Behavioral Ecology and Sociobiology最新文献

Evolutionary fitness is determined by how an organism allocates energy, or other limited resources, to reproduction during its lifetime. For iteroparous organisms, two alternative patterns of lifetime reproductive allocation are terminal investment and reproductive restraint. Terminal investment maximizes an individual’s current reproductive output by allocating all available resources to current reproduction at the cost of future reproduction. In contrast, the reproductive restraint strategy allocates the individual’s resources toward future survival and reproductive events. We used dynamic state variable modeling to investigate the conditions under which the burying beetle, Nicrophorus orbicollis, would balance between reproductive restraint and terminal investment over their lifetime. Our model provides a formal extension, specific to burying beetle biology, of the dynamic terminal investment threshold conceptual model. For young females, we show that delayed reproduction and reproductive restraint are the optimal tactic for all individuals except for those in the highest condition. However, as age increases, terminal investment becomes the optimal tactic over an increasingly broader range of individual conditions. Surprisingly, manipulation of a variety of factors, such as survival rate, resource availability, and metabolic costs, causes only minor changes in the general pattern observed. We suggest that in burying beetles, and other similar organisms, age plays a dominant role in determining the pattern of reproductive allocation over a lifetime. Individual energetic condition is important in changing the boundaries between alternative reproductive strategies, but it does not change the overall pattern of dominance of delayed reproduction or reproductive restraint at early ages and dominance of terminal investment with increasing age.

Abstract

Predator–prey interactions drive the evolution of prey visual camouflage, but prey species also must remain conspicuous to their conspecifics for social signaling purposes. Whether rapid body color change can help to balance conspecific visibility and predator concealment, in the eyes of each group’s respective visual systems, remains poorly understood. We tested this question using water anoles (Anolis aquaticus), a small lizard that uses rapid dark-to-light body color change to visually camouflage itself from its avian predators across diverse microhabitats. We used digital image analysis and visual modeling to assess the effectiveness of color-matching camouflage in dark- and light-phase A. aquaticus, as perceived by anoles and avian predators. Our findings reveal that A. aquaticus body coloration was perceived similarly by both groups. However, sex-specific differences in overall conspicuousness emerged, with males more consistently color matching their microhabitats compared to females. Females were less likely to color match their backgrounds in their lighter phase, suggesting a sex difference in preferred conspicuity in more exposed habitats. We highlight the context-dependence of color change, with sex-specific differences and microhabitat potentially affecting its function.

Significance statement

Predator and prey visual systems influence prey species’ visual camouflage evolution, but whether rapid body color changes allow animals to dynamically balance conspecific visibility with predator concealment is not well known. We used visual modeling techniques to examine if water anoles (Anolis aquaticus), small lizards that employ rapid body color changes to evade their avian predators, appear differently to their predators and conspecifics depending on color phase. Our findings reveal that A. aquaticus body coloration is perceived similarly by both groups. However, we observed sex-specific differences: males and larger individuals displayed more consistent color matching across different microhabitats, whereas females showed reduced matching in their lighter phase. Our study underscores the context-dependence of the function of color change in relation to factors including sex and microhabitat.

The efficacy of sexual signals in communication is often maximized under specific environmental conditions. Anthropic alterations of these conditions might, thus, negatively affect communication during reproductive behavior. In fossorial animals, inhabiting visually restricted environments, chemical senses are very important. We examined whether climatic episodes of heat-waves with unusual high temperatures may affect the information provided to females by the sexual chemical signals of males of a fossorial reptile, the amphisbaenian Blanus cinereus. The results showed that experimentally heat-altered substrate scent marks of males can still provide information to females about the presence of a male. Females spent more time on males’ scent marks, irrespective of the temperature treatment, than on control clean ones. However, heat-altered scent marks did not seem to convey information about the health state (immune response) of the producer. Females spent more time on unaltered scent marks of healthier males (probably indicating mating preferences for these males), while female preferences for some heat-altered scent marks were not related to size or immune response of the same individual males. Chemical analyses indicated that the overall chemical profile of precloacal secretions (used for scent marking) did not change with increased temperatures. However, the relationship between proportions of some compounds in secretions and males’ immune response found in unaltered secretions was lost in heat-altered ones. We conclude that unusual increased environmental temperatures may decrease the efficacy of underground sexual chemical signals in this amphisbaenian (i.e., a loss of information on male quality), and consequently, may negatively affect sexual selection and reproduction.

Abstract

Flexibility in animal foraging strategies can increase overall feeding efficiency for individuals. For example, group foraging can increase the efficiency of resource exploitation; conversely solo foraging can reduce intraspecific competition, particularly at low resource densities. The cost–benefit trade-off of such flexibility is likely to differ within and among individuals. Reef manta rays (Mobula alfredi) are large filter-feeding elasmobranchs that often aggregate to feed on ephemeral upwellings of zooplankton. Over three years in the Maldives, we free-dived to film 3106 foraging events involving 343 individually identifiable M. alfredi. Individuals fed either solo or in groups with a clear leader plus between one and eight followers. M. alfredi were significantly more likely to forage in groups than solo at high just prior to high tide and when aggregations were larger. Within aggregations, individuals foraged in larger groups when more food was available, and when the overall aggregations were relatively large suggesting that foraging in large groups was more beneficial when food is abundant, and the costs of intraspecific competition were outweighed by the efficiency resulting from group foraging strategies. Females, the larger sex, were more likely to lead foraging groups than males. The high within-individual variance (over 70%), suggested individuals were unpredictable across all foraging behaviours, thus individual M. alfredi cannot be classified into foraging types or specialists. Instead, each individual was capable of considerable behavioural flexibility, as predicted for a species reliant on spatially and temporally ephemeral resources.

Significance statement

Reef manta rays (Mobula alfredi), listed as “Vulnerable” on the IUCN Red List, are at risk from targeted and by-catch fisheries due to their slow life history and aggregative behaviour. M. alfredi feed together in aggregations on short-lived glut of microscopic zooplankton. Over three years in the Maldives, we filmed 3106 foraging events involving 343 individually identifiable M. alfredi. Manta rays were more likely to forage in groups than solo just prior to high tide and when aggregations were larger, attracted by the influx of zooplankton. Foraging groups included more individuals when plankton was more abundant. However, individuals flipped between solo and group foraging and did not specialise. Foraging groups were most often led by females, the larger sex. Individuals were very flexible in how they foraged, which makes sense for a species that relies on a food source that varies enormously in when, where and for how long it is available. Understanding manta ray foraging behaviour will help conservation management efforts and predict their responses to climate change.

Abstract

In many aquatic taxa, formation traveling can reduce the energetic expenditure of locomotion by exploiting the vorticity trails shed by neighbors or through drafting. Cetaceans, especially odontocetes, often swim in groups; nevertheless, the possibility that whales gain energetic benefits from swimming in formation remains poorly studied, apart from mother-calf pairs. Between June and September in 2019 and 2021, we recorded aerial videos of Southern Resident killer whales (Orcinus orca) in the Salish Sea (USA) travelling in groups. We estimated whale tailbeat and breathing frequencies as proxies of the relative energetic costs of swimming, and tested the effect of swimming speed, relative positioning (e.g., leaders, whales in the middle of groups, or followers), sex and estimated size on these observed proxies. Our results reveal a complex relationship between physical characteristics, relative positioning, and energetic proxies. Intervals between respiration lasted longer in large-sized trailing individuals, but the overall breathing frequency was similar for all whales regardless of their position. The tailbeat frequency was mainly associated to whale sex, size, and swimming speed; in addition, tailbeat frequency showed a decreasing trend as the number of individuals in the formation increased. We found moderate evidence that position-based energetic effects may be present in the formation swimming of killer whales, and it is likely that additional factors such as social ties and hierarchies, play a key role in determining individual positioning in travelling groups.

Significance

Swimming in formation has been extensively studied in fish and other aquatic animals and has been documented to provide energetic advantages. Our understanding of the potential energetic benefits of wild cetacean formation swimming has been constrained by the difficulties of studying the movement of whale groups from traditional observation platforms. In recent years, non-invasive observations of cetaceans using unoccupied aerial systems have significantly improved the observation of these species in the wild, providing an exciting opportunity to better understand their behaviors and habits. Our results show a tendency for formation swimming to affect two energetic proxies (tailbeat frequency and the duration of underwater intervals between surfacing events). The results of this study set the stage for further research to identify the multiple determinants affecting killer whale formation swimming which go beyond purely energetic advantages, e.g. social relationships.

Abstract

Correlations between brood sex ratios (BSRs) and parental or environmental quality have been found in many species. This phenomenon is called sex ratio adjustment, and is expected to evolve if certain factors affect the fitness return from the offspring in a sex-dependent way. However, it is seldom studied whether biased sex ratios are indeed adaptive. We manipulated BSRs in a cross-fostering experiment, and investigated parental costs in terms of feeding rate and survival in the collared flycatcher (Ficedula albicollis). In our population, male nestlings can grow faster under good conditions, but are more sensitive to adverse conditions. Assuming that the sensitivity of the males results from their larger energy requirement, we predicted increased costs in broods with male-biased experimental BSR. Assuming that BSR adjustment is adaptive and related to parental care giving capacity, we expected higher feeding and survival rate by parents that originally had more sons, and predicted that low quality parents are less able to adjust their feeding rates to the needs of their foster broods or pay higher survival cost. However, we found that the manipulated BSR and its interaction with original BSR affected neither the feeding rate nor the survival of the parents. Only male feeding rate was correlated with original BSR, however, contrary to our prediction: males with female-biased original BSR fed their foster chicks more frequently. Our results, with those of a previous report about the effects of the experiment on nestlings, do not support that the observed BSRs are adaptive in our population.

Significance statement

Many hypotheses propose that higher vertebrates adaptively adjust the primary sex ratio of their offspring to individual or environmental quality. While the potential adaptive value of the observed patterns is regularly discussed, studies that specifically test the adaptivity of sex ratio adjustment are very scarce and correlative. Using a special cross-fostering experiment, we investigated whether original brood sex ratios are related to the rearing capacity of the parents, and experimental sex ratios are related to the rearing costs in terms of feeding effort or survival. We found no effect of experimentally altered brood sex ratios on either parental feeding effort or survival. Furthermore, contrary to the adaptive scenario, males that had female-biased broods originally had higher feeding rates. So far, we have found no evidence that the sex ratio adjustment is adaptive in the collared flycatcher.

Abstract

Camouflage represents an important component of self-protection when animals cannot easily evade predators and is often altered by behavioural responses to a predation threat. The cryptic plumage of many precocial chicks inspired early theoretical work on camouflage mechanisms, but so far, limited efforts have gone towards empirically testing the crypsis of chick plumage properties in their natural environment. We studied background matching and hiding behaviour in precocial snowy plovers Charadrius nivosus in Bahia de Ceuta, Northwest Mexico. This ground-nesting wader breeds in sparsely vegetated open habitats such as salt flats and sandy beaches. The open habitats provide a challenge for young chicks to evade predator detection. Examining background matching of wild chicks for luminance, pattern and colouration at their hiding spots, we found that chicks matched the luminance of their chosen spot better than at unchosen nearby spots. Pattern and colouration matching were age-related, with the plumage of older chicks matching their hiding spots better than those of recently hatched chicks. This suggests that with increasing mobility, chicks may be better able to find hiding places that optimise camouflage. Finally, we found that chicks were more likely to hide in soil cracks than expected by chance, suggesting that chicks chose these soil features in a barren landscape as preferred hideouts. We conclude that the cryptic plumage is an understudied but essential part of the anti-predator repertoire of precocial chicks. The plumage most likely works hand-in-hand with the anti-predator behaviours of chicks and their parents to increase survival chances of precocial young.

Significance statement

Many chicks rely on effective camouflage to evade predators and survive until fledging. We studied how plumage characteristics and behavioural choices enable snowy plover chicks to hide effectively from approaching predators in an open landscape. These chicks leave their nest scrapes shortly after hatching, relying on their cryptic plumage for several weeks to evade predator detection. We found that chicks chose hiding spots where their plumage had a higher match in luminance and, for older chicks, a higher match in pattern and colouration than at adjacent spots. When available, chicks chose to hide in small cracks that appeared in the soil from the evaporation of moisture. This study represents the first quantitative characterisation of cryptic chick plumage features in a natural population. Our results demonstrate that plumage and behavioural responses jointly contribute to the effective camouflage of small chicks.

Visual and auditory signals are well-established components of avian courtship, but the role of chemical signaling remains poorly understood, particularly in mating systems with elaborate courtship displays. To test how chemical cues influence mating behavior we conducted two experiments in the lance-tailed manakin (Chiroxiphia lanceolata). First, in a field experiment, we tested the response of free-living males and females to manipulation of chemical cues at male display perches by cleaning the perches with ethanol or a dry cloth (control) and quantified a potential chemical signaling behavior (bill-wiping) in response to experimental manipulation. During bouts of dance perch maintenance and displays with a female present (i.e., activity relevant to female mate choice) males increased bill-wiping behavior during initial ethanol treatment periods. We also detected carryover effects of the ethanol treatment; in later treatment periods males bill-wiped more when the prior treatment was ethanol. The likelihood of a female either revisiting a display area or copulating with a male was unrelated to experimental treatment. Next, in captive trials, we assessed female preference for olfactory cues from males that differed in their genetic diversity, a trait previously identified as relevant to female mate choice. In contrast to similar trials in other bird species, females showed no clear preference. Together, these results provide some evidence for chemical signaling by males at display perches, but it remains unclear what information chemical cues convey.

The group augmentation hypothesis states that individuals gain benefits by increasing group size and is rarely studied because it often overlaps with other evolutionary mechanisms like reciprocity. When rescuing a fellow prey from death, the mere presence of that member in the group can yield different benefits that can be passive like risk dilution or active like delayed reciprocity. We were able to separate the effects of passive and active group augmentation benefits by experimentally manipulating the behaviour of prey (altruist vs. non-altruist) in a video game where the costs and benefits of altruism were easily measured. The game pits four players-prey that must acquire resources to survive, while avoiding getting captured by a fifth player-predator. We instructed half of the prey players to avoid rescuing other prey, and the other half to rescue when possible. Our data showed that increasing the frequency of altruistic prey in a group increased survival of all group members. Maintaining group size yielded passive benefits like improving resource acquisition and facilitating future rescues. These passive benefits had a higher impact on survival than the active benefits (e.g., being rescued in return through reciprocity). Thus, we were able to support the importance of passive benefits from anti-predator altruistic behaviour using a biologically relevant online video game.

In many gregarious species, sex-specific differences can lead to significant variation in movement patterns and, consequently, to social and spatial segregation by sex within the population. Specifically, in several long-distance migratory shorebird species, reverse sexual dimorphism has been proposed as a driver of spatial segregation during the non-breeding season. Thus, sex-specific costs associated with space use during these stationary periods could differentially condition subsequent movement patterns between females and males in these species. Using satellite tracking technology, we analyzed the space use and movement patterns of a population of Hudsonian godwits (Limosa haemastica), a gregarious long-distance migratory shorebird, during the non-breeding season in Chiloé, Chile. We predicted that larger females would show more restricted movements and higher local site fidelity, while smaller males would be less competitive and more exploratory. Most individuals exhibited restricted space use (i.e., a home range), while a smaller fraction showed exploratory movements leading to a nomadic movement pattern. Most of these nomadic individuals subsequently oversummered in Argentina rather than migrating back to breeding areas. Contrary to our main prediction, none of the observed movement patterns were sex-biased. Recent evidence suggests that female and male godwits access prey of different sizes within the same foraging sites on Chiloé. Thus, in accordance with our results, and supported by recent additional findings, resource-partitioning within the same foraging patches could reduce interference competition between the sexes by offsetting the competitive advantage associated with the reversed sexual dimorphism of females over males. Finally, we propose these sex differences in foraging strategies could be advantageous for gregarious migratory shorebird populations that show strong connectivity and high site fidelity during and between non-breeding seasons.