Abstract
Clinal analysis for fitness-related traits provides a well-known approach to investigate adaptive evolution. Several fitness-related traits (developmental time, thorax length, wing length and wing loading) were measured at two laboratory generations (G7 and G33) of D. buzzatii from an altitudinal gradient from northwestern Argentina, where significant thermal differences persist. Developmental time (DT) was positively correlated with altitude of origin of population. Further, DT was negatively correlated with maximal mean temperature at the site of origin of population, and this thermal variable decreases with altitude. Wing loading tended to be larger in highland than in lowland populations, suggesting that flight performance is subject to stronger selection pressure in highland populations. Developmental time showed a significant increase with laboratory generation number. There was no significant correlation between developmental time and body size across populations along the altitudinal cline of DT. This result illustrates that developmental time and body size do not always evolve in the same direction, even though both traits are often positively and genetically correlated in a well-known tradeoff in Drosophila.
Highlights
Clinal analysis for fitness-related traits provides a well-known approach to investigate adaptive evolution
Developmental time (DT) was substantially faster in laboratory generation G7 than in G33 (Fig. 1, standardized data pooled over population and sex; F1,2225 0/3507.69***; ***P B/ 0.005)
Developmental time for males and females of D. buzzatii derived from an altitudinal gradient from northwestern Argentina in laboratory generations (a) G7 and (b) G33
Summary
Clinal analysis for fitness-related traits provides a well-known approach to investigate adaptive evolution. This result illustrates that developmental time and body size do not always evolve in the same direction, even though both traits are often positively and genetically correlated in a well-known tradeoff in Drosophila. In wild populations of D. buzzatii, adaptation to temperature is apparent for developmental time and pre-adult survival but not for size-related traits, suggesting that developmental time is a trait more closely related to thermal adaptation than body size itself (NORRY et al 2001). Microevolution of size-related traits such as thorax and wing length in Drosophila might be further influenced by functional correlations for flight performance and/or other attributes of adult performance rather than thermal selection (NORRY et al 1997). Evolution of body size may not be a simple consequence of changes in developmental time
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