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.

In insects, some developmentally related traits are negatively correlated. Here, we mapped Quantitative Trait Loci (QTL) for traits of eye size and head capsule, in an intercontinental set of recombinant inbred lines (RILs) of Drosophila melanogaster. Composite interval mapping identified QTL on all major chromosomes. Two negatively correlated traits (size of eyes and between-eyes distance) were influenced by one QTL that appeared to be antagonistic between the traits (QTL cytological range is 25F5–30A6), consistent with a negative genetic correlation between these traits of the head capsule. Comparisons of QTL across traits indicated a nonrandom distribution over the genome, with a considerable overlap between some QTL across traits. Developmentally-related traits were influenced by QTL in a pattern that is consistent both with 1) the sign of the genetic correlation between the traits and 2) a constraint in the micro-evolutionary differentiation in the traits.