The evolution of parental sex roles

In many animals, parents provide care to their offspring, such as building nests, or feeding the young. Species differ considerably in how parental care is distributed between the male and the female parent. In my PhD thesis, I shed new light on the question how the baffling diversity of parental care patterns 1,101 bird species, in order to find out whether ecological factors (such as nest type) or life-history characteristics (such as body size) explain when species exhibit uniparental or biparental care. Although I could identify some significant factors (e.g., breeding in a colony), my main conclusion is that many hypotheses proposed in the literature are not confirmed by the data. Second, I constructed theoretical models in order to gain a better understanding of how and why diverse parental care patterns emerge in the course of evolution. I analysed these models by means of individual-based simulations, which are more versatile and based on fewer simplifying assumptions than standard mathematical approaches. My simulations provide surprising new insights. During evolution, regularly ‘care polymorphisms’ emerge where very different care strategies coexist in males and/or females. Although these polymorphisms may disappear again after a brief period of time, I could show that they are often decisive for the course and outcome of evolution. This finding has important implications for the evolution of parental sex roles, and it necessitates a reconsideration of many seemingly well-established predictions of sex role theory

Individual variation in parental care drives divergence of sex roles

In many animal species, parents provide care for their offspring, but the parental roles of the two sexes differ considerably between and within species. Here, we use an individual-based simulation approach to investigate the evolutionary emergence and stability of parental roles. Our conclusions are in striking contrast to the results of analytical models. In the absence of initial differences between the sexes, our simulations do not predict the evolution of egalitarian care, but either female-biased or male-biased care. When the sexes differ in their pre-mating investment, the sex with the highest investment tends to evolve a higher level of parental care; this outcome does not depend on non-random mating or uncertainty of paternity. If parental investment evolves jointly with sexual selection strategies, evolution results in either the combination of female-biased care and female choosiness or in male-biased care and the absence of female preferences. The simulations suggest that the parental care pattern drives sexual selection, and not vice versa. Finally, our model reveals that a population can rapidly switch from one type of equilibrium to another one, suggesting that parental sex roles are evolutionarily labile. By combining simulation results with fitness calculations, we argue that all these results are caused by the emergence of individual variation in parental care strategies, a factor that was hitherto largely neglected in sex-role evolution theory

Individual variation in parental care drives divergence of sex roles

In many animal species, parents provide care for their offspring, but the parental roles of the two sexes differ considerably between and within species. Here, we use an individual-based simulation approach to investigate the evolutionary emergence and stability of parental roles. Our conclusions are in striking contrast to the results of analytical models. In the absence of initial differences between the sexes, our simulations do not predict the evolution of egalitarian care, but either female-biased or male-biased care. When the sexes differ in their pre-mating investment, the sex with the highest investment tends to evolve a higher level of parental care; this outcome does not depend on non-random mating or uncertainty of paternity. If parental investment evolves jointly with sexual selection strategies, evolution results in either the combination of female-biased care and female choosiness or in male-biased care and the absence of female preferences. The simulations suggest that the parental care pattern drives sexual selection, and not vice versa. Finally, our model reveals that a population can rapidly switch from one type of equilibrium to another one, suggesting that parental sex roles are evolutionarily labile. By combining simulation results with fitness calculations, we argue that all these results are caused by the emergence of individual variation in parental care strategies, a factor that was hitherto largely neglected in sex-role evolution theory

Coevolution of sex specific parental roles and the sex ratio

There is much debate in the literatures about whether and how the adult sex ratio (ASR) and the operational sex ratio (OSR) determine the evolution of parental roles. Actually, sex ratio and parental roles coevolve due to feedback loops. We investigate these feedbacks by means of individual based evolutionary simulations

Prediction of shear strength and vertical movement due to moisture diffusion through expansive soils

This dissertation presents an investigation of engineering behavior of expansive soils. An analytical study was undertaken for the development and modification of a Windows-based two-dimensional finite element computer program FLODEF that performs a sequentially coupled flow-displacement analysis for the prediction of moisture diffusion and the induced volume change in soils supporting various elements of civil infrastructure. The capabilities of the model are illustrated through case studies of shear strength envelope forecast and parametric studies of transient flow-deformation prediction in highway project sites to evaluate the effectiveness of engineering treatment methods to control swell-shrink deformations beneath highway pavements. Numerical simulations have been performed to study the field moisture diffusivity using a conceptual model of moisture diffusion in a fractured soil mass. A rough correlation between field and the laboratory measurements of moisture diffusion coefficients has been presented for different crack depth patterns

Fatigue life assessment in bainitic steels based on the cumulative strain energy density

UIDB/00667/2020 016713 (PTDC/EMS-PRO/1356/2014) Project 3599Carbide-free bainitic steels are an example of high-strength steels that show an excellent combination of strength, ductility, toughness and rolling fatigue contact resistance and are progressively being introduced in the production of railways, crossings and automotive components. Although there are Mn-free approaches able to produce carbide-free bainitic steels, those based on the addition of Mn are less expensive. Therefore, it is important to fully understand the mechanical behavior of such materials to develop reliable engineering products. In this paper, three low-carbon bainitic steels, differing in Mn content, namely 0%, 2.3% and 3.2%, designated as steel A, B and C, respectively, were studied in a systematic manner. Low-cycle fatigue tests were conducted under symmetrical strain-controlled conditions for different strain amplitudes (0.6%, 0.7%, 0.8% and 1%). Independent of Mn content, a strong relationship between cumulative strain energy density and number of cycles to failure was found. Based on this relationship, a new predictive model, capable of estimating the fatigue lifetime, was developed. Predictions based on the new model were close to the experimental lives and were more accurate than those computed via the well-known Smith-Watson-Topper (SWT) and Liu criteria.publishersversionpublishe