Egg incubation temperature affects male reproductive success but not display behaviors in lizards

The complex ritualized displays of males in many territorial species suggest that selection has shaped male behaviors in ways that affect fitness. In this study, we evaluated the link between display behavior during male–male interactions and reproductive success in the Australian jacky dragon (Amphibolurus muricatus), a lizard species that uses a complex series of movement patterns for communication. We quantified variation in male display behaviors by using video playback experiments in the laboratory, and subsequently assessed variation in male reproductive success by paternity analyses of offspring. Because the lizards used in this study came from eggs incubated under three thermal environments, we also could evaluate the impact of developmental temperature on adult behavior and reproductive success. Incubation temperature had a strong effect on male reproductive success; males produced under intermediate temperatures sired more offspring than those produced under extreme developmental temperatures. However, incubation temperature did not affect male display behavior, nor was male behavior associated with reproductive success. Our findings do not support the common assumption that display behaviors used during male–male interactions affect reproductive success.     

Shifted balance of risk and cost after autotomy affects use of cover,escape, activity,and foraging in the keeled earless lizard (<Emphasis Type="Italic">Holbrookia propinqua</Emphasis>)

Autotomy of expendable body parts is often a successful last-chance antipredatory defense for a variety of invertebrates and vertebrates, especially lizards. However, loss of a body part imposes costs and risks, some of which may be reduced by modifying subsequent behavior. I studied effects of experimentally induced autotomy of the tail in the keeled earless lizard (Holbrookia propinqua) on use of cover, escape behavior, activity, and feeding. Autotomized lizards stayed closer to plant cover than sham-autotomized lizards (having intact tails) when approached by an investigator simulating a predator. Autotomized males, but not females, fled further than sham-autotomized lizards. Autotomy did not affect the distance from an approaching predator when the lizards began to flee. After autotomy, the number of days on which lizards were active differed between sexes and lizards made fewer attempts to catch prey per unit time than lizards with intact tails. Tail loss did not affect the percentage of time spent moving. Staying closer to refuge, fleeing further after autotomy, and decreasing surface activity may compensate for decreased maximum escape speed or agility, and may reflect use of a greater margin of safety when the tail is unavailable for autotomy. Decrease in surface activity may be comparable to use of safer microhabitats reported for other lizards and damselflies subsequent to autotomy. Several possible reasons for the lower rate of feeding attempts by autotomized lizards are discussed.     

Defense mechanisms and antipredator behavior in two sympatric species of spiny lobsters, Panulirus argus and P. guttatus

The congeneric spiny lobsters Panulirus argus and P. guttatus co-occur throughout the Caribbean Sea, where they may share the coral reef habitat. Despite their phylogenetic closeness, both species have many different life-history traits that may partially explain their coexistence. However, even though both species may face the same predators, their defense mechanisms and antipredator strategies had not been compared. We compared the performance between species in 18 morphological and behavioral defense mechanisms commonly expressed by most spiny lobsters, including predator-avoidance mechanisms (activity schedule, sheltering behavior, delay to disturbance, and effect of conspecific damage-released scents on shelter choice) as well as antipredator mechanisms (body size, several parameters of the escape response and limb autospasy, clinging strength, antennal strength, and cooperative defense). As hypothesized, both species expressed all these defense mechanisms (except cooperative defense, shown only by P. argus), reflecting their phylogenetic closeness, but performed significantly differently in most, in accordance with their particular ontogenetic traits. Their comparative performance in individual defense mechanisms as well as the antipredator strategies displayed by groups of lobsters of each species in the presence of a common predator (the triggerfish Balistes vetula) showed that, in general, the defensive behavioral type of P. argus is more bold and that of P. guttatus more shy. Therefore, their distinct defensive behaviors contribute to their niche differentiation.     

Tail loss reduces mating success in the Iberian rock-lizard,Lacerta monticola

Summary Many lizards autotomize their tails to escape when grasped by a predator. It is hypothesized that tail loss causes a reduction in social status, thereby potentially lowering their reproductive success. We experimentally induced tail loss in Lacerta monticola in a semi-natural enclosure, and show that tail loss reduced social status and mating access in males. Tailless males increased body mass more rapidly than tailed dominant males, probably due to lower aggression costs. Also, tailless females were courted less and copulated less than tailed females, supporting the hypothesis that tail loss decreases reproduction potential.Correspondence to: J. Martin     

Risk assessment in western mosquitofish (Gambusia affinis): do multiple cues have additive effects?

The threat-sensitivity hypothesis predicts that prey individuals will increase antipredator behaviors as apparent predator risk increases. An implicit assumption of the threat-sensitivity hypothesis is that predator risk is additive. In other words, all characteristics of a predator that indicate risk should contribute in an additive way to determine the degree of risk-sensitive behavior. We tested this assumption in the laboratory by presenting live predators (green sunfish, Lepomis cyanellus) to groups of western mosquitofish (Gambusia affinis). We examined effects of predator diet, hunger level, and size on predator avoidance and inspection behavior of mosquitofish. Both predator diet and predator hunger level were significant and additive determinants of distance maintained from a predator, resulting in a graded response to combinations of these predator cues. In contrast, whereas predator diet was the most important determinant of general avoidance distances, predator hunger level was more important in determining mosquitofish vertical distribution and inspection behavior. Thus, the relationship between predator cue and the antipredator behavior that it elicits is dependent on which cues and behaviors are examined. Our data suggest that during risky behaviors, such as predator inspection, mosquitofish rely mainly on visual cues (behavior differences between hungry and satiated predators), whereas general avoidance behavior is determined by additive responses from visual and chemical cues.     

Effect of water temperature on the courtship behavior of the Alpine newt Triturus alpestris

Temperature is expected to have an effect on the behavioral patterns of all organisms, especially ectotherms. However, although several studies focused on the effect of temperature on acoustic displays in both insects and anurans, almost nothing is known about how environmental temperature may affect ectotherm visual courtship displays and sexual performance. The purpose of this study was to determine the effect of environmental temperature on the sexual behavior of Alpine newts (Triturus alpestris). We subjected T. alpestris to two different temperatures in controlled laboratory conditions. Temperature had a major effect on both male and female behaviors: at low temperature, the frequencies of several displays, including tail-raising during sperm deposition, are lowered. This variation is caused indirectly by temperature because it is due to female responsiveness, which is temperature-dependent. However, the fanning movement of the males tail during its main courtship display is independent of female behavior: at lower temperatures, the tail beats at a lower rate, but for a longer time. The similar reproductive success (i.e. sperm transfer) at the two temperature ranges indicates that breeding in cold water is not costly but instead allows males and females to mate early in the season. This is particularly adaptive because, in many habitats, the reproductive period is shortened by drying or freezing conditions, which may impair survival of branchiate offspring. This study also demonstrates the necessity of considering environmental parameters when modeling optimality and characteristics of ectotherm behaviors.Communicated by W. Cooper     

Ancient behaviors of larval amphibians in response to an emerging fungal pathogen, <Emphasis Type="Italic">Batrachochytrium dendrobatidis</Emphasis>

Behaviors have evolved in response to various selection pressures over evolutionary time. However, not all behaviors are adaptive. Some presumably “ancient” behaviors, persistent for millions of years, may be detrimental in the face of novel selection pressures in modern times. These pressures include a multitude of emerging infectious diseases which may be stimulated by environmental changes. We examined how a globally emerging amphibian pathogen, Batrachochytrium dendrobatidis (BD), affected two key evolutionarily persistent behaviors displayed by amphibian larvae: aggregation and thermoregulation. Larval aggregation behavior is often essential for foraging, thermoregulation, and antipredator defense, but varies among species. Thermoregulatory behavior speeds larval development in ephemeral habitats. Specifically, we examined whether aggregation and thermoregulatory behaviors changed when exposed to the BD pathogen in two species (Bufo boreas and Rana cascadae) whose larvae aggregate in nature. In laboratory choice tests, larvae of neither species avoided infected conspecifics. BD-exposed B. boreas larvae aggregated, while unexposed R. cascadae larvae associated more frequently with BD-exposed conspecifics. There was no evidence of behavioral fever or altered thermoregulation in larvae of four species we examined (Pseudacris regilla, Rana aurora, B. boreas, R. cascadae). The absence of behavioral fever may suggest an inability of the larvae of some host species to mediate infection risk by this pathogen. Thermoregulatory behaviors may exhibit a high degree of evolutionary inertia in amphibian hosts because they are linked with host physiology and developmental rates, while altered aggregation behaviors could potentially elevate pathogen transmission rates, leading to increased infection risk in social amphibian species.     

Do mountain log skinks (<Emphasis Type="Italic">Pseudemoia entrecasteauxii</Emphasis>) modify their behaviour in the presence of two predators?

Prey often adopt antipredator strategies to reduce the likelihood of predation. In the presence of predators, prey may use antipredator strategies that are effective against a single predator (specific) or that are effective against several predators (nonspecific). Most studies have been confined to single predator environments although prey are often faced with multiple predators. When more than one predator is present, specific antipredator behaviours can conflict and avoidance of one predator may increase vulnerability to another. To test how prey cope with this dilemma, I recorded the behaviours of lizards responding to the nonlethal cues of a bird and snake presented singly and simultaneously. Lizards use specific and conflicting antipredator tactics when confronted with each predator, as evidenced by refuge use. However, when both predators were present, lizards refuge use was the same as in the predator-free environment, indicating that they abandoned refuge use as a primary mechanism for predator avoidance. In the presence of both predators, they reduced their overall movement and time spent thermoregulating. This shift in behaviour may represent a compromise to minimize overall risk, following a change in predator exposure. This provides evidence of plasticity in lizard antipredator behaviour and shows that prey responses to two predators cannot be accurately predicted from what is observed when only one predator is present.Communicated by W. Cooper     

Female preference for apparently symmetrical male sexual ornaments in the barn swallow Hirundo rustica

Summary The outermost tail feathers of barn swallows Hirundo rustica apparently reliably signal the quality of males, because individuals with the longest tails have the lowest degree of fluctuating asymmetry (random deviations from symmetry in the otherwise symmetrical tail trait) despite the size of their secondary sexual character. I experimentally tested whether females preferred males with symmetrical tails without altering the aerodynamic properties of birds by painting the tips of the outermost tail feathers with white or black correction fluid. Unmated males were randomly assigned to one of four treatments: (i) asymmetrical tails, where the outermost 20 mm of one tail feather was painted white and the other black; (ii) symmetrical tails where the outermost 10 mm of both tail feathers was painted white (symmetric I); (iii) symmetrical tails where the outermost 20 mm of both tail feathers was painted white (symmetric II); or (iv) controls where the outermost 20 mm of both tail feathers was painted black. The experimental treatment affected the duration of the premating period since it took longer for asymmetrical males to acquire a mate than for either group of symmetrical males or control males. This gave rise to a delayed start of laying among males with apparently asymmetrical tails. The seasonal production of fledglings therefore decreased from control males through males with either symmetrical treatment to males with the asymmetrical treatment. Females therefore pay direct attention to the level of fluctuating asymmetry in secondary sexual characters even when the asymmetry does not affect the aerodynamic properties of males.     

Signal use by collared lizards, Crotaphytus collaris: the effects of familiarity and threat

Many lizard species use lateral compressions of the body during agonistic encounters. I investigated the signal value of the frequency at which these displays are presented and how that rate is affected by familiarity and threat. The response of resident collared lizards (Crotaphytus collaris) to tethered strangers, neighbors on the correct boundary, and neighbors displaced to the opposite boundary, was recorded by counting the number of lateral displays directed at the intruder and the number of subsequent acts of escalated aggression. There was no relationship between size asymmetry of the opponent and the rate of lateral display or aggression, nor was there a relationship between body size and the rate of lateral display or aggression. However, there was a high positive correlation between lateral display rate and aggression, suggesting that the rate of lateral displays is a conventional signal of motivation to attack. The highest rates of display and aggression were directed toward displaced neighbors, somewhat less toward strangers, and the least toward neighbors at the correct boundary. The ratio of aggressive acts to lateral displays followed the same pattern, presumably because the perceived threat to the resident decreases in the same order. Taken together these data suggest that collared lizards are able to assess the threat of an opponent and signal motivation to respond aggressively towards that opponent.Communicated by S. Downes     

Behavioral response of a generalist predator to chemotactile cues of two taxonomically distinct prey species

Chemotactile cues unintentionally left by animals can play a major role in predator–prey interactions. Specialized predators can use them to find their prey, while prey individuals can assess predation risk. However, little is known to date about the importance of chemotactile cues for generalist predators such as ants. Here, we investigated the response of a generalized predatory ant, Formica polyctena, to cues of two taxonomically distinct prey: a spider (Pisaura mirabilis) and a cricket (Nemobius sylvestris). In analogy, we studied whether crickets and spiders showed antipredator behavior in response to ant cues. When confronted with cues of the two prey species, Formica polyctena workers showed increased residence time and reduced movement speed, which suggests success-motivated searching behavior and thus increased foraging effort. The ants’ response did not differ between cues of the two prey species, coinciding with similar aggression and consumption rates of dead prey. However, the cuticular hydrocarbons, which likely resemble part of the potential cues, differed strongly between the species, with only few methyl-branched alkanes in common. This suggests that ants respond to multiple compounds left by other organisms with prey-search behavior. The two prey species, in turn, showed no detectable antipredator behavior in response to ant cues. Our study shows that ants can detect and respond to chemotactile cues of taxonomically and ecologically distinct prey species, probably to raise their foraging success. Using such chemotactile cues for prey detection may drastically increase their foraging efficiency and thus contribute to the high ecological success of ants.     

The peculiar case of an insectivorous iguanid lizard that detects chemical cues from prey

Summary. Ecological and phylogenetic factors determine which sensory modalities organisms use in their day-to-day activities. Among lizards, empirical studies indicate a tight association between foraging strategies and the ability to detect chemical cues from prey. Consequently, ambush insectivores do not detect food chemicals and these differences have a phylogenetic basis, as ambush lizards mainly belong to the Iguania clade. These data contrast, however, with the widespread uses of chemoreception in the Iguania genus Liolaemus, which are mostly insectivorous ambush predators. Moreover, observations from different Liolaemus species suggest a capability to find prey through chemoreception. In order to clarify the abilities of Liolaemus to detect chemical cues from prey, the chemoreceptive behavior of the insectivorous ambush predator, L. lemniscatus, was studied. Lizards were given the choice between areas with and without chemical cues from a food item (mealworms). Results show that test animals stayed for longer, moved more, and did more chemical exploration (tongue flicks) in the area where chemical cues from mealworms were present. Furthermore, in this area, more individuals displayed behaviors that suggest maintenance and defense of the prey patch. Thus, L. lemniscatus is the first insectivorous Iguania reported to be able to detect chemical cues from prey. Although I propose a mechanism for acquiring chemical detection of prey cues in Liolaemus, I also remark that it is necessary to reanalyze both the abilities to detect and use chemical foraging cues in Iguania at large, and the methodologies traditionally used to study these issues.     

Innate antipredator responses of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) depend on predator species and their diet

The ability to discriminate between more dangerous and less dangerous predators can have serious fitness advantages for fish juveniles. This is especially true for hatchery-reared fish young used for stocking, because their post-release mortality is often much higher than that of wild-born conspecifics. We tested whether two coexisting fish predators and their different diets induce innate behavioral responses in predator-naive Arctic charr (Salvelinus alpinus) young originating from an endangered hatchery-bred population used for re-introductions. We predicted the antipredator responses of charr to be stronger towards chemical cues of brown trout (Salmo trutta) and pikeperch (Stizostedion lucioperca) than towards odorless control water. More pronounced antipredator behavior was predicted in treatments with predators fed on charr than when their diet consisted of another sympatric salmonid, European grayling (Thymallus thymallus), or when they were food-deprived. The Arctic charr young showed strong antipredator responses in all brown trout treatments, whereas odors of the less likely predator pikeperch were avoided with conspecific diet only. Freezing was the most sensitive antipredator behavior, as it was completely absent in control treatments. We found considerable individual variation in the amount and strength of antipredator responses. Although almost half of the charr failed to show antipredator behavior towards the piscivores, those with the innate ability showed highly sensitive recognition of predator odors. Our results indicate that the innate antipredator behavior of the juvenile fish is already finely tuned to respond specifically to chemical cues from different fish predators and even their diets.Communicated by J. Krause     

Foraging costs of a tail ornament: Experimental evidence from two populations of barn swallows Hirundo rustica with different degrees of sexual size dimorphism

Secondary sexual characters are assumed to be costly to produce or maintain. A test of this assumption was performed using the sexually exaggerated outermost tail feathers of male barn swallows Hirundo rustica, a trait currently subject of a directional female mate preference. A possible cost of sexual signalling in male barn swallows arises from increased flight cost during foraging in this aerially insectivorous species. A longer tail may impose a greater drag during flight and thereby affect foraging ability. This was tested by determining the relationship between experimentally modified male tail lengths and number and size of prey delivered to offspring in Spain, where sexual size dimorphism in tail length is small, compared to Denmark, where dimorphism is large. Food boluses contained significantly fewer small insects in Spain than in Denmark. Males with elongated tails captured more and smaller insects while males with shortened tails captured fewer and larger prey items at both sites. Males with naturally long tails were less affected by experimental treatment in terms of effects on the number and the size of prey delivered to their offspring, a finding consistent with a long tail being a condition-dependent viability indicator. The effect of a given degree of tail manipulation on prey size and number of prey per bolus was larger in Spain than in Denmark. These results demonstrate that (1) tail length in male barn swallows affects foraging, and (2) larger sexual size dimorphism occurs where the foraging cost of an increment in ornament size is smallest.Communicated by M. Zuk     

Does cadence of Iguana iguana displays facilitate individual recognition?

Iguanid lizards communicate threat, courtship and territorial advertisement through stereotyped headbob displays. It has been hypothesized that slight interindividual differences in these displays might enhance individual recognition and maintain dominance relationships within populations, but the precise display elements responsible have not been determined. The purpose of this study was to examine if experimentally induced differences in displays would decrease recognition of individual conspecifics. Specifically, social interactions between adult male green iguanas (Iguana iguana) were examined at normothermic and hypothermic body temperatures. Whereas the cadence (rate of muscle contraction) of stereotypic displays of individual lizards was slowed at hypothermic body temperature (Q ₁₀ 1.6), the amplitude (maximal muscle contraction) of hypothermic displays remained constant relative to normothermic displays. Normothermic lizards viewing a display from a hypothermic lizard responded to that display as if it were performed at a normothermic cadence. During paired encounters between lizards (one hypothermic, one normothermic), dominant/subordinate dyads within the group were unusually maintained regardless of which individual was hypothermic. The exception occurred when dominant individuals at the lowest experimental body temperatures retreated from subordinate individuals. The results suggest that individual lizards recognized their relative social status even when cadence of displays was radically altered, indicating that cadence alone probably does not function in individual recognition. Other morphological, display elements, or scent cues may provide information useful in individual recognition.Communicated by G.M. Klump     

Habituation to low-risk predators improves body condition in lizards

Habituation to nonlethal predation stimuli may provide benefits for animals living in areas with frequent encounters with low-risk predators. On the other hand, individuals can be very consistent in their antipredator responses, with shy individuals showing greater degree of responsiveness than bold individuals. However, the link between habituation or boldness and individual benefits has not been thoroughly investigated. We established whether and how two behavioral components associated with antipredator responses (habituation and boldness, and their interaction) would influence body condition, which is a parameter related to fitness. We conducted an outdoor semi-natural experiment with Iberian wall lizards (Podarcis hispanica). Individual boldness was consistent across contexts, but we did not find any effect of boldness or the interaction between boldness and habituation on body condition. However, those individuals that habituated more readily to a frequent predatory stimulus were able to increase their body condition more relative to lizards that habituated less. This finding highlights the importance of individual differences in behavioral plasticity, which could influence traits related to fitness. Habituation can provide benefits for individuals exposed to low-risk predators; however, individuals more prone to habituation could also experience mortality costs by wrongly habituating to a dangerous predator.     

Age and sex influence marmot antipredator behavior during periods of heightened risk

Animals adjust their antipredator behavior according to environmental variation in risk, and to account for their ability to respond to threats. Intrinsic factors that influence an animal’s ability to respond to predators (e.g., age, body condition) should explain variation in antipredator behavior. For example, a juvenile might allocate more time to vigilance than an adult because mortality as a result of predation is often high for this age class; however, the relationship between age/vulnerability and antipredator behavior is not always clear or as predicted. We explored the influence of intrinsic factors on yellow-bellied marmot (Marmota flaviventris) antipredator behavior using data pooled from 4 years of experiments. We hypothesized that inherently vulnerable animals (e.g., young, males, and individuals in poor condition) would exhibit more antipredator behavior prior to and immediately following conspecific alarm calls. As expected, males and yearlings suppressed foraging more than females and adults following alarm call playbacks. In contrast to predictions, animals in better condition respond more than animals in below average condition. Interestingly, these intrinsic properties did not influence baseline time budgets; animals of all ages, sexes, and condition levels devoted comparable amounts of time to foraging prior to alarm calls. Our results support the hypothesis that inherent differences in vulnerability influence antipredator behavior; furthermore, it appears that a crucial, but poorly acknowledged, interaction exists between risk and state-dependence. Elevated risk may be required to reveal the workings of state-dependent behavior, and studies of antipredator behavior in a single context may draw incomplete conclusions about age- or sex-specific strategies.     

Racketed tail of the male and female turquoise-browed motmot: male but not female tail length correlates with pairing success,performance, and reproductive success

Both males and females of many avian species maintain elaborate plumage traits, and elaborate monomorphic plumage may convey adaptive benefits to one or both sexes as inter- or intraspecific signals. Both sexes of the turquoise-browed motmot (Eumomota superciliosa) are elaborately plumed with long racket-tipped tail. I investigated whether the racketed tail functions as a sexually selected signal in one or both sexes by testing the predictions that males and/or females with the largest tails have: (1) greater pairing success, (2) greater reproductive performance (clutch-initiation date, clutch size, and hatching success), and (3) greater reproductive success. Yearling males with longer denuded rachises (wires) on the central tail feathers had greater pairing success. In addition, adult males with longer wires paired with females who laid larger clutches, had greater hatching success independent of clutch size, and fledged more young. There was no relationship between female tail plumage and pairing success, reproductive performance, or fledgling success. These results are consistent with the hypothesis that male tail plumage functions as a mate choice or status signal, but that the tail of the female does not function in a sexually selected context. I discuss alternative hypotheses for the evolutionary maintenance of the elaborate female tail plumage.     

Predation risk assessment by green frog (<Emphasis Type="Italic">Rana clamitans</Emphasis>) tadpoles through chemical cues produced by multiple prey

Many prey assess predation risk through predator chemical cues. Numerous studies have shown that (1) prey sometimes respond to chemical cues produced by heterospecifics and (2) that many species are capable of associative learning. This study extends this research by focusing on predation risk assessment and antipredator behavior in environments containing chemical cues produced by multiple prey species. The results show that green frog (Rana clamitans) tadpoles (1) assess risk from the chemical cue produced during predation by a heterospecific (gray tree frog, Hyla versicolor, tadpoles) and (2) can exhibit similarly strong behavioral responses to a mix of conspecific and heterospecific cues compared to conspecific cue alone, depending on their conditioning environment. I then discuss how the prey choice of the predators and the relative abundances of the prey species should influence the informational value of heterospecific cues.     

Mate choice in the yellow-shouldered widowbird: correlates of male attractiveness

Recent investigations of male ornaments in sexual selection have used experimental manipulation of tail length in three widowbird species, but only for one of these have correlates of male reproductive success been reported. I examined correlates of male attractiveness to nesting females over two breeding seasons for the polygynous yellow-shouldered widowbird, Euplectes macrourus, in order to discover which cues females may be using to select mates. The black, long-tailed ( 10 cm) males defend large territories and build nest frames, or cock's nests, which females then line and use for nesting. I examined various aspects of male morphology, five behavioral displays, territory characteristics, and the number of cock's nests that males built. Few correlates of mating success were found. The best predictor was the number of cock's nests that a male builds, though one courtship display also correlated with male mating success in 1 year, as did average grass height. Tail length did not correlate with male mating success. A partial correlation analysis confirmed that cock's nests and, in 1 year, grass height, were the primary contributers to male success. Females may choose where to nest primarily on the availability of suitable nesting sites. Long tails may be used by females seeking extra-pair copulations or in male-male competition for territories.