The evolutionary history of Drosophila buzzatti. XXVI. Macrogeographic patterns of inversion polymorphism in New World populations

Abstract

Inversion polymorphisms in the second and fourth chromosomes of the cactophilic Drosophila buzzatti in the native distribution range of the species are described. Over 5,000 flies from 26 localities were scored revealing interesting geographic structuring of arrangement frequencies. Multiple regression and partial correlation approaches showed that the frequencies of second and fourth chromosome arrangements vary clinically along latitudinal and altitudinal gradients and to a lesser extent with longitude. Although many non selective explanations can account for this pattern, its resemblance to the clinal pattern described in recently established Australian populations of Drosophila buzzatii, strongly suggests a selective explanation. Additionally, the correlated variation observed between the frequencies of arrangements 2St on the second chromosome and 4St on the fourth suggests a pattern of interchromosomal association, which, when considering the vast area surveyed, might be explained as the result of epistatic interactions. The analysis of population structure revealed a significant regional pattern, concordant with previously described phytogeographic regions. F-statistics showed that the patterns of variation were different not only between the second and fourth chromosomes, but also between second chromosome arrangements, suggesting that selective differentiation might have contributed to population structure.Since D. buzzatii breeds and feeds on the decaying tissues of diverse cactus species present in different phytogeographic regions, and given that latitude and altitude are strong determinants of phytogeography, it is difficult to distinguish the underlying causes of the geographic patterns observed. However, inversion heterozygosity is not correlated with the diversity of potential cactus hosts.The evidence presented suggests that differential selection may be the main cause for the population structure. It is also possible to conclude that the inversion polymorphism of D. buzzatti is flexible rather than rigid.

Bottlenecks, population differentiation and apparent selection at microsatellite loci in Australian Drosophila buzzatii

“…Although the frequency of the standard second chromosome arrangement decreases with increasing latitude in Australia (Knibb et al, 1987;Knibb and Barker, 1988) and in Argentina (Hasson et al, 1995), indicating selective differentiation of populations for inversion frequencies, only Db034 and Db052 are included within an inversion (Figure 2), and these loci showed no significant effects in any selection analysis. Although Db142 is near the proximal breakpoint of inversion 4s, this inversion has not been found in Australian populations (Knibb et al, 1987).…”

The Role of the Use of Different Host Plants in the Maintenance of the Inversion Polymorphism in the Cactophilic Drosophila Buzzatii

“…The site of collection (described in Hasson et al 1995) is in a temperate area with a wide temperature range over the year and is irregularly occupied by Opuntia vulgaris, which is the only potential breeding and feeding resource. Four second-chromosome arrangements are segregating in Otamendi: 2st, the ancestral gene order, 2j, 2jz 3 , and 2jq 7 .…”

“…However, this hypothesis has not been seriously tested, probably due to the poor knowledge of the ecology (breeding sites) of the species most thoroughly studied (reviewed in Krimbas and Powell 1992). However, cactophilic species of the repleta group have proven to be more rewarding models in this matter (Fontdevila 1991;Hasson et al 1995;Etges et al 1999). For instance, in D. mojavensis, inversion heterozygosities are higher in localities where a temporally and spatially more stable cactus host is present (Etges et al 1999).…”

Correlations among size-related traits are affected by chromosome inversions in an adaptive polymorphism in Drosophila buzzatii

“…The same traits were also scored in laboratoryreared flies (LRF5), derived from: (i) the Arroyo Escobar population; (ii) the Quilmes population (26°6'S, 65°9'W), where inversion j is almost fixed (inversion frequency 0.98, Hasson et al, 1995).…”