Experimental Evaluation of δ2H, δ13C and δ15N Variability in Blood and Feathers of Wild and Captive Birds: Implications for Interspecific Food Web Studies

Stable-hydrogen (δ2H), nitrogen (δ15N), and carbon (δ13C) isotopes are used to decipher broad movement patterns and trophic relationships among diverse species, and an improved understanding of factors controlling natural variation in tissue-isotope measurements will enhance these applications. To evaluate the rearing environment and family-related effects on the isotopic composition of tissues, we cross-fostered nestling tree swallows (Tachycineta bicolor, Vieillot 1808) and American kestrels (Falco sparverius, Linnaeus 1758) by swapping recently hatched birds (<4 days old) among nest boxes and collecting blood and feathers prior to fledging. To assess developmental effects, we measured δ2H in blood and feathers of captive mallard (Anas platyrhynchos, Linnaeus 1758) ducklings challenged energetically during growth. Stable isotope composition was not strongly related to nest box type or natal nest (i.e., family of origin) effects in swallows and kestrels; tissue-isotope composition was related to rearing environment, indicative of differences in nest and parental quality or parental provisioning tactics. Blood and feather δ2H values in swallows were positively related to antecedent maximum ambient temperature, and unrelated to elevated energy expenditure in mallards. The average differences between δ2H in blood and feathers were similar for nestling swallows (27‰, 32‰; two sites) and mallards (26‰, 30‰; two age groups), and lower than in nestling kestrels (50‰). Strong species-specific patterns in blood-feather differences were not observed for δ15N and δ13C in swallows or kestrels; divergent δ2H results may be related to differences in nest ambient conditions, diet composition, or physiological processes affecting hydrogen assimilation during growth and feather synthesis. In swallows, tissue-isotope values reflected parental prey selection from spatially distinct food webs during nestling development with little effect(s) of family of origin, egg composition, or early growth.

Influence of intrinsic and extrinsic attributes on neonate survival in an invasive large mammal

Understanding factors influencing survival of neonates for wild species is important for successful management, particularly for determining drivers of population dynamics. Wild pigs (Sus scrofa) are invasive and populations are rapidly increasing in part due to high reproductive capacity. Survival of adults is generally high, however, survival of piglets, and particularly neonates, is largely unknown. We located neonates at the natal nest and quantified survival in relation to individual and maternal biological attributes, and environmental variables. During 2017–2020, we captured 50 neonates from 13 litters and documented 28 mortalities (56%) over six weeks. Survival was positively influenced by pelage coloration, likely as a form of camouflage from predators. Male neonates had higher survival. They were born larger than females, which could be beneficial for thermoregulation and competition for milk. Neonates born to larger sows had lower survival. Sow size was positively correlated with litter size, and this finding may reflect the increased nutritional demands of sustaining large litters, or difficulties in defending more neonates against predators. Neonates born in warmer months had higher survival than those born in cooler months. Neonates are inefficient thermoregulators, thus being born in warmer months could be beneficial for maintaining homeostasis as well as access to more food resources. These are the largest and most complete data for neonate wild pig survival and will inform population models for the development of management strategies to reduce negative impacts of this destructive invasive species on native ecosystems.

Worker ants promote outbreeding by transporting young queens to alien nests

Choosing the right mating partner is one of the most critical decisions in the life of a sexually reproducing organism and is the basis of sexual selection. This choice is usually assumed to be made by one or both of the sexual partners. Here, we describe a system in which a third party – the siblings – promote outbreeding by their sisters: workers of the tiny ant Cardiocondyla elegans carry female sexuals from their natal nest over several meters and drop them in the nest of another, unrelated colony to promote outbreeding with wingless, stationary males. Workers appear to choose particular recipient colonies into which they transfer numerous female sexuals. Assisted outbreeding and indirect female choice in the ant C. elegans are comparable to human matchmaking and suggest a hitherto unknown aspect of natural history – third party sexual selection. Our study highlights that research at the intersection between social evolution and reproductive biology might reveal surprising facets of animal behavior.

Habitat Quality Determines Dispersal Decisions and Fitness in a Beetle – Fungus Mutualism

Delayed dispersal of sexually mature offspring is a fundamental component of cooperative breeding. In ambrosia beetles, female offspring temporarily remain in their natal nest and refrain from reproduction, instead investing in alloparental care. Previous work has demonstrated a link between helping behaviour and the increased need for pathogen defence, arising from their close association with fungal cultivars. In the ambrosia beetle Xyleborinus saxesenii, mature female offspring can effectively fight pathogen infections and manage the microbial composition within the nest by adjusting the frequency of different hygienic and nest maintenance behaviours. This suggests a potential to respond flexibly to the ecology of their nest, which calls for a better understanding of the connection between behaviour and the microbial community thriving within their nests. Here, we studied the significance of the mutualistic fungus garden composition for the beetles’ nest ecology and fitness by experimentally varying substrate quality. We found that the vertically transmitted ambrosia fungus garden is composed of at least two fungus mutualist species and a wide variety of other microbes varying in their relative abundance. This is strongly affected by the moisture content of the substrate, which in nature depends on the age and type of wood. We found that the mutualist fungi complement each other in terms of dryness-resistance, allowing the beetles to utilise a broad range of substrates over prolonged time during which the wood gradually desiccates. Under suboptimal humidity conditions, the interaction between host and multiple fungus species has important ramifications for the behaviour of philopatric helpers, including their alloparental investment, sibling cannibalism and the timing of dispersal. Rearing five generations of beetles consecutively in dry substrate resulted in transgenerational effects on philopatry and alloparental care, probably mediated through the dominance of a particular fungus species that was driven by the experimental habitat condition. Interestingly, the nests of these selection lines produced much more offspring after five generations than any first-generation nest, which may have reflected increased egg laying by non-dispersing daughters. Our study highlights the importance of considering the interactions between the microbial community and their insect hosts for understanding social evolution in cooperatively breeding beetles.

Hormone-mediated dispersal and sexual maturation in males of the social paper wasp Polistes lanio

ABSTRACTSex-biased dispersal is common in social species, but the dispersing sex may delay emigration if associated benefits are not immediately attainable. In the social Hymenoptera (ants, some bees and wasps), newly emerged males typically disperse from the natal nest whilst most females remain as philopatric helpers. However, little information exists on the mechanisms regulating male dispersal. Furthermore, the conservation of such mechanisms across the Hymenoptera and any role of sexual maturation are also relatively unknown. Through field observations and mark–recapture, we observed that males of the social paper wasp Polistes lanio emerge from pupation sexually immature, and delay dispersal from their natal nest for up to 7 days whilst undergoing sexual maturation. Delayed dispersal may benefit males by allowing them to mature in the safety of the nest and thus be more competitive in mating. We also demonstrate that both male dispersal and maturation are associated with juvenile hormone (JH), a key regulator of insect reproductive physiology and behaviour, which also has derived functions regulating social organisation in female Hymenoptera. Males treated with methoprene (a JH analogue) dispersed earlier and possessed significantly larger accessory glands than their age-matched controls. These results highlight the wide role of JH in social hymenopteran behaviour, with parallel ancestral functions in males and females, and raise new questions on the nature of selection for sex-biased dispersal.

Inclusive Fitness of Male and Facultatively Social Female Nesting Behavior in the Socially Polymorphic Bee, Ceratina australensis (Hymenoptera: Xylocopinae)

Male hymenopterans do not typically provide help with nest construction or maintenance. This is thought to be due to the decreased relatedness of males to their siblings compared to sisters, and selection for outbreeding resulting in male dispersal from natal nesting sites. However, some instances of male ‘helping’ behaviors have been observed and can usually be explained by increased access to mating with resident females. Here we report on the first observations of cohabiting males within the nests of reproductive females of the facultatively social small carpenter bee, Ceratina australensis. Social nesting in C. australensis occurs at a consistently low rate across populations. We used microsatellites markers to determine relatedness, combined with 3 yr of nest demographic data collected across three populations, to assess the relative fitness of reproductive, nonreproductive, and male individuals cohabiting in reproductive nests. We found that males were brothers of reproductive females, both remaining in their natal nest. However, there was no evidence that they were mating with their sisters across all nests observed. Males in reproductive nests did not gain any direct or indirect fitness benefits as they did not sire any brood and their presence did not increase brood productivity or survivorship. It is possible that males were waiting to mate with nieces who had not yet emerged. Why males were tolerated remains unknown. Mating biology is an important consideration in social theory which requires additional empirical studies. Future long-term studies are needed to capture unusual social behaviors including male nesting behaviors.

Juvenile socio-ecological environment shapes material technology in nest-building birds

Variation in animal material technology, such as tool use and nest construction, is thought to be caused, in part, by differences in the early-life socio-ecological environment—that is, who and what is around—but this developmental hypothesis remains unconfirmed. We used a tightly controlled developmental paradigm to determine whether adult and/or raw-material access in early life shape first-time nest construction in laboratory-bred zebra finches Taeniopygia guttata at sexual maturity. We found that juvenile access to both an unrelated adult and raw material of one color led to a majority preference (75%) by novice builders for this color of material over that for either natal-nest or novel-colored material, whereas a lack of juvenile access to both an unrelated adult and raw material led to a 4- and nearly 3-fold reduction in the speed at which novice builders initiated and completed nest construction, respectively. Contrary to expectation, neither the amount of time juveniles nor their adult groupmate spent handling the raw material appear to drive these early-life effects on zebra finches’ first-time nest construction, suggesting that adult presence might be sufficient to drive the development of animal material technology. Together these data show that the juvenile socio-ecological environment can trigger variation in at least two critical aspects of animal material technology (material preference and construction speed), revealing a potentially powerful developmental window for technological advancement. Thus, to understand selection on animal material technology, the early-life environment must be considered.

Artificial incubation does not affect the post-hatch development, health, or survival of the Lance-tailed Manakin (Chiroxiphia lanceolata), a tropical passerine

Artificial incubation of avian eggs is used in scientific research, conservation, zoo husbandry, and the commercial poultry industry. However, whether artificial incubation negatively impacts post-hatch nestling phenotypes and survival compared to naturally incubated young has not been explicitly tested. Here, we assess whether nestlings artificially incubated as eggs and returned to their natal nest after hatching experienced negative impacts in development, health, and survival. From 2007 to 2017, we measured mass, mass growth rate, tarsus length, tarsus growth rate, external lesions, ejection from the nest, fledging success, and recruitment of Lance-tailed Manakin (Chiroxiphia lanceolata) nestlings from 209 nests where 1 of 2 eggs was artificially incubated, along with 230 unmanipulated nests. We found no statistically significant difference in the development, health, and survival among nestlings artificially incubated as eggs, their naturally incubated nestmates, and nestlings from unmanipulated nests. Our results indicate that artificial incubation can be a safe and effective tool in the study of free-living birds.

Effects of parental and nest-site characteristics on nestling quality in the Tree Swallow (Tachycineta bicolor)

Natal environment and parental quality can influence offspring phenotype, including physiological and morphological traits. We investigated how offspring morphology and feather corticosterone (CORTf; a physiological index of allostatic load) may be related to nest environment and parental characteristics by cross-fostering 3-day-old nestling Tree Swallows (Tachycineta bicolor (Vieillot, 1808)) between quaking aspen (Populus tremuloides Michx.) and plywood nest boxes that differed in microclimate. We evaluated the relative importance of natal influences, common rearing environment, and nest-box environment on nestling quality. Nestlings raised in quaking aspen boxes tended to have lower CORTf, although this result only approached significance. Nestling body mass was best predicted by the biological mother’s mass and random effects of natal and rearing nest identity, wing length was best predicted by random effects of rearing nest, and head–bill length was best predicted by random effects of natal nest. Therefore, nest microclimate was more important than maternal characteristics in predicting nestling physiology (CORTf), while nestling morphology was influenced by maternal morphology, as well as natal and rearing nest environments. Our study provides important information about how environmental and parental influences affect nestling phenotype and will help future studies interpret similar morphological and physiological indices of nestling quality.

Multiple Aggressions Among Nestmates Lead to Weak Dominance Hampering Primitively Eusocial Behaviour in an Orchid Bee

Reproductive conflict expressed as aggression is common in social Hymenoptera. In eusocial species, as in honeybees, several mechanisms alleviate the conflicts and reduce aggressive interactions. Unlike their sister group, the orchid bees do not exhibit eusociality. Instead, most of the species seem to have lost sociality and some species have retained vestigial social behaviour. In the current study we investigated the aggressive interactions of females of Euglossa annectans Dressler through five generations of phylopatry and reuse of the natal nest. Although network analysis indicates that central individuals, those with more interactions, were more commonly the aggressors and others were more commonly the recipients, multiple attacks and several potential dominant female within the nest indicated a labile sociality. This suggests that there is an unstable social hierarchy in the species. Euglossa annectans, despite having overlapping generations, during which several individuals share a nest, there is no division of labour into reproductive and interactions are often competitive. Aggressive behaviours conducted by multiple fertile females were often followed by egg, larvae or pupae replacement.