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Detrimental impact of a heatwave on male reproductive behaviour and fertility

Abstract

Understanding how heatwaves impact on different aspects of mating behaviour and fertility is getting increasingly important. In this context, laboratory fertility and mating experiments involving manipulation and exposure of insects to different thermal conditions are common procedures. To conduct such experiments practical methods such as dyes are needed for an easy, non-invasive discrimination of individuals. We report here a study measuring the effect of an extended heat stress applied to males on several parameters of mating behaviour and fertility of laboratory populations of Drosophila subobscura derived from two distinct European locations. We found highly detrimental effects of heatwave on mating behaviour—with longer (courtship and copulation) latencies and lower mating occurrence but no changes in mating duration—and fertility, with reduced fecundity and reproductive success. Furthermore, we also tested the efficacy of food dye as a marker for individual discrimination and mating occurrence. While food dye did not allow to infer the occurrence of a mating based on a transfer of coloration from male to female, it did not affect mating and fertility, attesting its utility has a method for discriminating individuals within mating experiments in the context of thermal studies. Importantly, despite the fact that the heatwave was only applied in males, we observed an impact on behaviour of females that mated with stressed males, by often refusing their nuptial feeding. This opens possibilities for further integrated research on the changes of female and male mating behaviour and fertility under different thermal scenarios.

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Hoarding titmice predominantly use Familiarity, and not Recollection, when remembering cache locations

Abstract

Scatter-hoarding birds find their caches using spatial memory and have an enlarged hippocampus. Finding a cache site could be achieved using either Recollection (a discrete recalling of previously experienced information) or Familiarity (a feeling of “having encountered something before”). In humans, these two processes can be distinguished using receiver operating characteristic (ROC) curves. ROC curves for olfactory memory in rats have shown the hippocampus is involved in Recollection, but not Familiarity. We test the hypothesis that food-hoarding birds, having a larger hippocampus, primarily use Recollection to find their caches. We validate a novel method of constructing ROC curves in humans and apply this method to cache retrieval by coal tits (Periparus ater). Both humans and birds mainly use Familiarity in finding their caches, with lower contribution of Recollection. This contribution is not significantly different from chance in birds, but a small contribution cannot be ruled out. Memory performance decreases with increasing retention interval in birds. The ecology of food-hoarding Parids makes it plausible that they mainly use Familiarity in the memory for caches. The larger hippocampus could be related to associating cache contents and temporal context with cache locations, rather than Recollection of the spatial information itself.

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Spot the odd one out: do snake pictures capture macaques’ attention more than other predators?

Abstract

Detecting and identifying predators quickly is key to survival. According to the Snake Detection Theory (SDT), snakes have been a substantive threat to primates for millions of years, so that dedicated visual skills were tuned to detect snakes in early primates. Past experiments confronted the SDT by measuring how fast primate subjects detected snake pictures among non-dangerous distractors (e.g., flowers), but did not include pictures of primates’ other predators, such as carnivorans, raptors, and crocodilians. Here, we examined the detection abilities of N = 19 Tonkean macaques (Macaca tonkeana) and N = 6 rhesus macaques (Macaca mulatta) to spot different predators. By implementing an oddity task protocol, we recorded success rates and reaction times to locate a deviant picture among four pictures over more than 400,000 test trials. Pictures depicted a predator, a non-predator animal, or a simple geometric shape. The first task consisted of detecting a deviant picture among identical distractor pictures (discrimination) and the second task was designed to evaluate detection abilities of a deviant picture among different distractor pictures (categorization). The macaques detected pictures of geometric shapes better and faster than pictures of animals, and were better and faster at discriminating than categorizing. The macaques did not detect snakes better or faster than other animal categories. Overall, these results suggest that pictures of snakes do not capture visual attention more than other predators, questioning previous findings in favor of the SDT.

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Cognitive flexibility in a Tanganyikan bower-building cichlid, Aulonocranus dewindti

Abstract

Cognitive flexibility, the ability to modify one’s decision rules to adapt to a new situation, has been extensively studied in many species. In fish, though, data on cognitive flexibility are scarce, especially in the wild. We studied a lekking species of cichlid fish in Lake Tanganyika, Aulonocranus dewindti. Males create sand bowers as spawning sites and maintain them by removing any objects falling into it. In the first part of our experiment, we investigated the existence of spontaneous decision rules for the maintenance of the bowers. We showed that if a snail shell and a stone are placed in their bower, fish prefer to remove the shell first. In the second phase of our experiment, we took advantage of this spontaneous decision rule to investigate whether this rule was flexible. We tested five individuals in a choice against preference task, in which the fish had to modify their preference rule and remove the stone first to be allowed to then remove the shell and have a clean bower. While there was no overall trend towards flexibility in this task, there was variation at an individual level. Some individuals increased their preference for removing the shell first, deciding quickly and with little exploration of the objects. Others were more successful at choosing against preference and showed behaviours suggesting self-regulatory inhibition abilities. Bower-building cichlids could therefore be a promising model to study cognitive flexibility, and other aspects of animal cognition in the wild.

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Competition and sex-age class alter the effects of group size on vigilance in white-tailed deer Odocoileus virginianus

Abstract

Increased group size is predicted to dilute predation risk for individuals and increase predator detection at the group level. Individual vigilance tends to decrease with group size for many species. However, this pattern varies across species, context, space, and time. We explored the effects of group size on vigilance behaviors of white-tailed deer (Odocoileus virginianus) in relation to season, sex-age status, group composition, diminishing food returns, and intraspecific competition. We used classical behavioral observation methods and camera traps to study deer behavior. Sex-age class, season, intraspecific competition, and diminishing food returns interacted with group size to shape vigilance behaviors in deer. During spring, the effect of group size was essentially non-existent, and during winter, vigilance patterns exhibited a non-linear relationship with group size. Subadult deer benefited most in terms of increased foraging and decreased vigilance from the presence of 1–2 conspecifics, likely a maternal family group. This effect diminished in the presence of additional conspecifics (≥3), apparently as a function of contest competition. Individual deer spent less time at a site in areas with greater intraspecific abundance; however, in the presence of conspecifics, the relationship was reversed. Our research suggests that maternal family groups play an important seasonal role in vigilance behaviors of deer. Our study demonstrates the complex effects of group size in white-tailed deer. Group size effects are generally considered to be in response to changes in predation risk; however, our work supports a growing body of evidence that group size effects may also be influenced by intraspecific interactions.

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Feeding behavior and prey of three migratory shorebirds (Aves: Charadriiformes) during the nonbreeding season in southern Brazil

Abstract

Migratory shorebirds such as Calidris alba, C. fuscicollis, and Charadrius semipalmatus congregate in stopover areas like coastal wetlands to rest and feed, building up sufficient energy for their ongoing migration. To investigate the feeding ecology of these three shorebird species during their stopover, we conducted a comparative analysis of their feeding behavior and prey in Lagoa do Peixe National Park. We examined the feeding behavior using video recordings of 594 actively foraging individuals. Additionally, we determined the shorebirds’ diet by analyzing 106 droppings collected from two areas within the park: the beach’s intertidal zone and the lagoon’s mudflats. The results highlighted that shorebird species showed marked differences in feeding strategies and prey captured during foraging. C. semipalmatus employed a visual-run-stop strategy with surface pecking, with no significant variations observed between the beach and the lagoon. The two Calidris species utilized a tactile-continuous hunting strategy, involving pecking and probing, with some variations observed between the beach and the lagoon. Multiple probing was mostly used on the beach, and single probing in the lagoon. The variation in probing behavior between the Calidris species appeared to be associated with differences in substrate type and food availability in the respective habitats they frequented. Additionally, our findings indicated that visual searching led to a more diverse prey selection, particularly in the lagoon. These differences in foraging strategies suggest that shorebird species can exploit the park’s intertidal plains and trophic resources differently, emphasizing the importance of considering spatial and dietary variability in studying their foraging behavior.

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Interspecific differences in developmental mode determine early cognitive abilities in teleost fish

Abstract

Most studies on developmental variation in cognition have suggested that individuals are born with reduced or absent cognitive abilities, and thereafter, cognitive performance increases with age during early development. However, these studies have been mainly performed in altricial species, such as humans, in which offspring are extremely immature at birth. In this work, we tested the hypothesis that species with other developmental modes might show different patterns of cognitive development. To this end, we analysed inhibitory control performance in two teleost species with different developmental modes, the zebrafish Danio rerio and the guppy Poecilia reticulata, exploiting a simple paradigm based on spontaneous behaviour and therefore applicable to subjects of different ages. Zebrafish hatch as larvae 3 days after fertilisation, and have an immature nervous system, a situation that mirrors extreme altriciality. We found that at the early stages of development, zebrafish displayed no evidence of inhibitory control, which only begun to emerge after one month of life. Conversely, guppies, which are born after approximately one month of gestation as fully developed and independent individuals, solved the inhibitory control task since their first days of life, although performance increased with sexual maturation. Our study suggests that the typical progression described during early ontogeny in humans and other species might not be the only developmental trend for animals’ cognition and that a species’ developmental mode might determine variation in cognition across subjects of different age.