Inbreeding avoidance through kin recognition: choosy females boost male dispersal.

Inbreeding avoidance is predicted to induce sex biases in dispersal. But which sex should disperse? In polygynous species, females pay higher costs to inbreeding and thus might be expected to disperse more, but empirical evidence consistently reveals male biases. Here, we show that theoretical expectations change drastically if females are allowed to avoid inbreeding via kin recognition. At high inbreeding loads, females should prefer immigrants over residents, thereby boosting male dispersal. At lower inbreeding loads, by contrast, inclusive fitness benefits should induce females to prefer relatives, thereby promoting male philopatry. This result points to disruptive effects of sexual selection. The inbreeding load that females are ready to accept is surprisingly high. In absence of search costs, females should prefer related partners as long as delta<r/(1+r) where r is relatedness and delta is the fecundity loss relative to an outbred mating. This amounts to fitness losses up to one-fifth for a half-sib mating and one-third for a full-sib mating, which lie in the upper range of inbreeding depression values currently reported in natural populations. The observation of active inbreeding avoidance in a polygynous species thus suggests that inbreeding depression exceeds this threshold in the species under scrutiny or that inbred matings at least partly forfeit other mating opportunities for males. Our model also shows that female choosiness should decline rapidly with search costs, stemming from, for example, reproductive delays. Species under strong time constraints on reproduction should thus be tolerant of inbreeding.

Age-related change in melanin-based coloration of Barn owls (Tyto alba): females that become more female-like and males that become more male-like perform better

Ornament expression fluctuates with age in many organisms. Whether these changes are adaptively plastic is poorly known. In order to understand the ultimate function of melanin-based ornaments, we studied their within-individual fluctuations and their covariation with fitness-related traits. In barn owls (Tyto alba), individuals vary from reddish-brown pheomelanic to white and from immaculate to marked with black eumelanic spots, males being less reddish and less spotted than females. During the first molt, both sexes became less pheomelanic, females displayed larger spots and males fewer spots, but the extent of these changes was not associated with reproduction. At subsequent molts, intra-individual changes in melanin-based traits covaried with simultaneous reproduction changes. Adult females bred earlier in the season and laid larger eggs when they became scattered with larger spots, while adults of both sexes produced larger broods when they became whiter. These results suggest that the production of melanin pigments and fitness-related life history traits are concomitantly regulated in a sex-specific way.

Corticosterone shifts reproductive behaviour towards self-maintenance in the barn owl and is linked to melanin-based coloration in females.

Trade-offs between the benefits of current reproduction and the costs to future reproduction and survival are widely recognized. However, such trade-offs might only be detected when resources become limited to the point where investment in one activity jeopardizes investment in others. The resolution of the trade-off between reproduction and self-maintenance is mediated by hormones such as glucocorticoids which direct behaviour and physiology towards self-maintenance under stressful situations. We investigated this trade-off in male and female barn owls in relation to the degree of heritable melanin-based coloration, a trait that reflects the ability to cope with various sources of stress in nestlings. We increased circulating corticosterone in breeding adults by implanting a corticosterone-releasing-pellet, using birds implanted with a placebo-pellet as controls. In males, elevated corticosterone reduced the activity (i.e. reduced home-range size and distance covered within the home-range) independently of coloration, while we could not detect any effect on hunting efficiency. The effect of experimentally elevated corticosterone on female behaviour was correlated with their melanin-based coloration. Corticosterone (cort-) induced an increase in brooding behaviour in small-spotted females, while this hormone had no detectable effect in large-spotted females. Cort-females with small eumelanic spots showed the normal body-mass loss during the early nestling period, while large spotted cort-females did not lose body mass. This indicates that corticosterone induced a shift towards self-maintenance in males independently on their plumage, whereas in females this shift was observed only in large-spotted females.

Why do females mate with multiple males ? The sexually selected sperm hypothesis

One debated issues in evolutionary biology is, why in many species females mate with multiple males. Several hypotheses have been put forward, yet the benefits of multiple mating (here defined as mating with several males) remain unclear in many cases. The sperm sexual selection (SSS) hypothesis has been developed to account for the widespread occurrence of multiple mating in females. It argues that multiple mating by females may rapidly spread, when initially a small fraction of the females mate multiply, and if there is a heritable difference among males in one or several of the four characteristics: (1) the quantity of sperm they produce; (2) the success of their sperm in reaching and fertilizing an egg; (3) their ability to displace the sperm that females stored during previous mating; and (4) their ability to prevent any other male from subsequently introducing sperm (e.g., differential efficiency of mating plugs).

A higher mutational burden in females supports a "female protective model" in neurodevelopmental disorders.

Increased male prevalence has been repeatedly reported in several neurodevelopmental disorders (NDs), leading to the concept of a "female protective model." We investigated the molecular basis of this sex-based difference in liability and demonstrated an excess of deleterious autosomal copy-number variants (CNVs) in females compared to males (odds ratio [OR] = 1.46, p = 8 × 10(-10)) in a cohort of 15,585 probands ascertained for NDs. In an independent autism spectrum disorder (ASD) cohort of 762 families, we found a 3-fold increase in deleterious autosomal CNVs (p = 7 × 10(-4)) and an excess of private deleterious single-nucleotide variants (SNVs) in female compared to male probands (OR = 1.34, p = 0.03). We also showed that the deleteriousness of autosomal SNVs was significantly higher in female probands (p = 0.0006). A similar bias was observed in parents of probands ascertained for NDs. Deleterious CNVs (>400 kb) were maternally inherited more often (up to 64%, p = 10(-15)) than small CNVs < 400 kb (OR = 1.45, p = 0.0003). In the ASD cohort, increased maternal transmission was also observed for deleterious CNVs and SNVs. Although ASD females showed higher mutational burden and lower cognition, the excess mutational burden remained, even after adjustment for those cognitive differences. These results strongly suggest that females have an increased etiological burden unlinked to rare deleterious variants on the X chromosome. Carefully phenotyped and genotyped cohorts will be required for identifying the symptoms, which show gender-specific liability to mutational burden.

No evidence that within-group male relatedness reduces harm to females in Drosophila.

Conflict between males and females over whether, when, and how often to mate often leads to the evolution of sexually antagonistic interactions that reduce female reproductive success. Because the offspring of relatives contribute to inclusive fitness, high relatedness between rival males might be expected to reduce competition and result in the evolution of reduced harm to females. A recent study investigated this possibility in Drosophila melanogaster and concluded that groups of brothers cause less harm to females than groups of unrelated males, attributing the effect to kin selection. That study did not control for the rearing environment of males, rendering the results impossible to interpret in the context of kin selection. Here, we conducted a similar experiment while manipulating whether males developed with kin prior to being placed with females. We found no difference between related and unrelated males in the harm caused to females when males were reared separately. In contrast, when related males developed and emerged together before the experiment, female reproductive output was higher. Our results show that relatedness among males is insufficient to reduce harm to females, while a shared rearing environment - resulting in males similar to or familiar with one another - is necessary to generate this pattern.

The ontogeny of sexual size dimorphism of a moth: when do males and females grow apart?

Sexual dimorphism in body size (sexual size dimorphism) is common in many species. The sources of selection that generate the independent evolution of adult male and female size have been investigated extensively by evolutionary biologists, but how and when females and males grow apart during ontogeny is poorly understood. Here we use the hawkmoth, Manduca sexta, to examine when sexual size dimorphism arises by measuring body mass every day during development. We further investigated whether environmental variables influence the ontogeny of sexual size dimorphism by raising moths on three different diet qualities (poor, medium and high). We found that size dimorphism arose during early larval development on the highest quality food treatment but it arose late in larval development when raised on the medium quality food. This female-biased dimorphism (females larger) increased substantially from the pupal-to-adult stage in both treatments, a pattern that appears to be common in Lepidopterans. Although dimorphism appeared in a few stages when individuals were raised on the poorest quality diet, it did not persist such that male and female adults were the same size. This demonstrates that the environmental conditions that insects are raised in can affect the growth trajectories of males and females differently and thus when dimorphism arises or disappears during development. We conclude that the development of sexual size dimorphism in M. sexta occurs during larval development and continues to accumulate during the pupal/adult stages, and that environmental variables such as diet quality can influence patterns of dimorphism in adults.

Changes in insulin secretion and glucose metabolism induced by dexamethasone in lean and obese females

Résumé But: Chez les individus sveltes et en bonne santé, les modifications de la sensibilité à l'insuline secondaires à l'administration de dexaméthasone pendant deux jours sont compensées par une modification de la sécrétion d'insuline, permettant le maintien de l'homéostasie glucidique. Cette étude évalue les modifications du métabolisme glucidique et de la sécrétion d'insuline induites par une administration limitée de dexaméthasone chez les femmes obèses. Méthode de recherche: Onze femmes obèses ayant une tolérance au glucose normale ont été étudiées à deux reprises, 1° sans dexaméthasone et 2° après deux jours d'administration de dexaméthasone à faible dose. Un clamp hyperglycémique comportant deux plateaux (taux plasmatique de glucose à 7.5, respectivement 10 mM) avec du glucose marqué (6.6 ²H2 glc) a été utilisé pour déterminer la sécrétion d'insuline et le métabolisme du glucose du corps entier. Les résultats ont été comparés à ceux d'un groupe de huit femmes sveltes. Résultats : Sans dexaméthasone, les femmes obèses avaient un taux d'insuline plasmatique supérieur à jeun, durant le premier pic de sécrétion d'insuline, et aux deux plateaux hyperglycémiques. Elles avaient toutefois un métabolisme glucidique normal comparé à celui des femmes sveltes, ce qui indique une compensation adéquate. Après administration de la dexaméthasone, les femmes obèses avaient une augmentation du taux d'insuline plasmatique de 66 à 92%, mais une baisse de stockage du glucose de 15.4%. Ceci contrastait avec l'augmentation du taux d'insuline plasmatique de 91 à 113% chez les femmes sveltes et l'absence de changement de stockage du glucose du corps entier. Discussion : L'administration de dexaméthasone conduit à une baisse significative du stockage du glucose du corps entier pour une glycémie fixée chez les femmes obèses mais non chez les femmes sveltes. Ceci indique que les femmes obèses sont incapables d'accroître adéquatement leur sécrétion d'insuline. Abstract: Objective: In healthy lean individuals, changes in insulin sensitivity occurring as a consequence of a 2-day dexamethasone administration are compensated for by changes in insulin secretion, allowing glucose homeostasis to be maintained. This study evaluated the changes in glucose metabolism and insulin secretion induced by short-term dexamethasone administration in obese women. Research Methods and Procedures: Eleven obese women with normal glucose tolerance were studied on two occasions, without and after 2 days of low-dose dexamethasone administration. A two-step hyperglycemic clamp (7.5 and 10 mr1/1 glucose) with 6,6 2H2 glucose was used to assess insulin secretion and whole body glucose metabolism. Results were compared with those obtained in a group of eight lean women. Results: Without dexamethasone, obese women had higher plasma insulin concentrations in the fasting state, during the first phase of insulin secretion, and at the two hyperglycemic plateaus. However, they had normal whole body glucose metabolism compared with lean women, indicating adequate compensation. After dexamethasone, obese women had a 66% to 92% increase in plasma insulin concentrations but a 15.4% decrease in whole body glucose disposal. This contrasted with lean women, who had a 91% to 113% increase in plasma insulin concentrations, with no change in whole body glucose disposal. Discussion: Dexamethasone administration led to a significant reduction in whole body glucose disposal at fixed glycemia in obese but not lean women. This indicates that obese women are unable to increase their insulin secretion appropriately.

Having a good relationship with their mother: a protective factor against sexual risk behavior among adolescent females?

STUDY OBJECTIVE: To assess whether having a good relationship with their mother was a protective factor against risky sexual behavior for female adolescents and whether it was independent of family structure. DESIGN: Cross-sectional survey of in-school adolescents aged 14-19 years. SETTING: Catalonia, in northeast Spain. PARTICIPANTS: A total of 3677 females divided according on whether they had a good (n=3335) or a bad (n=342) relationship with their mother. MAIN OUTCOME MEASURES: Rates of sexual activity and sexual behavior. RESULTS: Adolescents in the good relationship group were significantly younger, more likely to live in an intact family, to have a good relationship with their father and siblings, and to talk about sexuality and their partner with their mother. They were also less likely to have ever had sexual intercourse. Among those sexually experienced, they were significantly older at first intercourse and less likely to have multiple partners or a history of STI. After adjusting for potential confounders, females in the good relationship group were less likely to be sexually active and to have had multiple partners, independently of family structure. CONCLUSIONS: Having a good relationship with their mother is a protective factor against sexual intercourse and having multiple sexual partners independently of family structure. Communication between generations and having a good relationship with their father and siblings also play an important role.

Markedly blunted metabolic effects of fructose in healthy young females compared to males

ABSTRACT : Objective: to compare the metabolic effects of fructose in healthy males and females Research Design And Methods: Fasting metabolic profile and hepatic insulin sensitivity were assessed by means of a hyperglycemic clamp in 16 healthy young males and female subjects after a 6-day fructose overfeeding Results: Fructose overfeeding increased fasting triglyceride concentrations by 71 % in males vs 16% in females (p<0.05). Endogenous glucose production was increased by 12%, alanin aminotransferase concentration was increased by 38%, and fasting insulin concentrations was increased by 14% after fructose overfeeding in males (all p<0.05), but were not significantly altered in females. Fasting plasma free fatty acids and lipid oxidation were inhibited by fructose in males, but not in females Conclusions: Short term fructose overfeeding produces hypertriglyceridemia and hepatic insulin resistance in males, but these effects are markedly blunted in healthy young females. Rapport de synthèse : Objectif : De récentes études ont démontré que l'ingestion de hautes doses de fructose modifie certains paramètres métaboliques. Peu d'entre elles se sont cependant intéressées à déterminer si les effets métaboliques du fructose étaient dépendants du sexe. L'objectif de la présente étude était donc de comparer les effets du fructose chez des volontaires sains, hommes et femmes. Méthode : Le profil métabolique à jeun et la sensibilité hépatique à l'insuline ont été déterminés au moyen d'un clamp hyperglycémique chez un collectif de 16 jeunes hommes et femmes après une période de 6 jours de régime riche en fructose. Résultats : La concentration de triglycérides à jeun après ce régime était augmentée de 71% chez les hommes contre 16% chez les femmes (p<0.05). La production endogène de glucose était augmentée de 12%, l'alanine aminotransférase de 38% et la concentration d'insuline à jeun de 14% chez les hommes (p<0.05 pour tous). Chez les femmes, ces paramètres n'étaient au contraire pas significativement modifiés. L'oxydation des acides gras libres et des lipides à jeun était inhibée par le fructose chez les hommes, mais pas chez les femmes. Conclusion : Ces résultats indiquent qu'une suralimentation de courte durée en fructose induit chez l'homme une hypertriglycéridémie et une résistance hépatique à l'insuline, alors que chez la femme jeune, ces effets sont nettement atténués. Il reste à éclaircir de manière plus approfondie les mécanismes sous-tendant ces différences.

The contribution of a pollinating seed predator to selection on Silene latifolia females.

Interactions, antagonistic or mutualistic, can exert selection on plant traits. We explored the role of Hadena bicruris, a pollinating seed predator, as a selective agent on its host, the dioecious plant Silene latifolia. We exposed females from artificial-selection lines (many, small flowers (SF) vs. few, large flowers (LF)) to this moth. Infestation did not differ significantly between lines, but the odds of attacked fruits aborting were higher in SF females. We partitioned selection between that caused by moth attack and that resulting from all other factors. In both lines, selection via moth attack for fewer, smaller flowers contrasted with selection via other factors for more flowers. In LF females, selection via the two components was strongest and selection via moth attack also favoured increased fruit abortion. This suggests that the moths act as more of a selective force on flower size and number via their predating than their pollinating role.

Altruism, spite and choosy females

Natural selection favours the genes which are able to introduce replicates of themselves in the next generation with higher certainty than do rival genes (Hamilton 1963). The fitness of an individual, it?s ability to produce future parents, depends on it?s own behaviour as well as on the behaviour of other individuals in the population. For instance, the intensity of competition an individual experience depends on the exploitation of resources by neighbours. The fitness is thus frequency dependent on what neighbours do. Behaviours can be classified according to the costs and benefits they have on the fitness of the behaver and it?s neighbours (Hamilton 1964, Hamilton 1975). According to this classification there exist four distinct social behaviours. (1) A gene confering the ability to use a new ressource is called selfish because it has a positive e_ect on the bearer of the gene but a negative e_ect on neighbours by the concomitant increase in competition. (2) An altruistic behaviour is defined as an action where an individual increases the fitness of a neighbour at the expense of it?s own. The e_ect is deleterious for the actor but positive for the receptor. (3) More surprinsingly, an individual might sacrifice a fraction of it?s ressources to harm another at no direct benefits. This spitefull behaviour incurs a cost for the actor but is also deleterious for the receptor. (4) Finally a cooperative behaviour breeds benefits for both actors and neighbours. In this thesis I will continue on the path traced by numerous evolutionnary biologist which attempt to fine tune our understanding of the evolution of social behaviours since Hamilton?s foundation (1963, 1964). A critical development over the last 40 years has been the realisation that competition between kin can partly or completely cancel out the role of relatedness as an agent favouring altruism (Wilson et al., 1992; Taylor, 1992a,b). Of importance is thus to determine the scale at which competition and altruism occur. One mechanism avoiding the complete dilution of relatedness by competition is the conditionnal expression of the social behaviors. Focus will be given in this thesis at the role played by di_erent recognition mechanism in paving the way to altruism (Komdeur and Hatchwell, 1999) when the population has a spatial structure. Further, the evolution of spite will also be considered in these settings. The thesis is fractionated into two parts. First, di_erent models promoting altruism cooperation and spite will be compared under the same theoretical umbrella. This is a rather informal and more personnal part of my thesis. It also serve as a justification and basis to "Altruism among kin and non-kin individuals" which is an article attempting to clas- sify the mechanisms leading to altruism and cooperation. Second, in the annexe, there are three research papers about kin selection, altruism and dispersal: "Is sociality driven by the costs of dispersal or the benefits of philopatry?: A role for kin-discrimination mechanism", "Altruism, dispersal and phenotype kin recognition" and "Inbreeding avoidance through kin recognition: choosy female boost male dispersal" this last paper incorporates kin recognition as an agent favoring sex-biased dispersal.

Conflict over multiple-partner mating between males and females of the polygynandrous common lizards.

The optimal number of mate partners for females rarely coincides with that for males, leading to a potential sexual conflict over multiple-partner mating. This suggests that the population sex ratio may affect multiple-partner mating and thus multiple paternity. We investigate the relationship between multiple paternity and the population sex ratio in the polygynandrous common lizard (Lacerta vivipara). In six populations the adult sex ratio was biased toward males, and in another six populations the adult sex ratio was biased toward females, the latter corresponding to the average adult sex ratio encountered in natural populations. In males the frequency and the degree of polygyny were lower in male-biased populations, as expected if competition among males determines polygyny. In females the frequency of polyandry was not different between treatments, and polyandrous females produced larger clutches, suggesting that polyandry might be adaptive. However, in male-biased populations females suffered from reduced reproductive success compared to female-biased populations, and the number of mate partners increased with female body size in polyandrous females. Polyandrous females of male-biased populations showed disproportionately more mating scars, indicating that polyandrous females of male-biased populations had more interactions with males and suggesting that the degree of multiple paternity is controlled by male sexual harassment. Our results thus imply that polyandry may be hierarchically controlled, with females controlling when to mate with multiple partners and male sexual harassment being a proximate determinant of the degree of multiple paternity. The results are also consistent with a sexual conflict in which male behaviors are harmful to females.