Hot off the presses! Mar 01 Behav Ecol

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Latest Articles Include:

• Boldness and behavioral syndromes in the bluegill sunfish, Lepomis macrochirus
  - Behav Ecol 20(2):231-237 (2009)
  In recent years, evidence for interindividual variation in "personality" within animal populations has been accumulating. Personality is defined as consistency in an individual's behavioral responses over time and/or across situations. One personality trait that has potentially far-reaching implications for behavioral ecology, and may provide insight into the mechanisms by which consistent behavioral correlations arise, is that of boldness. Boldness is defined as the tendency of an individual to take risks and be exploratory in novel contexts. Using the framework of behavioral syndromes, we tested for individual differences in boldness in the laboratory among field-caught juvenile bluegill sunfish (Lepomis macrochirus) within and across the contexts of exploratory behavior, activity, and risk taking (e.g., antipredator) behavior. After such testing, individuals were tagged and returned to their lake of origin as part of a mark-recapture study testing for the repeatabil! ity of individual differences in boldness. Here, we report strong and consistent individual differences in boldness within and across all 3 behavioral contexts. Additionally, we observed that at least some boldness behaviors were repeatable after a 1-3 month recapture period. This study provides novel evidence for a boldness syndrome in sunfish, as well as insight into how behavioral types (e.g., shy/bold) may evolve and be maintained in natural populations.
• Nine-spined sticklebacks deploy a hill-climbing social learning strategy
  - Behav Ecol 20(2):238-244 (2009)
  Theoretical models on the adaptive advantages of social learning lead to the conclusion that copying cannot be indiscriminate and that individuals should adopt evolved behavioral strategies that dictate the circumstances under which they copy others and from whom they learn. Strategies that exhibit hill-climbing properties, that would allow a population of individuals to converge on the fitness-maximizing behavior over repeated learning events, are of particular significance due to their potentially critical role in cumulative cultural evolution. Here, we provide experimental evidence that nine-spined sticklebacks (Pungitius pungitius) use public information adaptively and in accordance with a hill-climbing social learning strategy. Sticklebacks switch patch preferences to exploit a more profitable food patch if the returns to demonstrator fish are greater than their own but are less likely to copy when low-profitability patches are demonstrated. These findings reinfor! ce the argument that public-information use in nine-spined sticklebacks is an adaptive specialization. More generally, the observation of this sophisticated form of learning in a species of fish supports the view that the presence of enhanced social learning may be predicted better by specific sources of selection than by relatedness to humans.
• Family conflict and the evolution of sociality in reptiles
  - Behav Ecol 20(2):245-250 (2009)
  Mating systems and parental care are predicted to coevolve because the former dictates the cost-benefit ratio of the latter by affecting genetic relatedness between adults and offspring. Reptiles show only rudimentary forms of sociality and parental care and, hence, could provide important insights into the early stages of the evolution and maintenance of social systems. The skink genus Egernia exhibits the most complex form of sociality and parental care in lizards, with the formation of stable social groups typically consisting of a monogamous pair and their offspring. Here we show that, within a social group, offspring sired by males other than the social father are restricted to the area of the parental home range that is occupied exclusively by the mother. Thus, males rarely tolerate offspring within their home range that they are not genetically related to. This may increase the cost of multiple mating for females and offspring via increased risk of infanticide, ! reduced parental tolerance, and increased mother-offspring competition. We outline a verbal model for how this could generate a feedback loop in which selection favors reduced multiple mating by females and increased paternal care, thereby setting the stage for the evolution of complex sociality and genetic monogamy.
• Living with the dead: when the body count rises, prey stick around
  - Behav Ecol 20(2):251-257 (2009)
  Most terrestrial prey species are assumed to assess predation risk by detecting predators directly rather than using cues of previous attacks on conspecifics. However, such cues might represent valuable information, and prey can be expected to respond to the presence of congeners killed by enemies. Such cues are available in aphid colonies attacked by parasitic wasps because they do not remove parasitized hosts from the colony. Colonies are thus often a mixture of healthy, parasitized, and killed aphids, which corpses ("mummies") stay attached to the plant and can be encountered by live aphids. Aphids exhibit a dispersal polyphenism. Recent studies show that they produce more winged offspring when directly exposed to natural enemies or to alarm pheromone emitted by conspecifics. We hypothesized that aphids perceive the corpses of congeners killed by parasitoids and respond by increasing the production of winged morphs, but we surprisingly found the opposite. We determi! ned the adaptive value of this response by analyzing the foraging behavior of parasitoids in aphid colonies with killed aphids ("mummies"). Parasitoid females responded to the presence of mummies by reducing both their time allocation and parasitism activity in the patch. The strategy of aphids to reduce emigration (i.e., they produce more wingless morphs when mummies are present) is adaptive because the presence of killed congeners reduces parasitoid pressure on colonies. This demonstrates that the remains of individuals killed by natural enemies can still have an ecological relevance in prey populations and that enemy-induced phenotypic plasticity depends on the type of predation cues.
• Armament under direct sexual selection does not exhibit positive allometry in an earwig
  - Behav Ecol 20(2):258-264 (2009)
  The allometric scaling relationships of armaments and ornaments have been subject to extensive debate. A large body of empirical evidence suggests that sexually selected traits typically exhibit positive static allometry, where the large individuals express proportionally larger traits. Recent theory suggests that this need not be the case. We confirm this prediction using the earwig Euborellia brunneri as a model species--unusually, the male armament in this species does not exhibit positive allometry. We experimentally assessed the strength of direct and indirect selection on armament length and morphology and on body size and weight. In a 3-stage experiment, we first permitted females to choose between 2 males and assigned 1 male as the preferred and the other the nonpreferred male. We then allowed the same pair of males to establish a dominance hierarchy in fighting trials. Last, to evaluate the implications of female choice, we conducted mating trials where half t! he females were mated to their preferred male and half with their nonpreferred male. We found that male armament length and body weight were under direct sexual selection through intrasexual competition. In contrast, female mate preferences did not relate to any measured male trait. Finally, mating behavior was not related to male preference status or armament length. Thus, armament size is sexually selected through intrasexual competition although it does not exhibit positive allometry. Our finding suggests that researchers should be cautious when inferring the absence of sexual selection in traits that do not exhibit positive allometry.
• Long-term effects of early parasite exposure on song duration and singing strategy in great tits
  - Behav Ecol 20(2):265-270 (2009)
  Song is a sexually selected trait in many bird species and has been suggested to function as a signal of a male's health and parasite resistance. Here we present an experimental field study on the long-term effects of parasite exposure early in life on adult bird song. We exposed nestling great tits (Parus major) to ectoparasitic hen fleas (Ceratophyllus gallinae) and on their recruitment into the local breeding population assessed the response to a playback of a challenging male in their breeding territory. We show, to our knowledge for the first time in a wild bird population, that parasite exposure early in life affects bird song: song duration of males that were exposed to parasites early in life was reduced by 32% compared with males that grew up in a flea-free environment. Early parasite exposure also significantly reduced the degree of song overlap with the playback, which has been shown to correlate with social status. There was no effect of early parasite expo! sure on the number of different song types sung or on the latency until the males started the vocal response to the playback. These results suggest that mates or rivals can use song duration and song overlap as proxies for an individual's exposure to parasites early in life. It thereby highlights both the importance of parasites in maintaining honesty of sexually selected traits and the costs of parasitism in terms of reduced attractiveness and competitiveness.
• Intraguild predation, thermoregulation, and microhabitat selection by snakes
  - Behav Ecol 20(2):271-277 (2009)
  Intraguild (IG) predation, the killing and eating of potential competitors, can be a powerful force within faunal assemblages. If both the IG predator and its prey prefer similar microhabitats in spatially structured environments, avoidance of the predator may relegate IG prey to suboptimal habitats. In southeastern Australia, the broad-headed snake (Hoplocephalus bungaroides) is an endangered species sympatric with the small-eyed snake (Cryptophis nigrescens), an abundant and geographically widespread species known to eat other snakes. Both of these nocturnal ectotherms shelter diurnally beneath thermally distinctive "hot rocks," which are in limited supply. When selecting shelter sites, broad-headed snakes thus face a trade-off between predation risk and habitat quality. In laboratory experiments, we allowed broad-headed snakes to choose between retreat sites differing in thermal regimes, in scent cues from predators, and in the actual presence of the predator. Broad! -headed snakes displayed an aversion to sites with live predators and predator scent, yet nonetheless frequently selected those sites to obtain thermal benefits. In trials with live predators, adult broad-headed snakes shared hot rocks with small-eyed snakes, but most juveniles did not; data from a 16-year field study likewise suggest that broad-headed snakes only cohabit with small-eyed snakes if the two snakes are similar in body size. Our results suggest that thermoregulatory considerations are sufficient to prompt juvenile (but not adult) broad-headed snakes to risk IG predation, emphasizing the importance of microhabitat quality and body size in mediating IG predator-prey interactions.
• Prudent male mate choice under perceived sperm competition risk in the eastern mosquito fish
  - Behav Ecol 20(2):278-282 (2009)
  In contrast to what is known about adaptive mate choice in females, we know far less about how fluctuating reproductive costs might affect male mate choice. In many species, sperm competition can have a direct bearing on male fertilization success, and choosy males should be expected to respond adaptively to the perceived cost of sperm competition and to adjust their mate preferences accordingly. Here, we conducted a series of experiments investigating male mate choice under sperm competition risk in the eastern mosquito fish, Gambusia holbrooki. We tested male association preferences before and after manipulating their perceptions of sperm competition risk associated with initially preferred and nonpreferred females. We found that individuals were consistent in their preferences if they did not have the opportunity to witness other males associating with the initially preferred female. By contrast, males spent significantly less time with initially preferred females i! f, in the interim, she had been seen in the vicinity of another male. A similar opportunity to observe the initially nonpreferred female with another male had no effect on subsequent male mate choice. Our results suggest that choosy males may be capable of adjusting their preferences in response to shifts in their perception of sperm competition risk.
• Social enviroment influences aphid production of alarm pheromone
  - Behav Ecol 20(2):283-288 (2009)
  In most aphid species, the volatile sesquiterpene (E)-{beta}-farnesene (E{beta}f) is released as an alarm pheromone in response to predation and is also emitted continuously at low levels. Some aphid predators use E{beta}f as a foraging cue, suggesting that the benefits to aphids of signaling via E{beta}f must be weighed against the cost of increasing apparency to natural enemies. To determine whether aphids vary E{beta}f production in response to features of their social environment, we compared the production of E{beta}f by Acyrthosiphon pisum (Harris) individuals reared in isolation with that of individuals reared among conspecifics or individuals of a different aphid species, Myzus persicae. Production of E{beta}f by A. pisum reared in isolation was significantly lower than that of aphids reared among conspecifics or among M. persicae individuals. When we reared A. pisum individuals in isolation but exposed them to odors from an aphid colony, E{beta}f production wa! s similar to that of aphids reared among conspecifics, suggesting that aphids use a volatile cue to assess their social environment and regulate their production of alarm pheromone. It is likely that this cue is E{beta}f itself, the only volatile compound previously found in headspace collections of A. pisum colonies. Finally, we examined the attraction of a predatory hoverfly, which uses E{beta}f as a foraging cue, to groups of aphids reared in isolation or among conspecifics and found that groups comprising individuals reared in isolation were significantly less attractive to the predator, suggesting that the observed variation in E{beta}f production may be ecologically relevant.
• When are vomiting males attractive? Sexual selection on condition-dependent nuptial feeding in Drosophila subobscura
  - Behav Ecol 20(2):289-295 (2009)
  Nuptial gifts are any nutritious items or inedible tokens transferred from the male to the female as a part of courtship or copulation. Although nuptial gift donation has been studied in a variety of taxa, this behavior has been largely overlooked in Drosophila. We studied nuptial feeding in Drosophila subobscura, where the gift is a regurgitated drop of liquid, in order to examine the importance of this behavior for male mating success and female fecundity. We varied male and female condition by dietary restriction to assess any condition dependence of male nuptial feeding ability and female feeding behavior and mate discrimination. Our results show that there was directional selection for males in good condition that produced a higher number of regurgitated gifts. Interestingly, the strength of selection was also dependent on female condition. Females in poor condition showed strongest preference for males in good condition. Such females could increase their fecundit! y to a level similar to that of females in good condition by feeding on regurgitated gifts from males in good condition. However, male exploitation of female gustatory response is also a plausible explanation for the courtship feeding response, as we did not find an effect of nuptial feeding on the fecundity of females in good condition. These findings suggest that, in this monandrous species, selection has favored males who invest in nuptial gifts, possibly as an example of paternal investment as well as mating effort, but that the strength of selection on nuptial feeding is strongly subject to environmental variation.
• The elusive paradox: owner-intruder roles, strategies, and outcomes in parasitoid contests
  - Behav Ecol 20(2):296-304 (2009)
  Models of dyadic contests for indivisible resources have predicted that the owner-intruder role distinction can suffice as a cue for evolutionarily stable resolution. This outcome may be "common sense" (prior owners retain the resource) or counterintuitively "paradoxical" (the intruder takes over), but the most recent models predict paradoxes to be an infrequent result, and there are also very few candidate examples provided by empirical study. Possible paradoxical outcomes were recently reported from the parasitoid wasp Goniozus legneri in which adult females compete directly for hosts. Here we provide further investigation, taking into account influences of contest ability (body size) and the value of the host to each contestant (correlated with the developmental stage of the owner's brood). We additionally evaluate contest strategies in terms of respect for ownership as evidenced by attack behavior during contests. Goniozus legneri shows weak, and thus only partial,! respect for role asymmetries: such mixed strategies are predicted by recent models that assume population-level feedback on resource value parameters. Contest outcomes are influenced by asymmetries in resource value and body size and are generally common sense. Instances of paradoxical contests remain predictably elusive.
• Extrapair paternity in an insular population of house sparrows after the experimental introduction of individuals from the mainland
  - Behav Ecol 20(2):305-312 (2009)
  Several studies have found that island populations of passerines exhibit lower levels of extrapair paternity (EPP) than mainland populations. An explanation proposing that lower levels of genetic diversity in isolated populations reduce the indirect genetic benefits of EPP to females has been supported by observational study but not tested experimentally. Here, we present the results of a manipulative study on an island population of house sparrows (Passer domesticus), which previously exhibited a significantly lower frequency of EPP than mainland populations. Fifty adults from a mainland population with significantly more genetic diversity than the island population (across 17 microsatellite loci) were introduced into the island population, and the incidence of EPP was subsequently monitored over 3 breeding seasons. In the year of the introduction, the incidence of EPP rose to approximately the level seen in mainland populations of house sparrows but dropped to an int! ermediate frequency in the following 2 years. Unexpectedly, parentage assignment showed that in the year of the introduction, all females producing extrapair offspring were native island birds, as were all the extrapair and cuckolded males. These results suggest that EPP in this experimental population was not driven by females trying to maximize the genetic diversity of their offspring.
• Differential effects of structural complexity on predator foraging behavior
  - Behav Ecol 20(2):313-317 (2009)
  The choice of predator foraging mode has important consequences for ecological communities. Foraging mode designations are often made on the basis of predator activity, yet activity can be affected by various environmental stimuli independent of changes in foraging mode. Structural complexity can reduce predator activity by either interfering with predator vision and mobility or as part of a foraging mode shift. We examined the effects of simulated aquatic vegetation on multiple behaviors of 2 aquatic insect predators to distinguish between these 2 possible outcomes. Larvae of the diving water beetle (Dytiscus spp.) shifted from an active predator in treatments without structure to a sit-and-pursue (SAP) predator in treatments containing structure, as indicated by a decrease in activity and prey encounter rates and an increase in probability of capture. This trade-off between encounter rates and probability of capture resulted in an equal number of prey captures among ! the treatments. Dragonfly nymphs (Anax junius) remained SAP predators in both treatments, although interference from the simulated vegetation significantly reduced activity. Structure also slightly decreased the number of aeshnid prey captures. Physiological attributes of the predators, such as mode of respiration and method of prey detection, seemed to influence foraging behavior. This study emphasizes the benefits of measuring multiple predator behaviors when classifying predators to particular foraging modes.
• When predators become prey: flight decisions in jumping spiders
  - Behav Ecol 20(2):318-327 (2009)
  Current optimal escape theory focuses on economic distance-based models that predict that animals will flee at greater distances when risk of capture is greater. Although these models have been tested extensively on vertebrate prey animals using large approaching stimuli (e.g., humans), it has never been tested on an invertebrate generalist predator with a stimulus that is in the size range of potential prey. I presented adult jumping spiders, Phidippus princeps, with a small black model to test flight decisions when physically handicapped, under different levels of threat, and on surfaces that potentially hindered escape. Predator approach speed, running surface texture, and leg autotomy had no effect on flight decisions. I also measured running distance and speed under different levels of hunger and energy state to test how these variables affect the decision to flee or to turn and defend oneself against a predator. When prodded, larger spiders fled shorter distances! before switching to a defensive posture, hungry spiders fled longer distances than sated spiders, and rested spiders ran faster than tired spiders. There is likely a trade-off between body size and energy stores when deciding to flee from a threat or turning to defend oneself. These findings 1) reflect differences in how predators and prey assess risk in their environment and the distances at which they treat an approaching object as threatening and 2) suggest that future studies should focus on how animals optimize escape decisions in ways other than traditional distance-based economic models (e.g., relying absolutely on crypsis).
• Sperm precedence in monarch butterflies (Danaus plexippus)
  - Behav Ecol 20(2):328-334 (2009)
  We characterized sperm precedence in monarch butterflies (Danaus plexippus), using a series of experiments in which we manipulated male mating histories to vary spermatophore size and the number of sperm transferred. Several factors affected the outcome of sperm competition. There was a pattern of second-male sperm precedence, but second-male precedence was rarely complete, and several other factors had significant effects on paternity patterns. Larger males outcompeted smaller males when they were not matched for size. Phosphoglucose isomerase (PGI) genotype affected the outcome of sperm competition under very hot conditions. When sperm from the same pair of males competed in different females, males fared better when they transferred more sperm. These results demonstrate that sperm precedence within a species can be affected by many factors, including the circumstances under which it is measured.
• Sex allocation in response to local resource competition over breeding territories
  - Behav Ecol 20(2):335-339 (2009)
  Sex allocation according to local resource competition suggests that investment and offspring sex ratio should be biased toward the dispersing sex to limit the competition among the natal philopatric sex. Conversely, when competition over resources is low, parents should allocate more resources toward the philopatric sex. In this study, this reciprocal scenario of sex allocation is tested. More specifically, the effect of breeding territory availability on primary sex ratio is studied in the collared flycatcher, a migratory passerine bird, where males are the natal philopatric sex. As predicted, primary sex ratios were biased toward males in areas where available territories were abundant (estimated from population growth). No relationship between sex ratio adjustment and adult phenotypes as well as date of first egg was found. We discuss potential explanation for the male-biased broods in areas with many vacant territories and low levels of competition. We suggest tha! t sex ratio adjustment in relation to breeding territory quality and availability could be relatively common in birds.
• Correlation between exploration activity and use of social information in three-spined sticklebacks
  - Behav Ecol 20(2):340-345 (2009)
  Individual variation in the exploration of an unfamiliar environment and joining performance probably reflects the shy-bold continuum as risk-related behavior. We experimentally examined the association between individual variation in exploration activity in an unfamiliar laboratory environment and tendency to follow other conspecifics in limnetic (primarily shoaling planktivore) and benthic (opportunistic shoaling benthic feeder) populations of three-spined stickleback from Alaska. Using a maze aquarium, we initially observed individual differences in exploration activity, that is, how far along the unfamiliar maze single immature fish could progress and how quickly they could arrive there. Then, we measured individual tendencies for individuals to follow "demonstrators" that had already been trained to solve the maze. There is a positive correlation between the 2 measurements in both populations. This may indicate that individuals active in exploration in unfamiliar ! environments can quickly exploit social advantages provided by demonstrators, which is consistent with the conceptual framework of behavioral syndromes in a shy-bold continuum.
• Temporal variability in a multicomponent trait: nuptial coloration of female two-spotted gobies
  - Behav Ecol 20(2):346-353 (2009)
  Animals that breed more than once may face different environmental and physiological conditions at each reproductive event. Costs and benefits of sexual ornaments could therefore vary both within and between breeding seasons. Despite this, the ornaments are often assumed to be fixed, and temporal changes in ornamentation have rarely been investigated. Female two-spotted gobies (Gobiusculus flavescens) have colorful orange bellies when sexually mature and nest-holding males prefer females with more colorful bellies. This nuptial coloration is caused both by the carotenoids-rich gonads being directly visible through the skin and by the chromatophore pigmentation of the abdominal skin. Toward the end of the breeding season, males become rare and females become the more competitive sex. We show that female ornamentation of G. flavescens is a complex multicomponent trait and that the separate components, as well as their interactions, are variable. As gonads matured, they b! ecame more colorful while the abdominal skin became more transparent, causing more intense belly coloration in sexually mature females. However, coloration varied greatly also among fully mature females, suggesting that it may not only be a signal of readiness to spawn. Indeed, belly coloration predicted gonad carotenoid concentration, but there were several important seasonal differences in color expression. Females sampled toward the end of the breeding season were more colorful. This was due to seasonal increases in both gonad carotenoid concentration and skin coloration. Thus, at a time when competition over males is stronger and the terminal reproductive event approaches, females appear to invest more in signaling.
• Do polyandrous pygmy grasshopper females obtain fitness benefits for their offspring?
  - Behav Ecol 20(2):354-361 (2009)
  Explanations for polyandry in insects invoke material and genetic benefits that enhance female fitness via the production of more viable or more variable offspring. Here we use the color polymorphic pygmy grasshopper, Tetrix subulata, to evaluate effects of male quality, mate color morph resemblance (a proxy for compatibility), and polyandry on offspring performance. We experimentally mated females with different numbers and color morph combinations of males and reared offspring under either sun-exposed or shaded conditions using a split-brood design. We find a significant male identity effect on egg hatchability, consistent with the hypothesis that males vary in paternal quality. Offspring viability posthatching varied in a complex manner with solar regime, mating treatment, and parental resemblance. The effects of parental color morph resemblance on offspring performance suggest a potential role of compatibility and offspring variability. Monandrous females produced ! more viable offspring than polyandrous females (under shaded conditions) and we suggest as a hypothesis that the expected positive influence of polyandry on offspring performance may have been outweighed by more intense competition and antagonistic interactions among half-siblings. That an effect of mating treatment was evident under shaded but not under sun-exposed conditions suggests that great care is called for when making inferences from studies that show negative results.
• Conspicuousness-dependent antipredatory behavior may counteract coloration differences in Iberian rock lizards
  - Behav Ecol 20(2):362-370 (2009)
  Sexual selection favors more conspicuous male displays, whereas natural selection (via predator pressure) favors less conspicuous displays. However, this trade-off might be altered if males with more conspicuous displays could compensate behaviorally for their increased conspicuousness by acting more cautiously toward predators. The aim of this study was to explore in 2 species of Iberian rock lizards whether or not conspicuous coloration was associated with antipredatory behavior and whether conspicuousness-dependent regulation of antipredatory behavior existed. Our results suggested that male lizards may compensate for the negative effects of conspicuous sexual coloration on predation risk by modulating their antipredatory behavior (time inside refuges, false alarms, etc). We found that male Iberolacerta monticola, but not male Iberolacerta cyreni, compensated for the negative effects of blue lateral ocelli, which increased visual conspicuousness. However, male lizar! ds did not compensate for relatively unexposed ventral spots. We also found that male I. monticola in better condition and with more blue lateral ocelli were shier, whereas male I. cyreni in better condition and with more ventral spots were bolder. These 2 lizard species live in habitats that differ in refuge availability and in the number of potential predators, which may promote differences in the trade-off between predation risk and social behavior and may explain the observed interspecific differences in antipredatory behavior. This suggests that regulation of antipredatory behavior may also function as a condition-dependent cost promoting costly (honest) sexual signaling in some species.
• Antipredator behavior in blackbirds: habituation complements risk allocation
  - Behav Ecol 20(2):371-377 (2009)
  Several studies showed that animals allow closer approaches (measured through flight initiation distances, FIDs) by potential predators (e.g., humans) in high-predator density areas, which has been explained by habituation effects. We assessed whether this pattern could be produced by not only habituation but also risk allocation by simulating attacks on blackbirds Turdus merula by both usual (pedestrians) and novel (radio-controlled vehicle) potential predators in parks with different levels of human visitation. Individual blackbirds from parks with higher pedestrian rates showed lower FID than individuals from parks with lower pedestrian rates, in response to both usual and novel approaches. Blackbirds adjusted their antipredator behavior to the specific level of pedestrian rate encountered every morning and evening in each park, with higher FID in the period with lower pedestrian rate. Similar responses to usual and novel potential predators among parks and daily va! riation in antipredator behavior support the risk allocation hypothesis and could not be explained by habituation. However, the rate at which FID was reduced in individuals from low-visited parks to high-visited parks was greater for pedestrian attacks than for novel potential predator attacks, suggesting that habituation is also present in our system and complements the effects of risk allocation. Our results have applied implications: the reduction in FID with increasing human visitation in natural areas is usually attributed to habituation; however, we propose that risk allocation can also reduce antipredator behavior effort to survive in habitats with high levels of recreational activities at the expense of potential physiological costs.
• Caste-specific symbiont policing by workers of Acromyrmex fungus-growing ants
  - Behav Ecol 20(2):378-384 (2009)
  The interaction between leaf-cutting ants and their fungus garden mutualists is ideal for studying the evolutionary stability of interspecific cooperation. Although the mutualism has a long history of diffuse coevolution, there is ample potential for conflicts between the partners over the mixing and transmission of symbionts. Symbiont transmission is vertical by default, and both the ants and resident fungus actively protect the fungal monoculture growing in their nest against secondary introductions of genetically dissimilar symbionts from other colonies. An earlier study showed that mixtures of major and minor Acromyrmex workers eliminate alien fungus fragments even in subcolonies where their resident symbiont is not present. We hypothesize that the different tasks and behaviors performed by majors and minors are likely to select for differential responses to alien fungi. Major workers forage and cut new leaves and masticate them after delivery in the upper parts of! the fungus garden and so are likely to more frequently encounter alien fungus than minor workers maintaining the established fungus garden and caring for the brood. We show that major workers of Acromyrmex echinatior indeed express stronger incompatibility reactions toward alien fungus garden fragments than minor workers. This implies that only the major workers, through recognition and exclusion of foreign fungus clones at their point of entry to the nest, have a realistic possibility to eliminate alien fungal tissue before it gets incorporated in the fungus garden and starts competing with the resident fungal symbiont.
• Behavioral changes associated with a population density decline in the facultatively social red fox
  - Behav Ecol 20(2):385-395 (2009)
  Understanding the causal mechanisms promoting group formation in carnivores has been widely investigated, particularly how fitness components affect group formation. Population density may affect the relative benefits of natal philopatry versus dispersal. Density effects on individual behavioral strategies have previously been studied through comparisons of different populations, where differences could be confounded by between-site effects. We used a single population of red foxes (Vulpes vulpes) in the city of Bristol, UK, that underwent a natural perturbation in density to compare key changes in 1) group structure, 2) within-group relatedness, 3) mating system, 4) dispersal, and 5) dominance attainment. At high densities (19.6-27.6 adults km-2), group sex ratios were equal and included related and unrelated individuals. At low densities (4.0-5.5 adults km-2), groups became female biased and were structured around philopatric females. However, levels of within-group ! relatedness were unchanged. The genetic mating patterns changed with no instances of multiple-paternity litters and a decline in the frequency of extrapair litters of cubs from [≤]77% to [≤]38%. However, the number of genetically monogynous groups did not differ between periods. Dispersal was male biased at both high and low densities. At high density, most dominant males in the study groups appeared to have gained dominance after dispersing, but natal philopatry was an equally successful strategy at low density; conversely, most dominant females were philopatric individuals at both high and low densities. These results illustrate how density may alter behavioral strategies such as mating patterns and how this, in turn, alters group structure in a single population.
• Do hoverflies (Diptera: Syrphidae) sound like the Hymenoptera they morphologically resemble?
  - Behav Ecol 20(2):396-402 (2009)
  It has long been recognized that many hoverfly species (Diptera: Syrphidae) mimic the morphological appearance of defended Hymenoptera, such as wasps and bees. However, it has also been repeatedly suggested that some mimetic hoverflies respond with sounds on attack that resemble the warning or startle sounds of their hymenopteran models. In this study, we set out to quantitatively compare the spectral characteristics of the sounds produced by a range of nonmimetic flies, wasps, bumblebees, honeybees, and their hoverfly mimics when they were artificially attacked. The sounds made by wasps and honeybees after simulated attacks were statistically distinguishable from their hoverfly mimics. Bumblebee models of their hoverfly mimics share some similarities in the sound they produce on attack, but they were no closer acoustically to their model than a range of other hoverfly species that morphologically resemble other models. All the mimetic hoverflies tested in this study t! ended to sound similar to one another, regardless of the model they resemble morphologically. Overall, we found little evidence that mimetic hoverflies sound like their hymenopteran models on attack, and we question whether acoustic mimicry has evolved in this complex.
• Competition and brood reduction: testing alternative models of clutch-size evolution in parasitoids
  - Behav Ecol 20(2):403-409 (2009)
  Competition between siblings occurs in many taxa including parasitoid wasps. Larvae of solitary species eliminate competitors by engaging in aggressive behavior, thus restricting brood size to a single individual. In gregarious species, more than one offspring can develop per host. There are 2 models by which gregariousness can arise in a population of solitary individuals: 1) through a reduction in larval mobility (with the retention of aggressive behavior) or 2) through a reduction in fighting behavior or ability. When more larvae are present than can be supported by available host resources, these 2 models make opposing predictions regarding the process of brood size reduction: Mortality occurring early in larval development under the reduced mobility hypothesis versus mortality occurring throughout larval development under the reduced aggression hypothesis. Here, we measure changes in brood size over the course of larval development of the gregarious parasitoid, Co! tesia flavipes. Superparasitized hosts contained approximately twice as many C. flavipes eggs as hosts parasitized by a single parasitoid female. Brood sizes in superparasitized hosts declined gradually as C. flavipes individuals developed, whereas brood sizes remained constant during larval development in singly parasitized hosts. An absence of wounded or destroyed larvae suggested no aggressive behavior. Collectively, these results support the reduced aggression hypothesis.
• Lekking satin bowerbird males aggregate with relatives to mitigate aggression
  - Behav Ecol 20(2):410-415 (2009)
  Males in several lekking species aggregate with their relatives to display for females, suggesting that kin selection can affect sexual selection. Several hypotheses have been proposed to explain this behavior, but no general explanation has emerged. In most species with lek mating systems, neighboring males have intense aggressive interactions that can affect the quality of their sexual displays. Here we test the hypothesis that the presence of related neighbors mitigates the negative consequences of this aggression. Male bowerbirds build stick display structures (bowers) that are used by females in mate assessment and are commonly destroyed by males' 2 nearest neighbors. We show that kin aggregate as first or second nearest neighbors, and males direct fewer bower destructions toward kin than equidistant nonkin. Males with more relatives nearby receive fewer bower destructions. These results suggest that the restraining effect of relatedness on aggression favors the c! lose spatial association of related males' display sites. An alternative hypothesis, that related males aggregate to gain copulations from females attracted to successful relatives, was not supported.
• Conclusions beyond support: overconfident estimates in mixed models
  - Behav Ecol 20(2):416-420 (2009)
  Mixed-effect models are frequently used to control for the nonindependence of data points, for example, when repeated measures from the same individuals are available. The aim of these models is often to estimate fixed effects and to test their significance. This is usually done by including random intercepts, that is, intercepts that are allowed to vary between individuals. The widespread belief is that this controls for all types of pseudoreplication within individuals. Here we show that this is not the case, if the aim is to estimate effects that vary within individuals and individuals differ in their response to these effects. In these cases, random intercept models give overconfident estimates leading to conclusions that are not supported by the data. By allowing individuals to differ in the slopes of their responses, it is possible to account for the nonindependence of data points that pseudoreplicate slope information. Such random slope models give appropriate s! tandard errors and are easily implemented in standard statistical software. Because random slope models are not always used where they are essential, we suspect that many published findings have too narrow confidence intervals and a substantially inflated type I error rate. Besides reducing type I errors, random slope models have the potential to reduce residual variance by accounting for between-individual variation in slopes, which makes it easier to detect treatment effects that are applied between individuals, hence reducing type II errors as well.
• Group size effect caused by food competition in nutmeg mannikins (Lonchura punctulata)
  - Behav Ecol 20(2):421-425 (2009)
  When foraging group sizes increase, animals generally decrease the time devoted to antipredator detection and increase their foraging rate, the commonly reported group size effect. The increased foraging rate is thought to follow from increased safety from predators because as group size increases, more eyes are available to detect predators and the risk of being a predator's victim is diluted. This increased safety then allows higher feeding rates because individuals can reallocate time spent in vigilance to foraging. However, increased foraging rates can also be due to increased competition for resources as the number of companions increases. We tested whether increased feeding rates are the product of competition or antipredation when group size increases in nutmeg mannikins (Lonchura punctulata). We used edited video playbacks to change group size and type of competitor: vigilant only, feeding only, and controls. We found that the increased feeding rate associated ! with an increased group size only resulted when the companions were feeding. Video playbacks of nonforaging companions neither decreased an individual's use of vigilance while handling food nor did it release the full increase of feeding rate. Focal birds lowered their scanning time while feeding as the frequency of pecking by simulated nonvigilant companions increased. We conclude that the group size effect reported in nutmeg mannikins is not a product of safety benefits of group living but may also arise from the costs imposed by competition for resources.
• Livestock grazing behavior and inter- versus intraspecific disease risk via the fecal-oral route
  - Behav Ecol 20(2):426-432 (2009)
  Livestock herbivores are at risk of parasite/pathogen exposure from livestock and wild mammal feces during grazing. Livestock exposure to parasites/pathogens will be dependent on the behavioral contact processes between grazing livestock and host animal (both livestock and wild mammal) feces at the bite scale. Here we use 2 grazing experiments to determine the affect of feces from different species and in different defecation patterns on the grazing response of cattle. In experiment 1, there were 4 plots, each with 4 replicates of 5 patch treatments of different fecal contamination (240 g/m2 of Eurasian badger feces, cattle feces, fallow deer feces, Eurasian rabbit feces, and noncontaminated control patches). In experiment 2, there were 3 treatment patterns of badger fecal contamination (one 1-m2 circular patch contaminated with 960 g of badger feces; two 1-m2 circular patches each contaminated with 480 g of badger feces; and four 1-m2 circular patches each contaminate! d with 240 g of badger feces), divided into 2 plots per treatment. The cattle's grazing response was determined by measuring sward depletion at each of the treatment patches. In experiment 1, cattle-grazed control and rabbit fecal-contaminated patches the most, whereas badger-contaminated patches were grazed the least. In experiment 2, cattle grazed the treatment with the greatest number of fecal-contaminated patches the most. We conclude that cattle vary their grazing response to feces from different host species and to feces in different spatial patterns. Quantifying these behavioral responses to feces is a key step toward quantifying infection risk to herbivores via the fecal-oral route in grazing systems.
• Individual differences in protandry, sexual selection, and fitness
  - Behav Ecol 20(2):433-440 (2009)
  Protandry is the difference in arrival date between males and females, with competition among males for access to preferred territories (the rank advantage hypothesis) or mating success (the mate opportunity hypothesis) supposedly driving the evolution of protandry. The fitness costs and benefits of protandry accruing to individuals differing in degree of protandry (arrival date of a male relative to the arrival date of his partner) have never been quantified. We analyzed the fitness consequences of sex differences in arrival date in the barn swallow Hirundo rustica, in which arrival date can be precisely estimated and the fitness of pairs differing in degree of individual protandry assessed. Early arriving males had greater mating success than late arriving males. The number of extrapair offspring in own nests decreased with increasing degree of individual protandry, whereas the number of offspring fathered by a focal male was unrelated to individual protandry. There ! was directional selection on individual protandry as shown by pairs with a larger than average degree of protandry reproducing early and, hence, supposedly producing more recruits. There was also stabilizing selection on individual protandry as shown by pairs with an intermediate degree of protandry reproducing early. Annual production of fledglings increased with early arrival of males, but not with early arrival of females, once the effect of laying date had been considered, with no additional effect of individual protandry. Neither male nor female survival was significantly related to degree of individual protandry. These findings are consistent not only with the mate opportunity hypothesis but also with a sexual conflict hypothesis, suggesting that males and females differ in their optimal timing of arrival due to sex-specific fitness costs and benefits.
• Interactions between masculinity-femininity and apparent health in face preferences
  - Behav Ecol 20(2):441-445 (2009)
  Consistent with Getty's (2002. Signaling health versus parasites. Am Nat. 159:363-371.) proposal that cues to long-term health and cues to current condition are at least partly independent, recent research on human face preferences has found divergent effects of masculinity-femininity, a cue to long-term health, and apparent health, a cue to current condition. In light of this, we tested for interactions between these 2 cues. Participants viewed composite images of opposite-sex faces that had been manufactured in combinations of high and low apparent health and masculinity-femininity. Preferences for masculinity in men's faces and femininity in women's faces were stronger when judging the attractiveness of faces with high apparent health than when judging the attractiveness of faces with low apparent health. Similarly, preferences for high apparent health were stronger for judgments of masculine men's faces and feminine women's faces than for judgments of feminine men'! s faces and masculine women's faces, respectively. Interactions between apparent health and masculinity-femininity when forming face preferences may function to optimize how masculinity-femininity and apparent health are used to infer the quality of potential mates and highlight the complexity and sophistication of the perceptual mechanisms that underpin face preferences.
• Negotiation between parents over care: reversible compensation during incubation
  - Behav Ecol 20(2):446-452 (2009)
  Parental care is often beneficial for the young but costly for the caregiving parent. Because both parents benefit from care via the offspring, whereas they pay the costs individually, a conflict is expected about how much care each parent should provide. How do parents settle this conflict? We addressed this question by reducing nest temperatures during incubation in the Kentish plover Charadrius alexandrinus, a small ground-nesting shorebird in which the parents share incubation. By cooling the clutch using a remote-controlled device built under the nest, we experimentally increased the workload of either the male or the female in random order and recorded the behavioral responses of the targeted parent and its mate. Unlike most previous manipulations of parental effort, our manipulation sought to measure a parent's response to an increase, not a shortfall, in the partner's contribution. The manipulation was also short term and reversed between the members of a given! pair. We found that there is a trade-off between the efforts of parents because increased (or reduced) effort by the targeted parent was associated with decreased (or increased) effort by its mate, respectively. This result is consistent with theoretical models that predict compensation as a response to changed parental effort of the mate. We also found that compensation was consistent between treatments when the male or the female of a given pair was targeted. Furthermore, our results support the notion that parents adjust their effort in response to their mate's behavior in real time, that is, they negotiate parental roles.
• The social and genetic mating system in flickers linked to partially reversed sex roles
  - Behav Ecol 20(2):453-458 (2009)
  The type of social and genetic mating system observed in birds is influenced by the need of both sexes to provide parental care. In woodpeckers, unlike most birds, females are partially emancipated as males provide most of the care including nocturnal incubation. We analyzed the mating system of northern flickers Colaptes auratus and used microsatellite markers to assess parentage of 326 nestlings from 46 monogamous broods and 41 nestlings from 7 polyandrous broods. No cases of extrapair paternity were found in monogamous broods, but there was one such case in the brood of a secondary male of a polyandrous female. Intraspecific parasitism lead to 17% of broods containing at least one parasitic egg. The identity of the parasitic female was determined in 5 cases to be a close neighbor with a mate and clutch of her own. Between 0% and 5% of females annually were polyandrous with the timing of the 2 nests slightly staggered. Polyandrous females were older than average fema! les in the population, and their primary males were older than secondary males. Polyandrous females raised nearly twice as many (10.8) nestlings compared with monogamous females (5.5). Although most female flickers are strictly socially and genetically monogamous, some can benefit from engaging in the alternate reproductive tactics of polyandry and brood parasitism. Therefore, at least in flickers, such tactics of laying eggs in multiple nests are not the result of poor-quality females "making the best of a bad situation" but are a way to increase reproductive success.