Is an archaeon the ancestor of eukaryotes?

The origin of complex cellular life is a key puzzle in evolutionary research, which has broad implications for various neighbouring scientific disciplines. Naturally, views on this topic vary widely depending on the world view and context from which this topic is approached. In the following, I will share my perspective about our current scientific knowledge on the origin of eukaryotic cells, that is, eukaryogenesis, from a biological point of view focusing on the question as to whether an archaeon was the ancestor of eukaryotes.     

Indiscriminate Males: Mating Behaviour of a Marine Snail Compromised by a Sexual Conflict?

Background

In promiscuous species, male fitness is expected to increase with repeated matings in an open-ended fashion (thereby increasing number of partners or probability of paternity) whereas female fitness should level out at some optimal number of copulations when direct and indirect benefits still outweigh the costs of courtship and copulation. After this fitness peak, additional copulations would incur female fitness costs and be under opposing selection. Hence, a sexual conflict over mating frequency may evolve in species where females are forced to engage in costly matings. Under such circumstance, if females could avoid male detection, significant fitness benefits from such avoidance strategies would be predicted.

Methodology/Principal Findings

Among four Littorina species, one lives at very much higher densities and has a longer mating season than the other three species. Using video records of snail behaviour in a laboratory arena we show that males of the low-density species discriminate among male and female mucous trails, trailing females for copulations. In the high-density species, however, males fail to discriminate between male and female trails, not because males are unable to identify female trails (which we show using heterospecific females), but because females do not, as the other species, add a gender-specific cue to their trail.

Conclusions/Significance

We conclude that there is likely a sexual conflict over mating frequency in the high-density species (L. saxatilis) owing to females most likely being less sperm-limited in this species. This has favoured the evolution of females that permanently or optionally do not release a cue in the mucus to decrease excessive and costly matings resulting in unusually high frequencies of male-male copulating attempts in the wild. This is one of few examples of masking gender identity to obtain fewer matings.     

Sympatric Speciation: When Is It Possible in Bacteria?

According to theory, sympatric speciation in sexual eukaryotes is favored when relatively few loci in the genome are sufficient for reproductive isolation and adaptation to different niches. Here we show a similar result for clonally reproducing bacteria, but which comes about for different reasons. In simulated microbial populations, there is an evolutionary tradeoff between early and late stages of niche adaptation, which is resolved when relatively few loci are required for adaptation. At early stages, recombination accelerates adaptation to new niches (ecological speciation) by combining multiple adaptive alleles into a single genome. Later on, without assortative mating or other barriers to gene flow, recombination generates unfit intermediate genotypes and homogenizes incipient species. The solution to this tradeoff may be simply to reduce the number of loci required for speciation, or to reduce recombination between species over time. Both solutions appear to be relevant in natural microbial populations, allowing them to diverge into ecological species under similar constraints as sexual eukaryotes, despite differences in their life histories.     

Is the “Histone Code” an Organic Code?

Post-translational histone modifications and their biological effects have been described as a ‘histone code’. Independently, Barbieri used the term ‘organic code’ to describe biological codes in addition to the genetic code. He also provided the defining criteria for an organic code, but to date the histone code has not been tested against these criteria. This paper therefore investigates whether the histone code is a bona fide organic code. After introducing the use of the term ‘code’ in biology, the criteria a putative organic code such as the histone code must conform to in order to be recognised as an organic code are described. Our current knowledge of histones and their major post-translational modifications, and the specific protein binding domains that recognise and translate these into specific biological effects, is then reviewed in detail. The histone modification system is then placed in the context of an organic code and it is concluded that it fulfils all the requirements of an organic code. The marks produced on histones by processes such as acetylation and methylation act as organic signs that are translated into unique biological effects, their biological meanings. These translations are accomplished by effector proteins that consist of a binding domain that recognises a specific histone mark and a regulatory domain that mediates the biological effect. Crucially, these domains can be experimentally interchanged between different effector proteins, thus altering the rules that specify the relationships between sign and meaning. The effector proteins therefore fulfil the role of adaptor molecules.     

Is cellular senescence an example of antagonistic pleiotropy?

It is generally accepted that the permanent arrest of cell division known as cellular senescence contributes to aging by an antagonistic pleiotropy mechanism: cellular senescence would act beneficially early in life by suppressing cancer, but detrimentally later on by causing frailty and, paradoxically, cancer. In this review, we show that there is room to rethink this common view. We propose a critical appraisal of the arguments commonly brought in support of it, and we qualitatively analyse published results that are of relevance to understand whether or not cellular senescence-associated genes really act in an antagonistic-pleiotropic manner in humans.     

Does Sexual Conflict between Mother and Father Lead to Fertility Decline?

Fertility decline is a great challenge to evolutionary approaches to human behavior. In this study, we apply the perspective of sexual conflict between mother and father to the fertility decline. We predict that, under serial monogamy allowing for mate changes, the ideal number of children for women should be smaller than that for men, because the cost of reproduction for women should be higher than that for men. Our reasoning is that if the cost of child-bearing and child-rearing is higher for women than men, and if women, who therefore would want a smaller number of children than their husbands, have gained more power in reproductive decision-making within a couple owing to the modernization of society, fertility should decline. Until now, few evolutionary studies have analyzed empirical data in modern developed societies with such a perspective. Our questionnaire survey in an urban area in Japan revealed that mothers did experience greater cost during childcare than fathers. However, in contrast to our prediction, we found no sex differences in the ideal number of children between mothers and their husbands in many cases. About 60% of parents remembered wanting two children when they were childless. Moreover, mothers and their husbands had equal power in their decision-making regarding having children. After presenting these results, we discuss some perspectives to advance our understanding of fertility decline in terms of sexual conflict.     

Is Agrammatism an Anomaly?

Kolk, van Grunsven, and Keyser (1985) and Kolk and Hofstede (1987) answer "No" to the question posed in the title of this article. Let us consider instances when normal subjects use "telegraphic style." The authors mentioned above point to dialogue markers, talking to foreigners and children as such cases. However, the offered list seems incomplete and may be enlarged; in doing so, it is important to define the structure and function of agrammatical utterances in normal language users. A Russian author has an advantage in solving this because in the Russian scientific tradition the problem has been approached from both the linguistic (Potebnia, 1888; Iakubinsky, 1923; Zemskaia, 1973; Zemskaia, Kitaigorodskaia, and Shir'aev, 1981) and psychological (Vygotsky, 1934) perspectives.     

Is trans-race possible in an era of unsettled identities?

Brubaker’s book Trans is an important intervention in debates about sexual/gender and racial/ethnic identities in a period of generalized identity unsettlement. It challenges us to think precisely about identities and social categories. Thinking with trans proves to be intellectually productive, showing us the similarities and differences between transgender and trans-race. This contribution to the book symposium raises questions about the specificity of Indigenous identities framed by settler-colonial relations. It also discusses transgender in a global context where non-Western identities have been challenged, and where non-Western protagonists have responded to cultural liberalization at times with forms of gender and sexual repression.