Rapid response to perturbation of chromosome frequencies in natural populations of Drosophila robusta

Abstract

Perturbation of gene or chromosome frequencies in natural populations is one of the most powerful ways of demonstrating whether natural selection maintains genetic polymorphism or if other evolutionary forces are at work. Gene arrangement frequencies in two natural populations of Drosophila robusta were perturbed multiple times by releasing adult flies with contrasting karyotypes and carefully monitoring post-perturbation presence of hybrids and chromosome frequencies. In all cases, frequencies quickly returned to pre-perturbation levels, and in the following sampling periods, no evidence of the introduced chromosomes was apparent. Analysis of post-perturbation frequency changes included tests for heterogeneity among chromosome arrangements in rates of return to equilibrium values using population admixture analysis. In several cases, significant heterogeneity was detected indicating some form of natural selection was operating. Technical challenges to carrying out perturbation experiments in the wild are also discussed.

Climate change and chromosomal inversions in Drosophila subobscura

“…In this context, experiments in the field and/or in mesocosms may provide complementary approaches to the ones outlined in Section 4. Recent field release studies have been successfully employed to test the adaptive role of acclimatory responses in D. melanogaster (Loeschcke & Hoffmann 2007, Kristensen et al 2008) and the putative role of local adaptation as a determinant of chromosomal frequencies in D. robusta (Levitan & Etges 2009), and similar experiments might shed light on the mechanisms underlying the geographical and temporal changes in the chromosomal polymorphism of D. subobscura.…”

Commentary: When does understanding phenotypic evolution require identification of the underlying genes?

“…However, this approach is generally not available for detecting balancing selection; although test crosses can reveal an excess of heterozygotes, other mechanisms besides balancing selection (e.g., disassortative mating, the Wahlund effect, directional selection) can also produce this result. And although there are experimental means of detecting balancing selection through fitness measurements (Bright and Rausher 2008) or perturbation experiments (Eckert et al 1996;Subramaniam and Rausher 2000;Gigord et al 2001;Levitan and Etges 2009), results may often not be conclusive for at least two reasons: (1) the magnitude of balancing selection may be too weak to detect with even large field samples; and (2) balancing selection may act only intermittently and thus may not be detected in short-term field studies. In these situations, identifying the gene may be a necessity.…”

“…; Subramaniam and Rausher ; Gigord et al. ; Levitan and Etges ), results may often not be conclusive for at least two reasons: (1) the magnitude of balancing selection may be too weak to detect with even large field samples; and (2) balancing selection may act only intermittently and thus may not be detected in short‐term field studies. In these situations, identifying the gene may be a necessity.…”

Unexpected long-term changes in chromosome inversion frequencies in a Neotropical Drosophila species

“…Montane tropical biota are believed to be particularly vulnerable to global warm ing effects (Sheldon et al 2011). Several longterm studies on Drosophila inversion polymorphisms have shown that changes in inversion frequencies can be a valuable tool to monitor rapid genetic shifts caused by climatic change (Stamenkovic-Radak et al 2008, Balanyà et al 2009, Levitan & Etges 2009; for review see: Rieseberg 2008 andRezende et al 2010). None of these studies, however, addresses the potential effects of climate change on a Drosophila Neotropical species.…”