Ethology最新文献

Chimpanzees (Pan troglodytes) and humans cooperate in reciprocal patterns, but it is unclear whether these interactions are based on the same psychological foundations. While there is evidence suggesting that both species engage in long-term forms of reciprocity, there is very little work exploring their short-term behavioural contingencies with suitable methods. Here, we present a direct comparative study on short-term reciprocity in chimpanzees and human children using a novel, low-cost instrumental helping task. We investigated whether participants help a conspecific partner to obtain a tool for accessing a reward, and whether the level of helping depends on the partner's previous helpful or unhelpful behaviour. In line with prior research, both chimpanzees and children demonstrated helping behaviour towards their partner. However, the extent to which the two species showed short-term reciprocity differed considerably. After receiving help, tested children always helped in return. They helped substantially less when interacting with an unhelpful partner. Chimpanzees showed a higher tendency to help when interacting with a helpful compared to an unhelpful partner only in the first half the experiment. With increasing trial number, chimpanzees stopped discriminating between helpful and unhelpful partners. This study provides evidence for short-term reciprocity in human children and, to a lesser extent, in our closest living relatives. Our findings demonstrate that helping paradigms provide a useful context to investigate reciprocal motives in humans and chimpanzees alike.

Bumblebees are important pollinators in both natural and agricultural ecosystems, but their survival and pollination service are threatened by extensive pesticide use. Due to regulation changes, acetamiprid has become the only neonicotinoid substance that can be used without restrictions and in open-field cultivations in the European Union. Yet, we know little about how this active ingredient affects bumblebees' foraging behaviour and if such effects are similarly detrimental to those of other neonicotinoids. Here we investigated how a 14-day-long (chronic) exposure to low (5 ppb) and high (2500 ppb) concentrations of acetamiprid in syrup affected different aspects of foraging behaviour in buff-tailed bumblebees (Bombus terrestris, Linnaeus). We recorded individual foraging at artificial food patches during one-hour-long trials and then compared several foraging-related measures between differently dosed individuals. We found that 75.12% of the total syrup consumption occurred at the first-exploited patch, but individuals did not exhibit any bias toward pesticide-treated food patches. Chronic exposure to acetamiprid had little effect on individual foraging decisions at the first-exploited food patch but significantly affected the time to the first feeding and the number of feedings at the second-exploited patch in interaction with body mass. The duration of the first feeding was affected only by foragers' body mass. Our finding indicates that chronic exposure to a high but field-realistic concentration of acetamiprid may alter some aspects of bumblebees' foraging behaviour. If such behavioural changes accumulate during consecutive foraging bouts, chronic exposure to this pesticide might lead to a reduction of daily resource collection, ultimately jeopardising colony fitness or plant (crop) pollination.

As the females of most mosquitoes require a blood meal to provision their eggs, they can be a vector of parasites and pathogens that have profound impacts on both animal and human populations. Understanding the interactions between mosquitoes and their hosts, including animal and feeding site preferences, could thus provide valuable insights into disease transmission. In this study, we present a highly specific feeding strategy observed in a mosquito from Australia (Mimomyia elegans). Over 3 years of fieldwork, we found this mosquito feeding exclusively on the nostrils when using several amphibian species as hosts. Mosquitoes were observed initially landing on the backs of hosts before walking towards the nostrils, potentially minimizing detection and mitigating the risk of predation or defensive responses. This remarkable level of feeding site specificity suggests strong selection pressures that are causing the nostril to be the optimal location for blood extraction on amphibians. Possible explanations include the presence of thinner, more accessible skin tissue or enhanced vascular properties in the nostril region. Understanding mosquito host preferences, points of contact and feeding site specificity could provide valuable insights into disease transmission among amphibians, as mosquitoes have been identified as potential vectors of pathogens like the amphibian chytrid fungus.

Dogs interpret cues as being about location, which human infants would relate to objects. This spatial bias could shed light on the evolution of object-centered thought, however, research needs to rule out that this is not a by-product of dogs' weaker (compared to humans) visual capacities. In this study, we used a data set in which dogs were tested in two types of learning tasks (discrimination and reversal learning) with two types of rewarded cues (location and object features). In both tasks, dogs displayed spatial bias, that is, faster learning when the rewarded cue was a location. We investigated how sensory and cognitive capacity each contributes to this spatial bias. To this end, an estimate for general cognitive ability (g) was obtained from a battery of tests for some of the dogs. Cephalic index, a feature targeted in breeding and linked to differences in visual capacity, correlated negatively with the expression of spatial bias only in the easier discrimination learning task, while a negative correlation between g factor and spatial bias scores emerged in the more difficult reversal learning task. We conclude that dogs' spatial bias cannot be reduced to a sensory limitation and is easier to overcome with greater cognitive capacity.

Male Japanese bush warblers (Cettia diphone) produce not only typical songs but also long, conspicuous vocalizations (continuous songs) during the breeding season. In my preliminary observations, male warblers produced continuous songs in response to both the appearance of a predator and the calls of conspecific females. Although predator-elicited vocalizations by males have been studied in some species, there are no known cases in which an acoustically identical vocalization is also triggered in response to conspecific females. Here, I examined whether these continuous songs triggered in response to predators and females were acoustically similar. In field experiments, I presented dummies of a Eurasian sparrowhawk and a female warbler before (April) and after (June) female arrival at the breeding ground. Before female arrival, 11.1% of males responded with continuous songs to each of the hawk and female presentations; after female arrival, the respective values were 27.6% and 48.3%. Thus, more males responded to the model presentations with continuous songs after female arrival. There was no difference in the acoustic characteristics of the continuous songs between the two models. The males approached the female model more intensively than the hawk model. These findings do not support the hypothesis that the song functions as an alarm or predator deterrent. The function of these continuous songs remains unclear, but this study is the first to show an example where males produce the same vocalization in response to both predators and conspecific females. The continuous song contains a trill-like structure, which can be considered a performance-related song trait. Therefore, the continuous song may possibly be an honest signal of male quality for females. Further studies are required to understand the function of this novel vocalization, particularly the effects of female breeding stage on male singing activity and the female response to the songs.

Top marine predators, such as odontocetes, pinnipeds, and seabirds, are known to forage around fishing boats as fishermen aggregate and/or discard their prey. Recently, incidents of humpback whales interacting with fishing boats have been reported. However, whether humpback whales utilise discard fish as a food source and how they forage around fishing boats is unknown. This study reports, for the first time, the foraging behaviour of a humpback whale around fishing boats. Three whales were tagged using a suction-cup tag containing a video camera, and a behavioural data logger in the coastal area of Tromsø, Norway. Video data from one tagged whale showed that the whale remained in close vicinity of fishing boats for 43 min, and revealed the presence of large numbers of dead fish, fish-eating killer whales, fishing boats, and fishing gear. In waters with large numbers of dead fish, the whale raised its upper jaw, a motion associated with engulfing discard fish from fishing boats, and this feeding behaviour differed markedly from lunge-feeding observed in two other whales in the same area. This behaviour was defined as “pick-up feeding”. No lunge feeding was seen on the data logger when the whale foraged around fishing boats. This study highlights a novel humpback whale foraging strategy: low energy gain from scattered prey but also low energy costs as high-energy lunge feeding is not required.

Reciprocal altruism has been proposed to generate evolutionarily stable levels of cooperation, but empirical evidence in non-human animals is contentious. A series of experimental studies on Norway rats revealed that these animals reciprocate received help by using decision rules characterising direct and generalized reciprocity. The direct reciprocity decision rule states that individuals should help someone who previously helped them, whereas the generalized reciprocity decision rule implies that individuals should help anyone after having received help from someone. Here, we present results from meta-analyses assessing if Norway rats generally help partners according to the direct and generalized reciprocity decision rules by giving more help sooner and matching help received either to previously cooperative partners or to anyone after having received help from a conspecific. We also compared the rats' performance when applying the direct or generalized reciprocity decision rules. Results from these meta-analyses clearly show that female and male focal rats help partners according to the direct reciprocity decision rule. Rats did not adjust the amount of help they gave by matching the help they received according to both the direct and generalized reciprocity decision rules; however, they may adjust the duration to the first help they gave by matching the help they received according to the direct reciprocity decision rule. Female, but not male, focal rats help partners according to the generalized reciprocity decision rule. There was no apparent difference in the help given by female rats to partners between the direct and generalized reciprocity decision rules. These results (i) demonstrate, across a wide range of studies, the reciprocal cooperation of Norway rats by use of decision rules denoting direct and generalized reciprocity, and (ii) suggest that rats may frequently apply the cognitively less demanding decision rule of generalized reciprocity, unless they need to distinguish between individuals differing in helpfulness.

In recent years, temperatures have increased globally, and nestlings of many bird species are likely regularly exposed to increased temperatures both pre- and post-natally. Even small increases in nest temperature during incubation affect offspring growth and survival in a variety of species, one cause of which is thought to be increased production of pro-oxidants in embryos and nestlings. Defences marshalled in response to this oxidative stress could, in turn, result in trade-offs that lead to reduced survival or growth. If so, any downstream negative effects on nestlings of increased ambient temperatures during incubation could be counteracted by increasing their antioxidant intake. We predicted, therefore, that dietary supplements of an antioxidant would reduce or eliminate any detrimental effects on nestling growth and survival of experimentally increased nest temperature during the incubation period. We employed a split-brood design in which we increased the nest temperature of entire clutches and, after hatching, provided dietary supplements of the antioxidant vitamin E to half of the nestlings within broods. We also recorded female incubation and provisioning behaviour to control for the possibility that heating nests might also influence maternal behaviour. There was a significant interaction between nestbox heating treatment and vitamin E treatment in their effect on nestling mass, a trait that is positively correlated with survival and future reproductive success in the study population. Vitamin E supplementation promoted increased nestling mass in heated nests, whereas it had the opposite effect in control nests but these effects were weak. Heating significantly affected female incubation behaviour, with females in heated nestboxes investing less in incubation than those in unheated boxes. These results suggest that within at least some range of expected increased ambient temperatures during the 21st century, effects of climate change on nestling bird development can be mitigated by adjustments in female incubation behaviour.

Prosocial behaviour (i.e. benefitting others without receiving a direct gain) has long been perceived as an evolutionary puzzle but is nevertheless relatively common among non-human animals. Prosocial food provisioning has recently been documented in several large-brained bird species, such as corvids and parrots. Yet, to date, little is known about which factors influence food provisioning in these species. Here, we investigated whether kinship, reciprocity and dominance affected food provisioning in the group service paradigm in three corvid species, namely azure-winged magpies (Cyanopica cyana), carrion crows (Corvus corone) and common ravens (C. corax). In this paradigm, the subjects are tested in their regular social groups and can choose to make food available to their group members by landing on a simple seesaw apparatus. We found no evidence for an effect of kinship or reciprocity on food provisioning. Contrary to our predictions, the subjects' dominance was not positively correlated with their rate of food provisioning in any species. Among ravens, dominance was instead positively correlated with receiving food. We conclude that preferential provisioning for kin and direct reciprocity might have been impeded by the provider's inability to control who receives the food in the group service paradigm, but that our findings provide another piece of evidence that dominance is a highly important factor in the social interactions of common ravens.

Sexually monomorphic species have been historically overlooked in the sexual/social selection literature, but there is growing evidence that mutual ornamentation can be driven by selective forces such as mutual sexual selection or selection for individual recognition. Examining the properties of a trait may elucidate which forces most likely play a role, especially when comparing the characteristics of quality and identity traits. Atlantic puffins (Fratercula arctica) are an example of a mutually ornamented monomorphic species, where both males and females display a bright orange-red bill and orange gape rosette during the breeding season and are ornamented to similar degrees. In this study, we investigate whether the properties of the colorful bill and rosette, specifically lability across the breeding season and condition-dependence, more closely align with signals of quality or identity. Our findings support prior work that the bill is sexually monochromatic from an avian visual perspective. We also determined that the bill changes in a discriminable way within individuals across the breeding season and is especially dynamic in the fleshy rosette. However, no metric of color on any region of the bill or rosette was significantly related to current body condition. Ultimately, we argue that bill color could potentially function as a quality signal, although further study is needed to determine which aspect of quality coloration signals, if not condition. These results provide a basis for experimentally evaluating the signal value of the colorful bill in Atlantic puffins (e.g., color manipulation experiments), and more broadly, a framework for investigating the properties of mutual ornamentation in avian species.