Phylogenetic conservation of behavioural variation and behavioural syndromes.

Individuals frequently differ consistently from one another in their average behaviours (i.e. 'animal personality') and in correlated suites of consistent behavioural responses (i.e. 'behavioural syndromes'). However, understanding the evolutionary basis of this (co)variation has lagged behind demonstrations of its presence. This lag partially stems from comparative methods rarely being used in the field. Consequently, much of the research on animal personality has relied on 'adaptive stories' focused on single species and populations. Here, we used a comparative approach to examine the role of phylogeny in shaping patterns of average behaviours, behavioural variation and behavioural correlations. In comparing the behaviours and behavioural variation for five species of Gryllid crickets, we found that phylogeny shaped average behaviours and behavioural (co)variation. Despite differences among species, behavioural responses and variation were most similar among more closely related species. These results suggest that phylogenetic constraints play an important role in the expression of animal personalities and behavioural syndromes and emphasize the importance of examining evolutionary explanations within a comparative framework.

Parasitism, predation and the evolution of animal personalities.

Trade-offs between behavioural traits promoting high life-history productivity and mortality may fuel the evolution of animal personalities. We propose that parasites, including pathogens, impose fitness costs comparable to those from predators, and influence the adaptiveness of personality traits associated with productivity (PAPs). Whether personality traits are adaptive or not may also depend on individual immunological capacity. We illustrate this using a conceptual example in which the optimal level of PAPs depends on predation, parasitism and host compensation (resistance and tolerance) of parasitism's negative effects. We assert that inherent differences in host immune function can produce positive feedback loops between resource intake and compensation of parasitism's costs, thereby providing variation underlying the evolution of stable personalities. Our approach acknowledges the condition dependence of immune function and co-evolutionary dynamics between hosts and parasites.

Tama-kugel: hardware and software for measuring direction, distance, and velocity of locomotion by insects.

We have developed an accurate and inexpensive system for recording the path taken by a moving insect. The system consists of a low-mass ball on which the loosely tethered insect runs, an optical sensor to detect rotation of the ball, and software written in Visual Basic 6.0 that interprets and records the hardware's output. The ball floats on a cushion of air. The optical sensor's output is encoded as changes in x, y coordinates. The software monitors this output continually, and records each new x, y pair and the time at which it occurred. Since the system records only those data that have changed, the output files are compact. In its present form, the system is calibrated to detect changes in the animal's position roughly equivalent to one body length. It can accurately record the details of paths hundreds of meters long. We have applied the system to measure the paths taken by female crickets in response to male calls that differ in their temporal structure.

Adult bacterial exposure increases behavioral variation and drives higher repeatability in field crickets.

Among-individual differences in behavior are now a widely studied research-focus within the field of behavioral ecology. Furthermore, elements of an animal's internal state, such as energy or fat reserves, and infection status can have large impacts on behaviors. Despite this, we still know little regarding how state may affect behavioral variation. Recent exposure to pathogens may have a particularly large impact on behavioral expression given that it likely activates costly immune pathways, potentially forcing organism to make behavioral tradeoffs. In this study we investigate how recent exposure to a common bacterial pathogen, Serratia marcescens, affects both the mean behavioral expression and the among-individual differences (i.e. variation) in boldness behavior in the field cricket, Gryllus integer. We find that recent pathogen exposure does not affect mean behavioral expression of the treatment groups, but instead affects behavioral variation and repeatability. Specifically, bacterial exposure drove large among-individual variation, resulting in high levels of repeatability in some aspects of boldness (willingness to emerge into a novel environment), but not others (latency to become active in novel environment), compared to non-infected crickets. Interestingly, sham injection resulted in a universal lack of among-individual differences. Our results highlight the sensitivity of among-individual variance and repeatability estimates to ecological and environmental factors that individuals face throughout their lives.

A multichannel electronic monitor of acoustic behaviors, and software to parse individual channels.

We designed an electronic device to monitor calling behavior in male crickets. The device and its associated software can record to disk the activity of as many as 16 individuals simultaneously. The data recorded contain detailed information about the temporal structure of each individual's calls. The temporal resolution achieved with an ordinary PC is good enough to detect and record the occurrence of every pulse of sound from each cricket. The resulting data files are efficient and compact, and so the system is appropriate for experiments lasting many days.

Genetically-based variation between two spider populations in foraging behavior.

Optimal foraging theory is based on the assumption that at least some aspects of foraging behavior are genetically determined (Pyke et al. 1977; Kamil and Sargent 1980; Pyke 1984). Nonetheless, very few studies have examined the role of genetics in foraging behavior. Here, we report on geographical differences in the foraging behavior of a spider (Agelenopsis aperta) and investigate whether these differences are genetically determined. Field studies were conducted on two different populations of A. aperta: one residing in a desert riparian habitat, and the other in a desert grassland habitat. Data from the spiders' natural encounters with prey demonstrated that grassland spiders exhibited a higher frequency of attack than riparian spiders towards 13 of 15 prey types, including crickets and ants. Grassland spiders also had shorter latencies to attack 12 of 15 prey types, including crickets and ants, than riparian spiders. Subsequently, we reared grassland and riparian spiders under controlled conditions in the laboratory and observed their interactions with prey to determine whether the populational differences we found in the field could be genetic. Again, grassland spiders showed a shorter latency to attack prey (crickets, ants) than riparian spiders. These latencies were not significantly affected by the hunger state or age of the spiders. Finally, we reared a second generation (F2) of grassland and riparian spiders in the laboratory and observed their interactions with prey to determine whether the populational differences in the previous generation were due to genetic effects or maternal effects. As before, grassland spiders exhibited a shorter latency to attack prey (crickets) than riparian spiders. We conclude that the foraging differences we observed between these two populations of A. aperta are genetically determined. These differences probably have resulted from either natural selection acting directly on attack frequency and the latency to attack prey, or natural selection acting on traits which are genetically correlated with these aspects of foraging behavior.