Color change as a potential behavioral strategy

Within species, color morphs may enhance camouflage, improve communication and/or confer reproductive advantage. However, in the male cichlid Astatotilapia burtoni, body color may also signal a behavioral strategy. A. burtoni live in a lek-like social system in Lake Tanganyika, Africa where bright blue or yellow territorial (T) males (together ~ 10–30% of the population) are reproductively capable and defend territories containing food with a spawning site. In contrast, non-territorial (NT) males are smaller, cryptically colored, shoal with females and have regressed gonads. Importantly, males switch between these social states depending on their success in aggressive encounters. Yellow and blue morphs were thought to be adaptations to particular habitats, but they co-exist both in nature and in the laboratory. Importantly, individual males can switch colors so we asked whether color influences behavioral and hormonal profiles. When pairing territorial males with opposite colored fish, yellow males became dominant over blue males significantly more frequently. Moreover, yellow T males had significantly higher levels of 11-ketotosterone than blue T males while only blue NT males had higher levels of the stress hormone cortisol compared to the other groups. Thus color differences alone predict dominance status and hormone profiles in T males. Since T males can and do change color, this suggests that A. burtoni may use color as a flexible behavioral strategy.     

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.     

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.     

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.     

Prey availability affects territory size,but not territorial display behavior,in green anole lizards

The availability of food resources can affect the size and shape of territories, as well as the behaviors used to defend territories, in a variety of animal taxa. However, individuals within a population may respond differently to variation in food availability if the benefits of territoriality vary among those individuals. For example, benefits to territoriality may differ for animals of differing sizes, because larger individuals may require greater territory size to acquire required resources, or territorial behavior may differ between the sexes if males and females defend different resources in their territories. In this study, we tested whether arthropod abundance and biomass were associated with natural variation in territory size and defense in insectivorous green anole lizards, Anolis carolinensis. Our results showed that both male and female lizards had smaller territories in a habitat with greater prey biomass than lizards in habitats with less available prey, but the rates of aggressive behaviors used to defend territories did not differ among these habitats. Further, we did not find a relationship between body size and territory size, and the sexes did not differ in their relationships between food availability and territory size or behavioral defense. Together, these results suggest that differences in food availability influenced male and female territorial strategies similarly, and that territory size may be more strongly associated with variation in food resources than social display behavior. Thus, anole investment in the behavioral defense of a territory may not vary with territory quality.     

FREQUENCY‐DEPENDENT SOCIAL DOMINANCE IN A COLOR POLYMORPHIC CICHLID FISH

A mechanism commonly suggested to explain the persistence of color polymorphisms in animals is negative frequency‐dependent selection. It could result from a social dominance advantage to rare morphs. We tested for this in males of red and blue color morphs of the Lake Victoria cichlid, Pundamilia. Earlier work has shown that males preferentially attack the males of their own morph, while red males are more likely to win dyadic contests with blue males. In order to study the potential contribution of both factors to the morph co‐existence, we manipulated the proportion of red and blue males in experimental assemblages and studied its effect on social dominance. We then tried to disentangle the effects of the own‐morph attack bias and social dominance of red using simulations. In the experiment, we found that red males were indeed socially dominant to the blue ones, but only when rare. However, blue males were not socially dominant when rare. The simulation results suggest that an own‐morph attack bias reduces the social dominance of red males when they are more abundant. Thus, there is no evidence of symmetric negative frequency‐dependent selection acting on social dominance, suggesting that additional fitness costs to the red morph must explain their co‐existence.     

The Haremic Mating System and Mate Choice in the Wide-Eyed Flounder, Bothus podas

The social structure and reproductive behaviour of the wide-eyed flounder, Bothus podas, was studied in the coastal waters around the Azorean Islands. Both sexes are territorial throughout the year. Adult males defend large territories, which include several smaller female territories. Intraspecific agonistic behaviour was frequent and differed between sexes: males were more aggressive towards other males, while females were only aggressive towards each other and juveniles. During the reproductive season and only at dawn, territorial males court and mate successively with females in their territories, and females seem to show mating fidelity to their dominant male. Such territoriality and mating patterns indicate a haremic social system in the wide-eyed flounder. In order to identify potential factors influencing female mate choice acting on this haremic system, we examined male mating success and some of its potential correlates. We found no evidence for female preference for any of the males' physical or territory characteristics. However, courtship effort was strongly correlated with the total number of attempted and successful spawnings, indicating that females seem to mate preferentially with males that court them more vigorously. Thus, our data suggest that courtship plays an important role in determining male mating success in the wide-eyed flounder and, that it may possibly serve as an honest indicator of male `quality' for female choice.     

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.     

The Role of Learning in the Aggressive and Reproductive Behavior of Blue Gouramis, Trichogaster trichopterus

Like countless other vertebrates and even many invertebrates, blue gouramis, Trichogaster trichopterus, a freshwater tropical fish, can learn to associate environmental cues with the appearance of biologically important events. Research with blue gouramis reveals that this capacity for learning, which psychologists call Pavlovian conditioning, provides the means to enhance their territorial defense as well as reap large reproductive benefits. That is, males are able to defend their territories more efficiently when the appearance of a rival is signaled than when territorial invasion is less predictable. Not only does signaling enable Pavlovian-conditioned males to mount a more aggressive defense of their territories than males that do not have the benefit of signaling, but it helps them to concentrate their efforts at times when, or places where, the territory is most vulnerable. In addition, both males and females can learn to anticipate the appearance of a mate. Signaling of female accessibility enables Pavlovian-conditioned males to attenuate their initial aggressive response to arriving females without compromising their territorial defense. More important, when the arrival of a potential mate is signaled, Pavlovian-conditioned males are able to spawn with females sooner, clasp females more often, and produce more young than males that do not have the benefit of a signal. The ability of blue gouramis, among many other fish, to anticipate the appearance of such different biologically important events suggests that Pavlovian conditioning may play a significant role in their behavioral ecology. In addition, conditioning may provide a useful tool in several practical domains, including animal husbandry, zoological management, and conservation biology.     

Dominance hierarchies in male lizards: Implications for zoo management programs

Depending on spatial requirements and the distribution of key resources in the environment, social behavior among lizards varies from defense of exclusive territories to the establishment of dominance hierarchies. In captivity or under conditions where dispersal is not possible, dominance hierarchies often emerge in species that are otherwise territorial. This review explores some of the morphological, behavioral, and hormonal determinants of social status in male lizards and how these may lead to differential reproductive function in dominant and subordinate individuals. Emphasis is placed on the importance of population density, local resource dispersion, and the composition and stability of social groups in promoting hierarchical behavior. Results of these studies have ramifications for several aspects of zoo management, including exhibit design, choice of animals to be housed together, provision of resources in space and time, and orientation of enclosures within captive breeding facilities. © 1994 Wiley-Liss, Inc.     

Territory acquisition in a polymorphic lizard: An experimental approach

Males of the colour polymorphic Australian painted dragon lizard Ctenophorus pictus occur in red or yellow head colouration. In a previous experiment, we showed that red is associated with a higher probability of winning staged contests for resources (females or space) and that manipulation of male colouration by painting males in the opposing morph changed the dynamics of staged interactions by prolonging them 30‐fold. Thus, colour is linked to behavioural differences between males and is involved in information transfer between competing males. This inherent red dominance could result in yellow males being marginalized to poorer quality territories in terms of access to females, food, perch sites or shade. With an experiment in the wild, we test to what extent this prediction is upheld, and how colour manipulation affects morph‐specific success in territory acquisition when male body size, territory quality and emergence time from hibernation are controlled through manipulation or randomization. There was no significant effect of colour category per se, although on average red males remained closer to the release sites (our proxy for territory acquisition ability) than yellow males and artificially altered morphs moved the furthest away. There was a significant interaction effect between colour category and experimental release position, which may be linked to differences in how exposed (or not) these positions were and morph‐specific ability to cope with such exposure (e.g. ‘boldness’). Our data show that territory acquisition success is not merely a function of competitive ability but a composite outcome of a suite of factors, including signal perception.     

Androgen control of social status in males of a wild population of stoplight parrotfish, Sparisoma viride (Scaridae)

In the protogynous stoplight parrotfish (Sparisoma viride), large males defend territories that encompass the home-ranges of several mature females. However, high-quality habitat is in short supply, such that smaller, competitively inferior males do not defend territories. We investigated the role of 11-ketotestosterone (11KT) and testosterone (T) in the regulation of territorial behavior in a wild population of a protogynous reef fish, the stoplight parrotfish, at Glover's Reef, Belize. Radioimmunoassay of plasma samples from individuals of known social status revealed that nonterritorial males have lower levels of T and 11KT than territorial males. Nonterritorial males allowed access to vacant territories underwent pronounced increases in T and 11KT. When sampled 1 week after territory acquisition, levels of T and 11KT in new territorial males were significantly higher than the levels in established territorial males, but by 3 weeks after territory acquisition, there was no significant difference. We further investigated the hypothesis that such short-term increases in androgen levels are a response to intense male-male interactions during territory establishment. Simulated territorial intrusion promoted increased plasma levels of both T and 11KT while access to vacant territories without neighboring territorial males did not. These findings suggest that the endocrine system plays a role in fine-tuning the levels of territorial aggression exhibited by male stoplight parrotfish. We discuss these results in light of recent theory in behavioral endocrinology.     

Territorial male color predicts agonistic behavior of conspecifics in a color polymorphic species

Male cichlid fish, Astatotilapia burtoni, live in a lek-likesocial system in shore pools of Lake Tanganyika, Africa, asone of two distinct social phenotypes: territorial (T) malesthat comprise approximately 10–30% of the population andnonterritorial (NT) males that make up the rest. T males arebrightly colored either blue or yellow with chromatic body patternsand are larger, reproductively capable, and defend territoriescontaining a food resource used to entice females to spawn withthem. NT males are camouflage colored, smaller, have regressedgonads, and shoal with females. Importantly, males shift betweenthese social states depending on their success in aggressiveencounters. It is not known whether there is a difference betweenyellow and blue T morphs. Here we asked whether T males preferentiallydefend their territory against a male of the same or oppositecolor. T males observed in social groups had agonistic interactionspredominantly with neighboring T males of the opposite color,and yellow morphs initiated significantly more aggressive interactions.When agonistic preference was tested experimentally, T maleshad significantly more agonistic interactions toward males ofthe opposite color, and yellow T males became territorial inthe majority of those interactions. Taken together, these resultssuggest that male coloration is an important social signal amongneighboring T males in this species and support the hypothesisthat T males differentially direct agonistic behavior dependingon the color of neighboring males.     

Carotenoid status signaling in captive and wild red-collared widowbirds: independent effects of badge size and color

Carotenoid-based plumage ornaments are typically consideredto be sexually selected traits, functioning as honest condition-dependentsignals of phenotypic quality, but few studies have addressedthe function of carotenoid color variation in male contestcompetition. Using two experiments, we investigated the statussignaling function of the variable (ranging from yellow tored) carotenoid throat patch (collar) in the polygynous, sexually dimorphic red-collared widowbird (Euplectes ardens). First,we tested if the red collar functions as a dominance signalby painting spectrometrically controlled collar patches ontothe brown plumage of nonbreeding males and staging dyadic malecontests over food resources. Red-collared males dominatedorange males, which in turn dominated the control brown andnovel blue collars. Red dominance persisted when the collar manipulations were reversed within dyads and also when testedagainst testosterone implanted males. In the second experimentthe collar size and color of breeding males were manipulatedin the field before and after territories were established.All males with enlarged red and most with enlarged orange orreduced red collars obtained territories, whereas most maleswith reduced orange and all with blackened (removed) collarsfailed to establish or retain territories. In addition, amongthe territorial males, those with reduced signals defendedsmaller territories, received more intrusions, and spent moretime in aggressive interactions. Redness and, to a lesser extent,size of the carotenoid ornament both seem to independently indicate male dominance status or fighting ability in male contest competition.     

Population density,resource patterning,and territoriality in the Everglades pygmy sunfish

The means by which pygmy sunfish compete for food are influenced by the density of the population and the dispersion of the prey as well as by the sex and dominance status of the individual. At all densities when the prey were predictably located in a central clump, males established territories. When prey were dispersed randomly in both the high and low density population, males abandoned territorial behaviour and, like females, swam freely about the aquaria. Only in the intermediate density populations did the males maintain territories and continue to defend resources. Development of a simple cost-benefit model shows that male territorial behaviour is governed to a large extent by economic considerations. Despite these overall patterns, differences in competitive strategies were observed within populations. Dominant individuals tended to possess territories nearest the central patch of prey, and use the most intense and physiologically exhausting displays. Only under the most stressful conditions did they acquire significantly more food than subordinates, and even then these benefits were not translated into increased growth, largely because dominant fish engaged in disproportionately more energy-consuming contests.     

Pair territoriality in the longnose filefish,oxymonacanthus longirostris

The longnose filefish,Oxymonacanthus longirostris, usually lives in heterosexual pairs, the male and female swimming together and sharing the same territory. Pair territoriality in the species was examined in detail in relation to sexual differences in territorial defense activities. Rigorous pair territoriality was maintained only during the breeding season, although pairs used their home ranges exclusively to a certain extent, during the non-breeding season. The frequency of aggression against other conspecific pairs in the breeding season was higher than in the non-breeding season. Agonistic interactions appear to be over both mates and food resources, the strict pair territoriality in the breeding season possibly being due to mutual mate guarding. In intraspecific aggressive interactions, males usually led their partner females when attacking intruders. The feeding frequency of males was much lower than that of females in the breeding season. Mate removal experiments indicated that females could not defend their original territories solitarily and their feeding frequency decreased. Conversely, males could defend territories solitarily without a decrease in feeding frequency. These results suggest that males contribute most to the defense of the pair territory, with females benefiting from territorial pair-swimming with their partner males.     

The behavioral ecology of three Indian Ocean surgeonfishes (Acanthurus lineatus,A. leucosternon and Zebrasoma scopas): their feeding strategies,and social and mating systems

Synopsis The relationship between the morphology, feeding strategies and social and mating systems of three surgeonfishes was investigated. Adults of each defend feeding territories, intra-and interspecifically. The largest species, because of its morphological limitation, relies on food that has to be defended against many other species. It forms large colonies in which fishes singly defend small territories containing high standing crop algal mats. Colony formation is a mechanism by which the efficiency and effectiveness of interspecific territory defense is increased. The smallest species, because of its morphological adaptations, is able to rely most on food that other species cannot efficiently exploit. It forms pairs that defend large territories containing a thin algal mat. It is restricted to the poorest quality habitat by the aggressive activities of more dominant species. The third species, which also forms pairs, has an intermediate feeding strategy. The local coexistence of these three and other surgeonfishes results from a combination of (i) their partitioning both habitat and food resources, and (ii) the populations of two of the most dominant species apparently being below the carrying capacity. Territoriality and the absence of parental care facilitates pair formation in surgeonfishes. Permanently territorial species usually form pairs. The colonial species does not form pairs because the colonial habit facilitates interference of males in each other's spawnings.     

Too big for his boots: Are social costs keeping condition‐dependent status signalling honest in an Australian lizard?

Australian painted dragon lizards Ctenophorus pictus occur in three head colours (red, orange and yellow) that differ in their level of aggression (reds being most aggressive), hormone profile (reds having higher testosterone levels) and in their frequency in our study population over time. They are also polymorphic in bib colour; some males have a bright yellow area under the chin, while others lack this coloured area entirely. We show that red males with a bib are in better body condition than red males that lack a bib. This contrasts sharply to yellow males, in which males with a bib are in poorer condition than yellow males that lack a bib. Our analysis also shows that following exposure to a high percentage of red (more aggressive) neighbours, all males suffer a reduction in body condition, and importantly, males with a bib (regardless of their head colour) suffer a more severe loss of body condition than males that lack a bib. Finally, this condition loss is significantly higher for yellow bibbed males than for red bibbed males, suggesting that the cost of sporting a bib may be higher for them. Orange males showed a non‐significant difference in condition between bib morphs. Our analysis also shows that bibbed yellow males (the morph with lower body condition), but no other morph category, declined significantly in their frequency between 2 years.     

The Role of Lateral Blue Spots in Intrasexual Relationships Between Male Iberian Rock-Lizards, Lacerta monticola

Vertebrate males often show breeding colours that may function as reliable signals of status in intrasexual competition. In many lacertid lizards, males show a conspicuous row of small but distinctive blue spots that runs along their body side on the outer margin of the belly. However, no study has examined the role of these blue spots. We first analysed in a field population of the Iberian rock lizard, Lacerta monticola, the relationships between number of blue spots and some morphological traits, which are known to be related to males’ fighting ability. The number of spots seems to be an character showing ontogenetic change as large (generally older) males showed more blue spots than small (generally younger) males. Males with a higher body condition also showed a higher number of blue spots. Thus, a higher number of blue spots may be used to signal size, age or body condition. Many contiguous blue spots would result in a visual artefact consisting of a continuous blue band, which might be a reliable size‐ or condition‐dependent signal in some social contexts. We further examined in the laboratory whether male characteristics are related to dominance status. In males with similar body size or age, those with relatively larger heads were more dominant, whereas the number of blue spots was not important. Moreover, the number of blue spots in nature was not related to relative head size. Finally, we experimentally manipulated the presence and the number of blue spots of intruding males, and examined the aggressive response of resident males. Intruder individuals manipulated to cover all their blue spots received a lower amount of aggression. However, males with different numbers of manipulated blue spots received a similar number of aggressive responses. These results suggest that, during agonistic encounters, the presence of blue spots, but not their number, may elicit aggressiveness. Thus, blue spots may serve to identify an individual as an adult male, and to enhance body size of larger males.