Alternative reproductive tactics and sex-biased gene expression : the study of the bulb mite transcriptome

The sexes experience different selective pressures, which can lead to highly divergent phenotypes that are achieved via sex-biased gene expression. The effect of sexual dimorphism on the degree of sex-bias in gene expression can be studied in species characterized by sexually selected alternative male phenotypes. We analyzed gene expression in the bulb mite Rhizoglyphus robini (Acari, Acaridae), in which more sexually dimorphic, aggressive fighter males, possessing thickened legs of the third pair which are used to kill rivals, coexist with unarmored scrambler males. We sequenced transcriptomes of adult females and both types of males and de-novo assembled 114,456 transcriptome-based gene models (TGMs). Significantly more TGMs had male-biased expression than female-biased expression. Among TGMs that were over expressed in one, but not both, male morphs (compared to expression in females), we found about four times more fighter-biased genes than scrambler-biased genes. This demonstrates that the degree of expression bias reflects the degree of sexually selected dimorphism. However, the number of sex-biased genes was much higher than the number of genes differentially expressed between male morphs, and most male-biased genes were shared between morphs, suggesting that selection pressures act similarly on males irrespective of their morph. Furthermore, we found that male-biased genes evolved at a faster rate than female-biased genes, as evidenced by a higher rate of both gene-turnover and amino acid substitution, indicating that sexual selection, acting more strongly on males, accelerates the rate of molecular evolution. Interestingly, gene turnover was relatively higher, but amino acid substitution rate relatively lower among fighter-biased genes, suggesting that different components of sexual selection may have different effects on the evolution of sex-biased genes

Mating system affects population performance and extinction risk under environmental challenge

Failure of organisms to adapt to sudden environmental changes may lead to extinction. The type of mating system, by affecting fertility and the strength of sexual selection, may have a major impact on a population's chances to adapt and survive. Here, we use experimental evolution in bulb mites (Rhizoglyphus robini) to examine the effects of the mating system on population performance under environmental change. We demonstrate that populations in which monogamy was enforced suffered a dramatic fitness decline when evolving at an increased temperature, whereas the negative effects of change in a thermal environment were alleviated in polygamous populations. Strikingly, within 17 generations, all monogamous populations experiencing higher temperature went extinct, whereas all polygamous populations survived. Our results show that the mating system may have dramatic effects on the risk of extinction under environmental change

No evidence for reproductive isolation through sexual conflict in the bulb mite Rhizoglyphus robini

Sexual conflict leading to sexual antagonistic coevolution has been hypothesized to drive reproductive isolation in allopatric populations and hence lead to speciation. However, the generality of this speciation mechanism is under debate. We used experimental evolution in the bulb mite Rhizoglyphus robini to investigate whether sexual conflict promotes reproductive isolation measured comprehensively to include all possible pre- and post-zygotic mechanisms. We established replicate populations in which we either enforced monogamy, and hence removed sexual conflict by making male and female evolutionary interests congruent, or allowed promiscuity. After 35 and 45 generations of experimental evolution, we found no evidence of reproductive isolation between the populations in any of the mating systems. Our results indicate that sexual conflict does not necessarily drive fast reproductive isolation and it may not be a ubiquitous mechanism leading to speciation

Ruchome słowa Roberta Walsera. Analiza związków ruchu, kroków, materialności i słów w Mikrogramach

W tekście podjęto kwestie tego, jak materiał i narzędzia wpływają na zapisywaną treść. Przykład Mikrogramów Roberta Walsera, zbioru krótkich próz, które pisarz zapisywał ołówkiem na małych kawałkach papieru za pomocą bardzo drobnego pisma, pokazuje jak sam zapis tekstu literackiego kształtuje jego formę i ma realny wpływ na zawartą w nim treść. Dzięki temu tekst staje się zjawiskiem przestrzennym, zyskuje materialny ciężar, jest efektem nie tylko pracy intelektualnej, lecz także fizycznej. Teorie Michela de Certeau i Tima Ingolda wykorzystane przy analizie “Mikrogramów” ukazują, że znaczenie tekstów Walsera realizuje się w napięciu między myśleniem a działaniem oraz sztuką i techniką.Jakubowicz-Prokop examines how material and tools influence literary content inscription. The example of Robert Walser’s Microscripts – a collection of short prose pieces written on scraps of paper, remarkable for their tiny script in pencil – suggests how the very inscription of a text shapes its form and what a significant impact the means of inscription has on the content conveyed by that form. Thanks to this, the text becomes a spatial phenomenon, it gains material weight. The text is the effect not only of intellectual but also of physical labour. Building on the theories of Michel de Certeau and Tim Ingold, Jakubowicz-Prokop demonstrates that the meaning of Walser’s texts is realized in the tension between thinking and acting as well as between art and technology

Age dependence of male mating ability and sperm competition success in the bulb mite

In many species, the genetic quality of gametes is likely to decline with age of the male. Some form of discrimination against mating with old males, or against fertilization by their sperm, can be expected to evolve. We investigated the effect of male age on the probability of mating and on sperm competitiveness in the bulb mite, Rhizoglyphus robini. There was no significant difference between male age classes in the probability of mating with virgin females, but young males were more likely to mate with already mated females. Furthermore, young males won sperm competition against older males. This implies that polyandry may be an effective way of avoiding fertilization by the sperm of older males. It has also been suggested that polyandry insures females against the infertility of old males. Our results do not support this hypothesis: matings with older males did not result in female infertility significantly more often than matings with young males