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    ABSTRACT: Predators that have learned to associate warning coloration with toxicity often continue to include aposematic prey in their diet in order to gain the nutrients and energy that they contain. As body size is widely reported to correlate with energetic content, we predicted that prey size would affect predators' decisions to eat aposematic prey. We used a well-established system of wild-caught European starlings, Sturnus vulgaris, foraging on mealworms, Tenebrio molitor, to test how the size of undefended (water-injected) and defended (quinine-injected) prey, on different coloured backgrounds, affected birds' decisions to eat defended prey. We found that birds ate fewer defended prey, and less quinine, when undefended prey were large compared with when they were small, but that the size of the defended prey had no effect on the numbers eaten. Consequently, we found no evidence that the mass of the defended prey or the overall mass of prey ingested affected the amount of toxin that a predator was willing to ingest, and instead the mass of undefended prey eaten was more important. This is a surprising finding, challenging the assumptions of state-dependent models of aposematism and mimicry, and highlighting the need to understand better the mechanisms of predator decision making. In addition, the birds did not learn to discriminate visually between defended and undefended prey based on size, but only on the basis of colour. This suggests that colour signals may be more salient to predators than size differences, allowing Batesian mimics to benefit from aposematic models even when they differ in size.
    Animal Behaviour 06/2013; 85(6):1315-1321.
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    ABSTRACT: Toxic prey species living in the same environment have long been thought to mutually benefit from having the same warning signal by sharing the education of naïve predators. In contrast, 'saturation theory' predicts that predators are physiologically limited by the amount of toxin that they can eat in a given time period. Therefore, sympatric species that contain the same toxin should mutually benefit from reduced predation even when they are visually distinct, reducing the benefits to visual mimicry. For the first time, we found that mutualism can occur between unequally defended prey that are visually distinct, although the benefits to each prey type depends on the predators' abilities and/or motivation to visually discriminate between them. Furthermore, we found that this variability in predatory behaviour had a significant impact on the benefits of mimicry for unequally defended prey. Our results demonstrate that variability in the foraging decisions of predators can have a significant effect on the benefits of shared toxicity and visual mimicry between sympatric species, and highlights the need to consider how predators exert selection pressures on models and mimics over their entire lifetimes.
    PLoS ONE 01/2012; 7(9):e44895.
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    ABSTRACT: The evolution and maintenance of toxicity in a prey population is a challenge to evolutionary biologists if the investment in toxin does not benefit the individual. Recent experiments suggest that taste-rejection behaviour enables predators to selectively ingest less toxic individuals, which could stabilize investment in defences. However, we currently do not know if taste rejection of defended prey is accurate across different contexts, and that prey always benefit according to their investment. Using avian predators, we show that the rejection probability does not solely depend on the investment in defence by an individual, but also on the investment by other individuals in the same population. Therefore, taste rejection by predators could lead to destabilization in the investment in defences, and allow variability in prey defences to exist.
    Biology letters 03/2010; 6(5):617-9.
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    ABSTRACT: Recent studies have provided a new perspective on the relationship between the honey bee queen and her colony. They suggest that the queen produces a pheromone which pharmacologically manipulates her workers.
    Current biology: CB 08/2009; 19(14):R547-8.
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    ABSTRACT: Plants produce flowers with complex visual and olfactory signals, but we know relatively little about the way that signals such as floral scents have evolved. One important factor that may direct the evolution of floral signals is a pollinator's ability to learn. When animals learn to associate two similar signals with different outcomes, biases in their responses to new signals can be formed. Here, we investigated whether or not pollinators develop learned biases towards floral scents that depend on nectar reward quality by training restrained honeybees to learn to associate two similar odour signals with different outcomes using a classical conditioning assay. Honeybees developed learned biases towards odours as a result of differential conditioning, and the extent to which an olfactory bias could be produced depended upon the difference in the quality of the nectar rewards experienced during conditioning. Our results suggest that differences in reward quality offered by flowers influence odour recognition by pollinators, which in turn could influence the evolution of floral scents in natural populations of co-flowering plants.
    Proceedings of the Royal Society B: Biological Sciences 05/2009; 276(1667):2597-604.
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    ABSTRACT: Evolutionary theory suggests that maternal grandparents will invest more in their grandchildren than paternal grandparents, due to the difference between the certainty of maternity and the uncertainty of paternity. Most tests of this prediction have tended to use retrospective ratings by grandchildren rather than examining grandparental behaviour. Using a large-scale data set from the UK (n>7000), significant differences are shown between maternal and paternal grandparents in terms of frequencies of contact with their newborn grandchildren, while controlling for a wide range of other variables. Maternal grandparents also provided a significantly wider range of financial benefits than paternal grandparents. Maternal grandparents were also more likely to provide essentials and gifts and extras for the baby. Multiple correspondence analysis showed that contact frequencies systematically related to other measures of grandparental investment, indicating that contact frequencies are a useful proxy measure to examine overall investment. Findings are discussed with reference to the paternity uncertainty hypothesis.
    Journal of Biosocial Science 02/2009; 41(3):355-79.
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    ABSTRACT: There has been considerable speculation about the adaptive significance of the human female orgasm, with one hypothesis being that it promotes differential affiliation or conception with high-quality males. We investigated the relationship between women's self-reported orgasm frequency and the characteristics of their partners in a large representative sample from the Chinese Health and Family Life Survey. We found that women report more frequent orgasms the higher their partner's income is. This result cannot be explained by possible confounds such as women's age, health, happiness, educational attainment, relationship duration, wealth difference between the partners, difference between the partners in educational attainment, and regional location. It appears consistent with the view that female orgasm has an evolved adaptive function.
    Evolution and Human Behavior - EVOL HUM BEHAV. 01/2009; 30(2):146-151.
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    ABSTRACT: Many prey species have evolved bitter-tasting toxins that effectively protect them from potential predators. While predators can learn to associate the taste of defended prey with the noxious effects of the toxins, it is unclear whether bitter tastes also function as deterrents. We explicitly tested the effectiveness of a nontoxic distasteful chemical as an antipredator defence. We gave four groups of European starlings, Sturnus vulgaris, a sequential colour discrimination task, where one colour signalled undefended mealworms, Tenebrio molitor, and the other signalled defended mealworms that had either been injected with or coated with either a high or a low concentration of Bitrex solution (a nontoxic bitter-tasting solution). Birds ate all of the prey presented in this way, but performed disgust responses after eating prey coated in Bitrex solution. Birds were then given a series of trials in which they received defended and undefended prey items simultaneously. Birds that received prey injected with Bitrex attacked similar numbers of defended and undefended prey, whereas birds that received prey coated in Bitrex ate significantly fewer defended than undefended prey. Birds given prey coated in a high concentration of Bitrex showed a stronger preference for undefended prey than birds given prey coated in a low concentration of Bitrex. Our experiment demonstrates that a nontoxic distasteful chemical can protect insect prey from predation, but only under very specific conditions.
    Animal Behaviour. 01/2009;
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    ABSTRACT: We hypothesise on a number of grounds that the personality dimension of Agreeableness may be associated with inter-individual differences in theory of mind (ToM) functioning. However, it is important to distinguish social-perceptual from social-cognitive ToM. Previous findings on ToM in psychopathic individuals, sex differences in ToM and the associations between ToM and social relationships, all suggest that social-cognitive ToM is more likely than social-perceptual ToM to relate to Agreeableness. In separate empirical studies, we find that Agreeableness is substantially correlated with social-cognitive ToM performance, but uncorrelated with social-perceptual ToM performance. We suggest that the propensity or motivation to attend to the mental states of others may be central to the personality dimension of Agreeableness. Copyright © 2008 John Wiley & Sons, Ltd.
    European Journal of Personality 05/2008; 22(4):323 - 335.
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    ABSTRACT: Unpalatable insects often advertise their defences to predators using conspicuous colours, such as red and yellow. Perhaps not surprisingly, birds show unlearned biases against warningly coloured food. These biases are particularly evident when other components of insect warning displays, such as sounds and odours, are also present. Quinine, a bitter-tasting toxic chemical, can also enhance unlearned biases against red and yellow prey in naïve birds. However, whether this behaviour is performed specifically in response to quinine (which is chemically similar to many insect toxins) or can be elicited by other bitter-tasting chemicals is not known. The aim of our experiments was twofold. First, we investigated whether Bitrex, a bitter-tasting, nontoxic, man-made chemical, elicits colour biases similar to those elicited by quinine. Second, since avoidance learning can be affected by the number of bitter chemicals present in a prey population, we investigated whether the presence of both quinine and Bitrex enhanced unlearned biases against red crumbs compared to either chemical alone. We found that only quinine elicited attack biases against red prey, and there was no evidence that quinine and Bitrex in combination produced a stronger bias against red crumbs than quinine alone. These results indicate that colour biases incited by defence chemicals are chemical specific and may occur only in response to natural or toxic chemicals.
    Animal Behaviour. 03/2008;
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