Chromosomal inversion polymorphism in Drosophila mediopunctata: seasonal, altitudinal, and latitudinal variation

Abstract

The most polymorphic chromosome for inversions in Drosophila mediopunctata is the chromosome II, where 17 inversions have been found, eight of which occurring in the distal region and nine in the proximal region. We present an analysis of the chromosome II inversion polymorphism with respect to seasonal, altitudinal and latitudinal variation. In D. mediopunctata from the Parque Nacional do Itatiaia (southeastern Brazil), the frequencies of three of the distal inversions (namely DA, DS, and DP) vary seasonally. These inversions also show altitudinal clines in their frequencies. This microgeographic pattern was not observed on a macrogeographic scale. D. mediopunctata from Porto Alegre are less polymorphic for inversions than other populations, the most remarkable reduction occurring in the proximal region of chromosome II. There is a considerable difference between D. mediopunctata from Campinas and specimens from Serra do Japi, which are separated by only 50 km. In contrast, D. mediopunctata from Serra do Japi are much more similar to specimens from the Parque Nacional do Itatiaia, which is 200 km far.

No amicable divorce? Challenging the notion that sexual antagonism drives sex chromosome evolution

“…However, sex-linked non-recombining regions are exceptional in that the mechanism of sex determination, which is the cause of balancing selection upon sex-linked loci, tends to persist for long periods of evolutionary time. In this, it differs from other causes of balancing selection upon inversions, such as environmental gradients [54] and hostparasite co-evolution [55], which are relatively ephemeral selective agents, rarely persisting beyond the lifetime of a species. In contrast, a sex-linked inversion is held in a balanced polymorphic state until the function of sex determination shifts to another locus.…”

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

“…Gene arrangement DI did not show any seasonal variation or correlation with either temperature or altitude. This pattern suggests that natural selection is maintaining the observed variation (Ananina et al 2004, Klaczko 2006. Hatadani & Klaczko (2008) showed that Drosophila mediopunctata wing size and shape were influenced by second chromosome karyotype, sex, and temperature under controlled laboratory conditions.…”

“…Our collection strategy was designed to test the following hypo theses: (1) if the current overall frequency of gene arrangements was similar to those previously described by Ananina et al (2004), and if the overall correlations with environmental variables were still valid; we sampled different altitudinal points varying among a total of 9 points (from 590 to 1190 m above sea level, a.s.l., see Table A1 in Appendix 1) in each of the 7 collections in different seasons; (2) if gene arrangements DA, DS and DP were still significantly associated to altitude; we sampled fly populations from 7 different altitudes (from 590 to 1190 m a.s.l., Table A1) on one single occasion (cold-dry season 2009); and (3) if gene arrangements DA, DS and DP were still cycling seasonally; 2 areas (sites at altitudes of 750 and 950 m a.s.l.) were sampled on each of the 7 collecting dates to avoid confounding the effects of seasonal cycling and clinal variation of the inversion frequencies.…”

“…A natural population of Drosophila mediopunctata from the Parque Nacional do Itatiaia, Rio de Janeiro State, was investigated in the late 1980s, where an altitudinal cline was detected for morphological traits and inversion frequencies (Bitner-Mathé et al 1995, Bitner-Mathé & Klaczko 1999, Ananina et al 2004). Moreover, the frequencies of inversions DA, DP and DS showed cyclical seasonal variation (Klaczko 2006).…”

Climate change and chromosomal inversions in Drosophila subobscura

“…As mentioned previously, the observation of seasonal changes -repeated over the yearsin the frequencies of gene arrangements represented the first piece of evidence in support of the adaptive value of chromosomal inversion polymorphisms (Dobzhansky 1970, Lewontin 1974, Endler 1986). Seasonal cycling of chromosomal inversions has been recorded in a number of Drosophila species, including D. pseudoobscura (Dobzhansky 1947), D. persimilis (Dobzhansky 1956), D. funebris (Dubinin & Tiniakov 1945), D. flavopilosa (Brncic 1972), D. robusta (Levitan 1973, Etges 1984, D. melanica (Tonzetich & Ward 1973), D. melanogaster (Stalker 1980, Sánchez-Refusta et al 1990) and D. mediopunctata (Ananina et al 2004), highlighting the generality of this pattern across species with contrasting geographic distributions.…”