Temperature-Related Genetic Changes in Laboratory Populations of Drosophila subobscura: Evidence against Simple Climatic-Based Explanations for Latitudinal Clines

Abstract

Parallel latitudinal clines to the long-standing ones in the original Palearctic populations have independently evolved at different rates for chromosomal polymorphism and body size in South and North American populations of Drosophila subobscura since colonization around 25 years ago. This strongly suggests that (micro) evolutionary changes are largely predictable, but the underlying mechanisms are unknown. The putative role of temperature per se was investigated by using three sets of populations at each of three temperatures (13 degrees , 18 degrees , and 22 degrees C) spanning much of the tolerable range for this species. We found a lower chromosomal diversity at the warmest temperature; a quick and consistent shift in gene arrangement frequencies in response to temperature; an evolutionary decrease in wing size, mediated by both cell area and cell number, at 18 degrees C; no relationship between wing size and those inversions involved in latitudinal clines; and a shortening of the basal length of longitudinal vein IV relative to its total length with increasing standard dose. The trends for chromosomal polymorphism and body size were generally inconsistent from simple climatic-based explanations of worldwide latitudinal patterns. The findings are discussed in the light of available information on D. subobscura and results from earlier thermal selection experiments with various Drosophila species.

Response to selection and evolvability of invasive populations

“…Direct measurements of selection response in invasive or colonizing populations are still rare (Gibbs 2002;Lee 2002;Donohue et al 2005a;Santos et al 2005). Eurytemora affinis is a major component of food webs in estuarine and salt marsh ecosystems in the Northern Hemisphere.…”

Shape and size variation on the wing of Drosophila mediopunctata: influence of chromosome inversions and genotype-environment interaction

“…Even though our results are consistent with the hypothesis of natural selection favoring larger wings under lower temperatures, the adaptive nature of this relationship is still not clear. Santos et al (2006) argued that clines formed in North and South America for inversion frequencies and body size in D. subobscura were not related, 2 Confidence regions (95%) of first and second canonical variates obtained from partial warps and uniform components scores. The percentage of variance explained by each variate is shown in the label of each axis.…”

“…(a) total shape variation, (b) non-allometric shape variation based on laboratory populations, although natural populations in Europe exhibit a positive association between chromosome inversions and wing size along a latitudinal cline (Orengo and Prevosti 2002). Santos et al (2006) also proposed that clines in North and South America could not only be explained by temperature variation and suggested that other factors, including larval crowding, may have an important role in the formation of these clines. This hypothesis is consistent with our results: there was an overall effect of temperature on size because individuals developing under lower temperatures are larger than those growing under higher temperatures (Robertson 1987;Thomas 1993;Partridge et al 1994;Crill et al 1996;Pétavy et al 2001;Azevedo et al 2002;David et al 1994David et al , 1997David et al , 2006; there was an interaction between genotype (cross) and temperature, the inversions analyzed showed average differences in size (PA0 larger than PC0), and no interaction between inversion and temperature was found.…”

“…One possibility for this apparent disagreement is that wing morphology is affected by environmental factors other than temperature (e.g., larval crowding, as suggested by Santos et al 2006).…”

Fitness variation in response to artificial selection for reduced cell area, cell number and wing area in natural populations of Drosophila melanogaster

“…More puzzling information come from flies collected in the central area of the South American clines and kept under three different thermal selection regimes for two years. These flies show an unusual pattern of size change, mostly mediated by cell area in females and cell number in males [18]. …”