Effect of rearing environment and food availability on seismic signalling in male wolf spiders (Araneae: Lycosidae)

Effects of Wolf Spiders’ Captive Environment on Their Locomotor and Exploratory Behaviours

Simple Summary

Since the 1960s, abuses of domestic and of wild animals that have been tamed or are held in captivity have been legally prohibited and laws ensure their well-being. Many scientific investigations carried out in this context recommend ways to adapt farming and thus to avoid physical and/or psychological suffering. Evaluations of animals’ welfare in captivity entail the need to understand in detail the fundamental behaviours of the focus species and to know the degree of their variation to be able to establish objective bases that can ensure breeding conditions that respect the animals’ welfare. Current laws do not apply to invertebrate animals (such as insects or spiders) and consideration of the welfare of these animals in captivity is neglected. Here, I compared the behaviour of wild adult spiders just after collection and that of adult spiders hatched and bred in the laboratory. My results show that captivity induced rapid changes of wild spiders’ behaviour once in captivity. Therefore, it is important to establish the best breeding conditions for the needs of both invertebrate and vertebrate animals in order to promote their well-being.

Abstract

Here I detail the effects of the abiotic/captive environment of an adult wandering spider, Pardosa saltans (Lycosidae) on its behaviour. These studies focused on spiders collected as adults in their natural environment and spiders developed in the laboratory under controlled conditions. Wild-caught spiders were tested either immediately after capture or after being housed for 15 days post-collection. Laboratory reared spiders were kept in different environments: small or large space combined with the presence or absence of litter. Two tests evaluated by sex show the influence of these rearing conditions: an open-field test and a radial-arm maze test. The results show that wild caught spiders of both sexes tested immediately after capture weighed significantly less and were significantly more active than spiders housed in the laboratory for 15 days and spiders reared in the laboratory. Laboratory conditions induced a positive impact on body mass and negative impact on behaviour activities. The locomotor and exploratory activities of spiders of both sexes kept in container without substrate showed lower. My results suggest that the physical enrichment of the environment can reduce these negative effects for females, but not for males that seem to be more affected by being reared under controlled conditions.

'Hangry' Drosophila: food deprivation increases male aggression

Aggressive interactions are costly, such that individuals should display modified aggression in response to environmental stress. Many organisms experience frequent periods of food deprivation, which can influence an individual's capacity and motivation to engage in aggression. However, because food deprivation can simultaneously decrease an individual's resource-holding potential and increase its valuation of food resources, its net impact on aggression is unclear. Here, we tested the influence of increasingly prolonged periods of adult food deprivation on intermale aggression in pairs of fruit flies, Drosophila melanogaster. We found that males displayed increased aggression following periods of food deprivation longer than a day. Increased aggression in food-deprived flies occurred despite their reduced mass. This result is probably explained by an increased attraction to food resources, as food deprivation increased male occupancy of central food patches, and food patch occupancy was positively associated with aggression. Our findings demonstrate that aggressive strategies in male D. melanogaster are influenced by nutritional experience, highlighting the need to consider past nutritional stresses to understand variation in aggression.

Meta-analysis reveals that animal sexual signalling behaviour is honest and resource based

Animals often need to signal to attract mates and behavioural signalling may impose substantial energetic and fitness costs to signallers. Consequently, individuals often strategically adjust signalling effort to maximize the fitness payoffs of signalling. An important determinant of these payoffs is individual state, which can influence the resources available to signallers, their likelihood of mating and their motivation to mate. However, empirical studies often find contradictory patterns of state-based signalling behaviour. For example, individuals in poor condition may signal less than those in good condition to conserve resources (ability-based signalling) or signal more to maximize short-term reproductive success (needs-based signalling). To clarify this relationship, I systematically searched for published studies examining animal sexual signalling behaviour in relation to six aspects of individual state: age, mated status, attractiveness, body size, condition and parasite load. Across 228 studies and 147 species, individuals (who were predominantly male) invested more into behavioural signalling when in good condition. Overall, this suggests that animal sexual signalling behaviour is generally honest and ability-based. However, the magnitude of state-dependent plasticity was small and there was a large amount of between-study heterogeneity that remains unexplained.

Tail display is regulated by anaerobic metabolism in an Asian agamid lizard

Understanding the mechanism underlying signal variation is an important goal in the study of animal communication. Several potential causes have been proposed for signal variation, including environmental noise (e.g. wind, sound), energy limitation, and predation risk, among others, but the physiological control of many signals are often unclear. Here, we examined the correlation between tail display signal variation and energy metabolic activity using an Asian agamid lizard Phrynocephalus vlangalii. Individual tail display signals were observed in the field, and blood lactate concentration as well as 2 energy metabolic enzymes was assayed. Our results showed that average tail coil speed was positively associated with blood lactate concentration, while tail coil duration was negatively associated with LDH activity. We also found that average tail lash speed was positively associated with blood lactate concentration, suggesting that the tail display behavior of P. vlangalii was regulated by anaerobic metabolism. Furthermore, the correlation between tail display behavior and energy metabolism was not sex-dependent. Taken together, our research provides insight into the physiological mechanisms underlying tail display variation in lizards, and suggests that tail display variation likely transmits important information on individual body condition and resource holding potential.

Sister species diverge in modality-specific courtship signal form and function

Understanding the relative importance of different sources of selection (e.g., the environment, social/sexual selection) on the divergence or convergence of reproductive communication can shed light on the origin, maintenance, or even disappearance of species boundaries. Using a multistep approach, we tested the hypothesis that two presumed sister species of wolf spider with overlapping ranges and microhabitat use, yet differing degrees of sexual dimorphism, have diverged in their reliance on modality-specific courtship signaling. We predicted that male Schizocosa crassipalpata (no ornamentation) rely predominantly on diet-dependent vibratory signaling for mating success. In contrast, we predicted that male S. bilineata (black foreleg brushes) rely on diet-dependent visual signaling. We first tested and corroborated the sister-species relationship between S. crassipalpata and S. bilineata using phylogenomic scale data. Next, we tested for species-specific, diet-dependent vibratory and visual signaling by manipulating subadult diet and subsequently quantifying adult morphology and mature male courtship signals. As predicted, vibratory signal form was diet-dependent in S. crassipalpata, while visual ornamentation (brush area) was diet-dependent in S. bilineata. We then compared the species-specific reliance on vibratory and visual signaling by recording mating across artificially manipulated signaling environments (presence/absence of each modality in a 2 × 2 full factorial design). In accordance with our diet dependence results for S. crassipalpata, the presence of vibratory signaling was important for mating success. In contrast, the light and vibratory environment interacted to influence mating success in S. bilineata, with vibratory signaling being important only in the absence of light. We found no differences in overall activity patterns. Given that these species overlap in much of their range and microhabitat use, we suggest that competition for signaling space may have led to the divergence and differential use of sensory modalities between these sister species.

Courtship behavior and coloration influence conspicuousness of wolf spiders (Schizocosa ocreata (Hentz)) to avian predators

Signalers must balance the benefits of detection by intended receivers with the costs of detection by eavesdroppers. This trade-off is exemplified by sexual signaling systems, in which signalers experience sexual selection for conspicuousness to mates as well as natural selection for crypsis to predators. In this study, we examined how courtship behavior and body coloration influenced the conspicuousness of males to avian predators in the well-studied brush-legged wolf spider system (Schizocosa ocreata (Hentz)). We focused on three behaviors (courtship, walking, and freezing) and two coloration schemes (natural coloration and idealized background-matching coloration). We presented captive blue jays (Cyanocitta cristata) with video playbacks of male spiders in a presence-absence detection task and characterized conspicuousness by measuring response latency and detectability. We found that any type of motion significantly increased detectability, and that body coloration and behavior interacted to determine detectability while the spiders were in motion. Among spiders in motion, courting spiders were detected faster than walking spiders. Stationary (frozen) spiders, in contrast, were rarely detected. These results illustrate that male S. ocreata can be both highly conspicuous and highly cryptic to avian predators. Thus, while we find that courtship is conspicuous to avian predators in this system, we suggest that behavioral plasticity may mitigate some of the predation costs of the sexual signal.

Past and present resource availability affect mating rate but not mate choice in Drosophila melanogaster

The choices of when, where, and with whom to mate represent some of the most important decisions an individual can make to increase their fitness. Several studies have shown that the resources available to an individual during development can dramatically alter their mating rate later in life, and even the choice of mate. However, an individual's surroundings and available resources can change rapidly, and it is not clear how quickly the redistribution of resources towards reproduction can change. To address this important question, we measured mating rate and mate choice among Drosophila melanogaster males that were manipulated in terms of both past resources (control vs. starvation) and the resources available during mate choice (food vs. no food). We found that males given access to ample resources prior to mate choice showed higher mating rates than those that were starved, in agreement with previous studies. However, we also found that this effect can be reversed quickly, as starved males given the opportunity to mate in a high-quality environment mated at frequencies equivalent to their fed counterparts. Although past and present resources affected mating rate, they did not affect mate choice, as males mated with high-quality females at high frequencies regardless of their condition and environment. Our results show that both current condition as well as the promise of future resources can dramatically influence individuals' investment into reproduction and that such mating decisions are extremely plastic and reliant on environmental cues.

The sterile male technique: irradiation negatively affects male fertility but not male courtship

The sterile male technique is a common method to assign paternity, widely adopted due to its relative simplicity and low cost. Male sterility is induced by exposure to sub lethal doses of chemosterilants or irradiation, the dosage of which has to be calibrated for every species to provide successful male sterilisation, without affecting male physiology and behaviour. While the physiological effects of sterilisation are usually assessed for each study, the behavioural ones are rarely analysed in detail. Using the orb web spider Argiope keyserlingi as a model we first tested (1) the validity of the thread assay, which simulates male courtship behaviour in a standardised context, as a proxy representing courtship on a female web. We then investigated (2) the effectiveness of male sterilisation via irradiation and (3) its consequences on male courtship behaviour. Our results validate the thread assay and the sterile male technique as legitimate tools for the study of male courtship behaviour and fertilisation success. We show that these techniques are time and cost effective and reduce undesirable variation, thereby creating opportunities to study and understand the mechanisms underlying sexual selection.

The influence of vibratory courtship on female mating behaviour in orb-web spiders (Argiope keyserlingi, Karsch 1878)

Web-building spiders are important models for sexual selection. While our understanding of post-copulatory mechanisms including sperm competition and cryptic female choice is considerable, our knowledge of courtship and how it influences male and female mating decisions is still extremely poor. Here, we provide the first comprehensive description of male courtship behaviour and vibrations generated in the web by the orb-web spider, Argiope keyserlingi – a recognised model species. We identified three main elements of male courtship: shudders, abdominal wags and mating thread dances (including both plucks and bounces). The vibrations generated by these behaviours are described in detail. Male shuddering behaviour appears to have a strong influence on female latency to mate acceptance, with males that shudder at high rates without compromising shudder duration being preferred. Shuddering behaviour may also mediate female aggressive behaviour, with males that generate long shudders less likely to be cannibalised after copulation. Male abdominal wagging behaviour, however, appears to have only limited influence on female mating decisions. This study provides avenues for future work that synthesises pre- and post-copulatory mechanisms in web-building spiders to generate an all-encompassing model of how sexual selection operates.