Cannibalistic behaviour of rock-pool copepods: An experimental approach for space, food and kinship

Studies on cannibalism in harpacticoid copepods are restricted to predation on naupliar larvae in rock-pool harpacticoids of the genus Tigriopus. An earlier experimental study on the Mediterranean copepod Tigriopus fulvus indicated that females recognized their own larvae and preferentially preyed on nauplii other than their own. In a series of laboratory experiments, we tested if there were differences in naupliar predation as a function of crowding, food level and sex in Tigriopus brevicornis and T. fulvus. Results show that cannibalism was restricted to the first larval stages (N1 and N2). Both food availability and adult density significantly affected the predation rate. Contrary to earlier suggestions, adult males also preyed on the nauplii. We found no evidence that adults spare their own offspring, for neither T. fulvus nor T. brevicornis.This is in accordance with what one would expect for species having the life history characteristics of Tigriopus, i.e.: multiple broods and large number of offspring. Earlier results indicating parental care in Tigriopus must be taken with caution.     

Equine learning behaviour

Scientists and equestrians continually seek to achieve a clearer understanding of equine learning behaviour and its implications for training. Behavioural and learning processes in the horse are likely to influence not only equine athletic success but also the usefulness of the horse as a domesticated species. However given the status and commercial importance of the animal, equine learning behaviour has received only limited investigation. Indeed most experimental studies on equine cognitive function to date have addressed behaviour, learning and conceptualization processes at a moderately basic cognitive level compared to studies in other species. It is however, likely that the horses with the greatest ability to learn and form/understand concepts are those, which are better equipped to succeed in terms of the human-horse relationship and the contemporary training environment. Within equitation generally, interpretation of the behavioural processes and training of the desired responses in the horse are normally attempted using negative reinforcement strategies. On the other hand, experimental designs to actually induce and/or measure equine learning rely almost exclusively on primary positive reinforcement regimes. Employing two such different approaches may complicate interpretation and lead to difficulties in identifying problematic or undesirable behaviours in the horse. The visual system provides the horse with direct access to immediate environmental stimuli that affect behaviour but vision in the horse is of yet not fully investigated or understood. Further investigations of the equine visual system will benefit our understanding of equine perception, cognitive function and the subsequent link with learning and training. More detailed comparative investigations of feral or free-ranging and domestic horses may provide useful evidence of attention, stress and motivational issues affecting behavioural and learning processes in the horse. The challenge for scientists is, as always, to design and commission experiments that will investigate and provide insight into these processes in a manner that withstands scientific scrutiny.     

Impala social behaviour: birth behaviour

Data collected from observations of eighteen parturient impala females are presented. Females attempt to isolate from the breeding herds 2 to 3 h before parturition. They have a characteristic appearance and behaviour at this stage and are having obvious labour contractions. Nearly all the females sought some cover and a vegetation type including many bushes was used frequently as a birth site. Only four of eleven females left the herd and found cover without harassment by either the territorial male or bachelor males. Many were also followed by impala females. The birth process is described; final expulsion of the foetus occurs in a recumbent position. All birth fluids and membranes are eaten by the mother. Much attention is paid to cleaning up the birth site, baby and herself. Time from birth to expulsion of the placenta is variable and the placenta is normally eaten as soon as it is expelled. Impalas can stand at about 15 min after birth and attempt to suckle soon after this. Only some mothers help the baby to find the udder. Unsteady running occurred at about 25 min after birth. Impalas have a preference for giving birth between 10·00 and 14·00 hours. The significance of this behaviour and the other behaviours shown as anti-predator devices are discussed. Individual differences in behaviour and early care of the young are noted.     

Spread of costly prestige-seeking behavior by social learning

Mathematical and simulation models of cultural transmission in a population where individuals may differ in their social status are developed. High-status individuals are assumed to be more influential to others but no more fertile or viable than low-status individuals. Analysis of the models suggests that culturally transmitted values, beliefs, and preferences that cause individuals to engage in prestige-seeking behavior can sometimes invade the population, even if that behavior reduces the net reproductive success of the prestige seekers. It is argued that some of the seemingly maladaptive behaviors observed in human societies may be a result of cultural evolution based on the human capacity for social learning, rather than a product of the "time lag" before the evolutionary modification of the human predisposition in response to the recent drastic changes in the environment.     

Dairy cows' fear of people: social learning, milk yield and behaviour at milking

We examined the effects of the presence of an unfamiliar, a gentle or an aversive handler during milking on behaviour and milk yield, and whether cows can learn to approach or avoid a handler by observing the neighbouring cow's responses. In Experiment 1, Danish Friesian cows (n=16) were treated gently (offering hay and concentrates) by one handler and aversively (hit every 15s on the head with the hand) by another handler for six periods of 2min each. The two handlers wore different coloured overalls, and each cow received either gentle or aversive treatment in the first week and the other treatment the following week. All cows kept a longer distance to the aversive than to the gentle handler in a 1min test after treatment. Milk yield and residual milk did not differ when the aversive or the gentle handler was standing in front of the cow during milking, although the cows moved their legs and tail less when the aversive handler was present. When an unfamiliar person was standing in front of the cows during milking, behaviour and milk yield did not differ from control milkings. Cows and heifers (n=10) that had observed their neighbours receiving gentle treatment by one handler and aversive treatment from another handler did not differ in the distance they kept from these two handlers. In Experiment 2, cows (n=15) that had observed the neighbours receiving a gentle treatment (eight times for 2min) kept a shorter distance to that handler after treatment of their neighbours, and the distance they kept was correlated with the distance kept by the neighbouring cows. This suggests that responses of observer cows may be affected by the responses of the cows being treated. The cows rapidly learned to avoid an aversive handler, but although the cows showed clear avoidance response to the aversive handler there was no effect on milk yield when the aversive handler was present at milking.     

Effects of social learning on foraging behaviour and live weight gain in first-season grazing calves

When livestock are turned out to semi-natural grasslands, an effective onset of grazing is important both for animal productivity and for defoliation of the sward, which preserve the biodiversity of the vegetation. The aim of this study was to investigate whether foraging behaviour of naïve calves turned out to pasture was more intense, with a resulting diminished live weight loss, when experienced cattle accompanied them acting as social models. Twenty-six first-season grazing (FSG) dairy calves, allocated to groups with or without company of older, grazing-experienced steers, were turned out to semi-natural grasslands. Cattle behaviour was automatically recorded for 24 h during the first day on pasture and during 24 h after 1 month. Furthermore, the average live weight changes for the first day and for the first month on pasture were calculated. Calves turned out to pasture accompanied by grazing-experienced steers had similar grazing times (on average 42.7% of the day) to calves turned out to pasture in groups without older steers, but they had higher grazing activity during the first day on pasture (score 124 vs. 99, P = 0.005). Live weight changes were similar in calves kept with as in calves kept without company of grazing-experienced steers (?4.60 kg for the first day and ?0.30 kg day^?1 for the first month on pasture). In conclusion, the company of grazing-experienced conspecifics resulted in higher grazing activity in naïve calves, but their time spent grazing and live weight gains were unmodified. Hence, in this limited study we found no major positive effects on production of using grazing-experienced cattle as company to FSG calves on semi-natural grasslands.     

Optimizing foraging behaviour through learning

Manifestation of life-history strategy is through the allocation of resources acquired by foraging. Foraging efficiency can be improved by learning, as fishes adjust their behaviour to changing circumstances. We briefly review the influence of learning on the foraging behaviour of fishes and make recommendations for further research. We stress the importance of quantifying learning and memory in relation to ontogeny and life history.     

Rapid evolution of social learning

Culture is widely thought to be beneficial when social learning is less costly than individual learning and thus may explain the enormous ecological success of humans. Rogers (1988. Does biology constrain culture. Am. Anthropol.  90 : 819–831) contradicted this common view by showing that the evolution of social learning does not necessarily increase the net benefits of learned behaviours in a variable environment. Using simulation experiments, we re‐analysed extensions of Rogers’ model after relaxing the assumption that genetic evolution is much slower than cultural evolution. Our results show that this assumption is crucial for Rogers’ finding. For many parameter settings, genetic and cultural evolution occur on the same time scale, and feedback effects between genetic and cultural dynamics increase the net benefits. Thus, by avoiding the costs of individual learning, social learning can increase ecological success. Furthermore, we found that rapid evolution can limit the evolution of complex social learning strategies, which have been proposed to be widespread in animals.     

The genetical theory of social behaviour

We survey the population genetic basis of social evolution, using a logically consistent set of arguments to cover a wide range of biological scenarios. We start by reconsidering Hamilton''s (Hamilton 1964 J. Theoret. Biol. 7, 1–16 (doi:10.1016/0022-5193(64)90038-4)) results for selection on a social trait under the assumptions of additive gene action, weak selection and constant environment and demography. This yields a prediction for the direction of allele frequency change in terms of phenotypic costs and benefits and genealogical concepts of relatedness, which holds for any frequency of the trait in the population, and provides the foundation for further developments and extensions. We then allow for any type of gene interaction within and between individuals, strong selection and fluctuating environments and demography, which may depend on the evolving trait itself. We reach three conclusions pertaining to selection on social behaviours under broad conditions. (i) Selection can be understood by focusing on a one-generation change in mean allele frequency, a computation which underpins the utility of reproductive value weights; (ii) in large populations under the assumptions of additive gene action and weak selection, this change is of constant sign for any allele frequency and is predicted by a phenotypic selection gradient; (iii) under the assumptions of trait substitution sequences, such phenotypic selection gradients suffice to characterize long-term multi-dimensional stochastic evolution, with almost no knowledge about the genetic details underlying the coevolving traits. Having such simple results about the effect of selection regardless of population structure and type of social interactions can help to delineate the common features of distinct biological processes. Finally, we clarify some persistent divergences within social evolution theory, with respect to exactness, synergies, maximization, dynamic sufficiency and the role of genetic arguments.     

Vasopressin, oxytocin and social behaviour

Understanding the neurobiology of social behaviour in mammals has been considerably advanced by the findings from two species of vole, one of which is monogamous and pair bonds whereas the other species is promiscuous and fails to form any long-lasting social relationships. The combination of neurobehavioural studies and molecular genetics has determined behavioural differences between the two species linked to the neural distribution of vasopressin 1A receptor in the male brain. More importantly, vasopressin 1A receptor gene transfer including the upstream regulatory sequence has enhanced male social affiliation in a non-monogamous species. Male affiliative bonding depends upon release of both vasopressin and dopamine in the ventral striatum enhancing the reward value of odour cues that signal identity.     

Trade-offs between social behaviour and foraging by sheep in heterogeneous pastures

In heterogeneous pastures, groups of sheep may have to alter their social behaviour in order to graze patches of preferred vegetation. In this event, patch size, inter-patch distance and the contrast between patch and background vegetation are likely to affect behaviour. In this experiment, groups of five female Scottish Blackface sheep grazed for 2-h periods in 0.1ha grass plots containing seven 1.5mx1.5m patches of improved vegetation, with inter-patch distances of 1.5, 6 or 11.5m. Background vegetation was of either medium or poor quality. Control plots contained no patches. On average, sheep spent 44% of the time grazing patches, although patches comprised only 1.6% of the total plot area. Inter-patch distance did not affect accumulated time spent grazing patches during the first 30min, but patch residence time and the number of sheep on a patch increased with inter-patch distance. The distribution of nearest neighbour distances was altered when patches were 6 or 11.5m apart, compared to no patches. Accumulated time spent grazing patches and the number of sheep on a patch were greater with poor than medium backgrounds. Sheep visited patches frequently and for short periods and it is suggested that sheep often moved off patches as a result of competition. The results provide evidence that sheep make trade-offs between social and foraging behaviour and demonstrate the importance of interactions between social spacing and the size and spacing of vegetation patches, when sheep forage in heterogeneous pastures.     

Rapid Range Expansion Is Not Restricted by Inbreeding in a Sexually Cannibalistic Spider

Few studies investigated whether rapid range expansion is associated with an individual''s short-term fitness costs due to an increased risk of inbred mating at the front of expansion. In mating systems with low male mating rates both sexes share potential inbreeding costs and general mechanisms to avoid or reduce these costs are expected. The spider Argiope bruennichi expanded its range recently and we asked whether rapid settlement of new sites exposes individuals to a risk of inbreeding. We sampled four geographically separated subpopulations, genotyped individuals, arranged matings and monitored hatching success. Hatching success was lowest in egg-sacs derived from sibling pairs and highest in egg-sacs derived from among-population crosses, while within-population crosses were intermediate. This indicates that inbreeding might affect hatching success in the wild. Unlike expected, differential hatching success of within- and among-population crosses did not correlate with genetic distance of mating pairs. In contrast, we found high genetic diversity based on 16 microsatellite markers and a fragment of the mitochondrial COI gene in all populations. Our results suggest that even a very recent settlement secures the presence of genetically different mating partners. This leads to costs of inbreeding since the population is not inbred.     

Age-dependent social learning in a lizard

Evidence of social learning, whereby the actions of an animal facilitate the acquisition of new information by another, is taxonomically biased towards mammals, especially primates, and birds. However, social learning need not be limited to group-living animals because species with less interaction can still benefit from learning about potential predators, food sources, rivals and mates. We trained male skinks (Eulamprus quoyii), a mostly solitary lizard from eastern Australia, in a two-step foraging task. Lizards belonging to ‘young’ and ‘old’ age classes were presented with a novel instrumental task (displacing a lid) and an association task (reward under blue lid). We did not find evidence for age-dependent learning of the instrumental task; however, young males in the presence of a demonstrator learnt the association task faster than young males without a demonstrator, whereas old males in both treatments had similar success rates. We present the first evidence of age-dependent social learning in a lizard and suggest that the use of social information for learning may be more widespread than previously believed.     

Threshold learning dynamics in social networks

Social learning is defined as the ability of a population to aggregate information, a process which must crucially depend on the mechanisms of social interaction. Consumers choosing which product to buy, or voters deciding which option to take with respect to an important issue, typically confront external signals to the information gathered from their contacts. Economic models typically predict that correct social learning occurs in large populations unless some individuals display unbounded influence. We challenge this conclusion by showing that an intuitive threshold process of individual adjustment does not always lead to such social learning. We find, specifically, that three generic regimes exist separated by sharp discontinuous transitions. And only in one of them, where the threshold is within a suitable intermediate range, the population learns the correct information. In the other two, where the threshold is either too high or too low, the system either freezes or enters into persistent flux, respectively. These regimes are generally observed in different social networks (both complex or regular), but limited interaction is found to promote correct learning by enlarging the parameter region where it occurs.     

An experimental comparison of human social learning strategies: payoff-biased social learning is adaptive but underused

Analytical models have identified a set of social learning strategies that are predicted to be adaptive relative to individual (asocial) learning. In the present study, human participants engaged in an ecologically valid artifact-design task with the opportunity to engage in a range of social learning strategies: payoff bias, conformity, averaging and random copying. The artifact (an arrowhead) was composed of multiple continuous and discrete attributes which jointly generated a complex multimodal adaptive landscape that likely reflects actual cultural fitness environments. Participants exhibited a mix of individual learning and payoff-biased social learning, with negligible frequencies of the other social learning strategies. This preference for payoff-biased social learning was evident from the initial trials, suggesting that participants came into the study with an intrinsic preference for this strategy. There was also a small but significant increase in the frequency of payoff-biased social learning over sessions, suggesting that strategy choice may itself be subject to learning. Frequency of payoff-biased social learning predicted both absolute and relative success in the task, especially in a multimodal (rather than unimodal) fitness environment. This effect was driven by a minority of hardcore social learners who copied the best group member on more than half of trials. These hardcore social learners were also above-average individual learners, suggesting a link between individual and social learning ability. The lower-than-expected frequency of social learning may reflect the existence of information producer–scrounger dynamics in human populations.     

Raccoon dog scent marking by scats and its significance in social behaviour

Utilization pattern of latrines by raccoon dogs,Nyctereutes procyonoides viverrinus, was studied on a small island in western Kyushu, Japan. Seventy-eight latrines were spread over the study areas, these were mainly formed on the flat surface in woody areas. Although the site and number of latrines were fairly stable throughout the year, distribution of the utilized latrines and number of scats per latrine were changed seasonally. Latrines were grouped into several clusters and communal utilization of latrines by several animals was observed within the cluster. Seasonal changes of utilization pattern observed in communal utilization rate and cluster formation was assumed to be caused by the changing of the social unit of raccoon dogs. Familiarization within the home range and information site to conspecifics may be concluded as the function of latrines.     

Insect behaviour: learning for the future

Recent studies show that what, when and how a parasitic wasp learns is tailored to its specific ecological niche.