Fitness and life-history traits of the two major mitochondrial DNA haplotypes of Drosophila subobscura

Abstract

Mitochondrial DNA restriction site analyses on natural populations of Drosophila subobscura have proved the existence of two common, coexisting haplotypes (I and II), as well as a set of less frequent ones derived from them. To explain this distribution, experiments to date point practically to all possible genetic mechanisms being involved in the changes of gene frequencies (cytonuclear coadaptation, direct natural selection on mtDNA and genetic drift). In an attempt to find differences that help to understand the dynamics of these haplotypes and to detect the effect of selection, we measured certain fitness components and life-history traits (egg-larva and larva-adult viabilities and developmental times, longevity, resistance to desiccation and optimal density) of the two main haplotypes I and II when maintained in laboratory population cages. As a general trend, haplotype II showed a higher net fitness than haplotype I, which explains the superiority of haplotype II over haplotype I in experimental populations but not their coexistence in nature, where additional factors must be considered.

Mitochondrial DNA effects on fitness in Drosophila subobscura

“…This result could partially explain why haplotype VIII is the most frequent haplotype on some of the Canary Islands. Additionally, comparisons between haplotypes I and II did not give significative differences, contrarily to Castro et al (2003) and Christie et al (2004). These present results confirm that the fitness differences observed in these two haplotypes were surely due to cytonuclear interactions and not to direct selection upon the mtDNA.…”

“…PCR assays using 16S rDNA Wolbachia-specific primers on local populations were carried out in the recent past (García-Martínez et al, 1998;Christie et al, 2004), giving negative results. Original Drosophila stocks from Tenerife were treated with tetracycline, and PCR assayed.…”

“…The comparison of the several curves was made with the log-rank test, so called because it can be shown to be related to a test that uses the logarithms of the ranks of the data. E-statistic Christie et al, 2004) is a fitness parameter that combines data of viabilities and developmental times, and follows the optimality principle that the largest number of adults emerged in the shortest possible time gives the best fitness. The characteristic of this parameter is that it simultaneously maximises viability, V, and the reciprocal of the development time, DT, as follows:…”

“…Results indicated that natural populations have not yet reached a drift-selection equilibrium, because of periodic bottlenecks as well as some kind of selection, due to environmental heterogeneity (seasonal changes), possibly acting upon nuclear inversion polymorphism frequencies associated with mtDNA haplotypes. Many studies concerning the genetic dynamics of mtDNA in D. subobscura indicate the existence of cytonuclear interactions between the mtDNA and nuclear markers (Fos et al, 1990;García-Martínez et al, 1998;Oliver et al, 2002;Castro et al, 2003;Christie et al, 2004).…”

Nucleotide diversity of a ND5 fragment confirms that population expansion is the most suitable explanation for the mtDNA haplotype polymorphism of Drosophila subobscura

“…The analyses of the corresponding cytonuclear disequilibria were not conclusive because when such disequilibria were detected, they were transient. We then measured the fitness components under experimental conditions and studied fitness differences between haplotypes I and II in terms of mating behaviour (Castro et al 2003), when D. subobscura were competing in experimental population cages (García-Martínez et al 1998;Oliver et al 2005), or for a number of life history traits (Christie et al 2004). Although we were able to determine that haplotype II showed a higher fitness than haplotype I, in most cases this difference was not statistically supported.…”