Genetic genealogy comes of age: advances in the use of deep-rooted pedigrees in human evolutionary research (video)
Author(s): Larmuseau, MHD, Van Geystelen, A, Decorte, R
Research on the recent human evolution will benefit from the implementation of extended genetic genealogical data. The approach to combine deep-rooted pedigrees with genetic information advances the understanding of changes in the human population genetic structure during the last centuries. This recent advance is mainly based on the extensive growth of whole genome sequencing data and available genealogical data of high quality. Moreover, according to the latest genetic genealogical research the historical non-paternity rate in Western Europe is estimated around 1% per generation within the last four centuries, which means that the expected relationship between the legal genealogy and the genetics of DNA donors exists. Therefore, genetic genealogical data will help with three research aims of human evolutionary studies: (I) detecting signals of (past) population stratification and interpreting the population structure in a more objective manner, (II) obtaining the time scale and impact of particular detected gene flow events more accurately and (III) determining temporal genetic differentiation within a population by combining in-depth pedigree data with haploid markers. Each of these research aims will be discussed with examples of the human population in Flanders (Western Europe). At the end, we will discuss the advantages and pitfalls of using genetic genealogy within studies on human evolutionary genomics.
Detection of polygenic selection at different evolutionary levels (video)
Author(s): Excoffier L, Daub J
Most approaches aiming at finding genes involved in adaptive events have focused on the detection of outlier loci, which resulted in the discovery of individually ´significant´ genes with strong effects. However, a collection of small effect mutations could have a large effect on a given biological pathway that includes many genes, and such a polygenic mode of adaptation has not been systematically investigated in humans or other mammals. We therefore propose to evidence polygenic selection by detecting signals of adaptation at the pathway or gene set level instead of analyzing single independent genes. Using a gene-set enrichment test, we identify genome-wide signals of recent adaptation among human populations as well as more ancient signals of adaptation in the human lineage and in primates.
A genome-wide scan for relaxation of constraints in the human lineage affecting specific functional processes (video)
Author(s): Somel, M, Wilson-Sayres, M, Jordan, G, Huerta-Sanchez, E, Fumagalli, M, Ferrer-Admetlla, A, Nielsen, R
Changes in the subsistence mode of a species can lead to adaptive evolution of new functions, while it can also cause relaxed negative selection in previously essential functions. While positive selection in humans has been intensely studied, functional processes subject to relaxed constraints in the human lineage remain largely unknown. Here we present a framework for detecting relaxation of selective constraints that affect a particular functional process specifically in one taxon. Jointly using human and chimpanzee population genomic data with mammalian comparative genomic data, we identify olfactory receptors and proteasome subunits as candidates of relaxed constraints in humans: both gene sets contain high frequency non-synonymous mutations in humans while having conserved amino-acid sequences across other mammals. We further discuss the possible underlying causes of this signal.
Selection on penis size, body shape and height in humans: a simple multivariate method to quantify female preferences based on male physical attractiveness (video)
Author(s): Mautz, BS, Jennions, MD, Peters, RA, Wong, BBM
Compelling evidence from many animal taxa indicates that male genitalia are often under post-copulatory sexual selection for characteristics that increase a male’s relative fertilization success under sperm competition. There could, however, also be direct pre-copulatory female mate choice based on male genital traits. Before clothing, the non-retractable human penis would have been conspicuous to potential mates. This, in combination with claims that humans have a large penis for their body size compared to other primates, has generated suggestions that human penis size partly evolved due to female choice. We presented women with digitally projected fully life-size, computer-generated animations of male figures to quantify the (interactive) effects of penis size, body shape and height on female assessment of male sexual attractiveness. We generated 343 male figures that each had one of seven possible values for each of the three test traits (7x7x7 = 343). All seven test values per trait were within two standard deviations of the mean based on a representative sample of males. We calculate response (fitness) surfaces based on the average attractiveness rank each of the 343 male figure received. We also calculated individual response surfaces for 105 women (each women viewed 53 figures). Both methods yielded almost identical results. We discuss our finding in the context of previous studies that have taken a univariate approach to quantify female preferences. We discuss the hypothesis that pre-copulatory sexual selection might play a role in the evolution of genital traits.
Quantitative genetic variation, selection and secular change of skull shape in humans
Author(s): Klingenberg, C, Martínez-Abadías, N, Esparza, M, Sjøvold, T, Hernández, M
The combined use of geometric morphometrics and quantitative genetics provides a set of powerful tools for obtaining quantitative information that is crucial for many important questions concerning the evolution of shape. In particular, the demographic information that is available for human populations make humans a unique study system for studying the mechanisms of evolutionary change in morphological traits. We investigate skull shape in the population of Hallstatt (Austria), where a collection of human skulls with associated records offer a unique opportunity for such studies. We use an individual-based statistical model to estimate the genetic covariance matrix, and characterize selection using fitness estimates from demographic data. We find clear evidence for directional selection, but not for nonlinear selection (stabilizing or disruptive selection). The predicted response to this selection, computed with genetic parameters from the population, does not match the estimate of secular change over the 150-year range of the data. We discuss possible reasons for the mismatch.
What is "species recognition"?
Author(s): Mendelson, T
The concept of “species recognition” is widely used in the study of animal communication, typically referring to the tendency of organisms to distinguish members of their own species from heterospecifics. Yet, it is difficult to pinpoint a consensus definition of the concept, and close inspection reveals a host of underlying assumptions. First, I discuss definitions and underlying assumptions of species recognition as used in the literature and identify where these assumptions are either untested or logically flawed. I then discuss the implications of species recognition for the question of whether non-human animals have species concepts and articulate directions for research into the cognitive architecture of species boundaries in nature.
From sexual communication to species recognition: examples from the house mouse
Author(s): Ganem, G
Sexual communication involves transfer of information between potential mates on their identity, quality, compatibility and history. Both endogenous and exogenous factors are expected to shape the evolution of the complex systems made of signals, receptors and preferences. Further, variation in the latter factors could result in divergence between the sexes, populations and species. How potential mates make sense of the diverse information available for mate choice remains an unresolved question. My research addresses this question in rodent species using the olfactory chemosensory channel to communicate. For example, several pheromones involved in social and sexual communication have been described in the house mouse (Mus musculus domesticus). These chemical cues are mostly present in the mouse urine and the mouse marks its territory by depositing urine drops. Moreover, mice are both excellent noses and carry odor signatures that act as fingerprints. Still, despite of this remarkable individual variability population and species differences exist. The house mouse is involved in chromosomal diversification in parts of its range and share a hybrid zone with another subspecies (M. m. musculus) along a north south axis crossing Europe from Scandinavia to the Black sea. Using these different evolutionary and geographical settings, research in my laboratory has addressed the mechanisms involved in mate recognition system divergence. Referring to examples from my research I shall illustrate how genetic drift, local adaptation sexual selection and reproductive interference shape the house mouse mate recognition system and could facilitate speciation.
A quantitative genetics approach to equilibrium assessment and equilibrium fitness estimation; an application to study the polymorphism of the human ACP1 in Europe (video)
Author(s): Álvarez-Castro, JM
Studies of equilibrium and stability under selection are liable to further development. With multiple alleles, a tiny proportion of possible genotype frequencies are possible at polymorphic equilibria. I present a quantitative genetics (QG) method for checking whether a set of genotype frequencies are equilibrium frequencies that also provides estimates of the fitnesses of all genotypes. This method is here applied to a one-locus multiallelic system, but applications to multiple-locus systems with epistasis are also possible. Method Classical QG studies focused on directional selection on the phenotype. Considering instead that the trait is fitness enables tracking genotypic frequencies under other selection regimes. Thus, if the additive variance may be minimized to zero for a set of observed frequencies, then these are putative equilibrium frequencies and the corresponding fitnesses are estimates of the equilibrium fitnesses. Two exclusive properties of NOIA are crucial for performing such analysis: it generalizes previous models and it provides explicit expressions of variance components (Álvarez-Castro and Carlborg 2007, Álvarez-Castro and Yang 2011). The human ACP1 polymorphism in Europe Three alleles of ACP1 (A, B, C) coexist in human European populations and C was claimed to be deleterious using biallelic methods. The multiallelic method proposed here shows instead that the observed genotypic frequencies are consistent with a polymorphic equilibrium with fitnesses in accordance with physiological observations (AA affected by fetal macrosomia). NOIA reveals a fast rise of additive variance for slight fitness increases of AA (not published). This may actually be leading to fixation of A in European populations since fetal macrosomia--with the aid of pregnancy monitoring and reasonably safe caesarean sections--entails nowadays less of a problem than it did some decades ago. ALVAREZ-CASTRO & CARLBORG 2007 Genetics 176 ALVAREZ-CASTRO & YANG 2011 Genetica 139
Comparing phenotypic, quantitative genetic, and genomic approaches to measuring tradeoffs in a contemporary human population
Author(s): Stearns SC
In women born before 1940 in Framingham, Massachusetts, there was a significant negative correlation between number of children ever born and lifespan. Each additional child was associated with a reduction of about one year of life. Analysis of the 1500+ pedigrees containing 15,000+ people with an animal model that partially controlled for cultural and environmental effects yielded a large, significant, negative genetic correlation between children ever born and lifespan. A genome wide association study that looked for genes that alter the slope of the relationship between those two traits discovered several genes, some of which have previously been identified as involved in cancer. One, EOMES, has the sort of function one would expect of a gene that influences a tradeoff: its product affects many different processes. Statistical models with and without education as a covariate yielded results consistent with the idea that education is a cultural mimic of antagonistic pleiotropy: increases in level of education are associated with fewer children and longer life.
How has the genetic architecture of key life history traits responded to the demographic transition in a human population?
Author(s): Bolund, E, Lummaa, V
A central issue in evolutionary biology concerns the long-term reliability of predictions of evolutionary change. Theory predicts that the genetic architecture of life history traits (summarised by the additive genetic variance-covariance matrix, G) will change over time and thus affect how traits respond to selection. However, studies have found support both for fast changes as well as for a great consistency in G over time. It thus remains unclear how rapidly and in what manner G itself changes in response to changes in selection pressures or environment.
The demographic transition to low mortality and fertility rates in many recent human populations involves a drastic environmental change, but its consequences for the evolutionary potential of traits have rarely been addressed. We use genealogical data from 8 parishes in Finland, from natural high (5-6 offspring) to recent low (< 2 offspring) fertility over 350 years to address this question at the genetic level. We study four key life history traits; age at first and last reproduction, number of offspring and longevity, all of which show significant phenotypic changes during the time period. We use the animal model quantitative genetic approach to study whether and how the genetic architecture underlying these traits has also changed, by comparing the full G matrix in the periods before and after the demographic transition.
First, we establish significant additive genetic variance and heritability for all traits during both time periods. Second, we present the genetic covariances and correlations between all four traits during both periods. Third, we compare the overall G matrix of the two periods to elucidate if and how G has changed during the demographic transition. The results provide a novel insight in how traits can respond to selection in contemporary human populations and whether the potential for such responses might have changed along with the recent demographic and societal changes.
Divergent selection on, but no genetic conflict over, female and male timing and rate of reproduction in a human population
Author(s): Bolund E, Bouwhuis S, Pettay J, Lummaa V
The sexes often have different phenotypic optima for important life-history traits and because they share much of their genome, this can lead to a conflict over trait expression. In mammals, the obligate costs of reproduction are higher for females, making reproductive timing and rate especially liable to conflict between the sexes. While studies from wild vertebrate populations show support for such sexual conflict, it remains unexplored in humans. We used a pedigreed human population from pre-industrial Finland to estimate sexual conflict over age at first and last reproduction, reproductive lifespan and reproductive rate. We found that the phenotypic selection gradients differed between the sexes. For age at first and last reproduction and reproductive lifespan, the relationships with fitness (number of grandchildren) tended to be nonlinear in women, suggesting an intermediate optimum value, while they were linear in men. Both sexes showed a linear decrease in fitness with increasing reproductive rate. We next established significant heritabilities in both sexes for all traits. All traits, except reproductive rate, showed strongly positive intersexual genetic correlations and were strongly genetically correlated with fitness in both sexes. Moreover, the genetic correlations with fitness were almost identical in men and women. For reproductive rate, the intersexual correlation and the correlation with fitness were weaker but again similar between the sexes. These findings illustrate that apparent sexual conflict at the phenotypic level is not necessarily indicative of an underlying genetic conflict and further emphasize the need for incorporating a genetic perspective into studies of human life-history evolution.
Genetic constraints underlying human reproductive timing in a pre-modern Swiss village (pdf)
Author(s): Bürkli, A, Postma, E
The trade-off between reproductive investment in early versus late life is central to life-history theory. Despite abundant empirical evidence in support of different versions of this trade-off, the specific trade-off between age at first reproduction (AFR) and age at last reproduction (ALR) has received little attention, especially in long-lived species with a pronounced reproductive senescence such as humans. Using genealogical data for a 19th-century Swiss village, we (i) quantify natural selection on reproductive timing, (ii) estimate additive genetic (co)variances, and (iii) use these to predict evolutionary responses. Selection gradients were computed using multiple linear regressions, and the additive genetic variance-covariance matrix was estimated using a restricted maximum-likelihood animal model. We found strong selection for both an early AFR and a late ALR, which resulted from selection for an earlier and longer reproductive period (RP, i.e. ALR-AFR). Furthermore, postponing AFR shortened RP in both sexes, but twice as much in women. Finally, AFR and ALR were strongly and positively genetically correlated, which led to a considerable reduction in the predicted responses to selection, or even rendered them maladaptive. These results provide evidence for strong genetic constraints underlying reproductive timing in humans, which may have contributed to the evolution of menopause.
What is advantageous for the germline may be bad for the soma; the impact of germline selection on the mutational load in humans
Author(s): Arnheim, N, Calabrese, P
Some new germline mutations that arise in the testis may confer a selective advantage to the mutated germ cell relative to non-mutated cells. Theoretically, if a new mutation provided a germline selective advantage it could increase the frequency at which the mutated allele was introduced into the population by orders of magnitude even though, much to the species detriment, it reduced the fitness of the individuals that inherited it. We have shown examples of positive germline selection for three human disease mutations that arise sporadically each generation at frequencies ranging from 1/2,000 to 1/70,000 births. These sporadic disease cases occur at rates 100-1,000 times greater than would be expected based on what we know about genome average mutation rates. Using a testis dissection/mutation detection approach along with mathematical modeling we have shown that the high frequency of these de novo disease mutations cannot be explained by hyper-mutation at the disease-causing sites. Instead, our data are consistent with the idea that the newly mutated germline stem cells have a proliferative advantage over non-mutated stem cells resulting in germline mosaicism. Plausible molecular mechanisms can explain the selective advantage for each of the three disease mutations. Others previously suggested that alleles conferring a selective advantage in the germline may be disadvantageous in the adult and might lead to “mitotic drive” systems that increase the mutational load of a population. The three disease mutations we examined may be realizations of this idea.
Experimental studies of human social learning strategies: exploring sex differences
Author(s): Cross, C, Brown, G, Morgan, T, Laland, K
Objectives Culture is an important driver of recent biological evolution in humans. The mechanisms by which information is transmitted between individuals can be studied at the population level – by cultural evolutionists, and at the individual level – by social psychologists. We combined methods from these two approaches to investigate how sex differences in confidence might lead to sex differences in the use of a copy-when-uncertain social learning strategy. Methods Participants (Study 1: N=97; Study 2: N=89) completed a series of two-alternative forced-choice puzzles and reported their confidence in each answer. They then saw the decisions of some previous participants before being asked again for their answer. Social information use was inferred when participants switched their answer to match that of the majority. We modelled the probability of social information use with participant sex, confidence in initial decision, and accuracy of initial decision as predictors. Results Across both studies, confidence had a large effect on social information use, indicative of a copy-when-uncertain strategy. Accuracy predicted confidence, indicating that this strategy is adaptive. Confidence also differed by sex: women reported lower confidence (independent of any small sex differences in accuracy), which in turn increased their probability of using social information. Conclusions Although both sexes appear to use a ‘copy-when-uncertain’ strategy, women are more likely to feel uncertain. This means that a strategy observed to be used in a population (e.g. copy-when-uncertain) can vary according to individual differences in psychological traits. Further integration of these two levels of explanation is therefore needed.
Fitness meets fitness: taking an evolutionary approach to physical fitness in humans (pdf)
Author(s): Postma, E
Evolutionary biologists are usually the first to emphasize that Darwinian fitness has little in common with the meaning that is commonly attached to fitness by the general public, that is physical fitness. However, recent studies in humans and non-human animals are suggestive of an important role for physical fitness in shaping variation in Darwinian fitness via natural and sexual selection, both in the past and in the present. Indeed, it has been argued that it is selection on physical performance that has made us who we are today. To gain a better understanding of variation in (physical) fitness, I use concepts and methods from evolutionary biology and life-history theory and apply these to data on human running performance. Specifically, using a large (longitudinal and cross-sectional) data set for running performance by both men and women over a wide range of distances, I test for sex differences, the effects of ageing and training, and for trade-offs between long- versus short-distance and generalists versus specialists. I will use these findings to infer the selective pressures acting on physical fitness in humans, and to argue that Darwinian and physical fitness may have more in common with each other than is often assumed.
The demographic transition influences variance in fitness and selection on height and BMI in rural Gambia
Author(s): Courtiol, A
Recent human history is marked by demographic transitions characterized by declines in mortality and fertility. By influencing the variance in those fitness components, demographic transitions can affect selection on other traits. Parallel to changes in selection triggered by demography per se, relationships between fitness and anthropometric traits are also expected to change due to modification of the environment. Here we explore for the first time these two main evolutionary consequences of demographic transitions using a unique data set containing survival, fertility, and anthropometric data for thousands of women in rural Gambia from 1956–2010. We show how the demographic transition influenced directional selection on height and body mass index (BMI). We observed a change in selection for both traits mediated by variation in fertility: selection initially favored short females with high BMI values but shifted across the demographic transition to favor tall females with low BMI values. We demonstrate that these differences resulted both from changes in fitness variance that shape the strength of selection and from shifts in selective pressures triggered by environmental changes. These results suggest that demographic and environmental trends encountered by current human populations worldwide are likely to modify, but not stop, natural selection in humans.
A comparison between heritabilities of life history and morphological traits in human populations (pdf)
Author(s): Esparza, M, Martínez-Abadías, N, Sjovold, T, González-José, R, Hernández, M
According to Fisher's fundamental theorem of natural selection, the amount of additive genetic variance in a trait, and hence its heritability, should decrease as the strength of selection on this trait increases. Supporting this idea, many authors have reported lower heritability values in life history traits than in morphological and physiological traits for different species. But there are no studies comparing the evolvability of different types of traits in human populations. The pedigree collection of decorated skulls from the historical population of Hallstatt (Austria) offers an exceptional opportunity to compare the heritabilities of life history and morphological traits in humans. In this study we first used church records to reconstruct the pedigrees and to obtain the values of individual life history traits, such as fertility, age at first and at last child, mean interbirth interval, adult lifespan and lifetime reproductive success). Second, we measured a sample of 353 complete adult skulls falling into the pedigrees using a 3D Microscribe digitizer. A set of 50 landmarks were measured on each skull and from the 3D landmarks coordinates we estimated several size and shape variables reflecting the complex and modular structure of the human skull. We estimated the heritabilities of the life-history and morphological traits using a Restricted Maximum Likelihood method and statistically compared the resulting heritability values. On average, our results show lower heritabilities for life history traits than for morphological ones, confirming the initial hypothesis.
AgeGuess crowdsourcing human aging research (pdf)
Author(s): Steiner, U, Misevic, D
Human lifespan increases by 2.5 years every decade. This unprecedented change in life histories poses fundamental challenges for evolutionary theories. Some evidence indicates that this change is due to a delay in aging rather than a change in the rate of aging. AgeGuess is a citizen science project and online game that investigates the differences between perceived age (how old you look to other people) and chronological age (how old you actually are) and their potential power as an aging biomarker. Is the increased life expectancy reflected in how old one looks, i.e. are the new 60’s the old 50’s? Are people who look older than they are more likely to die early? Does the rate of looking older differ among individuals or some individuals just looking older all their lives, i.e. does the difference between estimated and real age change over time? Is the difference between perceived and real age heritable? Are there periods in life when one ages faster? The project aims at such questions by a simple on-line game in which you can post your photos, have other people guess your age, as well as guess the age of other users. Curious? Please visit AgeGuess.org
Cooperation and conflict in humans in traditional large joint families
Author(s): Pettay, JE, Lahdenperä, M, Lummaa, V
Group living can be associated with cooperation and even cooperative breeding whereby non-reproductive individuals help to raise offspring that are not their own. However, it can also lead to evolutionary conflict, which is a less studied phenomenon. Humans are considered to be cooperative breeders, since mothers commonly gain help in raising offspring from other (usually related) group members, such as grandmothers and siblings. Nevertheless, simultaneous breeding in the same household among reproductive-aged females, such as mothers-in-law and daughters-in-law, has also been linked with reduced success. The importance of cooperation and conflict is likely to vary according to ecology and social structure of populations, leading to differential selection pressures on dispersal patterns. We used life-history data on humans collected from church book records from 19th century Eastern Finland where joint-families were traditionally common. In joint families several adult offspring, usually sons, stayed in their natal farm with their families. This creates a situation where reproductive-aged women are not related to other women in the family, leading to possible conflict over resources and lowered fitness, but cooperation between women is also possible. We analyse mother’s fecundity and survival of her offspring in relation to the presence and reproductive history of other reproductive-aged women in the family by event history analysis, whist controlling for potential confounders such as presence of other family members and temporal variation in mortality and fertility rates. Preliminary analysis suggest that living in larger joint families was beneficial for women’s fitness, both in terms of fecundity and offspring survival, compared to smaller nuclear families. These results suggest that in this population cooperation between family members was more important than conflict, potentially favouring reduced dispersal among adult siblings
Reproduction and lifespan: only age at last reproduction matters
Author(s): Nenko, I, Jasienska, G
Reproduction is costly for mothers due to energetic and physiological requirements during pregnancy, lactation and childcare. Fathers are usually neglected by the studies since they do not pay direct costs of reproduction. However, including fathers in analysis is crucial, since it could suggests explanations about the mechanisms responsible for the relationships observed for mothers. Our study investigated how reproductive history is related to parental lifespan. We present results from historical Polish population belonging to the area of Mogielica Human Ecology Study Site. Demographic data for marriages that occurred from the year 1782 to 1882, collected from parish records were used. Relationship between number of children born, age at first reproduction and last reproduction, mean interbirth interval and parental longevity was analyzed controlling for year of birth, spouse’s longevity and first birth interval (as an indicator of energetic status at the beginning of reproduction for women). Moreover, sex of the last child was included in the model to control for maternal condition at the end of reproduction (since sons are more costly than daughters). In separate models, number of children that survived to adulthood was analyzed. Both maternal and paternal lifespans were affected only by the age at last reproduction. The later the last child was born the longer lives parents had (mothers: HR=0.96; CI=0.93-0.99 and fathers: HR=0.95; CI=0.92-0.98). Similar relationships were found when number of children who survived to adulthood was analyzed (mothers: HR=0.96; CI=0.94-0.98 and fathers: HR=0.95; CI=0.93-0.97). The results suggest that in studied population there are no trade-offs between costs of reproduction and lifespan. Only the age at last reproduction is significant predictor of length of life. However, the fact that the same relationship is observed for fathers suggests importance of social rather than biological factors.
Human evolutionary demography: illustrated with reference to the importance of kin for human reproductive success
Author(s): Sear, R
Evolutionary demographers working on our own species are fortunate: data on humans abounds, both from the real world (including large-scale national datasets collected by demographers and economists and data on small-scale traditional societies collected by demographers), and from the lab (psychological and medical). We also have access to the substantial amount of research done in the social and medical sciences on how to collect, analyse and think about such data. In this talk I will summarise the benefits of the cross-disciplinary approach of human evolutionary demography, which combines data, methods and insights from the social sciences with the theoretical framework of evolutionary biology. I will do this with particular reference to my research on kin influences on demographic outcomes, including child survival and fertility rates. As a social species, interactions with other individuals are important for human fitness. The ‘cooperative breeding’ and ‘pooled energy budget’ models of human social organisation suggest, in fact, that such interactions are essential for human reproductive success. Here I will present results from a comparative project which is investigating the empirical evidence that kin do matter for women’s fitness across a wide range of human populations, including: the analysis of nationally representative datasets from both high and low income countries; a comparative analysis of datasets from traditional, subsistence societies contributed by anthropologists; and psychological experiments. This evidence demonstrates that the presence of kin is often correlated with higher reproductive success, but also that interactions between kin are not always necessarily cooperative. There is also some evidence for local resource competition between kin, and conflicts of interest between affinal kin (those related by marriage).
Genetic trade-offs and the evolution of human life-histories
Author(s): Hayward, AD, Lummaa, V
Understanding life-history trade-offs is fundamental to explaining the diversity of life-history strategies in nature, and determining the genetic basis of trade-offs can identify how evolutionary constraint maintains life-history variation. Humans have evolved an unusual life-history compared to other primates, characterized by the menopause and long female post-reproductive lifespan (PRL). These have been hypothesized to evolve to enable (i) reduced reproduction when the costs of reproducing exceed the benefits, and (ii) enhanced grandchild survival. Previous tests of these hypotheses have examined phenotypic correlations between female reproductive rate and (i) PRL and (ii) offspring survival. However, environmental effects can mask genetic associations, and the direction and magnitude of these genetic correlations must be examined to determine the evolutionary potential of such traits. Using genealogical data from preindustrial Finnish church records for eight populations, we applied a multivariate quantitative genetic framework to examine the genetic basis of female reproductive rate, measured by inter-birth interval (IBI). We examined how additive genetic effects on IBI changed with age, and how age-specific genetic effects varied across environmental conditions. We determined the genetic trade-offs between IBI and both PRL and offspring survival, and how these trade-offs varied across ages and environments. Pilot analyses on four populations show a genetic basis to all traits, and suggest that genetic trade-offs between IBI and the other traits increased with age in poor environmental conditions, but were weak and age-independent in good conditions. IBI and PRL were positively related to lifetime fitness, suggesting that genetic trade-offs act as an evolutionary constraint. Our results will reveal new insight into human life-history evolution and generally highlight the fact that genetic correlations between traits may be age- and environment-dependent.
Social role specialisation promotes cooperation (video)
Author(s): Harrison, F, Székely, T, Liker, A, Barta, Z
Understanding the evolution of cooperation is crucial for understanding the evolution of breeding systems. An assumption implicit in almost all cooperation research is that cooperative behaviour in one specific ecological task evolves independently of other such tasks; however, this is often unlikely to be true. We use an individual-based simulation to relax this assumption, using biparental care as a model of cooperative behaviour. We show that synergistic costs of investing in two distinct care tasks, or a negligible sex-based asymmetry in their costs, select for sex-based task specialisation and stabilise cooperation between parents. Cooperation persists in spite of intense sexual selection and sex-biased mortality. Remarkably, with increased levels of cooperation, population size is also increased. We therefore show that ignoring the multivariate tasks animals face in nature leads to restrictive predictions of the ecological and demographic conditions under which biparental care in particular, and cooperation in general, are maintained.
Evolutionary history of the 17q21 human polymorphic inversion
Author(s): Alves, JMF, Lopes, A, Heutink, P, Chikhi, L, Amorim, A
With the aid of novel and powerful molecular biology techniques the study of the structural plasticity of the genome has gained momentum, and one particular subtype of chromosomal rearrangement – inversions – was recently found to be far more common than predicted from classical cytogenetics. Moreover, large inversions have been identified at high frequency in some human populations.
One particularly large inversion (900 kb) described in humans and several Great Apes, namely 17q21, has been shown to exhibit ‘frozen’ haplotypes (H1 and H2) which were originally identified by specific mutations and by their opposite orientations. The fact that they accumulate mutations independently is not necessarily surprising since recombination is expected to be limited between inverted regions. However, three surprising results were also found (i) age estimates of the inverted-associated haplotype (H2) are in the order of magnitude of millions of years, and (ii) the frequency of the inverted haplotypes vary between 5 and 35% in Europe only, (iii) cases were found in which the inversion status was in contradiction with the molecular haplotype, i.e. some H2 haplotypes (as defined by specific mutations) were in the same orientation as H1.
These results suggest that (i) the inversion might be recurrent despite its size, or (ii) the polymorphism was kept during a large evolutionary timescale and resisted various speciation processes since it is observed in other Apes.
In order to clarify the complex history of 17q21 human polymorphic inversion we are merging NGS data from 14 populations with cytogenetic (e.g. Fluorescent in situ hybridization) and molecular techniques. Furthermore, we will apply population genetics approaches to compare different evolutionary models.