When Do Opposites Attract? A Model Uncovering the Evolution of Disassortative Mating.

AbstractDisassortative mating is a rare form of mate preference that promotes the persistence of polymorphism. While the evolution of assortative mating and its consequences for trait variation and speciation have been extensively studied, the conditions enabling the evolution of disassortative mating are still poorly understood. Mate preferences increase the risk of missing mating opportunities, a cost that can be compensated by a greater fitness of offspring. Heterozygote advantage should therefore promote the evolution of disassortative mating, which maximizes the number of heterozygous offspring. From the analysis of a two-locus diploid model with one locus controlling the mating cue under viability selection and the other locus coding for the level of disassortative preference, we show that heterozygote advantage and negative frequency-dependent viability selection acting at the cue locus promote the evolution of disassortative preferences. We predict conditions of evolution of disassortative mating coherent with selection regimes acting on traits observed in the wild. We also show that disassortative mating generates sexual selection, which disadvantages heterozygotes at the cue locus, limiting the evolution of disassortative preferences. Altogether, our results partially explain why this behavior is rare in natural populations.

Episome partitioning and symmetric cell divisions: Quantifying the role of random events in the persistence of HPV infections.

Human Papillomaviruses (HPV) are one of the most prevalent sexually transmitted infections (STI) and the most oncogenic viruses known to humans. The vast majority of HPV infections clear in less than 3 years, but the underlying mechanisms, especially the involvement of the immune response, are still poorly known. Building on earlier work stressing the importance of randomness in the type of cell divisions in the clearance of HPV infection, we develop a stochastic mathematical model of HPV dynamics that combines the previous aspect with an explicit description of the intracellular level. We show that the random partitioning of virus episomes upon stem cell division and the occurrence of symmetric divisions dramatically affect viral persistence. These results call for more detailed within-host studies to better understand the relative importance of stochasticity and immunity in HPV infection clearance.

18-year evolution of asthma and allergic diseases in French urban schoolchildren in relation to indoor air pollutant levels.

BACKGROUND: An initial epidemiological study carried out 18 years ago in Marseilles indicated that the air quality in schools was poor and that there was an association between the level of fine particulates and the occurrence of asthma in children. The aim of the present study was to evaluate the change in the prevalence of childhood asthma and allergic diseases and their link with the levels of air pollutants and other factors of potential risk. METHODS: In 2016, using a questionnaire identical to the one used for the 1st survey in 1998-1999, we collected information regarding the symptoms, the diagnosis, and the potential confounding factors. We measured the main indoor and outdoor pollutants at the schools. RESULTS: Overall, the prevalence of asthma and of allergic diseases exhibited an increasing trend in the time interval between the two studies, significant only for dry cough and pollen allergy. The level of air pollutants decreased significantly indoors. In spite of this, we found a correlation and a dose-effect relationship between the level of PM2.5 and the prevalence of asthma. A family history of asthma and allergies, the insalubrity of the place of residence, and a non-Mediterranean diet were also associated with the risk of these diseases. CONCLUSION: In the time interval between the two studies, which were 18 years apart, despite a reduction in the level of air pollutants in classrooms, asthma was still related to PM2.5. Other potentially causative or contributing environmental factors were also related to asthma and allergies.