Behavioural correlates of group size and group persistence in the African ice rat Otomys sloggetti robertsi

The relationship between group size and fitness has attracted much interest, with many attempts made to detect an optimal group size. Group size is determined by the benefits and costs influencing group formation, which also influences whether groups persist or fail. We investigated whether group size is associated with success (individual survival and reproductive output) in the African ice rat Otomys sloggetti robertsi. Ice rats form mixed-sex plural-breeding colonies that trade-off the benefits of huddling below-ground against within-colony resource competition above-ground. We measured behavioural correlates of individual success in summer and winter, focusing on energy saving (basking), acquisition (foraging) and use (burrow maintenance, distance travelled for foraging) behaviours. We predicted that 1) individuals in larger colonies would forage and travel more to find food because of greater within-colony competition for resources; 2) individuals in larger colonies would bask less than individuals in smaller colonies because of the greater energy savings generated from huddling in larger groups; and 3) burrow maintenance would greater in smaller colonies because fewer individuals engage in this task. We showed that colonies succumbed or persisted as a group (i.e. most individuals present or all absent). In particular, in both seasons, individuals in smaller groups (≤ 5 individuals) were more likely to fail, while those in larger groups (≥ 12 individuals) were more likely to persist. The persistence of colonies was positively predicted by foraging and negatively by basking. Foraging was greater in larger colonies and burrow maintenance was greater in smaller colonies. While females of larger colonies produced more offspring in total, reproductive output (per capita offspring production) was not correlated with colony size. Individual ice rats in larger colonies accrued fitness benefits, which were predicted, proximally, by greater foraging and possibly energy savings in larger huddling groups

Paternal care in the striped mouse Rhabdomys pumilio: ontogeny and function

Paternal care is rare and its development is poorly studied. I studied the ontogeny and function of paternal care in captive striped mice Rhabdomys pumilio from the succulent karoo, South Africa. Male striped mice show extensive parental care, displaying all behaviours (e.g. huddling and retrieving pups) shown by mothers, except nursing. In a first set of experiments, I studied non-genetic and genetic influences on the development of paternal care. The experimental design involved studying the development of paternal care in sons raised by the mother alone, both parents, and parents separated by a barrier. Sons raised by mothers alone were better fathers (i.e. displayed greater levels of paternal care behaviour) than sons from the other treatments; in contrast, daughters always showed higher levels of maternal care behaviour, regardless of treatment. Parent-offspring regressions indicated a partial patrilineal genetic influence of maternal (daughters), but not paternal (sons), care behaviour. Finally, sons raised by the mother and a second care-giver (older female sibling) also displayed better paternal care. My results indicate that fathers do not influence the development of paternal care in their sons genetically or nongenetically. Instead, an unanticipated finding was that mothers overcompensated in their maternal care behaviour in the absence of a male and the presence of a second care-giver, which correlated strongly with the greater levels of paternal care behaviour shown by their sons. In a second set of experiments, I investigated the role of the father in offspring learning, and female mate choice for males with different levels of paternal care behaviour. Using two populations of striped mice (succulent karoo and grassland), my results indicated that mothers were more reliable demonstrators of information about novel food in both populations, but fathers were more reliable demonstrators for young succulent karoo striped mice only. In mate choice tests for olfactory cues of males with different levels of paternal care ability and experience, and for visual cues from males showing either paternal or no care, females preferred experienced males to inexperienced males, but showed no other preferences. In conclusion, my results indicate that fathers are reliable demonstrators about novel food, at least in the succulent karoo, and supports previous findings that fathers are important for offspring development and survival in this population. However, the development of paternal care does not appear to be transmitted from fathers to sons (i.e. good fathers do not necessarily produce sons that are better fathers). This, together with the inability of females to distinguish between better and poor quality fathers, suggests that the level of paternal care is not as important as its mere occurrence, so that any paternal care would be beneficial to offspring

Editorial: Proximate and ultimate approaches to behavior in a changing world

[Extract] Tinbergen's (1963) classic four questions for the study of animal behavior have been applied across a range of study species and contexts and provide a solid foundation for understanding species' responses to rapid environmental change. Tinbergen's (1963) proximate questions include understanding the mechanisms (causation) and development (ontogeny) of behavior, while the ultimate questions include understanding the function (adaptive significance) and evolution of behavior. Integrating proximate and ultimate approaches to understanding behavior in an increasingly human-dominated world gives insights into broader conservation and management strategies for mitigating the negative effects on animal species. The current collection of research reports provides insights into how a changing world affects different species, and provides some context for Tinbergen's focus. The contributors to this special issue demonstrate a varied and diverse approach to this topic, highlighting the inclusive nature of Tinbergen's approach to the study of animal behavior. While broad-scale conclusions cannot be drawn, the range of topics showcases how different experts are tackling these questions from a variety of angles

Variation in venom composition in the Australian funnel-web spiders Hadronyche valida

Mygalomorph venom properties and active components, which have importance in medicine, agronomy, venomics, ecology and evolution, have been widely studied, but only a small fraction have been characterised. Several studies have shown inter-individual variation in the composition of venom peptides based on ontogeny, sexual dimorphism, season and diet. However, intra-individual variation in venom composition, which could play a key role in the evolution, diversification and function of toxins, is poorly understood. In this study, we demonstrate significant intra- and inter-individual variation in venom composition in the Australian funnel-web spider Hadronyche valida, highlighting that individuals show different venom profiles over time. Fourteen (four juvenile and ten adult females) funnel-web spiders, maintained under the same environmental conditions and diet, were milked a total of four times, one month apart. We then used reversed-phase high performance liquid chromatography/electrospray ionisation mass spectrometry to generate venom fingerprints containing the retention time and molecular weights of the different toxin components in the venom. Across all individuals, we documented a combined total of 83 individual venom components. Only 20% of these components were shared between individuals. Individuals showed variation in the composition of venom peptides, with some components consistently present over time, while others were only present at specific times. When individuals were grouped using the Jaccard clustering index and Kernel Principal Component Analysis, spiders formed two distinct clusters, most likely due to their origin or time of collection. This study contributes to the understanding of variation in venom composition at different levels (intra-individual, and intra- and inter-specific) and considers some of the mechanisms of selection that may contribute to venom diversification within arachnids. In addition, inter-specific variation in venom composition can be highly useful as a chemotaxonomic marker to identify funnel-web species

Behaviour of the Sydney funnel-web spider Atrax robustus over different contexts, time, and stimuli

Atrax robustus is an iconic Australian spider because the venom can be lethal to humans. Moreover, some of the venom biomolecules have promise as therapeutic and bioinsecticidal leads. Nonetheless, aspects related to the life history and behaviour of this species, which might influence changes in venom components, have been overlooked. We assessed different behavioural traits (antipredator behaviour, defensiveness and activity) of juveniles and adult females across different contexts (predation, conspecific tolerance and exploration of a new territory) and stimuli (puff of air versus prod) over time. Adults responded to a puff of air faster than juveniles, but in response to a prod, both juveniles and adults become more defensive over time. No differences were observed between adults and juveniles for conspecific tolerance and exploration. Understanding behaviour of venomous species is important because behaviours may affect physiological traits, such as venom, and the ability of spiders to adapt to different conditions

Exploring behavioral traits over different contexts in four species of Australian funnel-web spiders

Australian funnel-web spiders are arguably the most venomous spiders in the world, with much research focusing on this aspect of their biology. However, other aspects related to their life history, ecology and behaviour have been overlooked. For the first time, we assessed repeatability, namely risk-taking behaviour, aggressiveness and activity in the contexts of predation, conspecific tolerance and exploration of a new territory in four species of Australian funnel-web spiders: two are closely related, Hadronyche valida and H. infensa, and two have overlapping distributions but occupy different habitats, H. cerberea and Atrax robustus. We also compared behaviors between species. At the species level, we found that H. valida showed consistency in risk-taking behavior when exposed to a predator stimulus, aggressiveness against conspecifics, and exploration of a new territory. In contrast, in the other species, only A. robustus showed repeatability in the context of exploration of a new territory. These results suggest that some behavioral traits are likely more flexible than others, and that the repeatability of behaviors may be species-specific in funnel-webs. When we compared species, we found differences in risk-taking behavior and defensiveness. This study provides novel insights to understanding variation in behavioral traits within and between species of funnel-web spiders, suggesting that some behavioral traits are likely context and/or species dependent, as a result of their evolutionary history. These findings provide key insights for understanding the ecological role of behavior and venom deployment in venomous animals, and a greater understanding of behavior in these medically significant and iconic spiders that are of conservation concern

Parental investment

[Extract] Sexually reproducing animals invest in offspring metabolically through the generation of gametes (eggs and sperm). Beyond this initial energetic investment, the majority of animals provide no additional investment in their offspring. However, in species that do provide parental investment following conception, the quantity, quality, form, and duration of investment vary dramatically between species, as well as between the sexes within species (Clutton-Brock 1991). In vertebrates, females often show a disproportionately higher metabolic level of investment than males through the generation of yolk or placenta that provides nourishment for the developing embryo (Clutton-Brock 1991; Trivers 1972)

Exploration influences problem solving in the fawn-footed mosaic-tailed rat (Melomys cervinipes)

The relationship between an animal's personality and its problem solving ability has become a popular topic of investigation. However, results are conflicting, suggesting that these relationships may be species-specific. We investigated these relationships in a native Australian rodent, the fawn-footed mosaic-tailed rat (Melomys cervinipes). We predicted that more exploratory and less anxious mosaic-tailed rats would be better problem solvers (e.g. faster to solve the problem) as they would interact with the puzzles more and would be more willing to engage with the task. We assessed personality across two contexts (exploration in an open field and novel object test, and anxiety under simulated predation risk in a light/dark box) and over time (three repetitions). We measured problem solving using two food-baited puzzle boxes (matchbox and cylinder), a Trixie Dog Activity Board with three problems (pillars, tiles and levers) and an obstruction task. Individual mosaic-tailed rats showed consistent individual differences in personality, but not problem solving ability. Furthermore, we found a positive relationship between personality and problem solving ability, with more exploratory individuals solving more problems, and solving problems faster, than less exploratory individuals. Exploratory individuals could be better problem solvers because they are more willing to interact with objects and are less neophobic than less exploratory individuals. However, less exploratory individuals still persist in the population, possibly due to differences in cognitive abilities, such as discrimination or recognition, that allow them to compensate for poorer problem solving abilities

Rodentia cognition

[Extract] Rodents (from the Latin rodere, meaning "to gnaw") are the largest mammalian order (40%),comprising nearly 2300 species. They are diverse and abundant, occurring in nearly every terrestrial environment on Earth, apart from Antarctica. Their habits extend from burrowing, hopping,and climbing to swimming, and they show great diversity in diet, ranging from strictly herbivorous(e.g., capybaras Hydrochoerus hydrochaeris) to strictly carnivorous (e.g., grasshopper mice Onychomys torridus). Rodents, like other animals, engage in costly behaviors, such as foraging, mating, territory selection, and defense, to access resources. To successfully access resources and avoid predation, rodents must be able to rapidly adjust their behavior based on the information they receive from their environment. Rodents rely extensively on olfactory cues to respond to environmental stimuli (Moriceau et al.2010). Rodents then use their cognitive abilities to decode and use this information

Interactions between physiology and behaviour provide insights into the ecological role of venom in Australian funnel-web spiders: Interspecies comparison.

Australian funnel-web spiders are iconic species, characterized as being the most venomous spiders in the world. They are also valued for the therapeutics and natural bioinsecticides potentially hidden in their venom molecules. Although numerous biochemical and molecular structural approaches have tried to determine the factors driving venom complexity, these approaches have not considered behaviour, physiology and environmental conditions collectively, which can play a role in the evolution, complexity, and function of venom components in funnel-webs. This study used a novel interdisciplinary approach to understand the relationships between different behaviours (assessed in different ecological contexts) and morphophysiological variables (body condition, heart rate) that may affect venom composition in four species of Australian funnel-web spiders. We tested defensiveness, huddling behaviour, frequency of climbing, and activity for all species in three ecological contexts: i) predation using both indirect (puff of air) and direct (prodding) stimuli; ii) conspecific tolerance; and iii) exploration of a new territory. We also assessed morphophysiological variables and venom composition of all species. For Hadronyche valida, the expression of some venom components was associated with heart rate and defensiveness during the predation context. However, we did not find any associations between behavioural traits and morphophysiological variables in the other species, suggesting that particular associations may be species-specific. When we assessed differences between species, we found that the species separated out based on the venom profiles, while activity and heart rate are likely more affected by individual responses and microhabitat conditions. This study demonstrates how behavioural and morphophysiological traits are correlated with venom composition and contributes to a broader understanding of the function and evolution of venoms in funnel-web spiders