Ethology最新文献

The conspicuous abdominal spines in females of Micrathena spiders have evolved independently in several species within the genus. Like other orb-web spiders, Micrathena species can serve as prey to parasitoid mud-dauber wasps, which paralyzes the spiders and inserts them into their nests to serve as food to their larvae. Based on this fact, some studies suggest that Micrathena spines evolved as an antipredator defense against the wasp. However, there is no direct evidence of how the spines could act to avoid the wasp behavior. Here, we present two distinct records involving an Amazonian species of spiny spider, Micrathena schreibersi, where the abdominal spines act as a mechanical barrier against mud-dauber wasps (Sceliphron spp.). These spines prevented the wasps from completely inserting the paralyzed spiders into their tubular nests, forcing the wasps to alter the opening shape to close it. In our second record, the wasp was not able to completely close the nest, leading to predation of her offspring by ants. We discuss the ecological implications of this potential defense trait for both species and propose future hypotheses to further elucidate how these spines may have evolved based on the foraging behavior of mud-dauber wasps.

Our understanding of elaborate signaling behaviors, such as bird song, has been hindered by historical biases towards male animals. Bird song has been shown to serve important functions like defending territories or attracting mates in both males and females, and singing in both sexes is likely the ancestral trait for songbirds. Female song is strongly associated with year-round territory defense, especially in the tropics. However, more studies of both male and female songs are needed to better understand the selection pressures acting on this elaborate signal trait. The common ancestor of the New World orioles (Icterus) was likely a nonmigratory tropical species, with both males and females singing and defending year-round territories. The Puerto Rican Oriole (Icterus portoricensis) has these natural history characteristics, but little is known about how each sex uses song in this understudied Caribbean endemic. We found that while male and female songs were significantly different acoustically, they were indistinguishable in the field, and showed no sex-specific pattern in syllable usage. Males sang at higher rates than females during the dawn chorus, but females sang frequently during the day. Song is likely evolving as a unified trait in this species, reflecting the characteristics of the common ancestor, but may serve different functions for each sex. In the future, playback studies and rate observations throughout the full day and throughout the year will provide additional insight into how males and females of this tropical songbird may be using their songs.

Parents may experience a trade-off between caring for offspring and protecting themselves from predators. The reproductive value hypothesis predicts that parents should take more risks for older, more valuable offspring, whereas the harm to offspring hypothesis predicts that parents should risk more for vulnerable offspring that would suffer most from a lack of parental care at the moment. After exposing parent mountain bluebirds (Sialia, currucoides) to a model predator, we recorded latency times for them to touch, to look into, and to enter their nestbox and the number of times they inspected the box across three breeding stages: nest-building, incubation and nestling-rearing. Females took greater risks than males during the nest-building and incubation stages by inspecting and entering boxes sooner and more times, consistent with their role in parental care at those early breeding stages that requires them to enter the box. Risk-taking in males was consistent with the reproductive value hypothesis, increasing across breeding stages. In contrast, females took the greatest risk during incubation, consistent with the harm to offspring hypothesis. Furthermore, the riskiest behaviours were not correlated between pair members, and both sexes assumed the risk to first inspect the nestbox approximately equally. This suggests there is not a ‘war of attrition’ between mates over risk-taking, but neither was there cooperation by the male to facilitate the rapid resumption of parental care by his mate. The results highlight that patterns of investment in nest defense in birds may be sex-specific.

Remaining immobile for an unpredictable period after being touched by a potential predator (post-contact immobility, PCI) may favor survival. However, the factors that determine variation in PCI duration are poorly understood. We tested whether PCI duration depends on the surrounding conspecific density (the selfish prey hypothesis) in the tropical antlion larvae Myrmeleon crudelis. These insects avoid predation by being immobile or burying themselves. The selfish prey hypothesis predicts a reduction in the PCI duration as conspecific density increases because this high density of conspecifics around can stimulate the redirection of the predator's interest in other nearby potential prey. In the field, we measured PCI and found that its duration was independent of the conspecific density. In the lab, we also measured the PCI of a subset of the same larvae in the absence of neighbors. Using a paired design, we found that PCI duration was lower in the lab in the absence of neighbors than in the field. Our results suggest that the antlion larvae did not follow the selfish prey hypothesis. We propose two alternative explanations. First, the larvae have a limited ability to detect neighbors in the field and keep up with the changing number of surrounding active pits. Second, burying may be more important than PCI as an antipredator strategy. In our lab experiment, larvae had a more accurate idea of the conspecific density around their pit because they explored the area. We propose that knowing the absence of conspecifics triggered a shorter PCI duration. Under a high predation risk (i.e., no other prey to which the predator would redirect its attention), the larvae select the unequivocal antipredator behavior of burying. This work illustrates the relevance of accurate information in deciding how to avoid predation, especially when prey can prioritize between alternative behaviors, with success varying between the contexts.

Intraspecific sexual communication, crucial in reproductive interactions, often involves the interchange of signals like vibrations, visual signals, and chemical compounds like sex chemical cues. Within the arachnids, solifuges (“camel spiders”) are an understudied group in terms of the detection of chemical compounds during mate searching and sexual interactions. In solifugids, the malleoli, chemoreceptor structures located on the ventral side of legs IV, are putative structures capable of capturing chemical signals. Our study focused on chemical male perception of female cues in Titanopuga salinarum (Ammotrechidae), examining associated behavioral modifications and the role of malleoli. We analyzed alterations in the motion pattern (activity pulse) and specific behaviors performed by males in association with female chemical stimuli. Using experimental arenas, we exposed males to female chemical cues stimuli similar to those available at the field. Stimuli comprised females (F) and cuticular extracts (CE), with corresponding controls. Males with intact malleoli (N = 26 with F, N = 20 with CE) were compared to those with malleoli removed (N = 21 with F, N = 17 with CE). We found partial evidence that males detect chemical cues of females deposited on the substrate. We observed no differences in the duration and number of the activity pulses spent in the zones with and without stimuli in any of the groups analyzed. However, the males exhibit significant changes in locomotion patterns in response to female chemical cues, suggesting a behavioral response to these stimuli. This finding suggests that the males of this species detect the female chemical cues and modify their behavior, and can quickly gather the necessary olfactory information where the stimulus is located. In addition, we found a possible condition-dependent regime for the detection of female cues by males, which would be expected from life-history characteristics of T. salinarum. Our findings prompt discussion from a sexual selection perspective, suggesting the importance of chemical communication in intraspecific interactions in this elusive but fascinating animal model.