Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria

Citation
Wu. Blanckenhorn, Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria, EVOL ECOL, 14(7), 2000, pp. 627-643
Citations number
52
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology
Journal title
EVOLUTIONARY ECOLOGY
ISSN journal
0269-7653 → ACNP
Volume
14
Issue
7
Year of publication
2000
Pages
627 - 643
Database
ISI
SICI code
0269-7653(2000)14:7<627:TEOESA>2.0.ZU;2-A
Abstract
Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A unifying explanation for thi s Bergmann's rule extended to ectotherms has not been found, and whether th is is an adaptive response or a physiological constraint is debated. The de pendence of egg and clutch size on the mother's temperature environment wer e investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where po ssible confounding variables were controlled for. As clutch size at the sam e time was unaffected by temperature, this effect was not due to a trade-of f between egg size and number. Temperature-dependent egg sizes even persist ed within individuals: when females were transferred to a cooler (warmer) e nvironment, they laid third-clutch eggs that were larger (smaller) than the ir first-clutch eggs. The fitness consequences of these temperature-mediate d egg sizes were further investigated in two laboratory experiments. Neithe r egg and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature corresponding t o the mother's temperature environment. This does not support the beneficia l 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 hypoth esis. In one experiment the smaller eggs laid at 24 degreesC had reduced su rvivorship 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.