On the relative roles of faster-X evolution and dominance in the establishment of intrinsic postzygotic isolating barriers

The modern theory of speciation assigns a prominent role to the recessivity of genetic incompatibilities in the two rules of speciation, namely Haldane's rule and the large X effect, and considers that the contribution of faster evolution of the X versus the autosomes to those patterns is generally of relatively minor importance. By extending Turelli and Orr's previous analysis of the model of two-locus Dobzhansky–Muller incompatibilities, I first show that when the X and the autosomes evolve at the same rate, the two dominance parameters involved in that model are not equally important for the declaration of a large X effect, but that the degree of recessivity of homozygous–homozygous incompatibilities is the major determinant for such a declaration. When the X evolves faster than the autosomes, the model obviously predicts that the importance of both dominance parameters will progressively vanish. It is then of importance to obtain estimates of the relative evolutionary rate of X-linked incompatibility loci. Several different procedures to obtain such estimates from the perspective of the large X effect are suggested. The application of the appropriate test to the only suitable data from Drosophila hybridizations so far available leads to the conclusion that the X actually evolves at least 2.5 times faster than the autosomes, as far as hybrid male sterility determinants are concerned, thus making dominance considerations absolutely irrelevant. Notwithstanding the necessity of further tests, the relative roles currently assigned to faster-X evolution and dominance in the theory of speciation should be revised, giving due prominence to faster-X evolution, at least for hybrid male sterility in the genus Drosophila.     

Female dominance in captive gray mouse lemurs (Microcebus murinus)

Female dominance or female feeding priority seem to be characteristic for many lemur species, but are rare traits in other primates and mammals in general. The nocturnal lemur species, however, are underrepresented in the quantitative studies on social dominance. The aim of this study is to investigate the pattern of intersexual dominance relationships in the gray mouse lemur (Microcebus murinus), a species that is generally thought to possess a number of ancestral lemur traits. The context, distribution, and outcome of intersexual conflicts are analyzed in four captive groups of gray mouse lemurs. Intersexual conflicts occurred in the study groups in different behavioral contexts and were mostly spatial interactions (chasing/fleeing, approach/avoidance). The majority of conflicts were decided, and were in all but one case won by females. This is the first evidence suggesting unconditional female dominance in a cheirogaleid primate. The existence of female dominance in most families of the Lemuriformes suggests it is an ancient trait that evolved in their common ancestor.     

害虫抗药性的显性水平与抗性进化

对杀虫剂的代谢抗性和主要靶标抗性的显性水平作了理论解释,其中包括昆虫对Bt抗性的显性水平的解释。并对抗性显性具有的多变性作了阐述。分析抗性显性水平与抗药性进化的关系,认为在抗性进化早期抗性表现为显性的基因频率上升快于抗性表现为隐性时;但在抗性等位基因频率较高且出现抗性纯合子个体时,抗性表现为隐性的基因频率上升显著快于抗性表现为显性时。最后论述抗性显性在抗性治理中的应用。     

Norm statement considered harmful: comment on ‘evolution of unconditional dispersal in periodic environments’

The mathematical symbol for the norm, which is heavily overloaded with multiple definitions that have both universal and specific properties, lends itself to confusion. This is manifest in the proof of an important theorem for population dynamics by Schreiber and Li on how dispersal increases population growth in a periodic environment. Here the theorem is placed in context, the proof is clarified, and the confusing but inconsequential errors corrected.     

Hitchhiking of Deleterious Alleles and the Cost of Adaptation in Partially Selfing Species

Self-fertilization is generally seen to be disadvantageous in the long term. It increases genetic drift, which subsequently reduces polymorphism and the efficiency of selection, which also challenges adaptation. However, high selfing rates can increase the fixation probability of recessive beneficial mutations, but existing theory has generally not accounted for the effect of linked sites. Here, we analyze a model for the fixation probability of deleterious mutants that hitchhike with selective sweeps in diploid, partially selfing populations. Approximate analytical solutions show that, conditional on the sweep not being lost by drift, higher inbreeding rates increase the fixation probability of the deleterious allele, due to the resulting reduction in polymorphism and effective recombination. When extending the analysis to consider a distribution of deleterious alleles, as well as the average fitness increase after a sweep, we find that beneficial alleles generally need to be more recessive than the previously assumed dominance threshold (h < 1/2) for selfing to be beneficial from one-locus theory. Our results highlight that recombination aiding the efficiency of selection on multiple loci amplifies the fitness benefits of outcrossing over selfing, compared to results obtained from one-locus theory. This effect additionally increases the parameter range under which obligate outcrossing is beneficial over partial selfing.     

Letters

Responses to reality, John Kramer

SA/V ratios and gaseous exchange, John Shone

Tautology and teleology John A. Horsfall     

The red queen coupled with directional selection favours the evolution of sex

Why sexual reproduction has evolved to be such a widespread mode of reproduction remains a major question in evolutionary biology. Although previous studies have shown that increased sex and recombination can evolve in the presence of host-parasite interactions (the 'Red Queen hypothesis' for sex), many of these studies have assumed that multiple loci mediate infection vs. resistance. Data suggest, however, that a major locus is typically involved in antigen presentation and recognition. Here, we explore a model where only one locus mediates host-parasite interactions, but a second locus is subject to directional selection. Even though the effects of these genes on fitness are independent, we show that increased rates of sex and recombination are favoured at a modifier gene that alters the rate of genetic mixing. This result occurs because of selective interference in finite populations (the 'Hill-Robertson effect'), which also favours sex. These results suggest that the Red Queen hypothesis may help to explain the evolution of sex by contributing a form of persistent selection, which interferes with directional selection at other loci and thereby favours sex and recombination.