A Continuum of Behavioral Plasticity in Urban and Desert Black Widows

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.

Invasive Widow Spiders Perform Differently At Low Temperatures than Conspecifics from the Native Range

Temperature challenges are one of the leading abiotic causes of success or failure of non-native species in a novel environment, and this is particularly true for low temperatures. Establishing and reproducing in a novel thermal environment can alter survival, behaviour, and traits related to fitness. It has been proposed that plasticity or adaptation of thermal tolerance may allow an introduced species to thrive, or that successful invaders may be those with a thermal breadth in their native habitat that encompasses their new environment. Here, we tested these hypotheses using native and invasive populations of Australian redback spiders (Latrodectus hasselti). We measured how exposure to temperatures (exposure to 15°C and 25°C, respectively) common to invasive and native range habitats affected behavioural and life-history traits and tradeoffs that may underlie fitness in an invasive population detected in 1995 in Japan and a native population from Australia. We found that the critical thermal minimum (CTmin) was higher in the invasive population from Japan than in the native population, but critical thermal maximum (CTmax) did not differ between populations. Compared to the invasive population, eggs from the native population had a longer development time and lower hatching success at 15°C. Both populations performed equally well at 25 °C, as measured by egg development time and hatching success. Invasive juveniles that developed at 15 °C were slower to explore a novel environment and less bold when tested at 25 °C vs. 15 °C. In comparison, the native population showed faster average exploration, with no differences in response at the two development or testing temperatures. Overall, L. hasselti from Japan maintained hatching success and development across a wider temperature range than the native population, indicating greater thermal breadth and higher behavioural plasticity. These results support the importance of plasticity in thermal tolerance and behaviour for a successful invasion under novel environmental temperatures.

Size matters: Antagonistic effects of body size on courtship and digging in a wolf spider with non-traditional sex roles

Body size, nuptial gift characteristics and courtship behaviour, among other traits, can reflect the quality of a potential mate and, thus, might be under sexual selection. To maximize their mating success, individuals can show behavioural plasticity in sexual context. Allocosa senex is a burrow-digging wolf spider that exhibits reversal in courtship roles and in sexual size-dimorphism expected for spiders. Males construct the mating refuge and females prefer males that build longer burrows, which are considered as nuptial gifts because they are delivered to them after mating. This study aims to determine whether male body size and female reproductive status influence burrow dimensions, courtship displays, female preferences and cannibalism rate in A. senex. For that purpose, we allowed males to construct burrows and performed sexual trials under laboratory conditions. Larger males were more courted by females, and in turn, they expressed more vibratory behaviours during courtship. However, and contrary to our expectations, smaller males constructed longer burrows. We suggest that males of A. senex exhibit size-dependent behavioural plasticity, and when they are smaller, they invest more in burrow construction to compensate their lower opportunities of courting intensively as larger males. In addition, females courted differentially according to their reproductive status, overriding male preferences for virgin females. This study opens several doors to future research regarding mutual choice in A. senex and the traits assessed by males and females during courtship, as well as about the influence of intrinsic and extrinsic factors shaping reproductive decision-making in this and other wandering spider species.

Beyond spider personality: The relationships between behavioral, physiological, and environmental factors

Spiders are useful models for testing different hypotheses and methodologies relating to animal personality and behavioral syndromes because they show a range of behavioral types and unique physiological traits (e.g., silk and venom) that are not observed in many other animals. These characteristics allow for a unique understanding of how physiology, behavioral plasticity, and personality interact across different contexts to affect spider's individual fitness and survival. However, the relative effect of extrinsic factors on physiological traits (silk, venom, and neurohormones) that play an important role in spider survival, and which may impact personality, has received less attention. The goal of this review is to explore how the environment, experience, ontogeny, and physiology interact to affect spider personality types across different contexts. We highlight physiological traits, such as neurohormones, and unique spider biochemical weapons, namely silks and venoms, to explore how the use of these traits might, or might not, be constrained or limited by particular behavioral types. We argue that, to develop a comprehensive understanding of the flexibility and persistence of specific behavioral types in spiders, it is necessary to incorporate these underlying mechanisms into a synthesized whole, alongside other extrinsic and intrinsic factors.

Urban heat island conditions experienced by the Western black widow spider (Latrodectus hesperus): Extreme heat slows development but results in behavioral accommodations

While shifts in organismal biology stemming from climate change are receiving increased attention, we know relatively little about how organisms respond to other forms of anthropogenic disturbance. The urban heat island (UHI) effect describes the capture of heat by built structures (e.g. asphalt), resulting in elevated urban temperatures. The UHI is a well-studied phenomenon, but only a handful of studies have investigated trait-based shifts resulting from the UHI, and even fewer have attempted to quantify the magnitude of the UHI experienced at the microclimate scale. Here, using a common urban exploiter, the Western black widow spider (Latrodectus hesperus), we show that the UHI experienced by spiders in July in their urban Phoenix, AZ refuges is 6°C hotter (33°C) than conditions in the refuges of spiders from Sonoran Desert habitat outside of Phoenix’s development (27°C). We then use this field microclimate UHI estimate to compare the development speed, mass gain and mortality of replicate siblings from 36 urban lineages reared at ‘urban’ and ‘desert’ temperatures. We show that extreme heat is slowing the growth of spiderlings and increasing mortality. In contrast, we show that development of male spiders to their penultimate moult is accelerated by 2 weeks. Lastly, in terms of behavioral shifts, UHI temperatures caused late-stage juvenile male spiders to heighten their foraging voracity and late-stage juvenile female spiders to curtail their web-building behavior. Trait-based approaches like the one presented herein help us better understand the mechanisms that lead to the explosive population growth of urban (sometimes invasive) species, possibly at the expense of urban biodiversity. Studies of organismal responses to the present day UHI can be used as informative surrogates that help us grasp the impact that projected climate change will have on biodiversity.

Parental food provisioning is related to nestling stress response in wild great tit nestlings: implications for the development of personality

Background

Variation in early nutrition is known to play an important role in shaping the behavioural development of individuals. Parental prey selection may have long-lasting behavioural influences. In birds foraging on arthropods, for instance, the specific prey types, e.g. spiders and caterpillars, matter as they have different levels of taurine which may have an effect on personality development. Here we investigated how naturally occurring variation in the amounts of spiders and caterpillars, provisioned to nestlings at day 4 and 8 after hatching, is related to the response to handling stress in a wild passerine, the great tit (Parus major). Broods were cross-fostered in a split-brood design allowing us to separate maternal and genetic effects from early rearing effects. Adult provisioning behaviour was monitored on day four and day eight after hatching using video recordings. Individual nestlings were subjected to a handling stress test at an age of 14 days, which is a validated proxy for exploratory behaviour as an adult.

Results

Variation in handling stress was mainly determined by the rearing environment. We show that, contrary to our predictions, not the amount of spider biomass, but the amount of caterpillar biomass delivered per nestling significantly affected individual performance in the stress test. Chicks provisioned with lower amounts of caterpillars exhibited a stronger stress response, reflecting faster exploratory behaviour later on in life, than individuals who received larger amounts of caterpillars.

Conclusions

These results suggest that natural variation in parental behaviour in wild birds modulates the developmental trajectories of their offspring's personality via food provisioning. Since parental provisioning behaviour might also reflect the local environmental conditions, provisioning behaviour may influence how nestlings respond to these local environmental conditions.