The legacy effects of keystone individuals on collective behaviour scale to how long they remain within a group

The collective behaviour of social groups is often strongly influenced by one or few individuals, termed here ‘keystone individuals’. We examined whether the influence of keystone individuals on collective behaviour lingers after their departure and whether these lingering effects scale with their tenure in the group. In the social spider, Stegodyphus dumicola, colonies'' boldest individuals wield a disproportionately large influence over colony behaviour. We experimentally manipulated keystones'' tenure in laboratory-housed colonies and tracked their legacy effects on collective prey capture following their removal. We found that bolder keystones caused more aggressive collective foraging behaviour and catalysed greater inter-individual variation in boldness within their colonies. The longer keystones remained in a colony, the longer both of these effects lingered after their departure. Our data demonstrate that, long after their disappearance, keystones have large and lasting effects on social dynamics at both the individual and colony levels.     

Personality composition is more important than group size in determining collective foraging behaviour in the wild

Describing the factors that shape collective behaviour is central to our understanding of animal societies. Countless studies have demonstrated an effect of group size in the emergence of collective behaviours, but comparatively few have accounted for the composition/diversity of behavioural phenotypes, which is often conflated with group size. Here, we simultaneously examine the effect of personality composition and group size on nest architecture and collective foraging aggressiveness in the social spider Stegodyphus dumicola. We created colonies of two different sizes (10 or 30 individuals) and four compositions of boldness (all bold, all shy, mixed bold and shy, or average individuals) in the field and then measured their collective behaviour. Larger colonies produced bigger capture webs, while colonies containing a higher proportion of bold individuals responded to and attacked prey more rapidly. The number of attackers during collective foraging was determined jointly by composition and size, although composition had an effect size more than twice that of colony size: our results suggest that colonies of just 10 bold spiders would attack prey with as many attackers as colonies of 110 ‘average’ spiders. Thus, personality composition is a more potent (albeit more cryptic) determinant of collective foraging in these societies.     

Mating alters the link between movement activity and pattern in the red flour beetle

Mating in arthropods is costly and has negative effects on survival. Such effects are often more strongly expressed when individuals are simultaneously exposed to other stress sources. Consequently, the behaviour of virgin and mated individuals often differs. Mated females, for example, search for suitable oviposition sites, whereas virgin females search more for mates. In the present study, we examine the effect of mating separately for females and males on four key behaviours of the red flour beetles: movement activity, movement along the edges of an arena, latency to emerge from shelter and preference for dark microhabitat. After mating, both sexes increase their activity at the same time as moving less along the arena edge, leading to a change in movement pattern. Females possibly change their movement pattern to locate suitable oviposition sites, whereas males perhaps do so to detect additional females with which to mate. Latency to emerge from shelter and dark preference are not influenced by mating, although they increase when measured again after 1 week. Of these behaviours, only movement activity is consistent at the individual level. We also examine whether mating incurs a cost as expressed in the time required to recover from a chill‐coma. The latter is a common proxy of cold tolerance in ectotherms. By contrast to our prediction, mating has no effect on chill‐coma recovery time, suggesting that either a single mating event does not incur sufficient stress or that there is possibly no trade‐off between the energetic cost of mating and of cold tolerance.     

Thermoregulatory and nonthermoregulatory heat production in burned rat

Severely burned patients are hypermetabolic within their thermoneutral zone (TNZ), where there are no thermoregulatory demands on heat production. The rat has been used as a model of postburn hypermetabolism without clear evidence that it behaves in a similar way. Male rats (400-500 g; n = 34-39) were placed as a group in a respiration chamber and metabolic rates for the average rat were determined over 3-6 h at ambient temperatures between 9 and 36 degrees C. Colonic temperatures (Tco) and body weights were measured after each run. Animals were studied sequentially as normals (N), after clipping (C) and following 50% total body surface scald burns. Clipping increased the lower critical temperature (LCT) from 27.7 to 29.1 degrees C without affecting resting heat production (N = 42.6 +/- 0.5; C = 42.0 +/- 0.8 W/m2; mean +/- S.E.) or Tco (N = 36.6 +/- 0.1; C = 36.6 +/- 0.1 degrees C) in the TNZ. Injury increased LCT to 32.8 degrees C and the burned animals were hypermetabolic (47.2 +/- 0.6 W/m2; P less than 0.05 vs. N) and febrile (36.9 +/- 0.1 degrees C; P less than 0.05 vs. N) in the elevated TNZ. These metabolic and temperature responses of burned rats are limited in magnitude but are qualitatively similar to those of patients. The extra heat production in the TNZ reflects the basic metabolic cost of injury.     

Temperature Mediates Shifts in Individual Aggressiveness,Activity Level,and Social Behavior in a Spider

Although in recent years behavioral syndromes have received a wealth of attention, how traits within syndromes respond to changing environments is not well resolved. Here, we test the effects of temperature on a suite of behavioral traits in the spider Anelosimus studiosus to determine (1) whether there are shifts in individuals’ social tendency, activity level, and foraging behavior in response to temperature, (2) if these traits shift are in the direction predicted by within‐population axes of trait covariance, and (3) whether the effects of temperature differ among individuals. In previous work, we documented a behavioral syndrome in A. studiosus where increased tolerance of conspecifics is correlated with decreased activity level and aggressiveness toward prey. Furthermore, there are distinct among‐population differences in behavior, where individuals from warm sites tend to be more aggressive and active than individuals from cold sites. Our data here reveal that at warmer temperatures A. studiosus exhibit diminished tolerance of conspecifics, increased activity levels, shorter latencies of attack, and increased tendencies to attack multiple prey items. Furthermore, we found that individual differences in behavior were consistent across temperature regimes for the majority of behavioral traits considered here: social tendency, activity level, and latency of attack. These findings are consistent with the hypothesis that these behaviors are linked together by shared genetic underpinnings (e.g., metabolic differences) and shift non‐independently in response to contemporary abiotic environment (i.e., temperature). Furthermore, our data suggest that temperature itself could be responsible for the among‐population variation in social structure in A. studiosus.     

DEG/ENaC but not TRP channels are the major mechanoelectrical transduction channels in a C. elegans nociceptor

Many nociceptors detect mechanical cues, but the ion channels responsible for mechanotransduction in these sensory neurons remain obscure. Using in?vivo recordings and genetic dissection, we identified the DEG/ENaC protein, DEG-1, as the major mechanotransduction channel in ASH, a polymodal nociceptor in Caenorhabditis elegans. But DEG-1 is not the only mechanotransduction channel in ASH: loss of deg-1 revealed a minor current whose properties differ from those expected of DEG/ENaC channels. This current was independent of two TRPV channels expressed in ASH. Although loss of these TRPV channels inhibits behavioral responses to noxious stimuli, we found that both mechanoreceptor currents and potentials were essentially wild-type in TRPV mutants. We propose that ASH nociceptors rely on two genetically distinct mechanotransduction channels and that TRPV channels contribute to encoding and transmitting information. Because mammalian and insect nociceptors also coexpress DEG/ENaCs and TRPVs, the cellular functions elaborated here for these ion channels may be conserved.     

Synthesis and evaluation of in vitro antioxidant capacities of some benzimidazole derivatives

New, except 1d, melatonin analogue benzimidazole derivatives were synthesized and characterized in the present study. The potential role of melatonin as an antioxidant by scavenging and detoxifying ROS raised the possibility that compounds that are analogous to melatonin can also be used for their antioxidant properties. Therefore the antioxidant effects of the newly synthesized compounds were investigated in vitro by means of their inhibitory effect on hydrogen peroxide-induced erythrocyte membrane lipid peroxidation (EMLP) and on various erythrocyte antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT) and glucose-6-phosphate dehydrogenase (G6PD). The synthesized benzimidazole derivatives showed remarkable antioxidant activity in vitro in the H₂O₂-induced EMLP system. Furthermore their effects on various antioxidant enzymes are discussed and evaluated from the perspective of structure- activity relationships.