Surf and turf: predation by egg-eating snakes has led to the evolution of parental care in a terrestrial lizard

Loss of sea turtle eggs drives the collapse of an insular reptile community

Marine subsidies are vital for terrestrial ecosystems, especially low-productivity islands. However, the impact of losing these subsidies on the terrestrial food web can be difficult to predict. We analyzed 23 years of survey data from Orchid Island to assess the consequences of the abrupt loss of an important marine subsidy. After climate-driven beach erosion and predator exclusion efforts resulted in the abrupt loss of sea turtle eggs from the terrestrial food web, predatory snakes altered their foraging habitats. This increased predation on other reptile species in inland areas, resulting in population declines in most terrestrial reptile species. Comparisons with sea turtle-free locations where lizard populations remained stable supported these findings. Our study emphasizes the cascading effects of generalist predators and the unintended consequences of single-species conservation, highlighting the importance of understanding species interconnectedness and considering potential ripple effects in marine-dependent insular ecosystems.

Beyond classical theories: An integrative mathematical model of mating dynamics and parental care

Classical theories, such as Bateman's principle and Trivers' parental investment theory, attempted to explain the coevolution of sexual selection and parental care through simple verbal arguments. Since then, quantitative models have demonstrated that it is rarely that simple because many non-intuitive structures and non-linear relationships are actually at play. In this study, we propose a new standard for models of mating dynamics and parental care, emphasizing the clarity and use of mathematical and probabilistic arguments, the meaning of consistency conditions, and the key role of spatial densities and the law of mass action. We used adaptive dynamics to calculate the evolutionary trajectory of the total care duration. Our results clearly show how the outcomes of parental care evolution can be diverse, depending on the quantitative balance between a set of dynamical forces arising from relevant differences and conditions in the male and female populations. The intensity of sexual selection, synergy of care, care quality, and relative mortality rates during mating interactions and caring activities act as forces driving evolutionary transitions between uniparental and biparental care. Sexual selection reduces the care duration of the selected sex, uniparental care evolves in the sex that offers the higher care quality, higher mortality during mating interactions of one sex leads to more care by that sex, and higher mortality during caring activities of one sex favours the evolution of uniparental care in the other sex. Both synergy and higher overall mortality during mating interactions can stabilize biparental care when sexual selection reduces the care duration of the selected sex. We discuss how the interaction between these forces influences the evolution of care patterns, and how sex ratios can vary and be interpreted in these contexts. We also propose new directions for future developments of our integrative model, creating new comparable analyses that share the same underlying assumptions and dynamical frameworks.

Female-female aggression in the Gila monster (Heloderma suspectum)

Historically, the role of aggression in the social lives of animals overwhelmingly focused on males. In recent years, however, female-female aggression in vertebrates, particularly lizards, has received increasing attention. This growing body of literature shows both similarities and differences to aggressive behaviours between males. Here, we document female-female aggression in captive Gila monsters (Heloderma suspectum). Based on four unique dyadic trials (eight adult female subjects), we developed a qualitative ethogram. Unexpected and most intriguing were the prevalence and intensity of aggressive acts that included brief and sustained biting, envenomation, and lateral rotation (i.e. rolling of body while holding onto opponent with closed jaws). Given specific behavioural acts (i.e. biting) and the results of bite-force experiments, we postulate that osteoderms (bony deposits in the skin) offer some degree of protection and reduce the likelihood of serious injury during female-female fights. Male-male contests in H. suspectum, in contrast, are more ritualized, and biting is rarely reported. Female-female aggression in other lizards has a role in territoriality, courtship tactics, and nest and offspring guarding. Future behavioural research on aggression in female Gila monsters is warranted to test these and other hypotheses in the laboratory and field.

The reproductive ecology drivers of egg attendance in amphibians

Parental care is extremely diverse but, despite much research, why parental care evolves is poorly understood. Here we address this outstanding question using egg attendance, the simplest and most common care form in many taxa. We demonstrate that, in amphibians, terrestrial egg deposition, laying eggs in hidden locations and direct development promote the evolution of female egg attendance. Male egg attendance follows the evolution of hidden eggs and is associated with terrestrial egg deposition but not with direct development. We conclude that egg attendance, particularly by females, evolves following changes in reproductive ecology that are likely to increase egg survival, select for small clutches of large eggs and/or expose eggs to new environmental challenges. While our results resolve a long-standing question on whether reproductive ecology traits are drivers, consequences or alternative solutions to caring, they also unravel important, yet previously unappreciated, differences between the sexes.

Terrestrial reproduction and parental care drive rapid evolution in the trade-off between offspring size and number across amphibians

The trade-off between offspring size and number is central to life history strategies. Both the evolutionary gain of parental care or more favorable habitats for offspring development are predicted to result in fewer, larger offspring. However, despite much research, it remains unclear whether and how different forms of care and habitats drive the evolution of the trade-off. Using data for over 800 amphibian species, we demonstrate that, after controlling for allometry, amphibians with direct development and those that lay eggs in terrestrial environments have larger eggs and smaller clutches, while different care behaviors and adaptations vary in their effects on the trade-off. Specifically, among the 11 care forms we considered at the egg, tadpole and juvenile stage, egg brooding, male egg attendance, and female egg attendance increase egg size; female tadpole attendance and tadpole feeding decrease egg size, while egg brooding, tadpole feeding, male tadpole attendance, and male tadpole transport decrease clutch size. Unlike egg size that shows exceptionally high rates of phenotypic change in just 19 branches of the amphibian phylogeny, clutch size has evolved at exceptionally high rates in 135 branches, indicating episodes of strong selection; egg and tadpole environment, direct development, egg brooding, tadpole feeding, male tadpole attendance, and tadpole transport explain 80% of these events. By explicitly considering diversity in parental care and offspring habitat by stage of offspring development, this study demonstrates that more favorable conditions for offspring development promote the evolution of larger offspring in smaller broods and reveals that the diversity of parental care forms influences the trade-off in more nuanced ways than previously appreciated.

What selective pressures alter the tradeoff between offspring size and number? A phylogenetic comparative approach shows that amphibians with direct development and those that lay eggs in terrestrial environments have larger eggs and smaller clutches, while different care behaviours and adaptations vary in their effects on the tradeoff.

Sum of fears among intraguild predators drives the survival of green sea turtle (Chelonia mydas) eggs

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata) and two mesopredators (the brown rat, Rattus norvegicus, and kukri snake, Oligodon formosanus). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.

Pain in dinosaurs: what is the evidence?

How far back can we trace behaviour associated with pain? Behaviour is not preserved in the palaeontological record, so, for dinosaurs, we are restricted to what we can deduce from fossilized bones and tracks. This review is a thought experiment using circumstantial evidence from dinosaur fossils and from the behaviour of their extant relatives to describe probable responses of dinosaurs to serious injuries. Searches yielded 196 papers and chapters with: reports of healed serious injuries, and limping gait and injured feet in trackways; information about physiology and behaviour relevant to healing; evidence of evolutionary connections with birds and crocodilians, and their behaviour; and information about relevant aspects of evolution. Clearly, many dinosaurs survived injuries that would have seriously hampered mobility, impairing hunting or escape from predators, and affecting social interactions. Recovery from severe injuries implies pain-mediated responses. Rates of healing seem faster than for other reptiles, possibily aided by warm-bloodedness. Nesting was often communal, raising the possibility of parental and group protection for injured young. The existence of family groups, packs or herds raises the possibility of protection or feeding from pack kills. This is the first study, to our knowledge, of possible pain behaviour and responses to injury in dinosaurs. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Coevolution influences the evolution of filial cannibalism, offspring abandonment and parental care

Understanding evolutionary patterns of parental investment and care has been a long-standing focus in studies of evolutionary and behavioural ecology. Indeed, patterns of investment and care are highly diverse, and fully understanding such diversity has been challenging. Recently, several studies have highlighted the need to consider coevolutionary dynamics in studies of parental care, as parental care is likely to co-occur and co-originate with a range of other traits. Two traits that commonly co-occur with parental care are offspring abandonment (the termination of parental investment prior to full independence in offspring) and filial cannibalism (the consumption of one's offspring). Here, we use a mathematical framework to explore how co-occurrence and coevolution among care, abandonment and cannibalism can influence the life-history conditions under which care is expected to evolve. Our results suggest that in some cases, the evolution of parental care can be inhibited by offspring abandonment and filial cannibalism. In other cases, abandonment and filial cannibalism that benefits parents can promote the evolution of parental care. It is particularly interesting that behaviours that seem so contrary to care-that is, eating or abandoning one's young-can in some cases broaden the conditions under which care can evolve. In general, our findings highlight that considering co-occurrence and coevolutionary dynamics between two or more traits is essential to understanding the evolution of trait diversity.

When males live longer: Resource-driven territorial behavior drives sex-specific survival in snakes

Phylogenetic analysis has shown that males' propensity to engage in aggressive encounters is associated with females having greater longevity. Here, we confirm the causal link between aggression and reduced longevity by looking at an egg-eating snake (Oligodon formosanus) in which females defend territories in the presence of sea turtle eggs. We monitored aggressiveness and survival at two sites: a control site with a stable supply of turtle eggs, and a second site where we collected data before and after a storm that eroded the beach on which turtles nested, thus leading to a loss of territoriality. We show that territoriality was the driver behind higher injury rates in females. Territorial females also had lower survival and decreased longevity compared with the nonterritorial males, but these differences disappeared when females were not territorial. Our study demonstrates how resource availability can influence the evolution of sex-specific patterns of survival across vertebrates.

Observations supporting parental care by a viviparous reptile: aggressive behaviour against predators demonstrated by Cunningham’s skinks

Most reptiles exhibit no parental care and aggressive behaviour towards heterospecific predators has rarely been recorded in the natural environment. Several species of the subfamily Egerniinae are amongst the most highly social of all squamate reptiles, exhibiting stable social aggregations and high levels of long-term social and genetic monogamy. We have examined Cunningham’s skinks, Egernia cunninghami, over a three-year period during late January and early February (total 32 days) in the alpine region of New South Wales using video and thermal imaging. Four birthing sessions were witnessed during our field studies of social aggregations of skinks. Our observations monitored skink encounters, in the presence of offspring, with an eastern brown snake, Pseudonaja textilis (two separate encounters, one recorded by video/imaging) and 12 encounters with the Australian magpie, Gymnorhina tibicen. All events were associated with aggressive chasing and/or attack by adult skinks. The first snake encounter involved the active targeting of a recently born juvenile with the mother of the juvenile attacking the snake (running towards the snake, biting and remaining attached for several seconds). The second encounter (the following year) comprised two adult skinks attacking and biting a snake, Pseudonaja textilis. All magpie encounters resulted in chases by adult skinks.

Pre-ovipositional maternal care alleviates food stress of offspring in the flower beetle Dicronocephalus wallichii

Unlike most other flower beetles, females of Dicronocephalus wallichii exhibit nesting behaviour. The female constructs a burrow in the soil, cuts dead plant leaves into small pieces to provision the nest, and then lays one egg inside the nest. Hatched larvae have been thought to feed on the nest materials prepared by their mothers, but the effects of pre-ovipositional care on larval performance have not been tested. The hatched larvae were found to stay in the nest for 15–30 days until they consumed the nest materials. We examined whether the presence of provisioned nests enhanced larval performance under both benign and food-stress conditions. With high-nutrient soil, larval survival rate and growth speed were not affected by the presence of provisioned nests. By contrast, with low-nutrient soil, mortality of the larvae was much higher in the absence than in the presence of provisioned nests. The growth speed of larvae with nests located in low-nutrient soil was as high as those reared in high-nutrient soil. These results indicate that females alleviate the food stress of larvae during their initial developmental stage by constructing provisioned nests.

Ontogenetic shifts in the diet of plains hog-nosed snakes (Heterodon nasicus) revealed by stable isotope analysis

Wild snake diets are difficult to study using traditional methods, but stable isotopes offer several advantages, including integrating dietary information over time, providing data from individuals that have not fed recently, and avoiding bias towards slowly-digesting prey items. We used stable isotope signatures of carbon and nitrogen from scale tissue, red blood cells, and blood plasma to assess the diet of wild plains hog-nosed snakes (Heterodon nasicus) in Illinois. We developed Bayesian mixing models which, taken together, predicted that H. nasicus shifted from a juvenile diet predominantly (31-63%) composed of six-lined racerunners (Aspidoscelis sexlineatus) and their eggs to an adult diet predominantly (44-56%) composed of eggs of the aquatic turtles Chrysemys picta and Chelydra serpentina, with a contribution from toads (Anaxyrus sp.; 6-27%) during their adolescent years. These results agreed with sparse data from gut contents. Combining traditional and isotopic techniques for studying the diets of wild snakes can increase the utility of both types of data.