Abstract Shoreline development of temperate lakes has increased steadily in recent decades, putting pressure on animal populations that live in lacustrine habitats. Common loons (Gavia immer) nest along lakeshores, and shoreline development has been identified as a likely cause of population decline in this species. Taking advantage of a marked loon population from a long-term study in northern Wisconsin, USA between 1992 and 2023, we investigated impacts of shoreline development and human disturbance on territory choice and nest defense behavior of breeding loons. Loons settled on territories that resembled their natal lakes in terms of shoreline development, an indication of natal habitat imprinting. Shoreline development did not affect the distance at which loons flushed from their nest at the approach of humans. However, nesting loons were less likely to flush from the nest late in the incubation period, suggesting a tendency for loons to defend nests according to likely fitness benefits. Loons' tendency to breed on lakes similar in human activity to their natal lake might reflect their effort to seek out lakes of familiar fish species composition rather than human activity. Natal habitat imprinting of this kind illustrates the potential of anthropogenic factors to affect behavior and, in turn, population dynamics.
Antipredator behaviours in animals rely on environmental cues that signify dangers, but responses to these cues are known to be context-dependent. Urbanisation in particular has been shown to decrease responsiveness to threats, especially to humans, however how this might interact with cue modality and especially with multi-modal cues, is less known. Our study investigated Eastern Water Dragons (Intellagama lesueurii): a native lizard that proliferates in highly urbanised spaces across eastern Australia. We exposed dragons at three sites spanning a gradient of urbanisation to threat, non-threat and human signals in three different modes: visual, audio and dual (visual and audio combined). We found that dragons in the most highly urbanised park tended to generalise threat type and cue mode, responding primarily by fleeing to humans and natural threat cues regardless of the signal mode. The peri-urban populations, however, showed much higher variability in responses to threat types, responding by fleeing significantly more often when a visual cue was present compared with audio-only cues. This study demonstrates that antipredator behavioural responses to environmental cues in an urbanised lizard are strongly site-dependent and do not necessarily conform to patterns commonly reported in urban ecology studies.
Abstract Individuals help to rear the offspring of other group members in many animal societies. In social mole-rats, conspicuous forms of alloparental care such as allolactation and offspring provisioning are absent, and group members cooperate primarily by digging tunnels to access the tubers on which breeders, and subsequently their offspring, feed. Despite interest in the organisation of mole-rat societies, it remains uncertain how group members adjust their cooperative behaviour across reproductive periods, and the potential for nest attendance to represent a form of direct offspring care has been overlooked. Using observations (∼24,000 h) of captive Damaraland mole-rats (Fukomys damarensis), we quantified group members’ time budgets across reproductive periods and tested whether non-breeders increased their nest attendance following the birth of pups, as expected if nest attendance contributes to alloparental care. Contrary to this prediction, non-breeding individuals of both sexes, as well as breeding males, reduced their nest attendance while increasing their work effort shortly after birth. A similar pattern occurred during late gestation. Breeding females spent more time in the nest, reduced work-related behaviours, and increased feeding activity during these same periods. Thus, we found no evidence that non-breeders care for offspring by increasing nest attendance. The increased work effort by non-breeders during reproductive periods may help to support breeders when they are energetically constrained and facilitate access to food resources for dependent pups when they first leave the nest. Our results highlight the importance of distinguishing direct alloparental care from other behavioural changes when interpreting the functional basis of cooperation.
Abstract The harsh environment hypothesis posits that sociality should preferentially evolve in extreme or unpredictable environments. Although comparative studies largely support this trend, it is becoming clear that there are multiple reasons underlying this pattern that may differ from system to system. Therefore, targeted behavioral experiments are needed to identify the precise costs and benefits of sociality in harsh environments in a wide variety of contexts. Here, we perform a series of experiments focused on wet soil as a harsh environment for the burying beetle Nicrophorus orbicollis, a model system for the study of biparental care. We confirm previous work that wet soil presents a challenging but usable breeding environment for this species by showing that young pairs choose not to reproduce while several old pairs did so successfully. We show that the costs of breeding in this environment accrue primarily to larvae, who suffer high mortality prior to eclosion, especially when they are larger. We next show that increased sociality, both in the form of biparental care and biparental care with older partners, increase the likelihood of reproduction in wet soil, but does not increase the fitness of larvae. We lastly show that even dramatic reductions of parental care do not affect the fitness of larvae in wet soil. We argue that increased effort from social partners only benefits each other by reducing costs associated with breeding. However, the increased mortality of larger individuals suggests the surprising potential for a negative association between sociality and harsh environments.
Abstract Through parental care, as well as abandonment, neglect, infanticide, and cannibalism, parents can play an active role in determining which of their offspring do and do not survive. In teleost fish, parental care is most often provided by the male alone and consumption of some offspring by the father is common. If partial brood cannibalism improves survival of the remaining offspring, mothers should favor egg-eating by males. If, however, some offspring are cannibalised to obtain energy for future reproductive attempts, this will result in sexual conflict between parents over cannibalism and may drive the evolution of counterstrategies in females to minimize offspring loss. In a comparative analysis, we find that males under stronger sexual selection, inferred from the degree of sexual dimorphism in body size, consume a greater proportion of their offspring, suggesting that the opportunity for future reproduction is an important driver of this behavior. Furthermore, we find that females show strong preferences for spawning with males that are already caring for broods in species where the risk of cannibalism by fathers is high. Finally, we show that by adding eggs to existing broods, mothers can dilute the risk of their eggs being cannibalized. A preference for caring males thus represents a strategy by which females can minimize reproductive costs arising from selfish investment by males in future mating success.
