that could allow females to detect and avoid the most heavily infected males.     

Growth and survivorship as proximate causes of sexual size dimorphism in peninsula dragon lizards Ctenophorus fionni

Males and females differ in body size in many animals, but the direction and extent of this sexual size dimorphism (SSD) varies widely. Males are larger than females in most lizards of the iguanian clade, which includes dragon lizards (Agamidae). I tested whether the male larger pattern of SSD in the peninsula dragon lizard, Ctenophorus fionni, is a result of sexual selection for large male size or relatively higher mortality among females. Data on growth and survivorship were collected from wild lizards during 1991–1994. The likelihood of differential predation between males and females was assessed by exposing pairs of male and female lizards to a predator in captivity, and by comparing the frequency of tail damage in wild‐caught males and females. Male and female C. fionni grew at the same rate, but males grew for longer than females and reached a larger asymptotic size (87 mm vs. 78 mm). Large males were under‐represented in the population because they suffered higher mortality than females. Predation may account for some of this male‐biased mortality. The male‐biased SSD in C. fionni resulted from differences in growth pattern between the sexes. The male‐biased SSD was not the result of proximate factors reducing female body size. Indeed SSD in this species remained male‐biased despite high mortality among large males. SSD in C. fionni is consistent with the ultimate explanation of sexual selection for large body size in males.     

The interplay between natural and sexual selection in the evolution of sexual size dimorphism in Sceloporus lizards (Squamata: Phrynosomatidae)

Sexual size dimorphism (SSD) evolves because body size is usually related to reproductive success through different pathways in females and males. Female body size is strongly correlated with fecundity, while in males, body size is correlated with mating success. In many lizard species, males are larger than females, whereas in others, females are the larger sex, suggesting that selection on fecundity has been stronger than sexual selection on males. As placental development or egg retention requires more space within the abdominal cavity, it has been suggested that females of viviparous lizards have larger abdomens or body size than their oviparous relatives. Thus, it would be expected that females of viviparous species attain larger sizes than their oviparous relatives, generating more biased patterns of SSD. We test these predictions using lizards of the genus Sceloporus. After controlling for phylogenetic effects, our results confirm a strong relationship between female body size and fecundity, suggesting that selection for higher fecundity has had a main role in the evolution of female body size. However, oviparous and viviparous females exhibit similar sizes and allometric relationships. Even though there is a strong effect of body size on female fecundity, once phylogenetic effects are considered, we find that the slope of male on female body size is significantly larger than one, providing evidence of greater evolutionary divergence of male body size. These results suggest that the relative impact of sexual selection acting on males has been stronger than fecundity selection acting on females within Sceloporus lizards.     

Male morphological characteristics and mating success in a protogynous coral reef fish, Halichoeres melanurus

Morphological sexual differences and their effects on male mating success were investigated in the tailspot wrasse, Halichoeres melanurus, on a subtropical coral reef of Okinawa, southern Japan. Male mating territories were established along the reef edge from late April to early October, during which time pair-spawning occurred just before sunset in the male territories. Territorial males were larger and brighter than females in this protogynous fish. The males had longer, colorful ventral fins and colorful caudal fins, both of which were used during courtship. Multiple regression analysis of the effects of male characteristics on male mating success revealed that the yellow spot at the pectoral fin base was the most effective. It is suggested that large body size is favored in male–male competition for establishing mating territories and that conspicuous body color is favored in female mate choice. Received: June 16, 1999 / Accepted: September 22, 1999     

Sizing‐up the Competition: Factors Modulating Male Display Behavior During Mate Competition

When competing for mates, males of many species use cues from their rivals to evaluate their chances of success. Signaling behavior is a vital component of male–male contests and courtship, and may inform males of a rival's quality or intentions. We used eastern fence lizards (Sceloporus undulatus) to investigate how the time a male spent signaling during mate competition is influenced by his quality, his rival's quality relative to his own, and the value of a contested female. Furthermore, we examined how a male's behavioral response to a competitor's signals would be mediated by his relative quality. We simulated natural encounters by allowing two males to compete over a single female in the laboratory. We measured the time males spent performing two types of displays (pushups and shudders) and categorized male behavioral responses to rival pushup and shudder displays. Time spent signaling was not related to a male's absolute quality (body and head size, condition, and badge sizes), or his quality relative to that of his rival, although males did spend more time performing pushups when competing over females in better condition. Male behavior was also influenced by his rival's signals, such that males of relatively lower quality than their opponents were more likely to aggressively respond to rival pushups and shudders. We discuss these results with respect to the evolution and function of signaling behavior in courtship and male–male contests.     

Observations of the mating behavior and dentition of the round stingray,Urolophus halleri

Synopsis The mating behavior and dentition ofUrolophus halleri, the round stingray was examined. Males frequently bite females during the mating period but most male biting does not result in copulation. In bites that do not lead to copulation, males bite the posterior (or occasionally the medial) portion of the females' disc but females often free themselves from these bites. In bites that precede copulation, males bite the anterior portion of the females' disc and females do not struggle to free themselves. Thus, females may exert some form of choice when they are bitten. Mature males have sexually dimorphic dentition that may aid in holding females. A principal component analysis (PCA) showed that in juvenile males, the relative size of the teeth decrease while the relative thickness of the disc increases as body size enlarges; adult males displayed no clear pattern. In adult females, there is a relative decrease in tooth size and increase in relative disc thickness as body size enlarges. The relative increase in females disc thickness in areas where they are bitten may function to minimize the amount of damage due to non-copulatory biting. There is no indication that biting functions to induce female receptivity but it may allow females and males to acquire information about potential mates. Thus, copulatory biting functions to maintain contact during copulation while the function of non-copulatory biting is less clear.     

Nonvisual mate choice in the Pyrenean mountain newt (<Emphasis Type="Italic">Euproctus asper</Emphasis>): females prefer small males

In many species, females prefer large males as mates. In this paper, we examined whether female Pyrenean mountain newts (Euproctus asper) would show a preference for large males in a simultaneous choice situation. When we tested for a visual preference relative to male body size using visual cues, females did not prefer large males. When chemical cues were presented, females did show a preference, but contrary to our prediction, they preferred the smaller of two males. E. asper males exhibit coercive mating behavior (amplexus), keeping females from feeding for several hours or even days, which may explain why females avoid large, physically stronger, and thus, more coercive males. The predominantly nocturnal lifestyle may explain why visual cues are less important for mate discrimination in this species.     

Preference for Male Traits Differ in Two Female Morphs of the Tree Lizard,Urosaurus ornatus

Non-random female mating preferences may contribute to the maintenance of phenotypic variation in color polymorphic species. However, the effect of female preference depends on the types of male traits used as signals by receptive females. If preference signals derive from discrete male traits (i.e., morph-specific), female preferences may rapidly fix to a morph. However, female preference signals may also include condition-dependent male traits. In this scenario, female preference may differ depending on the social context (i.e., male morph availability). Male tree lizards (Urosaurus ornatus) exhibit a dewlap color polymorphism that covaries with mating behavior. Blue morph males are aggressive and defend territories, yellow males are less aggressive and defend smaller territories, and orange males are typically nomadic. Female U. ornatus are also polymorphic in dewlap color, but the covariation between dewlap color and female behavior is unknown. We performed an experiment to determine how female mate choice depends on the visual and chemical signals produced by males. We also tested whether female morphs differ in their preferences for these signals. Female preferences involved both male dewlap color and size of the ventral color patch. However, the female morphs responded to these signals differently and depended on the choice between the types of male morphs. Our experiment revealed that females may be capable of distinguishing among the male morphs using chemical signals alone. Yellow females exhibit preferences based on both chemical and visual signals, which may be a strategy to avoid ultra-dominant males. In contrast, orange females may prefer dominant males. We conclude that female U. ornatus morphs differ in mating behavior. Our findings also provide evidence for a chemical polymorphism among male lizards in femoral pore secretions.     

Sex‐dependent infection causes nonadditive effects on kissing bug fecundity

The influence of parasites on host reproduction has been widely studied in natural and experimental conditions. Most studies, however, have evaluated the parasite impact on female hosts only, neglecting the contribution of males for host reproduction. This omission is unfortunate as sex‐dependent infection may have important implications for host–parasite associations. Here, we evaluate for the first time the independent and nonindependent effects of gender infection on host reproductive success using the kissing bug Mepraia spinolai and the protozoan Trypanosoma cruzi as model system. We set up four crossing treatments including the following: (1) both genders infected, (2) both genders uninfected, (3) males infected—females uninfected, and (4) males uninfected—females infected, using fecundity measures as response variables. Interactive effects of infection between sexes were prevalent. Uninfected females produced more and heavier eggs when crossed with uninfected than infected males. Uninfected males, in turn, sired more eggs and nymphs when crossed with uninfected than infected females. Unexpectedly, infected males sired more nymphs when crossed with infected than uninfected females. These results can be explained by the effect of parasitism on host body size. As infection reduced size in both genders, infection on one sex only creates body size mismatches and mating constraints that are not present in pairs with the same infection status. Our results indicate the fitness impact of parasitism was contingent on the infection status of genders and mediated by body size. As the fecundity impact of parasitism cannot be estimated independently for each gender, inferences based only on female host infection run the risk of providing biased estimates of parasite‐mediated impact on host reproduction.     

Pectoral fin size in a fish species with paternal care: a condition-dependent sexual trait revealing infection status

1. The three-spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition-dependency of relative pectoral fin size in males and the relationship with male parasite load. 2. Reproductively active males possessed relatively larger pectoral fins than females in both wild-caught and laboratory-bred fish. 3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs. 4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.     

Gametocyte sex ratio of a malaria parasite: experimental test of heritability

The gametocyte sex ratio of Plasmodium mexicanum, a malaria parasite of western fence lizards, was studied in a modified garden experiment. Each of 6 naturally infected lizards was used to initiate 20 replicate-infections in naive western fence lizards. A significant donor effect was observed for the sex ratios of recipient infections at their maximal parasitemia, and this effect was associated with the sex ratio of the donor infection. In 20 infections in which sex ratio was followed during the course of the infection, 9 revealed constant sex ratios and 11 showed an increase in proportion of males over time. Recipient sex ratio was correlated with another life-history trait, a composite of rate of asexual replication and peak parasitemia, such that higher Rate-Peak scores were associated with infections with less female-biased sex ratios. These results are placed into the context of sex ratio theory that concludes that the degree of selfing of parasite genotypes (number of parasite clones) within the vector will influence the evolution of gametocyte sex ratio. The theory predicts that the sex ratio should be under some genetic control and thus be heritable as observed in the experiment. Clonal diversity should also influence the life-history trait, Rate-Peak, which was found to be correlated with sex ratio.     

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.     

Sex differences in immune defenses and response to parasitism in monarch butterflies

Host susceptibility and patterns of infection are predicted to differ between males and females due to sex-based tradeoffs between the demands of reproduction and costly immune defenses. In this study, we examined immune defenses and the response to experimental infection by a protozoan parasite, Ophryocystis elektroscirrha, in male and female monarch butterflies, Danaus plexippus. We quantified two measures of immunity in late instar larvae: the concentration of circulating hemocytes and mid-gut phenoloxidase activity, and also quantified final parasite loads, body size, longevity, and wing melanism of adult butterflies. Results showed that females had greater average hemocyte counts than males in the absence of infection; males, but not females, showed an increased concentration of hemocytes in the presence of infection. However, higher hemocyte concentrations in larvae were not significantly correlated with lower adult parasite loads, and mid-gut phenoloxidase activity was not significantly associated with hemocyte counts or parasite treatments. Among unparasitized females, greater hemocyte concentrations were costly in terms of reduced body size, but for parasite-treated females, hemocyte concentrations and body size were positively associated. Across all monarchs, unparasitized butterflies showed greater wing melanism (darker forewings) than parasitized monarchs. Overall, this study provides support for differential costs of immune defenses in male and female monarch butterflies, and a negative association between parasite infection and monarch wing melanism.     

Chemoreception, symmetry and mate choice in lizards

Research on fluctuating asymmetry (FA)-mediated sexual selection has focused almost exclusively on visual signals and ignored chemical communication despite the fact that many species rely on chemical signals for attracting mates. Female mate choice based on visual traits appears to be rare in lizards. However, the femoral glands of male lizards produce pheromones which might transmit chemical information about an individual's developmental stability. Therefore, we hypothesized that mate choice may be based on chemical cues. We analysed the effect of the developmental stability levels of males on the attractiveness of males' scents to females in a laboratory experiment with the lizard Lacerta monticola. When we offered two males of similar body size, females preferentially associated with the scents of males with low FA in their femoral pores and also with the scents of males with a higher number of femoral pores. This suggested that the females were able to discriminate the FA of the males by chemical signals alone and that the females preferred to be in areas marked by males of high quality, thus increasing their opportunities of mating with males of high quality. We suggest that the quality and/or amount of male pheromones could communicate the heritable genetic quality of a male to the female and thereby serve as the basis for adaptive female choice in lizards.