Competing for crevices: interspecific conflict influences retreat-site selection in montane lizards

Species conflict at Earth’s edges – Contests, climate, and coveted resources

Direct conflict between species is an infrequently witnessed biological phenomenon. Potential drivers of such contests can include climate change, especially at Earth’s high elevation and latitudinal extremes where temperatures warm 2–5 times faster than elsewhere and hydro-geomorphic processes such as glacial recession and soil erosion affect species access to abiotic resources. We addressed a component of this broader issue by empirical assessments of mammalian conflict over access to four abiotic resources – minerals, water, snow, and shade – by annotation of past studies and by empirical data collection. Evidence for Nearctic and Palearctic mammals indicates that when desert waters are in short supply, contests intensify, generally favoring larger species regardless of their status as native or exotic. Our empirical data indicate that contests between two large and approximately similarly-sized mammals – mountain goats (Oreamnos americanus) and bighorn sheep (Ovis canadensis) – along a 2,500 km gradient at three high-altitude (above tree-line) sites in the Rocky Mountains of North America, result in striking asymmetries; goats dominated > 95% of interactions. Despite far fewer observations of encounters to access shade or snow patches, an increasingly prominent dialog needs to be held about rarely explored biological phenomena where less is known than we might otherwise presume, whether induced by climate or increasing anthropological alteration because of underpinnings to understand community structure and conservation planning. Observations on the frequency and intensity by which individuals escalate behavior to access abiotic resources remains an underappreciated arena to help identify the proximate importance of scarcity in the natural environment. Notwithstanding Darwin’s prediction some 165 years ago that populations in extreme environments (high-latitude, high-altitude) are more likely to be impacted by abiotic variables than biotic, conflict between species may be reflective of climate degradation coupled with the changing nature of coveted resources.

Predator interference and complexity-stability in food webs

It is predicted that ecological communities will become unstable with increasing species numbers and subsequent interspecific interactions; however, this is contrary to how natural ecosystems with diverse species respond to changes in species numbers. This contradiction has steered ecologists toward exploring what underlying processes allow complex communities to stabilize even through varying pressures. In this study, a food web model is used to show an overlooked role of interference among multiple predator species in solving this complexity–stability problem. Predator interference in large communities weakens species interactions due to a reduction in consumption rates by prey-sharing species in the presence of predators in response to territorial and aggressive behavior, thereby playing a key stabilizing role in communities. Especially when interspecific interference is strong and a community has diverse species and dense species interactions, stabilization is likely to work and creates a positive complexity–stability relationship within a community. The clear positive effect of complexity on community stability is not reflected by/intraspecific interference, emphasizing the key role of interspecific interference among multiple predator species in maintaining larger systems.

The ecology of sleep in non-avian reptiles

Sleep is ubiquitous in the animal kingdom and yet displays considerable variation in its extent and form in the wild. Ecological factors, such as predation, competition, and microclimate, therefore are likely to play a strong role in shaping characteristics of sleep. Despite the potential for ecological factors to influence various aspects of sleep, the ecological context of sleep in non-avian reptiles remains understudied and without systematic direction. In this review, we examine multiple aspects of reptilian sleep, including (i) habitat selection (sleep sites and their spatio-temporal distribution), (ii) individual-level traits, such as behaviour (sleep postures), morphology (limb morphometrics and body colour), and physiology (sleep architecture), as well as (iii) inter-individual interactions (intra- and inter-specific). Throughout, we discuss the evidence of predation, competition, and thermoregulation in influencing sleep traits and the possible evolutionary consequences of these sleep traits for reptile sociality, morphological specialisation, and habitat partitioning. We also review the ways in which sleep ecology interacts with urbanisation, biological invasions, and climate change. Overall, we not only provide a systematic evaluation of the conceptual and taxonomic biases in the existing literature on reptilian sleep, but also use this opportunity to organise the various ecological hypotheses for sleep characteristics. By highlighting the gaps and providing a prospectus of research directions, our review sets the stage for understanding sleep ecology in the natural world.

Mechanisms of reduced interspecific interference between territorial species

Interspecific territoriality has complex ecological and evolutionary consequences. Species that interact aggressively often exhibit spatial or temporal shifts in activity that reduce the frequency of costly encounters. We analyzed data collected over a 13-year period on 50 populations of rubyspot damselflies (Hetaerina spp.) to examine how rates of interspecific fighting covary with fine-scale habitat partitioning and to test for agonistic character displacement in microhabitat preferences. In most sympatric species, interspecific fights occur less frequently than expected based on the species’ relative densities. Incorporating measurements of spatial segregation and species discrimination into the calculation of expected frequencies accounted for most of the reduction in interspecific fighting (subtle differences in microhabitat preferences could account for the rest). In 23 of 25 sympatric population pairs, we found multivariate differences between species in territory microhabitat (perch height, stream width, current speed, and canopy cover). As predicted by the agonistic character displacement hypothesis, sympatric species that respond more aggressively to each other in direct encounters differ more in microhabitat use and have higher levels of spatial segregation. Previous work established that species with the lowest levels of interspecific fighting have diverged in territory signals and competitor recognition through agonistic character displacement. In the other species pairs, interspecific aggression appears to be maintained as an adaptive response to reproductive interference, but interspecific fighting is still costly. We now have robust evidence that evolved shifts in microhabitat preferences also reduce the frequency of interspecific fighting.

Honest signals and sexual conflict: Female lizards carry undesirable indicators of quality

Sex differences in animal coloration often result from sex-dependent regulatory mechanisms. Still, some species exhibit incomplete sexual dimorphism as females carry a rudimentary version of a costly male trait, leading to intralocus sexual conflict. The underlying physiology and condition dependence of these traits can inform why such conflicts remain unresolved. In eastern fence lizards (Sceloporus undulatus), blue iridophore badges are found in males and females, but melanin pigmentation underneath and surrounding badges is male-exclusive. We track color saturation and area of badges across sexual maturity, and their relationship to individual quality (body condition and immunocompetence) and relevant hormones (testosterone and corticosterone). Saturation and testosterone were positively correlated in both sexes, but hormone and trait had little overlap between males and females. Saturation was correlated with body condition and immunocompetence in males but not in females. Co-regulation by androgens may have released females from resource allocation costs of color saturation, even when in high condition. Badge area was independent of testosterone, but associated with low corticosterone in females, indicating that a nonsex hormone underlies incomplete sexual dimorphism. Given the evidence in this species for female reproductive costs associated with ornamentation, this sex-nonspecific regulation of an honest signal may underlie intralocus sexual conflict.

Interspecific social dominance networks reveal mechanisms promoting coexistence in sympatric charr in Hokkaido, Japan

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n = 761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4 years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.

Predatory functional responses under increasing temperatures of two life stages of an invasive gecko

The direct effects of temperature increases and differences among life-history might affect the impacts of native and invasive predators on recipient communities. Comparisons of functional responses can improve our understanding of underlying processes involved in altering species interaction strengths and may predict the effect of species invading new communities. Therefore, we investigated the functional responses of the mourning gecko Lepidodactylus lugubris (Duméril & Bibron, 1836) to explore how temperature, body-size and prey density alter gecko predatory impacts in ecosystems. We quantified the functional responses of juvenile and adult geckos in single-predator experiments at 20, 23 and 26 °C. Both displayed saturating Type-II functional responses, but juvenile functional responses and the novel Functional Response Ratio were positively affected by temperature as juvenile attack rates (a) increased as a function of increased temperature. Handling times (h) tended to shorten at higher temperature for both predator stages. We demonstrate that the effects of temperature on functional responses of geckos differ across ontogeny, perhaps reflecting life-history stages prioritising growth and maturation or body maintenance. This indicates that temperature-dependent gecko predatory impacts will be mediated by population demographics. We advocate further comparisons of functional responses to understand the invasiveness and future predatory impacts of geckos, and other invasive species globally, as temperatures change.

Social context alters retreat- and nest-site selection in a globally invasive gecko, Hemidactylus frenatus

Microhabitat orientation and structure and the presence of conspecifics may strongly influence the choice of habitat. We studied how these variables influence retreat- and nest-site selection in gravid females of a globally successful invasive species, the Asian house gecko (Hemidactylus frenatus). When provided with various substrates (vertical and horizontal ceramic tiles, vertical and horizontal plywood tiles, horizontal bark over leaf litter, vertical bark over a log, and sand) gravid female geckos preferred to retreat to, and nest in, materials with crevices commonly found in urban habitats. When housed alone, gravid females most frequently retreated to vertical ceramic tile or wooden crevices, and 66.7% nested in vertical ceramic tiles. When housed with two other conspecifics, gravid females most frequently retreated to vertical ceramic tiles, but selected a wider range of nest sites. Overall, gravid geckos housed alone typically nested in the same substrates that they used as diurnal retreats; when housed in groups, however, females oviposited in locations different from those they selected as retreats. Thus, H. frenatus females use a wider range of substrates when conspecifics are present. Invasion success in this species might be driven, in part, by preferences for retreat and nest substrates that are common in human-dominated habitats.

Experimental removal reveals only weak interspecific competition between two coexisting lizards

Competition for resources is an important mechanism that shapes ecological communities. Interspecific competition can affect habitat selection, fitness, and abundance in animals. We used a removal experiment and mark–recapture to test the hypothesis that competition with the larger and more abundant Striped Plateau Lizard (Sceloporus virgatus H.M. Smith, 1938) limits habitat selection, fitness, and abundance in Ornate Tree Lizards (Urosaurus ornatus (Baird in Baird and Girard, 1852)). Ornate Tree Lizards in the plots where Striped Plateau Lizards were removed switched between habitat types more frequently and moved farther than Ornate Tree Lizards in control plots. However, there were no significant changes in the relative densities of Ornate Tree Lizards in each habitat type or in microhabitat use. We also found no changes in growth rates, survival, or abundance of Ornate Tree Lizards in response to the removal of Striped Plateau Lizards. Our results suggest that interspecific competition was not strong enough to limit habitat use or abundance of Ornate Tree Lizards. Perhaps interspecific competition is weak between coexisting species when resource levels are not severely depleted. Therefore, it is important to consider environmental conditions when assessing the importance of interspecific competition.

Combining dispersal, landscape connectivity and habitat suitability to assess climate-induced changes in the distribution of Cunningham's skink, Egernia cunninghami

The ability of species to track their climate niche is dependent on their dispersal potential and the connectivity of the landscape matrix linking current and future suitable habitat. However, studies modeling climate-driven range shifts rarely address the movement of species across landscapes realistically, often assuming "unlimited" or "no" dispersal. Here, we incorporate dispersal rate and landscape connectivity with a species distribution model (Maxent) to assess the extent to which the Cunningham's skink (Egernia cunninghami) may be capable of tracking spatial shifts in suitable habitat as climate changes. Our model was projected onto four contrasting, but equally plausible, scenarios describing futures that are (relative to now) hot/wet, warm/dry, hot/with similar precipitation and warm/wet, at six time horizons with decadal intervals (2020-2070) and at two spatial resolutions: 1 km and 250 m. The size of suitable habitat was projected to decline 23-63% at 1 km and 26-64% at 250 m, by 2070. Combining Maxent output with the dispersal rate of the species and connectivity of the intervening landscape matrix showed that most current populations in regions projected to become unsuitable in the medium to long term, will be unable to shift the distance necessary to reach suitable habitat. In particular, numerous populations currently inhabiting the trailing edge of the species' range are highly unlikely to be able to disperse fast enough to track climate change. Unless these populations are capable of adaptation they are likely to be extirpated. We note, however, that the core of the species distribution remains suitable across the broad spectrum of climate scenarios considered. Our findings highlight challenges faced by philopatric species and the importance of adaptation for the persistence of peripheral populations under climate change.

Territoriality and Conflict Avoidance Explain Asociality (Solitariness) of the Endosymbiotic Pea Crab Tunicotheres moseri

Host monopolization theory predicts symbiotic organisms inhabiting morphologically simple, relatively small and scarce hosts to live solitarily as a result of territorial behaviors. We tested this prediction with Tunicotheres moseri, an endosymbiotic crab dwelling in the atrial chamber of the morphologically simple, small, and relatively scarce ascidian Styela plicata. As predicted, natural populations of T. moseri inhabit ascidian hosts solitarily with greater frequency than expected by chance alone. Furthermore, laboratory experiments demonstrated that intruder crabs take significantly longer to colonize previously infected compared to uninfected hosts, indicating as expected, that resident crabs exhibit monopolization behaviors. While territoriality does occur, agonistic behaviors employed by T. moseri do not mirror the overt behaviors commonly reported for other territorial crustaceans. Documented double and triple cohabitations in the field coupled with laboratory observations demonstrating the almost invariable success of intruder crabs colonizing occupied hosts, suggest that territoriality is ineffective in completely explaining the solitary social habit of this species. Additional experiments showed that T. moseri juveniles and adults, when searching for ascidians use chemical cues to avoid hosts occupied by conspecifics. This conspecific avoidance behavior reported herein is a novel strategy most likely employed to preemptively resolve costly territorial conflicts. In general, this study supports predictions central to host monopolization theory, but also implies that alternative behavioral strategies (i.e., conflict avoidance) may be more important than originally thought in explaining the host use pattern of symbiotic organisms.

Experimental assessment of social interactions in two species of the genus Teratoscincus (Gekkota)

Social organization of many reptile species that are rare in the wild remains rather unexplored due to difficulties when setting experiments in the field. Behavioral analysis of standard social situations in laboratory conditions is considered an indirect method to reveal social behavior in the field. We studied two rare species of geckos, Teratoscincus scincus and Teratoscincus keyserlingii, inhabiting sand dunes of Uzbekistan and Eastern Iran. A series of experiments was carried out to quantify responses in social interactions among conspecific adults as well as reactions of these towards conspecific/heterospecific subadults and juveniles. We also assessed the effect of species and sex on recorded behavior. Finally, the reaction to threat stimuli simulating predator attack was analyzed. The species effect was recorded only in the response to a simulated predatory attack: T. scincus typically escaped whereas larger T. keyserlingii attacked the stimulus. In accordance with the sexual competition hypothesis, agonistic interactions were nearly exclusively confined to male-male encounters while females were tolerant to each other. Male-female encounters regularly resulted in mating attempts, which suggests that females are not strongly selective in choosing partners. Therefore, male aggression can be linked to mate guarding or territoriality. Adults' lack of interest in immature geckos may indicate generalized tolerance of adults towards young.

The coexistence of seven sympatric fulvettas in Ailao Mountains, Ejia Town, Yunnan Province

The coexistence of ecologically similar species sharing sympatric areas is a central issue of community ecology. Niche differentiation is required at least in one dimension to avoid competitive exclusion. From 2012-2014, by adopting the methods of mist-nets and point counts to evaluate spatial niche partitioning and morphological differentiations, we explored the coexistence mechanisms of seven sympatric fulvettas in Ailao Mountains, Ejia town, Yunnan Province, China. The microhabitats of these seven fulvettas were significantly different in elevation, roost site height and vegetation coverage, indicating a spatial niche segregation in different levels. Approximately, 90.30% of the samples were correctly classified by linear discriminant analysis (LDA) with correct rates at 91.20%-100%, except the White-browed fulvetta (Alcippe vinipectus) (65.4%) and the Streak-throated fulvetta (A. cinereiceps) (74.6%). The seven fulvettas were classified into four guilds based on their specific morphological characters, suggesting that the species in each guild use their unique feeding ways to realize resource partitioning in the overlapped areas. These finding indicate that through multi-dimensional spatial niche segregation and divergence in resource utilizing, the inter-specific competition among these seven fulvettas is minimized, whereas, coexistence is promoted.

Determinants of habitat selection by hatchling Australian freshwater crocodiles

Animals almost always use habitats non-randomly, but the costs and benefits of using specific habitat types remain unknown for many types of organisms. In a large lake in northwestern Australia (Lake Argyle), most hatchling (<12-month-old) freshwater crocodiles (Crocodylus johnstoni) are found in floating vegetation mats or grassy banks rather than the more widely available open banks. Mean body sizes of young crocodiles did not differ among the three habitat types. We tested four potential explanations for non-random habitat selection: proximity to nesting sites, thermal conditions, food availability, and exposure to predation. The three alternative habitat types did not differ in proximity to nesting sites, or in thermal conditions. Habitats with higher food availability harboured more hatchlings, and feeding rates (obtained by stomach-flushing of recently-captured crocodiles) were highest in such areas. Predation risk may also differ among habitats: we were twice as likely to capture a crocodile after seeing it in open-bank sites than in the other two habitat types. Thus, habitat selection of hatchling crocodiles in this system may be driven both by prey availability and by predation risk.

Competition with wall lizards does not explain the alpine confinement of Iberian rock lizards: an experimental approach

Interspecific competition can limit the distribution of species along altitudinal gradients. It has been suggested that Western European rock lizards (genus Iberolacerta) are restricted to mountains due to the expansion of wall lizards (Podarcis), but there is no experimental evidence to corroborate this hypothesis. This study examines if interference competition with Podarcis muralis is a plausible explanation for the alpine confinement of Iberian rock lizards Iberolacerta cyreni. In a first experiment, we used an enclosure with four types of microhabitats to investigate whether adult rock and/or wall lizards shifted microhabitat or refuge preferences in the presence of the other species, and to detect aggressive interactions between them. In a second experiment, we staged heterospecific encounters between naïve, laboratory-born juveniles to identify behavioural differences and agonistic interactions. In the enclosure, neither rock nor wall lizards changed their microhabitat preferences in the presence of the other species. Nevertheless, rock lizards increased the diversity of microhabitats and nocturnal refuges used in the single species trials, which had twice the number of conspecifics. Aggressive interactions involved mainly large rock lizard males. Juveniles did not show any interspecific agonistic behaviour, but rock lizards spent more time basking and less time moving. Thus, we found no evidence of competition between both species in terms of habitat shifts or agonistic interactions, although intraspecific interactions seemed to explain the behaviour of adult rock lizards. We conclude that other factors are currently determining the alpine confinement of rock lizards.

Squeezed at the top: Interspecific aggression may constrain elevational ranges in tropical birds

Tropical montane species are characterized by narrow elevational distributions. Recent perspectives on mechanisms maintaining these restricted distributions have emphasized abiotic processes, but biotic processes may also play a role in their establishment or maintenance. One historically popular hypothesis, especially for birds, is that interspecific competition constrains ranges of closely related species that "replace" each other along elevational gradients. Supporting evidence, however, is based on patterns of occurrence and does not reveal potential mechanisms. We experimentally tested a prediction of this hypothesis in two genera of tropical songbirds, Catharus (Turdidae) and Henicorhina (Troglodytidae), in which species have nonoverlapping elevational distributions. Using heterospecific playback trials, we found that individuals at replacement zones showed aggressive territorial behavior in response to songs of congeners. As distance from replacement zones increased, aggression toward congener song decreased, suggesting a learned component to interspecific aggression. Additionally, aggressive responses in Catharus were asymmetric, indicating interspecific dominance. These results provide experimental evidence consistent with the hypothesis that interspecific competitive interactions restrict ranges of Neotropical birds. Our results also underscore the need to consider biotic processes, such as competition, when predicting how species' ranges will shift with climate change. Asymmetric aggression could be particularly important. For example, if warming in montane landscapes allows upslope range expansion by dominant competitors, then high-elevation subordinate species could be forced into progressively smaller mountaintop habitats, jeopardizing viability of their populations.

Repeatable intra-individual variation in plasma testosterone concentration and its sex-specific link to aggression in a social lizard

Individual hormone profiles can be important generators of phenotypic variation. Despite this, work on the consequences of hormone profiles has traditionally ignored the large inter-individual variation within natural populations. However, recent research has advocated the need to explicitly consider this variation and address its consequences for selection. One of the key steps in this process is examining repeatability in hormone profiles and their links to behavioral traits under selection. In this study we show that individuals within a free-ranging population of the Australian lizard Egernia whitii exhibit temporal repeatability in their circulating baseline testosterone concentrations as well as their aggressive response towards conspecific intruders. Furthermore, we show significant, sex-specific links between testosterone and aggression. Specifically, testosterone and aggression is negatively linked in males, while there is no relationship in females. As conspecific aggression has significant consequences for fitness-related traits (parental care, mating strategies) in this species, inter-individual variation in testosterone concentrations, through their effects on aggression, could have important implications for individual fitness. We discuss the potential causes and consequences of hormonal repeatability as well as provide explanations for its sex-specific links with aggression. Specifically, we suggest that these patterns are the result of alternative hormonal pathways governing aggression within Egernia and may indicate a decoupling of aggression and testosterone across the sexes.

Testing the independent effects of population and shelter density on behavioural and corticosterone responses of tree skinks

In animals, social organisation and behaviour can respond to variation in key ecological factors including population and resource density. As these two factors covary, their relative importance is difficult to estimate using field studies. Consequently, we conducted two manipulative experiments varying levels of either population or shelter density to separate their effects on solitary, affiliative and agonistic behaviour and physiology in the social tree skink, Egernia striolata. We used focal observations and plasma concentrations of the hormone corticosterone to measure behavioural and physiological responses to these manipulations. Aggressive behaviours occurred more frequently at high skink density, with males at high density exhibiting social stress, as indicated by increased levels of corticosterone. Skinks at low densities showed greater affiliative behaviour, spending more time basking as pairs. Changes in shelter density influenced exploratory behaviours, with males at low shelter densities exploring enclosures more than those at high shelter densities. Skinks sheltered as pairs more frequently at low shelter density, even after taking into account differences in frequency of pair sheltering expected by chance alone, suggesting that low shelter availability promotes pair behaviour. Corticosterone levels increased over time at low shelter density, which may have been a result of thermal stress coupled with a lack of microclimate variation in comparison to high shelter density. These results suggest that population and resource density are key factors that can independently influence social behaviour and endocrinology, and consequently social organisation, in different ways.

Larger than life: humans' nonverbal status cues alter perceived size

BACKGROUND

Social dominance and physical size are closely linked. Nonverbal dominance displays in many non-human species are known to increase the displayer's apparent size. Humans also employ a variety of nonverbal cues that increase apparent status, but it is not yet known whether these cues function via a similar mechanism: by increasing the displayer's apparent size.

METHODOLOGY/PRINCIPAL FINDING

We generated stimuli in which actors displayed high status, neutral, or low status cues that were drawn from the findings of a recent meta-analysis. We then conducted four studies that indicated that nonverbal cues that increase apparent status do so by increasing the perceived size of the displayer. Experiment 1 demonstrated that nonverbal status cues affect perceivers' judgments of physical size. The results of Experiment 2 showed that altering simple perceptual cues can affect judgments of both size and perceived status. Experiment 3 used objective measurements to demonstrate that status cues change targets' apparent size in the two-dimensional plane visible to a perceiver, and Experiment 4 showed that changes in perceived size mediate changes in perceived status, and that the cue most associated with this phenomenon is postural openness.

CONCLUSIONS/SIGNIFICANCE

We conclude that nonverbal cues associated with social dominance also affect the perceived size of the displayer. This suggests that certain nonverbal dominance cues in humans may function as they do in other species: by creating the appearance of changes in physical size.

Female aggression predicts mode of paternity acquisition in a social lizard

Individual differences in behaviour are ubiquitous in nature. Despite the likely role of selection in maintaining these differences, there are few demonstrations of their fitness consequences in wild populations and, consequently, the mechanisms that link behavioural variation to variation in fitness are poorly understood. Specifically, the consequences of consistent individual differences in behaviour for the evolution of social and mating strategies have rarely been considered. We examined the functional links between variation in female aggression and her social and mating strategies in a wild population of the social lizard Egernia whitii. We show that female Egernia exhibit temporally consistent aggressive phenotypes, which are unrelated to body size, territory size or social density. A female's aggressive phenotype, however, has strong links to her mode of paternity acquisition (within- versus extra-pair paternity), with more aggressive females having more offspring sired by extra-pair males than less aggressive females. We discuss the potential mechanisms by which female aggression could underpin mating strategies, such as the pursuit/acceptance of extra-pair copulations. We propose that a deeper understanding of the evolution and maintenance of social and mating systems may result from an explicit focus on individual-level female behavioural phenotypes and their relationship with key reproductive strategies.

Abiotic and biotic influences on the dispersal behavior of metamorph cane toads (Bufo marinus) in tropical Australia

A mechanistic understanding of factors influencing the dispersal behavior of metamorph cane toads (Bufo marinus) has direct conservation relevance in Australia. These invasive anurans are toxic to native predators, and if we can predict their distribution across the landscape, we can also predict (and perhaps, manage) the scale of their impact. We propose that the major drivers of metamorph distribution are the risk of dehydration (restricting the young toads to moist substrates near pond margins) and biotic advantages to dispersal away from the pond (especially, less risk of cannibalism). To test this model, we investigated the influence of abiotic and biotic cues on the behavior of individual toads in the laboratory. Substrate moisture levels strongly influenced metamorph activity levels and habitat selection: dry substrates induced most metamorphs to remain near water. The only biotic cue to influence metamorph dispersal was proximity of a larger (cannibalistic) conspecific; a cannibal's presence at the pond margin caused most metamorphs to spend less time there, and as a consequence, to dehydrate more rapidly. Our results suggest that the spatial and temporal distribution of metamorph cane toads reflects a trade-off between competing risks: the danger of desiccation tends to keep young toads close to the pond margin in dry conditions, whereas the danger of cannibalism stimulates dispersal.

How much stress do researchers inflict on their study animals? A case study using a scincid lizard, Eulamprus heatwolei

Research on live vertebrates is regulated by ethics committees, who prohibit ;excessively stressful' procedures. That judgment is based on intuition - a notoriously unreliable criterion when dealing with animals phylogenetically distant from humans. To objectively evaluate the stress imposed by research practices, we measured plasma corticosterone levels in lizards (Eulamprus heatwolei Wells & Wellington, Scincidae). Some procedures (handling and measuring, toe-clipping for identification, exposure to predator scent) did not induce significant increases in corticosterone levels, suggesting that these stimuli generated relatively little stress. However, other stimuli (testing locomotor speed, microchip implantation, blood sampling, an unfamiliar enclosure, tail autotomy, exposure to a heterospecific lizard) were more stressful, with corticosterone levels increasing only transiently in some treatments (<2 h for tail autotomy), but persisting much longer in others (14 days for microchip implantation). Overall, our data suggest that the levels of stress induced by routine laboratory procedures are no greater than those often experienced by lizards in nature; but that intuition provides a poor basis for evaluating the levels of stress induced by research. For example, toe-clipping is often criticized and sometimes banned; but our data suggest that this method is actually less stressful than the technique frequently recommended to replace it on ethical grounds (microchip implantation). Toe-clipping also was less stressful than superficially trivial manipulations such as housing the animal in an unfamiliar enclosure. More generally, we urge researchers to seek objective information on the effects of their activities on research subjects, rather than relying upon subjectivity and anthropomorphism in making these evaluations.

Interspecific aggression and behavioural dominance among four sympatric species of shrews

Level of interspecific aggression should reflect intensity of interference competition, and large dominant and small subordinate species should develop aggressive and passive agonistic behaviours, respectively, to achieve stable coexistence. We tested these ideas, investigating interspecific behavioural dominance in a four-species community of shrews varying in body size (Sorex minutus L., 1766; Sorex araneus L., 1758; Neomys anomalus Cabrera, 1907; Neomys fodiens (Pennant, 1771)) by placing interspecific pairs in a neutral field. The order of dominance (determined on the basis of duration of offensive and defensive behaviours, total time spent in the shelter, and a "final shelter resident" index) corresponded to the order of body size: N. fodiens > N. anomalus > S. araneus > S. minutus. The highest number of conflicts and the least pronounced dominance of N. anomalus over S. araneus suggest that the interference competition was strongest between these species. The different social organization of N. anomalus (tolerant and gregarious versus intolerant and solitary in the other three species) did not decrease its aggressiveness and dominance rank. The larger Neomys species were more aggressive and initiated relatively more offensive behaviours, whereas the smaller Sorex species initiated more defensive behaviours. The presence of food and shelter did not intensify conflicts. Nevertheless, dominant species restricted the access of subordinate species to the shelter.

A review of thermoregulation and physiological performance in reptiles: what is the role of phenotypic flexibility?

Biological functions are dependent on the temperature of the organism. Animals may respond to fluctuation in the thermal environment by regulating their body temperature and by modifying physiological and biochemical rates. Phenotypic flexibility (reversible phenotypic plasticity, acclimation, or acclimatisation in rate functions occurs in all major taxonomic groups and may be considered as an ancestral condition. Within the Reptilia, representatives from all major groups show phenotypic flexibility in response to long-term or chronic changes in the thermal environment. Acclimation or acclimatisation in reptiles are most commonly assessed by measuring whole animal responses such as oxygen consumption, but whole animal responses are comprised of variation in individual traits such as enzyme activities, hormone expression, and cardiovascular functions. The challenge now lies in connecting the changes in the components to the functioning of the whole animal and its fitness. Experimental designs in research on reptilian thermal physiology should incorporate the capacity for reversible phenotypic plasticity as a null-hypothesis, because the significance of differential body temperature-performance relationships (thermal reaction norms) between individuals, populations, or species cannot be assessed without testing that null-hypothesis.