Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria |
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Authors: | Wolf U Blanckenhorn |
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Institution: | 1. Zoologisches Museum, Universit?t Zürich, Winterthurerstrasse 190, CH 8057, Zürich, Switzerland
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Abstract: | Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A
unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response
or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were
investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were
controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between
egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a
cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness
consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg
and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature
corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead,
this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate
temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24 °C had reduced
survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation
of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint)
of unclear adaptive value.
This revised version was published online in November 2006 with corrections to the Cover Date. |
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Keywords: | adaptation Bergmann's rule clutch size egg size physiological constraint temperature |
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