PhDâ€theses - Ethologische Gesellschaft
PhDâ€theses - Ethologische Gesellschaft
PhDâ€theses - Ethologische Gesellschaft
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MATERNAL CARE STRATEGIES IN PHYLLONETA IMPRESSA (THERIDIIDAE)<br />
Nicole Gonswa<br />
nicolegonswa@alice‐dsl.net<br />
Research Update<br />
Diploma thesis, supervised by Prof. Dr. J.M. Schneider, Department of Biology, Zoological Institute &<br />
Museum, University of Hamburg<br />
Semelparous life‐history strategies evolve if chances of future reproduction are low due to<br />
extrinsic and intrinsic causes and often involve extreme forms of brood care. Brood care<br />
generally benefits the offspring by increasing survival and growth, and with maximal<br />
investment in a single brood or clutch females maximizes the number and/or the quality of<br />
their current young at the expense of future offspring. Semelparity in spiders evolved in<br />
several families and in some cases involves matriphagy: the consumption of the mother by<br />
the young. Obligate matriphagy as found in the eresid spider Stegodyphus lineatus implies<br />
that females forgo all possibilities of future reproduction even if their single brood turns out<br />
to provide suboptimal returns. However, conditions are rarely predictable and females<br />
should benefit if they retain the ability to opt for a second clutch if the first one survives and<br />
grows well without her terminal investment.<br />
I investigated whether the maternal care behaviour of Phylloneta impressa, a<br />
subsocial spider with excessive maternal care, shows plasticity. Females provide their young<br />
with regurgitated fluid and prey and finally, matriphagy terminates brood care. I collected<br />
females with cocoons and raised the offspring of these spiders to maturity in the laboratory.<br />
After maturation, females were mated and assigned to three different food treatments<br />
(high, low, no food availability) and maternal care behaviour and growth of young was<br />
documented.<br />
I found that these spiders practice facultative semelparity and flexibly adapt their<br />
brood care to the food availability and offspring needs. In the high food treatment, maternal<br />
care duration was shorter but the offspring developed slower than in other treatments.<br />
None of the females in the high food treatment was eaten by their young and 33 % of<br />
females survived the maternal care period and were able to successfully produce a second<br />
clutch. Matriphagy occurred only in broods with limited or no food. Additionally the<br />
occurrence of matriphagy depended on the number of spiderlings in the brood and was not<br />
observed in small broods. Matriphagy is the only form of cannibalism that was observed<br />
during my experiments; no siblicid was seen.<br />
My results show that a high plasticity is not excluded by the occurrence of<br />
matriphagy as an extreme form of brood care. My results further support the notion that<br />
matriphagy must not involve major physiological changes that preclude future reproduction.<br />
P. impressa opportunistally adjust their maternal investment in the current brood to<br />
offspring needs which are a function of the brood size and the availability of prey.<br />
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