Predatory interactions result in strong selection pressures acting on multiple aspects of animal behaviour. Anti-predator strategies are therefore common in most animals, typically signalling at various stages of a predation event. Many species of caprimulgids perform conspicuous anti-predator displays, including stereotyped behaviours and vocal signals. Here, we described distress calls of red-necked nightjars (Caprimulgus ruficollis), produced when birds are trapped and unable to escape during a predatory interaction. Distress calls are harsh, low-frequency guttural vocalisations with irregular amplitude modulations. The age and sex of birds partially explained the acoustic variation observed, whereas size-related morphological features were poor predictors of the acoustic structure. Age-sex differences in distress calls may respond to physiological constraints associated with sexual dimorphism and/or developmental variation. Alternatively, directional selection associated with differential predation risk on each age-sex class may have resulted in the observed differences in distress calls. The extremely deep voice and the harsh quality of distress calls fit the structure of aggressive signals and may resemble those produced by a larger animal. We propose that these calls serve as a last resort strategy to reduce post-encounter risk of predation, either as a startling effect to facilitate escape or to attract other predators that could intimidate the captor.
The flash coloration hypothesis postulates that otherwise cryptically colored animals suddenly displaying conspicuous colors during movement confuse predators, reducing capture. Morpho helenor butterflies have contrasting colors on dorsal (iridescent blue) and ventral (brown) wing surfaces, resulting in sequential blue “flashes” during flight. We tested whether this flashing pattern reduces avian predation on M. helenor in Atlantic rainforest by changing the flashing effect in three experiments. In Experiment 1, we added a blue band to the ventral wing. In Experiment 2, we covered the dorsal wing's blue band with a brown band. Control groups in each experiment were painted such that wing color patterns remained unaltered. Survivorship was evaluated through mark-recapture censuses and beak marks on the wings. Results show that survivorship of treated butterflies in Experiment 1 decrease markedly compared to unaltered control individuals, while survivorship of treated butterflies in Experiment 2 did not differ compared to control individuals. In Experiment 3, we detected scant predation on treated (blue band added to ventral wing) and control butterflies (brown band added to ventral wing) on the forest floor (wings closed), corroborating that flash coloration is an important protective mechanism during flight. Our field experiments provide the first evidence, to our knowledge, that flash coloration in bright blue Morpho butterflies is an effective defense mechanism against avian predators in a tropical rainforest.
Animal vocalisations are widely used to signal strength or motivation of a caller in competitive interactions, such as in territorial defence. Substantial understanding of signalling functions in territorial conflicts is based on singing by male songbirds. Yet, in many species, both pair members call during territorial conflicts, as well as in predator-induced situations, leading to complex signalling interactions in which calls overlap or alternate. This raises the question as to whether or not variation in how individuals in pairs time their calls is perceived as meaningful by receivers. Here, we tested with playback experiments whether Eurasian magpies (Pica pica), a species producing alarm calls (so-called chatter calls) in territorial defence, respond stronger to simulated pair-intruders who overlap their calls with each other than to those who alternate them. Magpies emitted a significantly longer first chatter calls in response to playback with overlapping calls but chattered significantly sooner and approached the loudspeakers significantly more closely in response to playbacks of alternating (and therefore longer) call sequences. These findings exemplify that the timing of calls by pair members matters, but in more complex ways than we predicted. The overlapping playback appeared to trigger a longer yet later initial chatter response and a weaker approach response, suggesting that the different ways in which magpies respond reflect different levels of arousal or defence strategies. The results may also reflect uncertainty by receivers due to a potential mismatch between signalled and perceived information: While overlapping calls may signal high arousal by both callers, a longer alternating sequence could be perceived as a more aroused longer signal. These findings expand on classical experiments on call function, suggesting that pairs can vary the message by coordinating their alarm calls in different ways, similar to how duetting pairs time their song contributions in advertisement signalling.
The overarching goal of neurobiology is to understand how complex behaviors are generated by the nervous system. The behavior of each species, and the brain that controls it, is shaped by the historical and current state of the environment that they inhabit. This fact is juxtaposed with the reductionist approach of neuroscience that isolates animals from their natural environment. Understanding how brains evolved to orchestrate the myriads of natural behaviors an animal performs in response to its environment requires an integrative approach to neuroscience that considers ecology, ethology, and evolution. Current technological developments are leading us to an inflection point at which studying brain functions in the wild is now possible. Ecological studies on how the environment affects behavior of animals (i.e., hibernation, foraging, food hoarding, and nest building) have framed a plurality of questions to be answered mechanistically, and yet, only few studies have addressed the relationship between the environment and the brain's anatomy and physiology. Neuroscience needs new animal models that allow us to tackle such questions in the wild. Here, we propose a new animal model for wild neuroscience, the agouti (Dasyprocta spp.), a large wild rodent playing a critical seasonal role in the maintenance of the central and south American rainforest ecosystems. We focus on how a rodent model, like the agouti, will allow for the investigation of large-scale brain dynamics during seasonal behaviors of ecological importance: scatter-hoarding and retrieval. We describe agouti evolution, ecology, and physiology as well as neuro-anatomical and neurophysiological studies, which have set the foundation for future neuroscience in natura. We suggest agoutis have the potential to be a groundbreaking model for wild neuroscience.
Natural cavities are monopolizable resources used as nest sites across many species exhibiting exclusive male care. However, our understanding of how the availability of this type of reproductive site influences male–male competition and the foraging costs associated with parental care is limited and based on studies of fish. The harvestman Magnispina neptunus offers the opportunity to explore these questions in invertebrates because males defend natural cavities used as oviposition sites and provide exclusive parental care. We hypothesized that low nest availability would increase male–male competition and the foraging costs of egg attendance. To test this hypothesis, we collected observational data in the field and conducted a laboratory experiment with two groups, low and high nest availability. Field data indicate natural cavity scarcity, as only 50% of the males were nest holders. Larger males were more likely to hold nests in the field, but body size did not predict nest ownership in the laboratory. In the field, nests with openings smaller than average were equally occupied by small and large males, while nests with openings larger than average were occupied almost exclusively by large males. The nest opening in the laboratory experiment was adjusted to be equal to the average found in the field, which may have increased nest defensibility, regardless of male size. Thus, prior residency may outweigh body size in determining nest possession. Because nest owners seem to have an advantage over intruders, the costs of abandoning a nest are likely high. This may explain why the frequency of nest takeovers and foraging outside the nests did not differ between experimental groups. In conclusion, although underexplored in empirical studies, external factors, such as the opening size of cavities defended by males of many species with resource-defense mating systems, may play a key role in the defensibility of nest sites.
The use of high-pitched auditory signals by species communicating alongside noisy streams has been often considered an adaptation, yet studies testing this hypothesis have yielded inconclusive results. The major challenge has been to quantify the proportion of across-species signal variation that could be attributed to either common history (phylogenetic load) or adaptation. We further advance in this approach by comparing the phylogenetic load between different components of anuran calls. Because stream noise allegedly represents a stronger selective pressure for call frequency than for call temporal traits, we predicted a weaker phylogenetic signal in call frequency, particularly in the taxa that breed alongside streams. We first built a phylogenetic hypothesis using four mitochondrial genes on each of three clades: the genus Hyloscirtus and the family Centrolenidae, which call alongside streams and the subfamily Phyllomedusinae, known to call at lentic water bodies. In parallel, we compiled data on the advertisement calls of 154 species and used them to calculate Blomberg's K values as a proxy for the phylogenetic load (signal) of the call traits. The phylogenetic signal was weaker in spectral than in temporal call traits within the Hyloscirtus calls and weak or absent in both spectral and temporal components of Phyllomedusine calls. Against our expectations, the phylogenetic signal was strong in call frequency, but absent in call temporal components of the centrolenid calls. Our results support uncoupled evolution between spectral and temporal components of anuran calls. They also indicate that the selective role of abiotic noise varies among taxa and that other factors must be invoked to fully understand among-species variation in advertisement calls.
Different environments place different cognitive demands on constituent taxa. Learning and memory involve cognitive processes with associated costs, and it is expected that different levels of learning will occur in taxa from different environments. Greater memory loads linked to increased environmental complexity require greater learning and memory capacities. We investigated the variation in learning and memory in sister taxa of striped mice (genus Rhabdomys). We studied two populations each of the mesic grassland-occurring R. d. chakae and the mostly arid-occurring R. pumilio. We conducted two sets of experiments. (1) In a novel object recognition (NOR) test, we assessed memory by recording the duration of exploration of similar and novel objects by test mice. (2) In an associative learning task, we assessed whether mice could associate specific scents with or without a food incentive or with different quantities of the food incentive in previous training phases. We measured the latency of mice to contact scents in a two-sample choice in the test phase. In the NOR test, R. pumilio spent less time investigating similar objects in a training trial than R. d. chakae but increased absolute exploration of the novel object when presented with a novel and a familiar object in the retention trial, suggesting a sensitization to the novel object by R. pumilio. In the associative learning experiments, R. pumilio approached the stimuli faster than R. d. chakae, whereas mice from both taxa preferred scents associated with a seed versus no seed and scents associated with 5 seeds versus 1 seed. The data provide evidence of taxon-level differences in learning and memory, likely related to environmentally modulated personality differences between the taxa.
In insects, aging produces deterioration in physiological and cellular functioning, affecting their reproductive potential. Anastrepha fraterculus and Ceratitis capitata are two fruit fly species where overwintering adults resume their reproductive activity in spring, giving old individuals the possibility of mating with young adults. Most age studies focus on male reproductive capacity; however, we lack information on how the interaction between the ages of both sexes can determine post-mating processes. Here, we studied sex and age effects on (i) female fecundity and fertility, (ii) failure to leave viable offspring (reproductive failure), and (iii) female remating behavior. We found that young pairs of both species had higher fecundity, but young C. capitata males mated with old females had the lowest fecundity. This suggests that overwintering flies in this species will not substantially contribute to the next generation. We also found in C. capitata more prevalent reproductive failure in hetero-age combinations, which could be due to age recognition between mates, resulting perhaps in differential ejaculate allocation. Copula duration was positively associated with female age, yet it was longer for older A. fraterculus females and shorter for C. capitata females. Female remating was lower when young females mated with old males in C. capitata. This would imply that males perceive young females of “good quality” and thus invest and transfer all the ejaculate possible to ensure the delay of renewal of female receptivity. Aging does not always cause a decline in reproductive potential, which may be important in species that overwinter as adults. Complex interactions between female physiology and male ejaculate senescence can impact postcopulatory behaviors that affect reproductive success for both sexes.
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