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International audience; Species that have sex determined by environmental conditions during development (i.e., environmental sex determination [ESD]) are especially vulnerable to environmental change, including altered stress levels, habitat loss, and species translocations. These factors can produce multigenerational trends in population size and eco-evolutionary dynamics not captured by existing theory based on lifetime reproductive success (R0). Here, we extend ESD theory to use per capita growth rate r as a more appropriate measure of evolutionary success (fitness), and we demonstrate the importance of this change when males and females can differ in maturation times and when maturation times vary with local conditions (plasticity). In these cases, we show that primary and secondary sex ratios may be strongly biased; that optimal maturation times, when locally plastic, depend on the balance between mortality and growth effects; and that plasticity of maturation times can ameliorate fitness costs of increasing environmental stress

Unrelated males sometimes share their nests and their mates, an example of male-male cooperation that calls for an evolutionary explanation. We developed a game-theoretic model of this situation under the assumption that males could be either "aggressors," attempting to drive off any other arriving male, or "tolerators," willing to share a nest and mates with another tolerator male. We modeled nest dynamics by changing the frequency of the two types in the population and determined how this affected their fitness. We use the sea lamprey as a case study to generate a plausible array of behavioral traits and ecological conditions for the model. Under these conditions, only aggressors or only tolerators could persist, not both, but we also show how exceptions can arise. Aggressors predominated for the standard conditions we chose, but tolerators could take over when females favored them through nest choice or increased mating rate. High nesting densities and high fighting costs also tended to favor tolerators. At moderate to low densities of individuals in the nesting area, female behavior, based on their own costs and benefits, should determine the outcome.

International audience; Besides egg fertilization, females of many taxa obtain direct fitness benefits from male mates, such as food, protection or paternal care. But males often increase their own fitness by mating with several females, among which they distribute sperm along with the above-mentioned benefits, reducing the benefits to individual females. These diverging interests lead to a conflict in which each female may try to ensure male fidelity and get exclusive access to male-provided benefits. Here, we use a theoretical model to show how a female of an externally fertilizing species may achieve mate fidelity by soliciting copulations at such a rate that the male has insufficient sperm left to increase his fitness with additional females. We show that three alternative condition-dependent evolutionarily stable mating relationships emerge in this scenario, based on whether one mate’s preference for mating rate dominates, or the conflict is resolved by what amounts to negotiation. We demonstrate how these outcomes depend on some features of physiology, ecology, and behavior. In particular, a greater reproductive benefit to a female from exclusive access to a male partner—or the occasional tendency of females to withhold eggs during mating—can increase male fidelity; and continuous sperm regeneration rather than an initially-set stock of sperm allows for multiple within-pair mating across all three mating pattern

We initiated the use of a replicated, remote-video, artificial stream system to determine the effects of conspecific cue, refuge availability, and day/night conditions on movement, aggression, dominance, downstream preference, and refuge use by the crayfish Procambarus clarkii. In line with previous research, we found that walking on the gravel substrate was greatly increased and refuge use decreased in the dark. Conspecific cue (macerated crayfish filtrate) increased walking, contrary to our prediction but consistent with cue as a signal of food availability or of risk either from cannibalism or from visual predators. Exposure to conspecific cue in the streams resulted in a reduced degree of dominance in subsequent pairwise dominance trials. We developed and implemented a new and broadly applicable way of determining the extent of linearity (consistency of dominance ranks) for incomplete dominance; for our data, this method found a lack of evidence for linear hierarchies in these stream systems. Our results suggest that streams may tend to feature weaker dominance and reduced linearity of social hierarchies, relative to standing-water systems, a hypothesis that requires further testing.

Decisions made while searching for settlement sites (e.g., nesting, oviposition) often have major fitness implications. Despite numerous case studies, we lack theory to explain why some species are thriving while others are making poor habitat choices after environmental change. We develop a model to predict (1) which kinds of environmental change have larger, negative effects on fitness, (2) how evolutionary history affects susceptibility to environmental change, and (3) how much lost fitness can be recovered via readjustment after environmental change. We model the common scenario where animals search an otherwise inhospitable matrix, encountering habitats of varying quality and settling when finding a habitat better than a threshold quality level. We consider decisions and fitness before environmental change, immediately following change (assuming that animals continue to use their previously adaptive decision rules), and after optimal readjustment (e.g., via learning or evolution). We find that decreases in survival per time step searching and declines in habitat quality or availability generally have stronger negative effects than reduced season duration. Animals that were adapted to good conditions remained choosy after conditions declined and thus suffered more from environmental change than those adapted to poor conditions. Readjustment recovered much of the fitness lost through a reduction in average habitat quality but recovered much less following reductions in habitat availability or survival while searching. Our model offers novel predictions for empiricists to test as well as suggestions for prioritizing alternative mitigation steps.

While a large body of research has focused on the physiological effects of multiple environmental stressors, behavioral effects remain far less studied. However, behavioural plasticity can not only directly drive responses to stressors but can also mediate physiological responses. Here, we provide a conceptual framework incorporating four fundamental tradeoffs explicitly linking animal behaviour to life history-based pathways for energy allocation, shaping the impact of multiple stressors on fitness. We first address how small-scale behavioural changes can drive conflicts between the effects of multiple stressors and alternative physiological responses. We then discuss how animal behaviour gives rise to three additional understudied and interrelated trade-offs: balancing the benefits and risks of obtaining the energy needed to cope with stressors, allocation of energy between life-history traits and stressor responses, and larger-scale escape from stressors in space or time via dispersal or dormancy. Finally, we outline how these trade-offs interactively affect fitness and qualitative ecological outcomes resulting from multiple stressors. Our framework suggests that animal behavior could underlie the extensive context dependence in results from stressor research, highlighting promising avenues for future empirical and theoretical research.

Concealed fecundity and extended female sexual receptivity have evolved in some primates, including humans, conferring advantages both within primarily monogamous relationships (e.g., benefits from paternity assurance) and from extrapair liaisons (e.g., better access to good genes). As humans evolved the intellectual capacity for decision-making, women became capable of altering their own fertility. In some circumstances, they may choose to ameliorate risks and responsibilities associated with pregnancy by reducing sexual motivation near the perceived most fecund time of their menstrual cycle. But three findings-a general inability of women to accurately recognize their own intervals of fecundity, high variability in ovulation timing, and unconscious transmission and reception of cues associated with fecundity-constitute a physiological and behavioral syndrome that can be considered self-deception. In this study, I develop a descriptive model to determine implications of the hypothesis that these features of female and male physiology and behavior have been shaped by natural selection in response to female decision-making. My analysis shows that consensus motivation for coitus between partners influences both the importance of variable ovulation date and the probability of conception, under the influence of self-deception. It also identifies priorities for future empirical work.

Most flowering plants are simultaneous hermaphrodites. Within species and even within local populations, sex allocation is usually highly plastic. Here, we link pollen sufficiency to the size of pollen-exchanging groups (i.e., pollen neighborhoods) and to pollen transfer efficiency, using an individual-based game-theoretic framework to determine the stable distribution of sex allocation that does not require the unrealistic assumption of infinitely large, panmictic populations. In the absence of selfing, we obtain the novel result that pollen limitation destabilizes hermaphroditism and favors separate sexes, whereas hermaphroditism remains stable without pollen limitation. With mixed mating, hermaphroditism is stable except when the fitness value of selfed offspring is less than half that of outcrossed offspring (i.e., strong inbreeding depression). In that case, the size of pollen neighborhoods, pollen transfer efficiencies, and the relative fitness of selfed offspring determine whether separate sexes or hermaphroditism is the stable outcome. The model thus predicts that separate sexes can derive from either of two ancestral states: obligate outcrossing under pollen limitation, or mixed mating (competing self-fertilization) under severe inbreeding depression. It also predicts conditions under which variance in sex-allocation among hermaphrodites within pollen exchanging groups along a gradient of pollen limitation can range from high (dioecy) to near zero (equal proportions of male and female investment).

We addressed the implications of limb loss and regeneration for multispecies interactions and their impacts on ecosystem engineering in freshwater stream environments.We included regenerative and nonregenerative crayfish as well as fish predators in a 2 × 2 factorial design to assess the effects on water turbidity of interactions between crayfish ecosystem engineers differing in regenerative status and their fish predators.We demonstrated that crayfish limb loss and predation risks lead to more turbidity in field and mesocosm conditions. Moreover, ongoing regeneration of crayfish increased turbidity, while fish presence seemed to hinder crayfish turbidity‐inducing behaviors (such as tail‐flipping and burrowing) in the mesocosm experiment.We confirmed that greater numbers of crayfish produce a greater amount of turbidity in situ in streams.Although mechanical burrowing crayfish capacities may depend on crayfish burrowing classification (primary, secondary, or tertiary), our work emphasizes the implication for turbidity levels of crayfish autotomy in freshwater streams., We addressed the implications of limb loss and regeneration for multispecies interactions and their impacts on ecosystem engineering in freshwater stream environments. We demonstrated that crayfish limb loss and predation risks lead to more turbidity in field and mesocosm conditions. Although mechanical burrowing crayfish capacities may depend on crayfish burrowing classification (primary, secondary, or tertiary), our work emphasizes the implication for turbidity levels of crayfish autotomy in freshwater streams.

Quercus (oak) regeneration failure threatens many forest and savanna communities worldwide, where preservation of vegetation structure and composition depends on acorns germinating and surviving into adulthood. However, predation on the acorns and browsing of seedlings limits oak regeneration. To better understand the effects of these 2 mechanisms on oak recruitment in the endangered Bluegrass savanna—woodland of Kentucky, we compared seed predation and herbivory on Quercus muehlenbergii (Chinquapin Oak) with Carya laciniosa (Shellbark Hickory), a successfully regenerating tree species. Compared to hickory nuts, acorns were predated more, cached less, and dispersed shorter distances. Neither the distribution of the seedlings under the parent canopy nor browse damage differed between the 2 species. Our results suggest that seed-predation prevents regeneration of oaks in this endangered community.

Clonal organisms persist at a range of population sex ratios, from equal numbers of males and females to single-sex systems. When intersexual competition is strong enough to drive one sex locally extinct, the maintenance of the sexes is facilitated by the semi-independent dynamics of populations within a metapopulation. These semi-independent dynamics are influenced by dispersal and recolonization rates, which are affected by the spatial arrangement of populations. To establish the quantitative relationship between spatially complex metapopulations and the maintenance of the sexes, we used a mathematical model of the liverwort Marchantia inflexa. This clonal organism is found in discrete patches on rocks and along the banks of streams, which form single-sex and two-sex metapopulations. In this system, asexual propagules mainly disperse short distances. Long-distance between-patch dispersal and recolonization mainly occurs via sexual propagules, which require both sexes to be present. Dispersal of these two types of propagules could interact with the spatial arrangement of populations to affect the maintenance of the sexes. With our mathematical model, we found that at intermediate distances between populations, metapopulations maintained both sexes, and the spatial arrangement of populations changed the threshold at which one sex was lost. On the other hand, when populations were close to one another, one sex was lost and the single-sex metapopulation persisted through dispersal of asexual propagules. When populations were far apart, one sex was lost, and the metapopulation either went extinct due to lack of recolonization by asexual propagules or persisted because clumped populations facilitated recolonization. These idealized spatial arrangements help clarify the effects of the spatial arrangement on the maintenance of the sexes and the persistence of metapopulations of clonal organisms, which can help explain geographic parthenogenesis and the distribution of asexual populations, the persistence of asexual species, and inform the conservation of clonal organisms.

Parental management of early offspring development is a complex but essential contribution to reproductive success for oviparous species. Mothers faced with incubating eggs in a variable environment maximize reproductive success by adaptively adjusting offspring number in a clutch and incubation schedules to facilitate egg development while meeting their own energetic demands. However, the optimal resolution of these trade-offs varies with physiological and ecological factors and is thus hard to determine using empirical data from natural systems. To untangle the complex factors driving optimal maternal decisions, we developed an ecophysiological model that identifies optimal maternal strategies and their implications for offspring, comparing results for example altricial and precocial species. We showed how plastic maternal strategies can ameliorate effects of food scarcity, offspring mortality risk, variable levels of biparental care, and constraints on producing multiple clutches within a season. In the altricial case in particular, we identified important downstream fitness effects from decisions made in the incubation stage. Additionally, we showed that seasonal decreases in clutch size may result from cumulative fecundity costs for the altricial case and from a seasonal decline in female quality for precocial species. Many of the novel results in this study are testable in future empirical work.

Equation 3 of the original published version of this article was incorrect. Correct presentation is given below.

Correlations between behavioral, physiological, and morphological traits linked to life history have been given the label “pace-of-life syndrome” (POLS), hypothesized to arise through variation in the resolution of a trade-off between present and future reproduction. However, other trade-offs over energy allocation may also have effects and influence the present-future trade-off. We analyzed an optimality model of basal metabolic rate (BMR) across variation in food availability and two types of mortality. The model contained three major features: (1) feedback between activity and energy acquisition, (2) links between BMR and the use of energy for other traits, and (3) allocation trade-offs between BMR and all other traits, between activity and defense, and between defense against activity-related risk and activity-independent risk. The model produced an intermediate optimal BMR that was usually highest at an intermediate level of food availability. Food availability and both types of mortality risk interacted to influence the exact value of optimal BMR. Trait correlations expected in the POLS existed under some environmental conditions, but these correlations flipped sign under different conditions and were not always strong. Our model reproduces trait correlations consistent with the POLS, but also generated a “sloppy” syndrome with considerable non-POLS-like variation. In addition, among-individual, non-adaptive variation in BMR produced adjustments of the other traits. These fit a best-of-a-bad job strategy, and the adjustments further weakened trait correlations. The results emphasize that variation in resources and mortality risk creates a diversity of correlation structures. This complexity means the POLS is likely to be a variable construct. Many attributes important for reproduction and survival are associated. Such associations may arise through common physiological processes and correlated selection. We modeled metabolic rate within a system in which foraging behavior both depended on and mediated the acquisition of resources necessary for metabolism, while energy was allocated among multiple attributes. Variation in several environmental variables (food availability and two types of mortality risk) influenced basal metabolic rate, activity, and defenses against mortality risk. This variation affected the correlations between the traits in complex ways. When basal metabolic rate was non-optimal, evolution of the allocation of energy to other traits partially compensated, but this further eroded consistent trait correlations. Our results indicate that complexity in how energy is acquired and used can potentially disrupt trait correlations normally associated with the pace-of-life syndrome.

Simultaneous hermaphrodites that exchange gametes within pairs allow us to test whether equity of resource exchange is positively associated with duration of cooperative partnerships. The chalk bass (Serranus tortugarum) provides an excellent model system for such research because they spawn daily, trading sex roles with the same mating partners in repeated spawning bouts (a tactic called "egg parceling"). Even so, they live in site-attached aggregations with opportunities for extra-pair matings. We asked whether individuals spawn preferentially with 1 long-term partner and whether partner fidelity was associated with matching in the number of eggs produced in a single day by individuals within pairs. In addition, we observed random focal individuals during spawning to determine whether egg parceling was coordinated within pairs: we asked whether parcel number (per day) was well matched within pairs and whether parcels were exchanged in nonrandom sequences. We did not witness any "break-ups" in our long-term pairs; during each monthly census, all identified pairs were found spawning and courting with their "primary" mating partner until one or both of them disappeared. Daily egg production and the number of egg parcels exchanged within primary partnerships were coordinated. The sequence of parcel exchange was fairly regular, although ca. 20% of focal individuals fertilized or exchanged a few egg parcels with another partner(s); parceling allows individuals the option to exchange eggs outside of the primary pair. Our study provides novel empirical evidence of strong pair bonds and resource matching even in relatively large social groups with extra-pair trading opportunities.

Building on previous work, we derive an optimization model for a two-state stochastic environment and evaluate the fitnesses of five reproductive strategies across generations. To do this, we characterize spatiotemporal variation and define grain (=patch) size as the scale of fitness autocorrelation. Fitness functions of environmental condition are Gaussian. The strategies include two specialists on each of the environmental conditions; two generalists that each fare equally well under both conditions, but one (a conservative bet hedger) optimizes the shape of the fitness function; and a diversified bet hedger producing an optimal mix of the two specialists within individual broods. When the environment is primarily in one of the two states, the specialist on that state achieves the highest fitness. In the more interesting situation where the two environments are equally prevalent in the long term, with low-moderate environmental variation, a generalist strategy (that copes with both states well) does best. Higher variation favors diversified bet hedgers, or surprisingly, specialists, depending mainly on whether spatial or temporal variation predominates. These strategies reduce variance in fitness and optimize the distribution of offspring among patches differently: specialists by spreading offspring among many independently varying patches, while diversified bet hedgers put all offspring into a few patches or a single patch. We distinguish features consistent with strategies like diversified bet hedgers that spread risk in time from features linked to strategies like specialists that spread risk in space. Finally, we present testable hypotheses arising from this study and suggest directions for future work.

The seasonal availability of food resources is an important factor shaping the life-history strategies of organisms. During times of nutritional restriction, physiological trade-offs can induce periods of immune suppression, thereby increasing susceptibility to infectious disease. Our goal was to provide a conceptual framework describing how the endemic level bovine brucellosis (Brucella abortus) may be maintained in Yellowstone bison based on the seasonality of food resources and the life-history strategies of the host and pathogen. Our analysis was based on active B. abortus infection (measured via bacterial culture), nutritional indicators (measured as metabolites and hormones in plasma), and carcass measurements of 402 slaughtered bison. Data from Yellowstone bison were used to investigate (1) whether seasonal changes in diet quality affect nutritional condition and coincide with the reproductive needs of female bison; (2) whether active B. abortus infection and infection intensities vary with host nutrition and nutritional condition; and (3) the evidence for seasonal changes in immune responses, which may offer protection against B. abortus, in relation to nutritional condition. Female bison experienced a decline in nutritional condition during winter as reproductive demands of late gestation increased while forage quality and availability declined. Active B. abortus infection was negatively associated with bison age and nutritional condition, with the intensity of infection negatively associated with indicators of nutrition (e.g., dietary protein and energy) and body weight. Data suggest that protective cell-mediated immune responses may be reduced during the B. abortus transmission period, which coincides with nutritional insufficiencies and elevated reproductive demands during spring. Our results illustrate how seasonal food restriction can drive physiological trade-offs that suppress immune function and create infection and transmission opportunities for pathogens.

Understanding the role of adaptive plasticity under random environmental variation is a central challenge of contemporary life history analysis. An important class of plastic responses is “cohort splitting” ( Sunderland et al., 1976 ), in which groups of organisms beginning development at nearly the same time follow discrete developmental pathways or tracks differing in duration. We identify published studies on the topic and focus on three mechanisms predominant in those studies; we refer to the mechanisms as initiation asynchrony , in which differences in start-up timing can cause a split; mid-point cueing , a bifurcation at some seasonal time and intermediate developmental stage; and diversified tracking , in which individuals are assigned to developmental tracks probabilistically at the outset of development. We use optimization models to evaluate production of cohort splits by these mechanisms. We show that initiation asynchrony is generally a possible explanation but is highly sensitive to environmental conditions. Initiation asynchrony may result either from random variation in development or environment, with subsequent adaptive choices of life-cycle pathway—or from adjustments in developmental onset via diversified bet hedging. Mid-point cueing requires sufficiently high random variation in developmental rates. The adaptive response for Mid-point cueing results from matching the fitness-maximizing pathway to the stage of development at the bifurcation point. Diversified tracking can result from diversified bet hedging, but in this case, high random variation between pathways in reproductive success is essential for diversified tracking to prove adaptive. When diversified tracking results instead from frequency dependence of survival or reproductive success, this mechanism is potentially independent of environmental variation, but frequency dependence is challenging to demonstrate. Additional empirical analyses, especially experimental and comparative approaches, are high priorities for future work.

Invasive species are often able to establish and spread with the help of diseases they bring that can infect native competitors. But sometimes, seemingly successful invasions, in which the invasive species may reach high densities, suddenly collapse, with abrupt decline and extinction of the invader. Diseases have been implicated in invasion collapses, though the underlying mechanism accounting for the entire invasion arc is unresolved. In this study, we simulated a disease-mediated invasion (DMI) by constructing a susceptible-infected-susceptible model for infection and population dynamics of a native and an invasive species. We found that when a competitively dominant native species became an inferior competitor due to infection with the invader’s disease, the native population could often withstand replacement and could sometimes reverse the invasion by evolving an effective disease defense—a resistance-driven evolutionary rebound leading to invasion collapse. The collapse pattern depended on a lag between the disease advance and the invader advance, creating a region of time and space in which the native populations contended only with the disease, evolving disease resistance before confronting the competing invader. We determined the biological conditions and spatial scale in which a DMI may end in evolutionary rebound and collapse, and we present testable predictions for DMI community dynamics.

When females choose mates, males may respond in several ways: by allowing an evaluation by the female and investing substantially in subsequent reproduction (here, type 1), by allowing evaluation but withholding investment following mating (type 2), or by preventing evaluation and attempting to coerce the female to mate (type 3). In this modeling analysis, we examine the conditions under which these strategies, individually or in combination, are expected to persist in the population primarily using the criterion of evolutionary stability. We also consider the roles of female resistance, social policing, and extra-pair paternity in influencing these outcomes. Using six focal systems taken from primates, fish, birds, and insects, we derived parameters for a game-theoretical model to determine the expected evolutionary stable frequencies or unstable combinations of the male strategies based on system-specific parameter magnitudes. In chimpanzees, guppies, Japanese water striders, and scorpionflies, males making the highest investment in each reproductive event were the sole persisting type; in mallard ducks, an evolutionarily stable mixture of types 1 and 3 prevailed; and in humans, a stable mixture of types 1 and 2 persisted. In accord with the infrequency of consistent coercion across taxa, our results suggest that coercion may often be evolutionarily unstable and available only opportunistically as the strategy of last resort. Our game theory model examined mate choice in six species of primates, fish birds, and insects to identify patterns predicted to persist from an evolutionary perspective. We found that differences in ecological, physiological, and behavioral characteristics resulted in the persistence of individual or multiple male mating strategies generally consistent with observations in nature. In particular, coercive males could persist in a population when fertilization rates and reproductive outcomes were similar to those of less forceful males.

Tradeoffs – negative reciprocal causal relationships in net benefits between trait magnitudes – have not always been studied in depth appropriate to their central role in life-history analysis. Here we focus on allocation tradeoffs, in which acquisition of a limiting resource requires allocation of resource to alternative traits. We identify the components of this allocation process and emphasize the importance of quantifying them. We then propose categorizing allocation tradeoffs into linear, concave and convex relationships based on the way that resource allocation yields trait magnitudes under the tradeoff. Linear relationships are over-represented in the literature because of typically small data sets over restricted ranges of trait magnitudes, an emphasis on simple correlation analysis, and a failure to remove variation associated with acquisition of the limiting resource in characterizing the tradeoff. (We provide methods for controlling these acquisition effects.) Non-linear relationships have been documented and are expected under plausible conditions that we summarize. We note ways that shifting environments and biological features yield plasticity of tradeoff graphs. Finally, we illustrate these points using case studies and close with priorities for future work.

Body size can strongly influence the components of fitness. We investigated the role of body mass in the reproductive success of the parasitoid Copidosoma bakeri (Howard) (Hymenoptera: Encyrtidae). Copidosoma bakeri develops polyembryonically, producing thousands of genetically identical individuals from one egg. In this species, the brood size and body mass of clonal individuals developing within a host are in a trade-off relationship, which flexibly responds to the environment while maintaining female-biased sexual size dimorphism. We addressed the following questions regarding several possible effects of body mass on male and female reproductive success. (1) Is longevity positively related to body size in both sexes? (2) Is potential fecundity positively related to female body size? (3) Is mating competitiveness positively correlated with male body size? We found that body size increased with longevity of females, but not of males. Copidosoma bakeri was weakly synovigenic; a few eggs were produced after female maturation. Also, egg volume increased with age of the females. We did not detect a relationship between body size and potential fecundity, but mated females produced more eggs than unmated females. Thus, larger females may increase their opportunities to mate, find hosts, and oviposit primarily by living longer. Male mating competitiveness was not related to body mass. Mating reduced male longevity, suggesting a cost of mating that was independent of body mass. Differences between males and females in the effects of body mass on longevity suggest sex-specific selection pressures on body mass that may explain female-biased sexual size dimorphism.

Recent releases of mosquitoes infected with different Wolbachia types into Australia have led to conditions that have not been observed naturally and that have not been considered theoretically. In an ongoing public health campaign, two Wolbachia infection types have been introduced, and the infections differ in their fitness cost imposed on the host mosquito. The dynamics of each infection type as it interacts with the indigenous uninfected host population have been previously examined via models and empirical tests. Here we conduct a modeling analysis to predict the dynamics when the two infection types do not remain geographically isolated. The results demonstrate the potential replacement and loss of the more costly infection type, which may not be the desired public health outcome.

Many temperate bat species deal with harsh winter conditions by hibernating. Brief periods of arousal from torpor occur at regular intervals throughout hibernation, although energetically costly. Factors that increase arousal frequency, such as the recently discovered white-nose syndrome (WNS), can thereby greatly decrease survival rates of overwintering bats. Evidence increasingly suggests that evaporative water loss (EWL) may be an important driver of arousal behavior in infected bats. We examined the role that EWL could play in torpor arousals and energy expenditures by developing an individual-based energetics model using EWL as the stimulus for arousal in populations of healthy and WNS-affected little brown myotis (Myotis lucifugus). Our model also examined how EWL could affect spatial distributions of healthy and infected bats within a cave throughout winter. We calculated mean torpor bout duration and survival of populations that inhabited 2 modeled caves typical of both northern and midrange hibernacula. In a northern cave, the mean torpor bout duration was 19.97 days 6 5.49 SD between arousals for healthy bats and 8.60 6 2.11 days for WNS-affected bats, accompanied by survival rates of 0.80 6 0.07 SD (healthy) and 0.04 6 0.02 (infected). In a midrange cave, the mean torpor bout duration was 20.88 6 6.22 days for healthy bats and 8.88 6 2.47 for infected bats, and survival rates were 0.98 6 0.02 (healthy) and 0.55 6 0.05 (infected). When bats clustered, survival rates increased in both healthy and diseased populations; however, slight changes in relative humidity or the rate of EWL from infected skin counteracted these advantages. We show that, by causing an increase in arousal rates, EWL could play an important role in the pathology of WNS. Additionally, populations experiencing shorter southern winters could persist longer than their northern counterparts when faced with WNS, a fact that could be critical in maintaining viable populations for WNS-vulnerable species.

Ambient temperature can influence development through effects on metabolic rate and by inducing physiological stress. In this study, we assessed temperature effects on a host–parasitoid interaction and on the body size and brood size of emerging wasps. By examining the development at two different temperatures of the koinobiont parasitoid, Copidosoma bakeri, and its host, Agrotis ipsilon, we asked: (1) Does the growth response to temperature by A. ipsilon depend on whether the moth caterpillar is parasitized? (2) Does the allocation pattern of body size and brood size in C. bakeri change with temperature? To answer these questions, we exposed A. ipsilon larvae parasitized by C. bakeri to high or low non-lethal temperatures when A. ipsilon was in early or late larval stages and measured their development time and body mass for all four treatment combinations. We also examined the brood size and body mass of emerging wasps. Whether parasitized or not, A. ipsilon larvae decreased development time, but generally did not decrease final body mass, at the higher temperature. When parasitized A. ipsilon was exposed to the higher temperature only late in their development, enlargement of the host by the parasitoid was reduced. C. bakeri brood size significantly increased when the higher temperature was applied early in host development. We did not detect a shift with temperature in the allocation pattern of the size–number trade-off for wasp offspring, suggesting that this trade-off relationship may be under selection strong enough to yield insensitivity to temperature.

Summary Life-history traits that shift in response to environmental conditions are well studied; however, allocation patterns of traits in the context of a trade-off shifting with the environment are hardly examined. Using a polyembryonic parasitoid wasp system, we revealed features of the plasticity in allocation by observing the trade-off outcome between individual body mass and the number of offspring in a wasp brood in response to different host conditions. We manipulated food availability to the host caterpillar at two different phases of development: early host instars during wasp embryo division and late host instars after completion of wasp embryo division. The food manipulation allowed us to shift the rate of development and the total mass of the wasp brood both separately and together through altered host development time and final size. With greater host mass, the trade-off relationship between wasp body mass and brood size shifted, to the same extent for both sexes, towards higher wasp brood size and individual body mass. On the other hand, with faster host development, the trait combinations shifted towards greater wasp body mass but smaller brood size along the same trade-off relationship. These shifts indicate a reduction of wasp brood size when resource level is reduced late in host development. This adjustment yields wasp brood size and body mass in rough proportion to each other and positively related to resource availability late in development. Our demonstration of simultaneous shifts in traits under the trade-off relationship indicates that wasp broods respond differently to the different environmental conditions by altering body mass and the number of wasp individuals, suggesting that the plastic response in the trade-off allocation pattern may be adaptive.

In peninsular Florida, USA, the palm-feeding guild is dominated by the black bear (Ursus americanus floridanus, Pallas) and the giant palm weevil (Rhynchophorus cruentatus, Fabricius). Bears damage palms by consuming their hearts, allowing the weevil to reproduce within the exposed palm tissue. The giant palm weevil reproductively benefits from bear-damaged palms, and bears gain a valuable fat-rich food supply from consuming the insects, an apparent intraguild mutualism. We analyzed a natural experiment across widely distributed sites based on presence or absence of bear populations to test the hypothesis that the presence of bears increases the abundance of the giant palm weevil. Results support the hypothesis; data also show greater attraction of females than males to pheromone traps and indicate a predominance of activity by the insect during the day and at lower summer temperatures. This interaction closely resembles one previously documented involving indigenous humans in Amazonia.

Contest outcomes are usually determined by differences in resource-holding potential, the social histories of the combatants, and perceptions of resource value. One aspect of gaining an advantage is the residency effect. Prior occupancy of a particular place can affect the knowledge and motivation of the resident. There could be a tactical advantage in knowing the terrain or an increased willingness to fight to maintain control of a familiar area. In this study, we evaluated the importance of shelter residency effects relative to size differences between rusty crayfish (Orconectes rusticus) as potential competitors for access to shelter. The intensity of any residency effects was manipulated by altering the number of shelters in the arena. Our results suggest that any residency effect is very weak in this system, and if present, may often be masked by the strong and pervasive influence on contest outcome of the relative body sizes of the contestants. We also found that both shelter number and crayfish size asymmetries had strong, independent effects on levels of aggression. Dominance, but not residency status, was a factor in shelter use.

Global positioning system (GPS) collars have revolutionized the collection of animal location data; however, it is well-recognized that considerable bias can be present in these data due to habitat or behavior-induced obstruction of satellite signals resulting in inaccurate or missing locations. To date, no explicit theoretical framework of GPS fix acquisition specific to animal telemetry has been presented, and studies make differing assumptions regarding factors influencing GPS fix acquisition and how these data should be analyzed. Inappropriate statistical models have been used, interaction effects have been misunderstood, and the implementation of bias mitigation techniques has been problematic. Herein we outline current conceptual and analytical problems in the GPS animal telemetry literature, and subsequently present a theoretical model-based framework for GPS fix acquisition that clarifies the single and interactive effects of habitat and behavioral obstruction, fix interval, and collar model on GPS collar performance. By recognizing that GPS fix acquisition is a Bernoulli process, it becomes apparent that all forms of obstruction inherently interact with each other, making generalizations across study areas, study species, and collar models problematic. Stationary collar tests to determine the probability of fix acquisition (PFA), location accuracy, and the response to sources of obstruction are thus of limited applicability to animal-deployed collars. Bias mitigation techniques that extrapolate PFA models across samples, especially those using stationary collar tests to correct animal-deployed collars, are theoretically unsound. It is also demonstrated that nonlinearities in the relationships between sources of obstruction and PFA complicate PFA modeling with limited data and that even slight model misspecification can lead to considerable errors in correction factors, especially when using inverse weighting to mitigate bias. By emphasizing the importance of GPS collar sensitivity and ephemeris retention, the theoretical framework predicts that newer, more sensitive GPS collars will be less severely biased by sources of obstruction than reported for the older, less sensitive collars that have been used in the majority of GPS performance studies to date and we expect this trend to continue. This heuristic modeling exercise should be of value to researchers planning and analyzing studies using GPS collars and it also establishes a starting point for future theoretical investigations into GPS collar performance and bias mitigation.

Summary 1. Disease management along the boundaries of wildlife reserves is a growing conservation problem worldwide, as infected wildlife can migrate outside protected areas and pose a threat to livestock and human health. The bison Bison bison population in Yellowstone National Park has long been infected with Brucella abortus, but culling of Yellowstone bison to prevent transmission to cattle has been ineffective at reducing brucellosis infection. This management strategy is negatively affecting long-term bison conservation because of difficulties in diagnosing actively infected animals. 2. We integrated age-specific serology and B. abortus culture results from slaughtered Yellowstone bison to estimate probabilities of active brucellosis infection using a Bayesian framework. Infection probabilities were associated with age in young bison (0–5 years old) and with elevated antibody levels in older bison (>5 years old). Our results indicate that Yellowstone bison acquire B. abortus infection early in life but typically recover as they grow older. 3. A tool was developed to allow bison management to better reflect the probability that particular animals are infective, with the aim of conserving Yellowstone bison while reducing the risk of brucellosis transmission to cattle. Combining selective removal of infectious bison with additional management practices, such as vaccination, has the potential to advance an effective brucellosis reduction programme. 4. Synthesis and applications. We conclude that active B. abortus infection in Yellowstone bison is age dependent, which allows true infection probabilities to be estimated based on age and quantitative diagnostic tests. These findings have important application to disease management worldwide where accurate diagnostic tests for wildlife are unavailable. Estimation of true infection probabilities can replace culling practices that conflict with wildlife conservation. The ability to identify infective individuals can improve management practices that support conservation, particularly when human health is at risk or endangered wildlife species are involved.

Hybridization and genetic introgression can be associated with secondary contact between closely related species. Previous models have examined the ecological and demographic conditions leading to hybridization and introgression, but few have examined the role of behavior. Alternative mating behaviors are common throughout the animal kingdom but have rarely been recognized as a potential mechanism for hybridization. We developed an individual-based genetic model to examine the hypothesis that extra-pair copulations (EPCs) can lead to hybridization and genetic introgression even when assortative mating preferences are intact. Our model showed that female choice, whether pre- or post-copulation, reinforced species boundaries and that hybrids were relatively uncommon when no EPCs occurred. However, when EPCs were introduced into the model, the proportion of hybrids in the population depended on the strength of female mate or sperm choice, the strength of male pursuit of EPCs, and habitat-induced effects on the species composition of the neighborhood. As predicted, male pursuit of EPCs caused extensive introgression, but female preference for conspecific paternity reinforced species differences. Inclusion of mitochondrial markers of species identity revealed significant effects of interspecific and intersexual behavior during EPCs on the direction of introgression. These results suggest that an alternative mating tactic may have major effects on the level of genetic homogenization and can cause local extinction of a species.

OBJECTIVE: To examine the association between malaria and HIV prevalence in East sub-Saharan Africa. METHODS: Using large nationally representative samples of 19735 sexually active adults from the 2003-04 HIV/AIDS indicator surveys conducted in Kenya Malawi and Tanzania and the atlas malaria project we analysed the relationship between malaria and HIV prevalence adjusting for important socioeconomic and biological cofactors. RESULTS: In adjusted models individuals who live in areas with high Plasmodium falciparum parasite rate (PfPR > 0.42) had increased estimated odds of being HIV positive than individuals who live in areas with low P. falciparum parasite rate (PfPR

In principle, the intensity of sexual conflict is best measured as a loss of fitness associated with the expression of conflict-related traits. But because the relevant traits may be difficult to manipulate and fitness difficult to assess, proxy variables linked to conflict intensity may provide important tools for empirical measurement. Here we identify two common types of sexual conflict—one within mating pairs over the less expensive male role, and one between mating pairs and intruders seeking to obtain fertilizations—and consider how they vary in intensity along gradients of population density and predation risk. To do this, we develop and analyze a model of mating dynamics in the chalk bass, an egg-trading simultaneous hermaphrodite that lives on Caribbean coral reefs. In this species, within-pair sexual conflict leads each female-role partner to provide in each mating episode only a subset (parcel) of its egg clutch to its mate for fertilization. Pair-intruder sexual conflict (i.e., sperm competition) increases the proportion of the gonad allocated to male function. In the model, more parceling and greater male allocation both resulted in lower fitness at the ESS, our measure of conflict intensity. Male allocation increased along the density gradient but decreased along the predation-risk gradient, reflecting shifts in intrusion frequency. Parcel number sharply increased and then decreased more gradually along a gradient of increasing local density, initially responding to increased availability of alternative mates across low densities and then to diminishing clutch size toward higher densities. Parcel number decreased with predation risk as each mating episode became more dangerous. Conflict intensities were usually greatest at intermediate positions along the two environmental gradients, and each conflict ameliorated the intensity of the other. Overall, parceling and sex allocation may be good though imperfect proxies for intensities of within-pair and pair-intruder sexual conflicts among chalk bass.

Summary 1. Endocrine disrupting chemicals (EDCs) are chemicals that interfere with proper hormonal functioning in exposed animals. They enter the natural environment through multiple sources, and many non-target wildlife species are exposed to them via several modes. Exposure causes altered hormone levels, importantly gonadal hormones, resulting in changed reproductive characteristics. 2. Vertebrate male mating signals convey important mate quality information to females. These signals are dependent on androgens for their production and maintenance. Female responses to signals depend on oestrogens. Disrupting these pathways jeopardizes signal production and reception, which has implications for mating system ecology. 3. Besides affecting various aspects of the vertebrate physiology, EDCs can impair hormonal functioning by binding to or blocking hormone receptors, or by altering production and function of hormones or hormone receptors. 4. We consider the ecological implications of multi-generational signal disruption by EDCs. Altered signals can influence population dynamics and sex ratios; local extinctions are possible. Community-level dynamics may be affected via interspecific dependence on signals or population fluctuations. 5. We then address the evolutionary effects of EDC-altered male mating signals in vertebrates and discuss how females may respond to altered signals over evolutionary time. Trans-generational reduction in signal reliability can lead to reduced preference and eventual loss of the signal trait and to the evolution of new traits as signals of mate quality. Genetic divergence between endocrine disrupted and undisrupted populations may result, perhaps giving rise to speciation. 6. Finally, we recommend areas of research to further explore some of the issues addressed in this review. We suggest field surveys to document existing alterations in mating systems and genetic divergence in endocrine disrupted populations. Long-term mesocosm studies and mathematical models would be useful to predict the fate of mating signals and female responses as a result of prolonged endocrine disruption. EDCs have been the focus of ecotoxicology for some time now, and we feel that this analysis should now enter the realm of evolutionary biology to determine the subtle, yet far-reaching effects on exposed non-target wildlife.

In seed plants, the occurrence of spatial segregation of the sexes (SSS) along environmental gradients is well documented. SSS in bryophytes is usually more extreme than in seed plants, yet few bryophyte studies have explicitly linked SSS to environmental variables. For Marchantia inflexa, in which males are found beneath more tree-canopy openness than are females, we tested whether morphological, physiological and life history patterns are consistent with this sex-specific association to canopy openness. To accomplish this, we quantified morphology, physiology and life history differences between two light conditions for each sex. Responses to light levels were mostly analogous to sun and shade leaves of seed plants. However, we found that males had lower chlorophyll a:b ratios (indicative of low-light plants) than females, contrary to our prediction.

The trade-off between the number of offspring in a brood and the sizes of those offspring has been documented in a diverse array of species. Here we consider the factors that might account for the way that the trade-off achieves a particular size-number balance for female offspring. In particular, we determine whether bet hedging, along with traits influencing the expected short-term reproductive success of the brood, could select for a brood size and body mass that maximize long-term fitness. We also evaluate whether the optima based on these characteristics agree qualitatively with documented responses to brood resource levels. To develop a model incorporating these phenomena and keep it as simple and general as possible, we consider an organism that produces clonal broods, eliminating the complexities associated with parent-offspring and sibling conflict. We use the polyembryonic parasitoid wasp Copidosoma bakeri as the focal example. We find that bet hedging effects and key reproductive traits (the number of searching females, their host-finding efficiency, and survival prospects) are often sufficient to produce an optimal size-number balance and can account for the frequent tendency of both brood size and body mass to increase with brood resources (host size). Under some conditions, however, balancing the trade-off requires an additional minimum body-size constraint. Future empirical work and spatially explicit models must better establish the parameter magnitudes and functional relationships so that a deeper understanding and more precise predictions are obtained.

Polyembryonic parasitoids producing single-sex broods of clonal offspring provide an unusually clear window into the classic tradeoff between the number and size of offspring. We conducted a laboratory study of the encyrtid parasitoid Copidosoma bakeri parasitizing the noctuid Agrotis ipsilon to examine the way that size and number of offspring tradeoff in broods of each sex and to determine how the fit between host and parasitoid brood is achieved. We found that brood mass (wasp body massbrood size) was proportional to host mass, independent of brood sex, indicating a tight fit between brood and host and ensuring a sizenumber tradeoff. By correcting brood size and body mass of each brood for host mass, we demonstrated the expected inverse relationship between wasp variables. We postulated that the wasp brood might achieve the fit to the host by (1) adjusting brood size based on information available early in host development before and during division of the embryo, (2) manipulating host size late in host development after completion of embryo division, or (3) simply adjusting individual wasp mass to fill the host. We evaluated host responses to parasitismand correlations between brood size and host growth early and late in developmentfor broods of each sex. The data are consistent with adjustment of brood size to the amount of host growth early in host development and with manipulation of host mass late in host development. The tight link between host mass and brood mass also suggests a final adjustment by parasitoid growth to achieve complete filling. Within the tight fit, female broods were smaller but contained larger individuals than male broods. The sex-specific balance point of the tradeoff and sex differences in balancing mechanisms and responses to host size suggest different selection pressures on each sex requiring future investigation.

Sex allocation (SA) models are traditionally based on the implicit assumption that hermaphroditism must meet criteria that make it stable against transition to dioecy. This, however, puts serious constraints on the adaptive values that SA can attain. A transition to gonochorism may, however, be impossible in many systems and therefore realized SA in hermaphrodites may not be limited by conditions that guarantee stability against dioecy. We here relax these conditions and explore how sexual selection on male accessory investments (e.g. a penis) that offer a paternity benefit affects the evolutionary stable strategy SA in outcrossing, simultaneous hermaphrodites. Across much of the parameter space, our model predicts male allocations well above 50 per cent. These predictions can help to explain apparently ‘maladaptive’ hermaphrodite systems.

1. The flexibility of hymenopteran sex ratios is well documented, particularly in structured populations featuring sib mating. 2. Using game theoretic models, the present study examines species producing single-sex broods in which sib mating is unlikely, and focuses on the role of population density in determining evolutionarily stable oviposition strategies. 3. Since only mated females can produce offspring of both sexes while unmated females produce only male offspring, mated females are under selection to produce more females overall to balance the primary sex ratio. 4. As the proportion of all females that are mated should increase with density, offspring sex ratio of mated females is strongly linked to density at low to moderate densities. The present study shows that when density becomes low enough for fewer than half of all females to have mated, then female offspring generate higher fitness. 5. In this low density situation, females may gain a fitness benefit from waiting at their emergence site or from using other costly means to find and mate with males before ovipositing. 6. The predicted correspondence between females waiting at the emergence site and fewer than half of females in the population containing sperm, can be tested empirically, as can the somewhat counter-intuitive prediction that greater access to males should yield a more male-biased sex ratio in the offspring of mated females. 7. The present study also indicates how measuring the variance in giving up times by females waiting for males at low density, can provide insight into mechanisms determining waiting times.

Fitness in self-incompatible simultaneous hermaphrodites incorporates gains and costs from both male and female reproductive function, and evolutionarily stable allocation of gonadal tissue to male or female function depends on these gains and costs. Paradoxically, despite the often equal expected gains but different costs associated with each sex, contributions to expected reproductive success through male and female function must be identical. Whenever allocation costs are unequal and limiting resources are energetically expensive or risky to acquire, these costs must ultimately be paid through reduced survival, resolving the paradox by equally diminishing expected reproductive success as male and as female. Maximizing fitness as lifetime reproductive success – not just reproductive rate alone, as in previous studies – maximizes the product of expected survival time and reproductive rate. The analysis shows how male-biased allocation can thereby arise and generate novel predictions on the relation between intensity of sperm competition and allocation to male function.

Summary 1 When the two sexes compete so intensively that one of them may be consistently excluded from patches of habitat, how can they coexist in the population as a whole? 2 To address this question, we constructed a population model capable of simulating the dynamics of sex-specific life-history stages within frequently disturbed patches and across a multipatch system strongly influenced by extinction and colonization (metapopulation). 3 We parameterized the model based on the dioecious bryophyte Marchantia inflexa, attempting to capture sufficient biological realism for the results to be quantitatively comparable with natural patterns. 4 In nature, M. inflexa spreads by tissue extension and dispersal of asexual propagules within patches or sexual spores between patches. Females have faster tissue expansion and males greater production of asexual propagules. Some patches and even entire populations lose males or, more rarely, females. 5 In the model, males were often eliminated by competition from individual patches, but both sexes almost always persisted in the metapopulation (as in nature), with females typically predominating. Male advantage during patch filling and spores produced and dispersed where males (the fugitive sex) had not yet been eliminated kept both sexes in the model system. 6 Similar mechanisms may maintain both sexes in other systems, particularly small, highly disturbed populations where life-history traits and mortality differ between the sexes.

Using a framework based on the Hawk–Dove game, we constructed a model of the interaction between two males, which may or may not be related, competing for access to females. We parameterized the model with laboratory data from size-matched house mice and tested the model's predictions against independent laboratory data. The predictions that mate sharing is more frequent, fighting is less frequent and reproductive skew is lower when males are brothers than when they are unrelated were supported by the data. The qualitative and quantitative match between the model's predictions and the frequencies of fighting, sharing and dominance outcomes were generally good, except that the model predicts occasional fighting between brothers when none was observed. The empirically corroborated prediction on relatedness and reproductive skew is consistent with incomplete control of the subordinate male by the dominant, rather than with reproductive incentives, although the magnitude of skew in the model arises from frequencies of outcomes and not from these more specific mechanisms. The analysis demonstrates that these types of male–male interactions and their frequencies may be adequately characterized by a few main features such as relatedness of males, reproductive skew associated particularly with social dominance, and the costs of fighting. The model also makes testable predictions about results to be expected under more natural conditions.

The claim that the Florida panther Puma concolor coryi has been genetically rescued by the introduction of Texas cougars P. c. stanleyana is based on the questionable development and interpretation of a maximum likelihood model, data dredging and a misleading presentation of historical data. In addition, the claim that Florida panther ‘hybrids are expanding the known range of habitats panthers occupy and use’ is offered in the absence of data or supporting analyses. By (1) ignoring regional differences in habitat quality, (2) ignoring the earlier extinction of the hybrid Everglades population, (3) ignoring the influence of social structure on the relative success of Texas cougars and their offspring, (4) using cursory spatial analyses of panthers before and after intervention and (5) choosing a second-best model, a misleading scenario was presented. Undoubtedly hybrid animals have increased in abundance and distribution on the south Florida landscape, but it is quite possible that current patterns of abundance and distribution would be similar if purebred Florida panthers had been introduced instead of Texas cougars in 1995. This is because all the demographic events that have occurred since genetic intervention in 1995 can be more reasonably explained by factors relating to panther social structure and habitat variability. We are hopeful that the current genetic management effort will contribute to the recovery of this endangered population; however, it is too early to claim that this intervention has succeeded or failed. We suggest a number of ways in which more reliable insight on this issue might be obtained.

Sexual size dimorphism and biased sex ratios are common in animals. Rensch's rule states that sexual size dimorphism (SSD) would increase with body size in taxa where males are larger than females and decrease with body size in taxa where females are larger. We tested this trend in dragonflies (Odonata) by analysing body size of 21 species and found support for Rensch's rule. The increase in SSD with increasing size among species can be explained by sexual selection favouring large males. We also estimated the slope of the relationship between sex ratio and size ratio in populations of the 21 species. A negative slope would suggest that the larger sex suffers from high mortality in the larval stage, consistent with riskier foraging. The slope of this relationship was negative, but after correcting for phylogentic non-independence with independent contrasts the relationship was no longer statistically significant, perhaps because of phylogenic inertia or low sample size. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86, 507–513.