The active metabolic rate predicts a male spider's proximity to females and expected fitness

Behavioral and physiological evidence that increasing group size ameliorates the impacts of social disturbance

Intra-group social stability is important for the long-term productivity and health of social organisms. We evaluated the effect of group size on group stability in the face of repeated social perturbations using a cooperatively breeding fish, Neolamprologus pulcher In a laboratory study, we compared both the social and physiological responses of individuals from small versus large groups to the repeated removal and replacement of the most dominant group member (the breeder male), either with a new male (treatment condition) or with the same male (control condition). Individuals living in large groups were overall more resistant to instability but were seemingly slower to recover from perturbation. Members of small groups were more vulnerable to instability but recovered faster. Breeder females in smaller groups also showed greater physiological preparedness for instability following social perturbations. In sum, we discover both behavioral and physiological evidence that living in larger groups helps to dampen the impacts of social instability in this system.

Metabolic and behavioral responses of predators to prey nutrient content

Predators feed on a diversity of prey that can vary widely in nutrient content. While prey nutrient content is known to have important consequences for life history traits, less is known about how it affects physiology and behavior. The purpose of this study was to test how diet affected the physiology and behavior of the wolf spider Hogna carolinensis. We hypothesized that higher protein intake would result in a lower metabolic rate due to less energy intake. Further, we also expected the high protein group to exhibit increased activity levels and aggression in an attempt to increase energy intake. Spiders were maintained on three different treatment diets in order to simulate prey with differing macronutrient composition: high protein, intermediate, and high lipid. Spider respiration was measured to quantify the baseline metabolic rate (SMR), digestive metabolic rate (SDA), and active metabolic rate (AMR). We found no significant effect of diet on metabolic rates. However, the SDA coefficient (i.e. digestive cost relative to prey content) was higher in the high protein group, meaning that this group metabolized a greater portion of their prey during digestion and had a lower net energy intake from prey. In our behavioral assays, spiders in the high protein group were significantly more active and attacked prey more quickly in their first trial. Our results demonstrate that diet had relatively little effect on predator metabolism but more of an effect on behavior. These findings suggest that diet regulation should be analyzed by studying multiple responses together, including metabolism and behavior, to gain a more comprehensive understanding of the effects of diet on organism performance and fitness.

Predatory chemical cues decrease attack time and increase metabolic rate in an orb-web spider

Animals are able to assess the risk of predation and respond accordingly via behavioural and physiological changes. Web-building spiders are in the unique situation where they reside in the middle of their web and are therefore relatively exposed to predators. Thus, these spiders might moderate either their web-building behaviour or their behaviour on the web when exposed to the threat of predation. In this study, we experimentally explored how predatory chemical cues influence foraging behaviour and metabolic rate in female of the orb-web spider, Argiope keyserlingi. We found that female spiders restricted their foraging time budget when exposed to the predatory cues from a praying mantid: they responded 11 percent and 17 percent quicker to a vibratory stimulus compare to control and non-predator cues, respectively, and spent less time handling the prey. Moreover, spiders were less likely to rebuild the web under predatory cues. Female A. keyserlingi exposed to the praying mantid cue significantly elevated their metabolic rate compared to the control group. Our findings revealed short-term modifications over two weeks of the trials in foraging behaviour and physiology of female spiders in response to predator cues. This study suggests that under predator cues the spiders move quicker and this could be facilitated by elevation in metabolic rate. Reduced foraging activity and less frequent web repair/rebuilding would also reduce the spiders’ exposure to praying mantid predators.

The Ecology of Exercise: Mechanisms Underlying Individual Variation in Behavior, Activity, and Performance: An Introduction to Symposium

SYNOPSIS

Wild animals often engage in intense physical activity while performing tasks vital for their survival and reproduction associated with foraging, avoiding predators, fighting, providing parental care, and migrating. In this theme issue we consider how viewing these tasks as "exercise"-analogous to that performed by human athletes-may help provide insight into the mechanisms underlying individual variation in these types of behaviors and the importance of physical activity in an ecological context. In this article and throughout this issue, we focus on four key questions relevant to the study of behavioral ecology that may be addressed by studying wild animal behavior from the perspective of exercise physiology: (1) How hard do individual animals work in response to ecological (or evolutionary) demands?; (2) Do lab-based studies of activity provide good models for understanding activity in free-living animals and individual variation in traits?; (3) Can animals work too hard during "routine" activities?; and (4) Can paradigms of "exercise" and "training" be applied to free-living animals? Attempts to address these issues are currently being facilitated by rapid technological developments associated with physiological measurements and the remote tracking of wild animals, to provide mechanistic insights into the behavior of free-ranging animals at spatial and temporal scales that were previously impossible. We further suggest that viewing the behaviors of non-human animals in terms of the physical exercise performed will allow us to fully take advantage of these technological advances, draw from knowledge and conceptual frameworks already in use by human exercise physiologists, and identify key traits that constrain performance and generate variation in performance among individuals. It is our hope that, by highlighting mechanisms of behavior and performance, the articles in this issue will spur on further synergies between physiologists and ecologists, to take advantage of emerging cross-disciplinary perspectives and technologies.

Respiration in spiders (Araneae)

Spiders (Araneae) are unique regarding their respiratory system: they are the only animal group that breathe simultaneously with lungs and tracheae. Looking at the physiology of respiration the existence of tracheae plays an important role in spiders with a well-developed tracheal system. Other factors as sex, life time, type of prey capture and the high ability to gain energy anaerobically influence the resting and the active metabolic rate intensely. Most spiders have metabolic rates that are much lower than expected from body mass; but especially those with two pairs of lungs. Males normally have higher resting rates than females; spiders that are less evolved and possess a cribellum have lower metabolic rates than higher evolved species. Freely hunting spiders show a higher energy turnover than spiders hunting with a web. Spiders that live longer than 1 year will have lower metabolic rates than those species that die after 1 year in which development and reproduction must be completed. Lower temperatures and starvation, which most spiders can cope with, will decrease the metabolic rate as well.

Functional morphology of the respiratory organs in the cellar spider Pholcus phalangioides (Arachnida, Araneae, Pholcidae)

Morphometric evaluation of the lungs of male and female cellar spiders (Pholcus phalangioideus) was carried out in 2 test groups with different body masses (mean value 10.8, males, and 26.6 mg, females). Males have significant higher lung volume to body mass ratios (2.49 vs. 2.13 × 10(-3) cm(3) g(-1)), which might result from the differences in body mass between sexes. Moreover, males have slightly more respiratory surface area per body mass (8.2 vs. 7.7 cm(2) g(-1)) and a little bit larger morphological diffusing capacities for oxygen (9.3 vs. 8.2 nmol s(-1) g(-1) kPa(-1)) than females, but both values were not significant. Metabolic rates were measured using flow through respirometry under video tracking: the CO2 release of male and female spiders was measured. Resting rates were 1.7 (males) and 1.5 nmol s(-1) g(-1) (females). Gluing of one spiracle did not influence the resting metabolic rate. Factorial scopes during stimulation to maximum metabolic rates were about 12 in intact animals, while elimination of one spiracle reduced the factorial scope to 5.2. Comparison with other araneomorph spiders strengthens the hypothesis that tracheae in spiders increase the metabolic rates of the tracheated species and do not only replace reduced lung capacity.

Metabolic efficiency in courtship favors males with intermediate mass in the Australian redback spider, Latrodectus hasselti

Recent studies have suggested that metabolic efficiency may be an important factor in male mating success when females require vigorous and/or prolonged courtship. In capital breeding animals in which a male's resource pool is fixed at adulthood the relationship between energy expenditure and courtship performance may be especially important, as males are expected to utilize their finite resources efficiently when soliciting mates. Males may benefit from being efficient, i.e., achieving a sufficiently high level of courtship signaling at low energetic cost, if it enables them to acquire mates before their limited energy reserves are depleted. We investigated the relationship between metabolic efficiency and courtship vibrational signaling in the Australian redback spider, Latrodectus hasselti, a semelparous capital breeder where males invest heavily in courtship to secure a mating. We assessed metabolic rate in a sample of males and measured two courtship components (duty cycle and amplitude) that reflected the energy content of web-borne vibrations. We then calculated two indices of metabolic efficiency for these courtship properties. There was a quadratic relationship between mass and duty cycle such that the highest duty cycle signals were performed by males having intermediate mass. Furthermore, intermediate-mass males were also the most metabolically efficient. Prolonged courtship is necessary in L. hasselti for successful mating, and the results of this study suggest that intermediate-mass males are superior courters because they utilize their finite resource pool most efficiently to produce high energy vibrational signals.