Assortative Mating and Fertility in twoDrosophila subobscuraStrains with different Mitochondrial DNA Haplotypes

Abstract

The mating pattern and female fertility on the two main mitochondrial DNA haplotypes (I and II) of Drosophila subobscura were studied, in an attempt to find possible differences between them in relation to sexual selection or isolation that could explain the populational dynamics and the co-existence of these two strains in nature. The mating pattern indicated an assortative mating in population cages, where couples of the same haplotype, mainly those of haplotype I, mated more often. However, the significations detected in laboratory conditions disappeared in wild populations, where random mating was the rule. The female fertility also showed differences in the laboratory compared to the wild, since couples with haplotype I males were more efficient in the laboratory populations. These results, together with others that we previously obtained, either point to selection acting directly on the mtDNA or to the presence of some kind of cytonuclear co-adaptation in these two haplotypes, although this must be modulated by other factors that change with the seasons and time. The end result could well be a balance of opposite forces acting on both haplotypes.

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.…”

“…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).…”

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

“…Nevertheless, males contribute with nuclear genes, which generates the nuclear variability necessary in cytonuclear relationships. In this sense, as indicated above, we also consider the mating pattern relevant, and this is an experiment that we carried out (Castro et al, 2003); in this experiment, the mating pattern indicated an assortative mating in population cages, where couples of the same haplotype …”

“…), so a direct extrapolation to nature is not possible. In fact, Castro et al (2003) found, in relation to female fertility, that the adaptation to laboratory conditions gave a more global efficiency in the production of the offspring. In this situation, we can only say that under laboratory conditions, flies with haplotype II have a higher fitness than flies with haplotype I, and, thus, haplotype II would displace haplotype I in competition experiments.…”

“…In addition, we also studied the optimal density (OD) (density at which the food medium yields the highest number of adult individuals) to measure the way in which the medium is exploited (Wallace, 1981;Castro et al, 1985). Other fitness components, such as mating pattern and female fertility, which are especially important in mtDNA dynamics due to maternal inheritance, were studied in flies from population cages (the same used in the present paper) and in a recently collected lines from a natural population (Castro et al, 2003).…”