Untitled

Abstract

Background: The clear dominance of two-gender sex in recent species is a notorious puzzle of evolutionary theory. It has at least two layers: besides the most fundamental and challenging question why sex exists at all, the other part of the problem is equally perplexing but much less studied. Why do most sexual organisms use a binary mating system? Even if sex confers an evolutionary advantage (through whatever genetic mechanism), why does it manifest that advantage in two, and exactly two, genders (or mating types)? Why not just one, and why not more than two?

Evolution of asymmetric gamete signaling and suppressed recombination at the mating type locus

“…This could explain why the co-existence of mating types with pansexuals is rare in natural populations (Billiard et al, 2011; Billiard et al, 2012). This is in contrast to previous models where pansexual types were very hard to eliminate due to negative frequency dependent selection (Hoekstra, 1982; Czárán and Hoekstra, 2004; Hadjivasiliou et al, 2013). For example, in the case of the mitochondrial inheritance model, uniparental inheritance raises fitness not only in individuals that carry genes for uniparental inheritance but also for pansexual individuals (benefits ‘leak’ to biparental individuals) (Hadjivasiliou et al, 2013; Christie and Beekman, 2017b).…”

“…A similar pattern is seen with inbreeding avoidance because the spread of self-incompatibility reduces the population mutation load, and so reduces the need for inbreeding avoidance (Czárán and Hoekstra, 2004). These dynamics are reversed in the present model where there is positive frequency dependent selection.…”

“…Several hypotheses have been proposed to explain the evolution of isogamous mating types (Billiard et al, 2011; Billiard et al, 2012; Perrin, 2012). Mating types could serve as a restrictive mechanism preventing matings between related individuals thereby avoiding the deleterious consequences of inbreeding (Charlesworth and Charlesworth, 1979; Uyenoyama, 1988; Czárán and Hoekstra, 2004). Another idea is that mating types facilitate uniparental inheritance of mitochondria, which leads to improved contribution of the mitochondrial genome to cell fitness (Hastings, 1992; Hurst and Hamilton, 1992; Hutson and Law, 1993; Hurst, 1996; Hadjivasiliou et al, 2012; Hadjivasiliou et al, 2013; Christie et al, 2015; Christie and Beekman, 2017a).…”

Toward application of biocontrol to inhibit wine spoilage yeasts: The use of statistical designs for screening and optimisation

“…On the other hand, it is also possible that certain inhibition factors for one or both yeasts generate an equilibrium between toxin release (biocontroller yeast multiplication) and toxin's adherence to spoilage yeast, influencing spoilage yeast multiplication (Pommier et al, 2005, Sinclair, 2014. Other authors hypothesised about toxin consumption by sensitive yeast and the distance through the existence of patches (Czárán and Hoekstra, 2003;Sinclair, 2014). This can be explained through the absence of agitation in the fermentation medium (Károlyi et al, 2005).…”

Cell–cell signalling in sexual chemotaxis: a basis for gametic differentiation, mating types and sexes

“…Another dominant hypothesis proposes that mating types are important because they promote outbreeding and prevent same clone fusions [ 13 ]. This hypothesis has a strong appeal, as inbreeding can indeed be detrimental in many higher animals and plants [ 14 ], and high levels of inbreeding are harmful in some protists [ 15 ].…”