Altitudinal life history variation in the dung flies Scathophaga stercoraria and Sepsis cynipsea |
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Authors: | W U Blanckenhorn |
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Institution: | Zoologisches Museum der Universit?t Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland fax: +(41) 1-364-0295; e-mail: wolfman@zoolmus.unizh.ch, CH
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Abstract: | Field phenologies of high- (ca. 1500 m) and low- (ca. 500 m) altitude populations of the two most common European species
of dung flies, Scathophaga stercoraria and Sepsis cynipsea, differ quite markedly due to differences in climate. To differentiate genetic adaptation due to natural selection and phenotypic
plasticity, I compared standard life history characters of pairs of high- and low-altitude populations from three disjunctive
sites in Switzerland in a laboratory experiment. The F1 rearing environment did not affect any of the variables of the F2
generation with which all experiments were conducted; hence, there were no carry-over or maternal effects. In Sc. stercoraria, high-altitude individuals were smaller but laid larger eggs; the latter may be advantageous in the more extreme (i.e. more
variable and less predictable) high-altitude climate. Higher rearing temperature strongly decreased development time, body
size and the size difference between males and females (males are larger), produced female-biased sex ratios and led to suboptimal
adult emergence rates. Several of these variables also varied among the three sites, producing some interactions complicating
the patterns. In Se. cynipsea, high-altitude females were marginally smaller, less long-lived and laid fewer clutches. Higher rearing temperature strongly
decreased development time and body size but tended to increase the size difference between males and females (males are smaller);
it also increased clutch size but decreased physiological longevity. Again, interpretation is complicated by variation across
sites and some significant interactions. Overall, genetic adaptation to high-altitude conditions appears weak, probably prevented
by substantial gene flow, and may be swamped by the effects of other geographic variables among populations. In contrast,
phenotypic plasticity is extensive. This may be due to selection of flexible, multi-purpose genotypes. The results suggest
that differences in season length between high- and low-altitude locations alone do not explain well the patterns of variation
in phenology and body size.
Received: 21 March 1996 / Accepted: 1 September 1996 |
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Keywords: | Body size Development Phenology Phenotypic plasticity Season length |
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