Behavioral Ecology and Sociobiology最新文献

Abstract

Large predators are essential in maintaining ecosystem functioning, and comprehending how their feeding habits change across natural and human-dominated landscapes is crucial to preserve biodiversity. In this study, the diet of Iberian wolves (Canis lupus signatus) during pup rearing season (July to September) has been studied in relation to prey abundance and putting emphasis in the analysis of the differences between zones, wolf groups and individual factors (age, sex and social status). For this, non-invasive monitoring was carried out in three zones of Spain where nine different wolf breeding groups were detected (Galicia, n = 4; Zamora, n = 4 and Valladolid, n = 1). Faecal samples were collected near breeding sites for dietary and genetic analyses, registering if it was or not a scent mark to know the social status of the individuals. Prey availability was determined by camera trapping or requesting the official census of wild prey in the study areas. We found differences in wolf’s diet depending on the zone and the breeding group however, the diet did not vary depending on the age, sex and social status. In general, Iberian wolves mainly fed on wild ungulates (wild boar, roe deer and red deer), feeding on the most abundant prey, except for Baldriz group in Galicia which seems to be specialized in hunting roe deer. Domestic animals’ consumption (sheep, goat, donkey, pig) was not high, but it occurred specially in agriculture and livestock areas (Ferreras in Zamora and Valladolid) where wild prey were less available.

Significance statement

In this study, we shed light on the vital role of Iberian wolves in the ecosystem by investigating the dietary preferences during pup rearing season across different landscapes. Our research revealed differences in wolf diets based on geographic location and breeding groups, emphasizing their adaptability. We found that age, sex, and social status did not significantly influence their dietary preferences. Iberian wolves predominantly target wild ungulates, except for a specialized group in Galicia. Our study introduces a novel approach as it is the first to analyse wolf diet based on individual factors and using nitrogen analysis. Additionally, the study highlights previously overlooked dietary patterns of the Iberian wolf subspecies, despite its critical role in the ecosystem as a top predator. Furthermore, we emphasize the necessity of conserving wild ungulate populations to reduce livestock attacks by ensuring a stable supply of wild prey, promoting coexistence between humans and wolves.

It seems self-evident that generalist foragers switch more between resources than specialists but despite diverse ecological and evolutionary implications, how variation in switching relates to variation in preference warrants additional study. Here we tested predictions based on a simple probability model, using flower-foraging bees as a model system. In laboratory assays, we presented bumble bee (Bombus impatiens) workers with flowers of two species, Tecoma stans and T. alata, from which they could collect nectar and/or pollen. We quantified landing preference and occurrence of switching between species in successive visits. Bees varied greatly in floral preference. Almost half showed statistically significant preferences for one or the other species, while the rest were generalists in preference. As expected, generalists using both flower species switched more in successive visits than bees that were more specialized, a pattern fit to a quadratic function. However, generalist individuals switched more than expected based on null expectation. A Modified Jacob’s Index (MJI) of switching was significantly positively correlated with degree of preference: generalist bees had more negative MJI’s than specialist bees, indicating that even after the expected statistical effect of preference on switching was accounted for, they switched more than specialists. A simulation ruled out the possibility that the pattern was due to bias in MJI. Generalist-specialist differences in which food was collected (nectar versus pollen) were also ruled out. We offer possible explanations for our observed pattern and advocate consideration of preference and switching throughout behavioral ecology.

Abstract

Polyandry in social Hymenoptera is associated with reduced within-colony relatedness and increased colony-level ecologic fitness. One explanation for this sees increasing within-nest genetic diversity as a mechanism for improving group task efficiency and colony competitiveness. A queen on her mating flight captures nearly 90% of her breeding population’s allele potential by her tenth effective mating (m_e ~ 10 males). Under this population allele capture (PAC) model, colony fitness gains track mating number in an asymptotic manner, leveling out after about the tenth mating. A supporting theory we call the genotype composition (GC) model sees genetic novelty at mating levels higher than the m_e ~ 10 asymptote, the hyperpolyandry zone, resulting from unique genotype compositions whose number are potentially infinite. Colony fitness gains under the GC model will track mating number in a linear manner. We set up field colonies with Apis mellifera queens each instrumentally mated with 1, 2, 4, 8, 16, or 32 males, creating a polyandry gradient bracketing the qualitative divide of m_e ~ 10, measured tokens of colony level fitness, and collected observation hive data. Our results lead us to conclude that (1) ancestral colony traits fundamental to eusociality (cooperative brood care) respond to mating level changes at or below m_e ~ 10 in a manner consistent with the PAC model, whereas (2) more derived specialized colony phenotypes (resistance to the non-native parasite Varroa destructor) continue improving with increasing m_e in a manner consistent with the GC model. By either model, (3) the mechanism for increasing colony fitness is an increase in worker task specialisms and task efficiency.

Significance statement

Polyandry is a female’s practice of mating with many males, storing their sperm, and using it to produce genetically diverse offspring. In complex social bees, a queen captures nearly 90% of her breeding population’s diversity potential by her tenth mating; however, queens in nature routinely mate with many more than ten males. We tested two models that, together, explain how social bee colonies ecologically benefit from queen mating numbers ranging from 2 to potential infinity. A population allele capture (PAC) model focuses on colony fitness gains at mating numbers at or below 10, and we provide evidence that it was at these polyandry levels that significant gains were made in an ancestral eusocial trait, cooperative brood care. A genotype composition (GC) model focuses on colony fitness gains at higher mating numbers, and we believe these gains are centered around more recently evolved ecologic specialisms such as parasite resistance.

The performance of ant workers in a given task can be highly variable, generating a non-homogenous workload in the colony. However, there is no information on whether high performance workers are more efficient, or have any morphometric and physiological variation that causes them to both start earlier and continue executing the task longer. Here, we demonstrate that non-homogeneous task distribution is common in small colonies and that different performance levels occur even among Acromyrmex subterraneus workers of the same size class. High Activity workers did more work and were faster, so they were more efficient than Low Activity workers. However, their efficiency was not related to their leg length, as it was for Low Activity workers. Also, the delay of the first loaded trip of High Activity workers was shorter than that of Low Activity workers, indicating an earlier response of the former to the task. Delay variation was not affected by mass-specific metabolic rate. Considering the first five trips, we found that the first trip had a longer duration than the others, and High Activity workers were faster than Low Activity workers, suggesting that the higher efficiency of High Activity workers may be related to the reinforcement mechanism, which in turn lessens their response threshold to the task. Finally, workers had similar mandible morphometry (length of the first and second tooth, number of teeth), and body mass components (water content, lean dry weight and lipid content) despite their activity category, indicating that these variables did not explain differences in performance or efficiency among workers. The hypometric mass scaling metabolic rate showed that Non-transporters had proportionally lower energy expenditure than other categories. High Activity workers showed remarkable performance, efficiency, and faster responses to foraging stimulus. We suggest that this heightened level of individual proficiency is in line with the threshold model, explaining the operation of the task allocation mechanism within the same worker size class.

Dishonest vocal signals about body size are rarely encountered, however, dogs are capable of modifying indexical information in their growls. This apparent acoustic body-size manipulation could be affected by the level of threat experienced by the dog. We tested whether this natural size manipulation actually affects how listeners assess the size of the dog, thus whether it could be considered as a successful indexical information manipulation. We requested human participants to assess dog growls, originally recorded when dogs encountered various ‘threatening strangers’ (of different sex, stature). The participants heard several sets of growl pairs, where they had to guess, which growl belonged to the ‘larger dog’. In the Control condition, dog growls originated from two different dogs in a pair; in the Test condition, growls of the same dog were presented pair by pair, always recorded in the presence of different threatening humans. Human listeners reliably picked the larger dog from two differently sized animals based on their growls alone. In the Test condition, participants thought that the dog was ‘larger’ when it was threatened by a female experimenter, and when the dog was growling at a larger sized human. We found that while growl length modulation was the main factor behind size-choice decisions in the case of female strangers, formant dispersion difference contributed the most when listeners chose which dog was the larger in the case of male opponents. Our results provide firsthand evidence of dogs’ functionally deceptive vocalizations towards humans, a phenomenon which has not been shown before in any interspecific scenario.

Abstract

Family life often involves interactions between individuals who have different fitness goals, leading to conflict. Resolution of this conflict is key for the stabilisation of family life. Here, we used a lizard, Liopholis whitii, that lives in facultative family groups to characterise the nature and extent of sibling conflict and test the role that individual and litter characteristics play in shaping conflict between family members. We found significant variation in conflict between family groups, specifically in relation to siblings. In approximately half of the litters, siblings were aggressive towards one another, while in the other half of litters, there was no aggression observed between siblings. There were no differences between aggressive and non-aggressive litters in the key factors predicted to mediate conflict, including sex, offspring size, or litter size. However, in aggressive litters, the maximum amount of within-litter conflict decreased with an increase in the spread between births of siblings. First-born offspring were significantly more likely to be aggressive towards their siblings compared to second and third born offspring. While one offspring was usually the target of that aggression, we found no evidence that any individual-level factor predicted who received aggression. In aggressive litters, aggressive offspring spent a greater amount of time with their mother compared to non-aggressive offspring. Similar asymmetries in the amount of time offspring spent with their mother between siblings were also observed in non-aggressive litters. Combined, our results suggest that birth order is the main driver of sibling conflict in aggressive litters in this facultatively social lizard species, suggesting that birthing asynchrony may provide females with a mechanism to manage conflict.

Significance statement

Conflict is a ubiquitous aspect of family life; it occurs between adults, between parents and offspring as well as between siblings. We show that the extent of conflict between siblings varies considerably within and between families in a lizard that exhibits prolonged associations between parents and offspring. We found no effects of offspring sex or size on within or between litter conflict. Instead, the number of days that passed between the birth of offspring appears to be the main factor that influences how much conflict there is between siblings. Furthermore, birth order was the main factor predicting which offspring was dominant. Combined this suggests that birthing asynchrony, the ability of females to spread out births across multiple days, may play a crucial role in the management of conflict in this system. As the moderation of conflict is crucial for the stabilisation of family life, these results provide important insights into the early evolution of social life.

Abstract

Animals often engage in contests over limited resources. The probability of winning a contest is primarily determined by the individual's fighting ability relative to its opponent and the perceived value of the disputed resource. Individuals of the hermit crab Calcinus californiensis frequently fight over gastropod shells. We conducted a free-choice experiment to assess the factors that determine individuals’ choice of opponent, contest initiation, and contest resolution. We placed hermit crabs occupying two shell species into a large container and monitored agonistic interactions between crabs. We assessed the asymmetries in fighting ability based on the differences in body mass between the opponents. The shell species and fit (i.e., shell size relative to crab body size) were used as measures of the objective and subjective resource value, respectively. Motivation influenced contest initiation; the crabs occupying too-tight shells were more likely to initiate a contest than the ones in looser-fitting shells. In most cases, the attackers fought for a shell with a looser fit, even if that meant losing a tighter-fitting shell of the preferred shell species. The fighting success for attackers was positively associated with the number of bouts of rapping and the shell size improvement. However, success was negatively correlated with body size asymmetry; attackers that chose opponents larger than themselves were more likely to evict their opponent than the attackers that chose opponents that were smaller. Experimental designs that allow animals to select their own opponents, rather than assigning specific opponents, can strongly contribute to knowledge of agonistic interactions.

Significance statement

Fighting dynamics are commonly assessed by estimating the influence of the resource-holding potential and resource value in pair-matched opponents. Here, however, we examined the influence of asymmetries in resource-holding potential and the objective and subjective value of gastropod shells on the choice of a contender and contest resolution through a free-choice opponent experiment in hermit crabs. The contest initiation was driven by the motivation to obtain a better gastropod shell species or one with a better size fit—factors which are known to improve individual fitness. Furthermore, fighting success was associated with an individual's persistence in displaying aggressive behaviors and its motivation to obtain a better resource. However, contrary to the predictions of game theoretical models, fighting success was higher when attackers chose opponents larger than themselves. Our results highlight the relevance of assessing fighting under more natural conditions by allowing animals to select their opponents.

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.