Temperature‐Related Genetic Changes in Laboratory Populations ofDrosophila 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.

Recombination Load in a Chromosomal Inversion Polymorphism of Drosophila subobscura

“…Loss of inversion polymorphism has certainly been observed in cage populations of D. melanogaster (e.g., Inoue 1979). In contrast, a recent laboratory natural selection experiment in D. subobscura showed that although chromosome inversion frequencies consistently shifted according to experimental temperature, every one of the replicated population cages maintained all the initial chromosomal diversity, namely, a total of 16 polymorphic gene arrangements (5 in chromosome O) segregating in the five major chromosomes (Santos et al 2005a). How this can happen is unclear, but it is intuitively tempting to presume that selection in heterogeneous environments is just one piece in the puzzle of the maintenance of inversion polymorphisms in this species, albeit not necessarily the most important one.…”

Why tropical forest lizards are vulnerable to climate warming

“…Similarly, genetic adaptation could potentially buffer the impact (Hoffmann & Blows 1993;Travis & Futuyma 1993;Angilletta 2009), and rapid response to temperature in selection experiments is common in invertebrates (Santos et al 2005). Nevertheless, artificial selection on heat tolerance of a fish was unsuccessful (Baer & Travis 2000).…”

Climate change and chromosomal inversions in Drosophila subobscura

“…In an attempt to determine if differences in temperature could account for the observed latitudinal patterns in chromosomal inversion frequencies, lines derived from a South American population of Drosophila subobscura from Puerto Montt (the epicenter of the American invasion) were maintained in the laboratory for several generations at 3 constant temperatures: 13°C (cold), 18°C (around the optimum temperature; see Krimbas 1993) and 22°C (warm) (Santos et al 2004(Santos et al , 2005. If temperature was the main factor driving the evolution of latitudinal clines of gene arrangements, one would expect chromosomal frequencies of laboratory lines subjected to colder temperatures to resemble those from natural populations at increasing latitudes.…”