Behavioral Ecology最新文献

[This corrects the article DOI: 10.1093/beheco/araf097.].

Transitional ecosystems, such as the land-sea interface, propagate nutrient flow and species interactions. Organisms spanning these boundaries act as important models for understanding the evolution of sensory modalities that promote movement between physically distinct media, and the ecological consequences of ecosystem connectivity. Behavior is fundamentally guided by sensory processing; yet how sensory information is transmitted and collected is heavily dependent on the physical environmental medium. The flow of stimuli across the land-sea interface and the behavioral responses to stimuli are understudied. Vertebrates that span the land-sea boundary offer the opportunity to document how stimuli can be used to complete complex behaviors across transitional ecosystems. We determined that California moray eels (Gymnothorax mordax) can use chemical stimuli (odor and taste) to locate prey across intertidal boundaries on Santa Catalina Island. We tested moray responses to chemical stimuli from 4 prey types during high and low tidal conditions, the latter requiring emergence from the water to navigate the land-sea interface. Gymnothorax mordax can navigate to a prey source using only chemical stimuli; both when fully submerged underwater and when emerged in the intertidal. Morays showed greater discernment between prey types when exposed in the intertidal zone. When emerged, we observed morays rubbing their faces on the substrate, suggesting odor may be important for detection, with taste further assisting in prey location. This research broadens our understanding of ecosystem connectivity, illustrating how stimuli can cross the land-sea boundary and be used to facilitate predation through a combination of multisensory modalities.

Animal personality variation is characterized by among-individual differences in behavior that are consistent across ecological contexts and over time. However, processes influencing the amount of personality variation are not well understood. In this study, we tested 1 hypothesized mechanism through which variation in personalities may be maintained: spatial variation in natural selection. Through laboratory behavioral assays, we demonstrated that 2 personality traits-exploration and risk taking-are moderately repeatable for wavy turban snails, Megastraea undosa (mean repeatability values = 0.320 and 0.297, respectively). We also found that there could be up to a 1.7-fold difference in among-individual variation in behavior for different populations. We next measured natural selection on these behavioral traits by experimentally transporting assayed snails to field populations in a mark-recapture study to examine the relationships between behavioral traits and growth and survival. We studied 4 populations: 2 that had an abundance of slow-moving predators (whelks, sea stars) and 2 where slow-moving predators were absent and the major predators were fast-moving species (lobsters). Selection on behavioral traits varied significantly among local populations. Depending on location, patterns of selection could be predominantly stabilizing, disruptive, or correlational. Fitness surfaces were not necessarily similar for local populations with similar predator communities, and nearby locations could have strikingly different patterns of selection. Behavioral tendencies that were associated with high fitness in 1 population could be neutral or associated with low fitness in a nearby population. Such effects likely contribute to maintaining variation in animal personality within the broader population.

The Marginal Value Theorem, a widely used model of how long an animal should spend foraging on a given patch, has often been invoked in the context of diving animals to predict optimal underwater foraging time. Here, we highlight and address two main issues regarding using the Marginal Value Theorem in this context. First, we show that the theorem's central assumption of diminishing returns from foraging may not always be correct or necessary, and provide an analysis demonstrating that both ecological and physiological influences on patch residency time-based on prey abundance and aerobic capacity, respectively-which have sometimes been presented as alternatives are, in fact, both important and interacting. Second, we attempt to clarify common confusions around interpreting how environmental quality should affect optimal foraging time, in the cases of homogeneous and heterogenous habitats, for which the effect of quality differ. Finally, we discuss a case in which the foraging gain depends on both foraging time and depth, and prove that the optimal foraging depth is not necessarily the depth at which the energetic rate of gain peaks. Altogether, the clarifications and general proofs we provide should improve future interpretations of models of optimal foraging in diving animals.

Sex steroids, such as testosterone, are critical for the development of secondary sexual characteristics and shape traits beneficial for competition over mates and resources. Testosterone profiles may thus differ depending on variation in female and male mating strategies. Sex and mating system differences may also be found in hematocrit profiles, given elevated hematocrit levels during energetically demanding life stages such as migration or during sexual competition. Thus, males of polygynous species should maintain higher testosterone and hematocrit throughout the breeding season compared to monogamous or polyandrous males. Less is known about how mating systems affect testosterone and hematocrit in females: a recent study found higher testosterone in females of classically polyandrous species with reversed sex roles compared to females with typical sex roles. Here we compare baseline and peak plasma testosterone levels (induced by injecting gonadotropin releasing hormone GnRH) and hematocrit values in polygynous pectoral sandpipers and in classically polyandrous red phalaropes. In males, baseline testosterone concentrations were higher in the polygynous than in the classically polyandrous species, whereas in females, this pattern was reversed, with testosterone concentrations tending to be higher in the classically polyandrous species than in the polygynous one. In both sexes, the magnitude of the GnRH-induced increase in testosterone did not differ between species. Hematocrit was higher in the sex with higher competition for mates: in pectoral sandpipers, males had higher hematocrit than females; in red phalaropes, females had higher hematocrit than males. In conclusion, our results show that physiological parameters partially reflect differences in mating strategies.

Contests over resources are widespread in nature. To optimize outcomes, animals assess fighting abilities, deciding to escalate conflicts based on their own strength (self-assessment) or comparing their own strength with that of their rival (mutual assessment). While most research focuses on one-on-one (dyadic) contests, the assessment strategies employed by groups remain poorly understood, even though animal groups from ants to humans engage in intergroup conflict. Mutual assessment is frequently assumed, as more information is thought to improve decision-making; however, this assumption has rarely been tested. Here we used a dataset spanning 21 years and 633 intergroup contests in a banded mongoose (Mungos mungo) population in Queen Elizabeth National Park, Uganda. Our results support a model of self-assessment: groups with many males tend to escalate conflicts regardless of the rival group's strength, thus contrasting the commonly held assumption that decisions during intergroup contests are made by mutual assessment. We suggest that assessing rival group strength during conflict could be disproportionately costly, compared with assessing own group strength, which can be done over longer time periods and is easier to obtain. Greater understanding of these dynamics can shed light on the drivers and escalation patterns of intergroup conflict across social species, including humans.

Social network structures play an important role in the lives of animals by affecting individual fitness and the spread of disease and information. Nevertheless, we still lack a good understanding of how these structures emerge from the behavior of individuals. Generative network models provide a powerful approach that can help close this gap. Empirical research has shown that trait-based social preferences (preferences for social partners with certain trait values, such as sex, body size, relatedness etc.) play a key role in the formation of social networks across species. Currently, however, we lack a good understanding of how such preferences affect network properties. In this study: 1) we develop a general and flexible generative network model that can create artificial (simulated) networks where social connection is affected by trait-based social preferences; 2) we use this model to investigate how different trait-based social preferences affect social network structure and function. We find that the preferences can affect the networks' efficiency at transmitting disease and information, and their robustness against fragmentation when individuals disappear, with the effects often-but not always-going in the direction of slower transmission and lower robustness. Furthermore, the extent and form of the effects depend on both the type of preference and the type of trait it is used with. The findings lead to new insights about the potential mechanisms driving the structural diversity of animal social networks, the importance of trait value distributions for social structure, the degree distributions of social networks, and the detectability of trait effects from network data. Overall, the study shows that trait-based social preferences can have effects that go far beyond direct benefits individuals gain from social partner choice, and that the types of preferences which are present in a population can have far-reaching consequences for the population. We discuss the implications of the results for social evolution and the empirical study of animal social networks.

The adaptiveness of alloparenting for donors, recipients and both natal and transferred offspring remains unsettled despite long-standing interest. Using decade-long data on individually marked female and duckling common eiders (Somateria mollissima), which frequently transfer offspring between broods, we examined factors influencing the likelihood of females donating young and ducklings being adopted. We explored how donor traits, including maternal body condition, relative head size (a validated proxy of relative brain size, potentially associated with risk assessment and reproductive decision-making) and relative hatching date, and offspring characteristics such as body condition relative to siblings, relate to these processes. At least one offspring was permanently adopted in 34.7% of brood observations. Females in better body condition and larger relative head size were less likely to donate offspring, while offspring transfer was more likely from larger natal broods. Offspring donation was most likely just before the population's hatching peak, suggesting that recipient availability influences adoption. Ducklings in poorer body condition than their natal broodmates and those whose mothers were in lower body condition were, respectively, significantly and marginally significantly more likely to be adopted. Taken together, duckling transfer is associated with physical and cognition-related characteristics of donors and adoptees, without necessarily implying an adaptive strategy for either. Multiple tending females per brood prevented assignment of adopted ducklings to a unique recipient; nonetheless, previous studies suggest recipient females may accrue fitness benefits. Future research quantifying the fitness consequences for all parties in different environmental contexts is required for a more comprehensive understanding of alloparental behavior.

The expression of visual signals such as coloration can be altered by parasitic or pathogenic infections through multiple pathways, including resource reallocation, impaired tissue structure, and reduced pigment acquisition. These effects may compromise the functions of coloration and overall fitness. Conversely, the link between pigments and immunological defences can aid differently colored individuals in coping with infection. While the pigmentation-condition association has been widely studied in the context of sexual selection, far less is known about how pathogens affect defensive coloration, such as aposematic signals. Here, we investigated whether infection by the fungal pathogen Batrachochytrium dendrobatidis (Bd) is reflected in characteristics of the melanin- and/or carotenoid-based coloration of the aposematic poison frog Dendrobates tinctorius in the wild. Using ddPCR to identify the frogs' infection status, and multispectral digital imaging to quantify their coloration traits, we show that neither type of coloration is a reliable indicator of Bd infection. Instead, body size influenced both infection outcomes and coloration, with sex-specific patterns suggesting potential ontogenetic or life-history trade-offs. Our findings highlight that the links between color expression and condition are more context- and taxa-dependent than often assumed, and suggest that, in D. tinctorius, defensive signals may remain stable despite pathogen exposure.

Parents must decide how to allocate energy gained from foraging between self and offspring. Storm-petrels (Procellariiformes: Hydrobatidae) are pelagic seabirds that travel hundreds of kilometers across multiple days before returning to the nesting burrow to feed a dependent chick. Parents return to the nest with food stored in the proventriculus, a portion of which is regurgitated to their offspring. As the chick grows, provisioning demands increase. However, it is unknown whether parents meet this increasing demand by (1) altering their foraging strategies to acquire more food or (2) allocating a greater proportion of their intake to the chick. We designed, validated, and implemented a new technology-the Burrow Scale Monitor-to measure Leach's storm-petrels (Hydrobates leucorhous) as they entered and exited the nesting burrow. We monitored breeding adults over the first 30 d of chick rearing to determine whether storm-petrel parents adjust their foraging intake to the age of the chick or simply adjust energy allocation at the nest. Food delivery increased with chick age, but this increase was driven to a much greater extent by parents delivering a greater proportion of their body mass as food (ie, a shift in parental allocation) rather than by adults adjusting their foraging strategy to match chick age. Only by measuring adult body mass on arrival and exit at the nesting burrow could we understand how parents adapt their provisioning strategy to the increasing demands of the growing chick.