Behavioral Ecology and Sociobiology最新文献

Most animal behaviors show large within- and among-individual variation, and this includes competitive male behaviors. With male fighting for example, aggressiveness often correlates with dominance, and contest duration varies with age. However, few studies have directly quantified how mean aggressiveness and contest duration, the variation among individuals in both traits, and the relationship among them, vary with age. Here we address these gaps and examine the effect of male age and genotype on two key aspects of male fighting behavior - aggressiveness (here measured as latency to fight) and contest duration - and the relationship between them. We do this using isogenic lines of the broad-horned flour beetle Gnatocerus cornutus. We observed fighting behavior of paired males of similar body size and age. Using uni- and multivariate mixed models, we show that although there was a significant difference between younger and older males in contest duration, mean aggressiveness was not affected by male age. However, the variation in aggression and fight duration varied with age, being greater in younger and older males respectively. Additionally, although there was a positive correlation between aggressiveness and contest duration in younger males, this relationship was not found in older males. Finally, the only significant genetic effect was for aggression in younger males. Our study shows that age differentially shapes key components of male fighting behavior as well as the relationship among them, highlighting the dynamic nature and context-dependence of fighting.

Abstract

In many social hymenopterans, workers of different ages engage in different tasks; younger workers remain inside the nest as intranidal workers, while older workers go outside the nest as extranidal workers (i.e., age polyethism). Previous studies have shown that ovarian activity is diminished in old, extranidal workers, but it remains unclear whether workers’ reproductive ability persists for life or whether they exhibit post-reproductive lifespans. In this study, we investigated the age-dependence of worker reproductive ability in a monomorphic ponerine ant Diacamma cf. indicum. In Diacamma ants, all females in a colony have reproductive ability, but effective reproduction is limited to one or a few dominant females, and the remaining females act as sterile helpers. Using long-term laboratory rearing, we investigated whether worker reproductive ability lasts throughout a worker’s lifetime. The ages of workers were accurately tracked, and the reproductive ability of young and old workers was examined by creating several gamergate-less sub-colonies. Results showed that at least one individual in each sub-colony developed ovaries, even in the sub-colonies that solely consisted of very old workers (> 252 days old). Interestingly, in the presence of younger workers, old workers rarely showed ovarian development. Besides age, we found a positive correlation between the amount of fat (i.e., nutritional condition) and ovarian development in old workers. Our data suggest that reproductive activity of old workers is low but maintained throughout their life in Diacamma.

Significance statement

Females of social animals, such as cetaceans, are known to stop reproducing before the end of their lifespan. It is suggested that the reproductive ability of ant queens does not decline and is maintained throughout their lives; however, it is unclear whether this is also true in ant workers. We maintained ant colonies for more than 500 days and then tested whether the reproductive ability of ant workers is maintained throughout their lifespan. Even in small groups composed of only very old workers (> 252 days old), at least one individual in each group always reproduced actively. Interestingly, the presence of young workers seemed to suppress the reproduction of old workers. In addition, fat content was positively associated with the individual’s reproductive potential.

Abstract

Males and females often differ in use of antipredator behaviors, particularly when antipredator behavior comes at the cost of missed mating opportunities or territory defense. When using thermally suboptimal refugia, ectotherms are especially vulnerable to these costs, as their performance is linked to body temperature. To flee from predators, semi-aquatic Anolis lizards dive underwater for long periods and rebreathe from a bubble of air. We hypothesized that using aquatic refugia would result in body heat loss, that dive duration is influenced by sex, and that oxygen consumption when diving would help explain sex differences. We tested these hypotheses by measuring dive length and body temperatures in A. aquaticus, and by recording oxygen consumption and final oxygen partial pressure during controlled dives in several semi-aquatic Anolis species. Not only was there a significant thermal cost to diving, but A. aquaticus males and females appeared to tolerate different levels of this cost: males re-emerged from water more quickly and at higher body temperatures than did females. Body temperature decreased according to an exponential decay function, dropping up to 6 °C in 5 min. Oxygen consumption rates in semi-aquatic anoles were primarily explained by the expected allometric scaling relationship with mass and, therefore, are unlikely to lead to sex differences in physiological limits to dive times. Instead, shorter male dives may help them maintain physiological performance, mating opportunities or territory defense. Antipredator diving behavior is physiologically costly but undoubtedly beneficial to both sexes, highlighting the need for further study of sex-based antipredator optimization.

Significance statement

To avoid predators, semi-aquatic Anolis lizards can dive underwater and remain there for an extended time by rebreathing a bubble of air over their heads. In this study, we reveal that diving to escape predators also comes with a cost: submersion in water reduces lizard body temperatures. Reduced body temperature can impair a lizard’s ability to move quickly and defend mates or territories, suggesting that there may be divergent diving behaviors in males and females. Our findings confirm that males do indeed spend less time underwater than females. We measured oxygen consumption during dives, and our data suggest that sex differences in diving behavior are unrelated to oxygen use. This study sheds light on the sex-specific balance of antipredator behaviors and the maintenance of optimal body temperatures, and more broadly contributes insight into adaptive responses to environmental challenges.

Abstract

Both pollution and invasive species are threats for freshwater environments and their native ichthyofauna. The Mexican mojarra is the only cichlid fish species native to the Amacuzac River of central Mexico. Its habitat has been modified by the presence of invasive cichlid fishes, such as the convict cichlid, and by the presence of heavy metals such as lead. Since pollutants may affect invasive and native species differently, the combined effects of these two threats on native fish are not easily predictable and may be synergistic. We evaluated the effects of Pb exposure on interspecific contest dynamics and resolution between juvenile Mexican mojarras and convict cichlids. We performed ten interspecific contests between native and invasive cichlid at an environmentally relevant water concentration of Pb (38.2 µg L⁻¹) in three phases: Pb absence, Pb exposure, and Pb depuration, as well as ten interspecific control contests without Pb. The Mexican mojarra consistently won the contests, regardless of Pb exposure, showing no differences in contest resolution between the Pb group and control group. The presence of Pb increased the number of aggressions in convict cichlids but reduced them in the Mexican mojarra, and contest duration decreased in the Pb exposure relative to the control group. However, these differences were not maintained during the Pb depuration period. Thus, we found effects of Pb on the agonistic interactions between the native Mexican mojarra and the invasive convict cichlid. Other invasive cichlid fishes and pollutants deserve attention in the context of the conservation of the Amacuzac River and its native ichthyofauna.

Significance statement

Native cichlid Mexican mojarra have been negatively affected by the introduction of the invasive convict cichlid and by the presence of heavy metals such as lead (Pb). Here, we evaluated the effects of Pb exposure on contest dynamics and outcome between Mexican mojarras and convict cichlids. Pb did modify the contest dynamics, augmenting the aggression in the Mexican mojarra and reducing fight duration. Our results show that invasive species may be favored in contaminated environments and that native species are more sensitive to pollution, further increasing their vulnerability to biological invasions.

Reciprocity allows animals to balance the costs and benefits of cooperative interactions by switching roles over time. Reciprocity can be based on two different processes: a within-dyad process based on temporal relations between cooperative events (partner control) and an across-dyad process based on preferences for the most cooperative partners (partner choice). The relative roles of the two processes remain debated. The aim of our study was to assess how the opportunity of interaction modulates grooming reciprocity in wild Geoffroy’s spider monkeys (Ateles geoffroyi), a species with low grooming rates and variable opportunities for group members to interact due to a high degree of fission-fusion dynamics. We investigated the roles of the aforementioned processes in grooming reciprocity, and the factors affecting them. Receiving grooming increased the probability of immediately returning grooming to the same partner (within-dyad temporal relations between cooperative events). In contrast, we found no evidence that spider monkeys directed most of their grooming to those individuals from which they received most grooming during the entire study period (across-dyad preferences for the most cooperative partners). The probability of returning grooming to the same partner was higher for dyads that spent less time together in the same subgroup, but was unaffected by maternal kinship. Our results suggest the opportunity to interact is a potent modulator of reciprocity. In species characterized by a high degree of fission-fusion dynamics and low grooming rates, short-term reciprocation based on partner control can be favored at the expense of a longer-term process based on partner choice.

Abstract

The parasite-mediated sexual selection hypothesis predicts that color expression in color patches of animals can honestly reflect male quality in terms of resistance to parasites. Sceloporine lizards have structural-based blue color patches that can act as intraspecific signals and may thus reflect immunocompetence. However, both color patch expression and intensity of parasitic infections in lizards can vary across seasons. In consequence, we might expect that coloration would honestly reflect immunocompetence to resist parasites only during the mating season. We sampled males of Sceloporus torquatus in central Mexico in spring, summer, and autumn and quantified the reflectance of two structural-based color patches (throat and venter), abundance of two categories of parasites (mites and hemoparasites), and lizards’ local inflammatory response to a mitogen (IRM) as a measure of immunocompetence. We examined whether (i) the coloration of lizards changed across seasons in the population, (ii) there is a relationship between coloration and parasite load and/or IRM, and (iii) the latter relationships remained consistent across seasons. Our study shows that color expression seasonally varied; the structural-based coloration of the two patches was significantly more intense in summer, before the mating season. Furthermore, the throat color was more intense in those males with lower parasite load and higher IRM. However, season had no effect on these relationships, suggesting that color expression in the males of S. torquatus can consistently reflect some components of their immunocompetence throughout the year, supporting the honesty of the structural-based coloration in this species.

Significance statement

In this study, we aimed to investigate the seasonal variation in structural coloration of a lizard species and its potential relationship with male quality in Torquate lizards (Sceloporus torquatus). Our results revealed distinct seasonal differences in color expression, and furthermore, we found that males displaying more intense blue coloration exhibited lower parasite loads and stronger immune responses. These findings contribute to our understanding of two key aspects: (i) the potential role of structural coloration as an honest signal in organisms of this nature, and (ii) the significance of considering sampling times in organisms with structural coloration, as it can vary throughout the year.

Abstract

Darwin’s finch species in the Galápagos Islands are famously distinguished by their morphology but less attention has been given to behavioral differences between species. In this study, we compared behavior between four Darwin’s finch species on Floreana Island: small ground finch (Geospiza fuliginosa), medium ground finch (G. fortis), small tree finch (Camarhynchus parvulus), and medium tree finch (C. pauper). After capturing birds using mist-nets, we measured three behavioral traits: (1) boldness during human handling, (2) exploration in a novel environment, and (3) aggressiveness towards their mirror image. First, we found that ground finches were bolder and more exploratory than tree finches, consistent with their distinct ecological niches on Floreana Island and with the theoretical prediction that diet generalists should be less wary of novelty. Second, we tested the ecological validity of these behavioral variables at the individual level by relating them to territory defense behavior and breeding success. We found that males that were more exploratory in the novel environment also reacted more aggressively to a simulated territory intruder and showed lower offspring hatching success during the breeding season. Hence, our findings support previous work showing behavioral differences between Darwin’s finch species and also suggest pathways by which behavioral differences among individuals might influence fitness.

Significance statement

Closely-related species that overlap in their geographical range may differ in their morphology and/or behavior, allowing them to occupy different ecological niches. In this study, we explored behavioral differences between four Darwin’s finch species on Floreana Island in the Galápagos Archipelago. We found clear interspecies differences in behavior, with the ground finches struggling more often during handling (boldness) and visiting more sectors in a novel environment (exploration) compared to the tree finches. After birds were released, we continued to observe a subset of male finches in the wild. An individual’s exploration behavior significantly predicted both its aggressive response to a territory intruder (simulated using song playback) and offspring hatching success during the breeding season. This suggests that individual differences in exploration behavior can potentially be used as a proxy for territorial behavior in the wild and may also predict fitness outcomes.

Abstract

Bees of Ptiloglossa and Xylocopa explore the chiropterophilous flowers of Pseudobombax longiflorum at twilight, but how the bees find the flowers in low light is unclear. In field experiments, we investigated if visual and olfactory floral cues are used by these bees to find P. longiflorum flowers, and which behaviors are triggered by these cues. While the crepuscular Ptiloglossa bees were more attracted to flowers with a combination of visual and olfactory cues than to isolated cues, the diurnal Xylocopa bees were equally attracted to the combination of visual and olfactory cues and to flowers with visual cues alone. Ptiloglossa bees visit the flowers under lower light intensity than Xylocopa bees. This indicates that the synergy between visual-olfactory cues facilitates flower detection in crepuscular bees. However, in higher light intensities, the large size of flowers with their broad spectrum reflectance may be enough to produce a reliable visual signal for the Xylocopa bees. Olfactory stimuli alone trigger only floral approaches in bees, while visual ones frequently trigger approaches followed by landings on flowers. This suggests that olfactory cues guide the bees to the flowers in twilight, but the presence of a visual cue is necessary to trigger landings and collection of floral resources.

Significance statement

Crepuscular and some large diurnal bees fly in the twilight and collect pollen and nectar from flowers with nocturnal anthesis. However, finding food in a dimly lit environment is not an easy task! In this study, we used a combination of visual and chemical approaches to describe, for the first time, how bees do it. We showed that although bees use olfactory and visual floral stimuli as cues, they have different strategies for finding flowers. Furthermore, olfactory and visual cues play different roles during bee foraging. Floral odors are responsible for guiding bees toward flowers in the dark, and the visual cues are responsible not only for guiding bees but also for triggering landings and floral resource collection.

Abstract

Female mate choice is usually based on traits that signal male quality as a sexual partner. According to the “good parent” hypothesis, female mate choice may also consider male quality as a caregiver in species with male-only care. Because parental activities may be costly, males in good condition should be more attractive to females than those in poor condition. We experimentally manipulated the body condition of non-parental and parental males of the egg-tending harvestman Iporangaia pustulosa and then evaluated how it affected their mating success and ability to protect eggs under field conditions. For non-parental males, individuals in good condition had twice the probability of mating than those in poor condition. For parental males, individuals in good condition had two times more chances of mating and acquired five times more eggs than those in poor condition. Surprisingly, males’ body condition had no effect on the efficiency of egg protection. Although our results indicate that the male condition is a sexually selected trait, we found no support for the “good parent hypothesis” given that an increase in body condition does not improve the survival of the offspring under male care. Instead, these findings are congruent with predictions of the “essential male care” model, which suggests that, when the costs of parental care are low (as is the case of egg attendance), most males can provide the minimum necessary care for offspring survival. However, only males in good condition can allocate surplus energy to advertise their overall quality and attract more mates.

Significance statement

Studies examining female mate choice based on condition-dependent traits that serve as reliable indicators of male caregiving quality are mostly limited to vertebrates. We present one of the first empirical examples demonstrating that male body condition influences male attractiveness in an arthropod species exhibiting male-only care. Our field-based results show that females prefer males, whether non-parental or parental, in good body condition over those in poor condition. However, we found no evidence that an increase in body condition improves the survival of the offspring under male care. We propose that males in good body condition are more attractive because the relatively low costs of egg attendance allow them to allocate their surplus energy into advertising their overall quality. Our findings are congruent with predictions of the “essential male care” model, which explores resource allocation between paternal care and sexual advertising.