Do Active and Passive Antipredator Defences in the Toad Epidalea calamita Differ between Males and Females from Natural Habitats and Agrosystems?

Due to their assumed costs, simultaneous antipredator strategies are expected to face trade-offs, which, however, could be milder in individuals subjected to a more intense predator pressure. In this work, I studied the relationship between locomotion and parotoid glands in the natterjack toad, Epidalea calamita. Specifically, I predicted that individuals with reduced sprint speed would rely more on their chemical defences, having larger and more aposematically coloured parotoid glands. In addition, I expected this trade-off to be more evident in females and toads from pine grove habitats, because, according to previous work, males and toads from agrosystems are under greater predator pressure. However, sprint speed showed no relationship with coloration, but toads with proportionally greater parotoid glands were also proportionally faster. Thus, the costs of these antipredator traits might not be high enough to make them interfere, or the benefits of simultaneous optimisation of sprint speed and parotoid gland size might outweigh the costs of it in some individuals. In any case, habitat and sex did not affect these relationships, so the trends detected are valid across sexes and the habitats studied.

No link between nymph and adult coloration in shield bugs: weak selection by predators

Many organisms use different antipredator strategies throughout their life, but little is known about the reasons or implications of such changes. For years, it has been suggested that selection by predators should favour uniformity in local warning signals. If this is the case, we would expect high resemblance in colour across life stages in aposematic animals where young and adults share similar morphology and habitat. In this study, we used shield bugs (Hemiptera: Pentatomoidea) to test whether colour and colour diversity evolve similarly at different life stages. Since many of these bugs are considered to be aposematic, we also combined multi-species analyses with predation experiments on the cotton harlequin bug to test whether there is evidence of selection for uniformity in colour across life stages. Overall, we show that the diversity of colours used by both life stages is comparable, but adults are more cryptic than nymphs. We also demonstrate that nymphs and adults of the same species do not tend to look alike. Experiments on our model system suggest that predators can generalise among life stages that look different, and exhibit strong neophobia. Altogether, our results show no evidence of selection favouring colour similarity between adults and nymphs in this speciose clade.

Antipredator strategies of pupae: how to avoid predation in an immobile life stage?

Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be ‘avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue ‘The evolution of complete metamorphosis’.

Reproductive behavior and development in Spilotes sulphureus (Serpentes: Colubridae) from Ecuador

Reproductive behavior and development in Spilotes sulphureus (Serpentes: Colubridae) from Ecuador. The Birdsnake Spilotes sulphureus is a large-sized species that occurs from the Amazon region to the Atlantic forest of South America. Despite the wide distribution little is known about its natural history. Here we report, for the frst time, reproductive behavior displayed by this species observed in a pair of Ecuadorian specimens in captivity. A ritualized pre-copulatory behavior followed a colubrine pattern similar to the congeneric species Spilotes pullatus. The repertoire included chin-rubbing, continuous tongue ficking, head raising, body jerking, cloacal gaping, and partial mounting. Oviposition occurred 86–98 days after of the frst copulation. Females lay clutches of 7–14 eggs. Juvenile coloration is remarkably different from adults. Newborns have a dorsum with transverse brown or gray bands, and white or pale gray interspaces; young of 1–2 years have green bands and yellow-green interspaces; adults have dark green bands. Ontogenetic color changes are presumably associated with antipredator strategies, change in size, vulnerability or habitat and microhabitat selection.

Escape behaviour of aposematic (Oophaga pumilio) and cryptic (Craugastor sp.) frogs in response to simulated predator approach

Crypsis and aposematism are common antipredator strategies that can each be coupled with behaviours that maximize predator deterrence or avoidance. Cryptic animals employ camouflage to conceal themselves within their environment and generally rely on immobility to avoid detection by predators. Alternatively, aposematic animals tend to rely on an association between conspicuous colouration and secondary defence to deter potential predators, and tend to exhibit slow movements in response to predators. The goal of the present study was to determine how cryptic Craugastor sp. and aposematic Oophaga pumilio respond to simulated human and bird model predators. Oophaga pumilio responded more often with movement to both the human (17/22) and bird (9/25) predators than Craugastor sp. (human: 2/21; bird: 0/21). The increased movement resulted in a greater average flight initiation distance, latency to move, and distance fled in O. pumilio. These findings suggest that cryptic Craugastor sp. rely on immobility to avoid detection, whereas aposematic O. pumilio utilize movement, possibly as a mechanism to increase the visibility of their warning signals to potential predators. Furthermore, O. pumilio exhibited greater movement in response to humans, suggesting that they actively avoid trampling by large threats, rather than considering them predators.