Ethology最新文献

Adult female spiders lay batches of eggs in silken egg sacs, and after hatching, the spiderlings live for transient periods in their mother's web before dispersing. Sibling cannibalism is frequently observed among spiderlings of many species under conditions of food deprivation. Here, we conducted assays in small Petri dishes with different densities of newly hatched (second instar) spiderlings of the false widow spider, Steatoda grossa, using a split-clutch design. Prey (freshly killed fruit flies) availability was manipulated both numerically and temporally. Offspring from 10 different females were separated as siblings into densities of two, four, or eight spiderlings per Petri dish and these were provided with either 0 flies (starvation control), two flies, four flies, or eight flies that were replenished weekly or every 3 weeks. A further control was conducted with solitary spiderlings in Petri dishes deprived of flies. The number of surviving spiderlings per Petri dish was counted every 3 days until only one remained (or until death of the solitary spiderling). Our results show that the rate of cannibalism was lower with increasing spiderling density and when fresh flies were replenished more frequently, whereas the number of flies that were provided did not affect cannibalism. In S. grossa, juvenile cannibalism occurs primarily under conditions of extreme food limitation, although in synanthropic habitats where the spider is abundant, it may be an adaptive strategy owing to the potential scarcity of prey. Under certain conditions, cannibalism in spiderlings is adaptive by eliminating competitors and providing nutrient-rich food.

Silk is an important communication medium for spiders with roles in species recognition, sex identification, and mating status assessment. Spiders may benefit by discriminating between their own or another same-sex conspecific's silk. Silk-mediated self-recognition could allow spiders to identify areas that they have previously visited, competitively block silk advertisements from sexual rivals or minimize redundant signaling in an area. Silk deposition behavior may also be contingent upon silk cues detected from same-sex conspecifics. We tested if males and females of the wolf spider Pardosa milvina show different silk deposition patterns when encountering their own silk versus the silk of another spider of the same sex. Using a within-between-subjects design, we quantified male and female deposition of three silk types: draglines, cord silk, and attachment disks on substrates containing either their own silk or the silk of an adult same-sex conspecific (N = 23 males, 28 females). Both males and females significantly increased dragline and cord silk deposition on substrates containing conspecific rather than their own silk with males producing more cord silk than females. Males significantly increased attachment disk deposition on conspecific male silk compared to their own while females showed the opposite response, decreasing attachment disk deposition on conspecific female silk. Both male and female P. milvina can recognize their own silk, but we found significant qualitative and quantitative sex differences in silk deposition suggesting sex-specific functions for attachment disks compared to cord or dragline silk.

In animals, reproductive interference associated with mimicry can result in the evolution of private communication channels, as suggested for Heliconius butterflies, where cryptic color wavelength would drive male preference for conspecific over intergeneric co-mimics. Here, we tested this hypothesis in two co-mimic pairs (intra and intergeneric) and measured the efficacy and symmetry of color pattern as a reproductive barrier in a non-co-mimic, possibly hybridizing pair of Heliconius species. We conducted pairwise experiments of preference where a group of males was presented to a conspecific and heterospecific female model made with real wings and free of chemical volatiles. We did not detect any indication of the expected use of cryptic recognition signals to mate choice in the intergeneric co-mimic pair. Additionally, we detected an unexpected male preference for heterospecific female models between intrageneric co-mimics towards the species with larger red patches, suggesting a supernormal stimulus based on a general preference for the red color. Finally, we found an asymmetry in the behavioral reproductive barrier between the non-co-mimic closely related species that also agrees with the hypothesis of a general preference for red and with an expected permeability of the reproductive barrier between them. Since the costs imposed by heterospecific courtships can limit the convergence of signaling phenotypes, our results contribute to explaining the maintenance of multiple aposematic color pattern between unpalatable and closely related sympatric Heliconius species.

Ants occupy huge biomass in the terrestrial ecosystem. Several ant species are highly aggressive and equipped with venomous stingers and/or formic acid. Therefore, ants are abundant but potentially unpalatable prey for some predators. So far, however, the role of ants as prey is not well understood. In this study, we focused anurans (frogs and toads) as one of the major predators of terrestrial arthropods. Using two anuran species and three ant species sharing the habitats, we asked two questions. First, we hypothesized that the anuran preference for prey is ant-species specific, and tested whether anuran prey preference is affected by ant aggressiveness. Second, we hypothesized that the anurans may innately avoid aggressive ants. To test this hypothesis, ant-naïve anuran juveniles (Bufo toad and Rana frog) were reared from tadpoles, and juveniles' preferences for three ant species with variable aggressiveness were tested. The exposure to different ant species showed that anuran juveniles highly avoided aggressive ants (Lasius and Brachyponera) compared to less aggressive ants (Tetramorium). Additionally, ant-naive juvenile toads avoided the aggressive ants without prior experience. In contrast, ant-naïve juvenile frogs attacked the most of firstly encountered ants and then learned to avoid the unpalatable ants. These findings suggest that (1) some anurans selectively avoid aggressive ant species, (2) Bufo toads have innate avoidance to some ants, while Rana frogs learn to avoid the unpalatable prey.

Problem-solving and innovation have been studied extensively, yet urban animals are overlooked despite opportunities to innovate in urban areas. We studied problem-solving in yellow mongooses (Cynictis penicillata) in an urban setting. Using novel puzzle box experiments, we investigated whether yellow mongooses could solve a task of increasing complexity in three locations with varying extents of anthropogenic interactions. Mongooses in a residential ecological estate took the longest time to solve the problem, whereas those frequenting a residential garden solved the problem the fastest. Mongooses solved the puzzle box problem at each of the four stages of complexity, but were the fastest during the least complex first stage, followed by the third stage and requiring more time in the second and fourth stages of complexity. Overall, the location of the mongoose colonies and the complexity of the task were the main correlates of the speed of solving the problem. Urban-living yellow mongooses can interact with novelty in an anthropogenic environment and solve novel problems through innovation to obtain a food incentive.

In cooperatively breeding species, subordinates can obtain group membership through social interactions with other group members or by providing services such as helping with territory defence. Large subordinate individuals, which can reproduce, are expected to adjust their behaviour as a function of the demand of help and group size because if the environmental conditions allow, they may either leave the group to start breeding or queue for the breeding position in their natal group. The number of helpers in a group is expected to affect the need of help by dominants and consequently also the level of subordination shown by helpers. In a series of field experiments, we manipulated the need of help and the opportunities for subordinates to show submissive behaviour in a wild population of the cooperatively breeding species Neolamprologus pulcher. We assessed if group size determines the social behavioural strategy of large subordinate individuals. When experimentally eliciting submissive behaviour, large subordinates from small groups showed a lower frequency of submissive behaviour compared to large groups; moreover, they tended to show a higher frequency of sand digging than in large groups. In contrast, neither territory defence in the presence of a heterospecific egg and larvae predator nor dispersal propensity, measured as prospecting frequency in neighbouring territories, was affected by group size. A principal component analysis revealed that prospecting is uncorrelated with submissive behaviour and helping behaviour. Our results suggest that group size may be involved in shaping behavioural phenotypes of juvenile subordinates.

Eusocial animals exhibit a sophisticated division of labour. The self-organized colony requires coordination of local interactions at the individual level. Termites are a well-known group exhibiting social organization among castes within a colony, and helper castes have facilitated their ecological and evolutionary success. Termites have soldier castes specialized in defence, but other castes are also known to exhibit defensive behaviour depending on the context. However, it is unclear how variation in the frequencies of defensive behaviour is emerged. Here, we investigate the effects of the presence of nestmates on individual defensive behaviour in the dampwood termite Zootermopsis nevadensis. We experimentally prepared three conditions and observed biting behaviour against the ant Camponotus obscuripes. First, the frequency of biting was significantly higher in soldiers than that in pseudergates (i.e. workers) under isolated conditions. Second, the results showed that the frequencies of biting exhibited by soldiers were much higher than those of pseudergates in the pseudergate–soldier pairs. Finally, we investigated the social conditions in the presence of the same castes, that is, pseudergate–pseudergate and soldier–soldier pairs. The frequencies of biting exhibited by first-biting individuals were significantly higher than those exhibited by second-biting individuals in both paired conditions. Our findings demonstrate that defensive behaviour can be frequently observed in first-biting individuals despite the presence of two individuals of the same caste, suggesting that the variation of defensive behaviour may be increased in the presence of nestmates.

Animals engage in agonistic interactions to gain exclusive access to territories and resources. Understanding these interactions in bats, however, has proven difficult given their high mobility and nocturnal habits. For bats, roosts are a critical resource; thus, the study of agonistic behaviors associated with the use of these resources could provide valuable information to understand how and whether individuals monopolize them. Here, we used Thyroptera tricolor to study agonistic behaviors associated with access to a roosting resource. We experimentally studied the behavioral responses of focal groups when interacting with different intruders during the occupation of an ephemeral roosting resource. We found that T. tricolor responds more aggressively to intruders than to members of its own group, increasing the number of aggressive vocalizations. We also found differences in the rate of agonistic behaviors based on the identity of the intruders. Specifically, we observed that bats produced a large number of aggressive vocalizations when interacting with nearby intruders, supporting the “nasty neighbor” hypothesis. This study provided the first empirical evidence that aggressive vocalizations may serve as a mechanism to defend and maintain exclusive roosting sites in social groups of T. tricolor.

When learning to discriminate between palatable and unpalatable prey, predators may encounter the prey either simultaneously or in a sequence. The two types of discrimination tasks, which are frequently used in experiments focused on aposematism and mimicry, may considerably differ in difficulty, as they differ in the information available to predators during individual encounters with prey. Surprisingly, there are very few studies directly comparing the performance of predators between sequential and simultaneous discrimination tasks using otherwise identical experimental design, the same predators and prey. We tested the effect of the type of discrimination task on the effectiveness of discrimination learning in adult and juvenile great tits (Parus major). Birds were trained to discriminate between palatable and unpalatable artificial prey items baited with mealworms soaked either in water or quinine. Prey shape, colours and patterns were derived from real shield bug species. We compared the performance of birds tested with two discriminative cues, colour and pattern, using three discrimination tasks: (1) sequential—alternating presentation of one palatable and one unpalatable prey item, (2) two-choice—simultaneous presentation of one palatable and one unpalatable prey item and (3) multiple-choice—simultaneous presentation of multiple palatable and unpalatable prey items. Colour was a more effective discriminative cue than pattern for both adult and juvenile birds. Adults performed better than juveniles regardless of task. The birds performed equally well in the sequential and two-choice tasks, but their performance in the multiple-choice task was worse than in the other two tasks. However, these differences were only present when the birds used the pattern as a discriminative cue. The birds tested with colour, a more salient cue, performed equally well in all three tasks. Type of discrimination task may therefore affect the learning performance of predators, but the effect also depends on the saliency of a particular discriminative cue.

Individual specialization (IS) in resource use is common within populations of several animal species because some individuals can be more efficient than others in obtaining specific food items. Spiders are usually classified as euryphagous predators, but the broad diet of populations may result from many individuals specializing in capturing different types of prey. Empirical evidence supporting this pattern, however, is still scarce. In this study, we hypothesized that (1) the diet of individuals of Tidarren haemorrhoidale is more restricted than the population's diet and (2) individual diet restrictions are not determined by the spatial distribution of prey types. We collected the prey remains of 74 webs of females in a conservation area of the Atlantic Forest. Our results indicated that T. haemorrhoidale could be considered a euryphagous predator because its diet comprised Opiliones, Diplopoda, and eight orders of insects. However, spiders exhibited moderate and high degrees of IS for prey size and taxa, respectively. There was no modularity for both prey attributes in the food web, but there was a medium nestedness. Most individuals captured ants, but additional prey taxa were of different orders. There was no correlation between the dissimilarity of prey taxa and the distances between the webs, suggesting that IS did not occur based on the spatial distribution of their potential prey. The diversity of prey defensive strategies may induce spiders to perform specific behavioral routines after prey interception. If this occurs, cognitive constraints may limit their ability to use different capture routines efficiently. Our study supports the predictions of individual niche specialization theory for a euryphagous spider species and highlights the potential of spiders as a study model to investigate the underlying mechanisms.