PhDâ€theses - Ethologische Gesellschaft

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MATERNAL CARE STRATEGIES IN PHYLLONETA IMPRESSA (THERIDIIDAE) Nicole Gonswa nicolegonswa@alice‐dsl.net Research Update Diploma thesis, supervised by Prof. Dr. J.M. Schneider, Department of Biology, Zoological Institute & Museum, University of Hamburg Semelparous life‐history strategies evolve if chances of future reproduction are low due to extrinsic and intrinsic causes and often involve extreme forms of brood care. Brood care generally benefits the offspring by increasing survival and growth, and with maximal investment in a single brood or clutch females maximizes the number and/or the quality of their current young at the expense of future offspring. Semelparity in spiders evolved in several families and in some cases involves matriphagy: the consumption of the mother by the young. Obligate matriphagy as found in the eresid spider Stegodyphus lineatus implies that females forgo all possibilities of future reproduction even if their single brood turns out to provide suboptimal returns. However, conditions are rarely predictable and females should benefit if they retain the ability to opt for a second clutch if the first one survives and grows well without her terminal investment. I investigated whether the maternal care behaviour of Phylloneta impressa, a subsocial spider with excessive maternal care, shows plasticity. Females provide their young with regurgitated fluid and prey and finally, matriphagy terminates brood care. I collected females with cocoons and raised the offspring of these spiders to maturity in the laboratory. After maturation, females were mated and assigned to three different food treatments (high, low, no food availability) and maternal care behaviour and growth of young was documented. I found that these spiders practice facultative semelparity and flexibly adapt their brood care to the food availability and offspring needs. In the high food treatment, maternal care duration was shorter but the offspring developed slower than in other treatments. None of the females in the high food treatment was eaten by their young and 33 % of females survived the maternal care period and were able to successfully produce a second clutch. Matriphagy occurred only in broods with limited or no food. Additionally the occurrence of matriphagy depended on the number of spiderlings in the brood and was not observed in small broods. Matriphagy is the only form of cannibalism that was observed during my experiments; no siblicid was seen. My results show that a high plasticity is not excluded by the occurrence of matriphagy as an extreme form of brood care. My results further support the notion that matriphagy must not involve major physiological changes that preclude future reproduction. P. impressa opportunistally adjust their maternal investment in the current brood to offspring needs which are a function of the brood size and the availability of prey. 13
MEANS‐END COMPREHENSION IN PARROTS: A COMPARATIVE APPROACH Anastasia Krasheninnikova anastacia.k@web.de Research Update Master thesis, supervised by Dr. Ralf Wanker and Prof. Dr. Jutta Schneider, Department of Biology, University of Hamburg, Martin‐Luther‐king‐Platz 3, 20146, Hamburg, Germany Two opposing theories explain the evolutionary history of intelligence. The “adaptive specialization approach” suggests that differences in the ecological and social problems faced by a species lead to domain‐specific cognitive abilities. Alternatively, the “general process view” proposes a broader set of cognitive abilities as a consequence of the evolution of large brains. The aim of this study was a comparative approach to test the cognitive abilities of several distantly related parrot species with a means‐end problem, the string discrimination paradigm. I have presented subjects with string‐pulling tasks where I have varied the spatial relationship between the strings, the presence of a reward and the physical contact between the string and the reward to determine whether the parrots perform differently in cognitive tasks requiring means‐end comprehension. The results suggest that the ability to pull the string is a domain‐general capability in psittacids, but the degree of means‐end comprehension vary according to the different degree of the social complexity of the tested species. The more complex the social system, the more advanced the cognitive capabilities. This is the first evidence of the evolutionary history of certain cognitive skills in parrots and the role that the social complexity may play in this process. 14
Page 2 and 3: Content Newsletter No. 64 Content G
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Page 10 and 11: HEART RATE IN GREYLAG GEESE (ANSER
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