Birth order and male androphilia in Samoan fa'afafine

The manner in which male androphilia is publicly expressed varies cross-culturally. As such, it is unclear whether distinct or common underlying causal processes characterize male androphilia in different cultures. Establishing the existence of cross-cultural universals in male androphilia is one means of ascertaining whether common biological bases underlie this phenomenon despite its culturally distinct forms. The evidence that the number of older biological brothers increases the odds of androphilia in later-born males has been well documented for Western samples (i.e. the fraternal birth order effect); but there is little evidence for this effect in non-Western samples. Here, we compare the birth order of androphilic males (i.e. fa'afafine) and gynephilic males from the politically autonomous Polynesian nation of Independent Samoa. Results indicate that relative to gynephilic males, fa'afafine tend to have more siblings and are generally later born when birth order is quantified using Slater, fraternal and sororal indices. More specifically, fa'afafine tend to have a greater number of older brothers, older sisters and younger brothers. We discuss the observed effects in relation to the differing reproductive patterns exhibited by the mothers of fa'afafine and gynephilic males, and to existing social and biological theories for sexual orientation.     

Kin selection and ethnic group selection

Ethnicity looks something like kinship on a larger scale. The same math can be used to measure genetic similarity within ethnic/racial groups and relatedness within families. For example, members of the same continental race are about as related (r = 0.18–0.26) as half-siblings (r = 0.25). However (contrary to some claims) the theory of kin selection does not apply straightforwardly to ethnicity, because inclusive fitness calculations based on Hamilton's rule break down when there are complicated social interactions within groups, and/or groups are large and long-lasting. A more promising approach is a theory of ethnic group selection, a special case of cultural group selection. An elementary model shows that the genetic assimilation of a socially enforced cultural regime can promote group solidarity and lead to the regulation of recruitment to groups, and to altruism between groups, based on genetic similarity – in short, to ethnic nepotism. Several lines of evidence, from historical population genetics and political psychology, are relevant here.     

植物的亲缘选择

亲缘选择是指在一个随机交配群体中的个体基于亲缘关系而以一种非随机性的方式相互作用,其作用结果是亲缘个体得到更大的广义适合度。综述了亲缘选择和亲缘竞争两种观点以及各自的试验支持证据;分析了导致亲缘选择试验结果出现分歧的原因,认为这主要是由于对亲缘选择理解上的模糊以及试验设计的不严谨所致。植物间的亲缘选择研究不仅相对较少,对亲缘选择的机制研究更为欠缺,这就造成了目前对此问题在科学认识上出现不少盲点。综合前期研究,提出今后对亲缘选择的研究应该首先界定"亲缘"程度,同时改良试验设计方案,选择多种不同生境下的物种对亲缘选择进行深入研究,并且考虑环境因子对植物亲缘选择的影响。同时,对植物亲缘识别机制的研究应该从生理生化方面出发,通过定性定量地分析探索植物根系分泌物在植物亲缘识别中的作用和作用途径。     

Kin selection in age-structured populations

There have been several discussions in the literature as to how to weight interactions between individuals of different ages in models of kin selection. It has commonly been assumed that the reproductive value of a given age is the most appropriate weight, for the purpose of calculating its contribution to inclusive fitness. This paper analyses a model of kin selection in an age-structured population. It is shown that reproductive value is relevant to behavioural interactions involving effects on survival, although the reproductive value of a given age does not provide an exact weighting of its fitness contribution in either discrete- or continuous-time populations. Reproductive value is not relevant to interactions involving effects on fecundity. The results are discussed in relation to observations on behavioural asymmetries involving age differences.     

Kin selection and conflict in seed maturation

There are four genetically distinct components in the developing seeds of flowering plants: maternal sporophyte, gametophyte, endosperm, and embryo. Each component can potentially influence the quantity or quality of nutrients provided to the embryo of its seed, thereby reducing the amount available to embryos in other seeds of that plant. The theory of kin selection predicts that each component will be selected to favor its own embryo over the other embryos to the extent that it is more closely related to its own. Under this criterion, an embryo should be selected to try to acquire more nutrients than the endosperm should be selected to provide, the endosperm should try to supply more than the gametophyte should, and the gametophyte more than the parent sporophyte. Evidence for this conflict of interests is found in the higher frequency of endopolyploidy, nutrient-absorbing haustoria, and food storage tissues in the embryo and endosperm than in the gametophyte of maternal tissues.This theory also suggests how the gametophyte, which is the nurse tissue of gymnosperm seeds, was displaced from this role in the flowering plants by an endosperm initiated by a secondary fertilization. “Neoteny” in the pro-angiosperms created conditions in which (1) an endosperm initiated by double fertilization would be more closely related to the embryo than is the gametophyte and (2) the endosperm would be formed early enough to be of significant aid to the embryo.If this theory is correct it (1) requires a different approach to the study of seed morphology and physiology, (2) increases the plausibility of arguments that flowering plants are a polyphyletic group, (3) provides evidence that parents cannot always control the outcome of conflict with their offspring, and (4) forges a conceptual link in our understanding of the evolution of social interactions in plants and animals.     

Kin selection does not explain male aggregation at leks of 4 manakin species

In lek-mating systems, males aggregate at display arenas andfemales visit solely for the purpose of mating. This breedingsystem is characterized by high variance in male mating successwith one male often receiving most copulations. High reproductiveskew among males has led to question why males join leks whentheir chances of reproductive success are so low. Kin selectionhas been invoked as a mechanism to explain the evolution oflekking behavior, whereby nonreproducing but genetically relatedmales gain indirect inclusive-fitness benefits. Evidence forkin selection among lek-mating birds is, however, mixed. Here,we show that kin selection is unlikely to be an important explanationfor evolution of lekking behavior in manakins (Aves: Pipridae).We found that for 4 species chosen from several major cladeswithin Pipridae, males within leks were not significantly morerelated than expected from random assortment of males in thepopulation. This means that nonreproducing males do not gainindirect inclusive-fitness benefits by joining leks. This resultsuggests alternative mechanisms must be invoked to explain theevolution of lek-mating systems in manakins.     

Validite D'Orbitolina subconcava Leymerie, 1878

A detailed revision of the type localities of a new species, Orbitolina subconcava, described by A. Leymerie, has permitted the authors to demonstrate the invalidity of this taxa. As a result of R.C. Douglass' work (3), O. subconcava LEYM. sensu SCHROEDER [(4)–(6)] must be a junior synonym of Orbitolina (Mesorbitolina) texana (ROEMER, 1852); however the previous investigations of R.C. Douglass (3) should be confirmed by a further revision of the type material of F. Roemer.     

Kin selection in density regulated populations.

The process of kin selection has both intra- and inter-group components (Hamilton, 1975, in: Biosocial Anthropology Wade, 1980). Group advantageous characteristics can evolve when inter-group differences in fertility are sufficiently great to overcome any within-group disadvantage of the trait. The potential magnitude of inter-group differences in fertility is determined largely by the way a population is regulated. Inter-group differences decrease as the spatial scale over which a population is regulated becomes increasingly localized. The present paper extends previous work by Boyd (1982, Anim. Behav. 30, 972-982) on the quantitative relation between kin selection and density regulation. A simple genetic model is employed to examine the conditions under which the interaction of local density regulation and kin selection can maintain a stable polymorphism. The ecological factors determining the spatial and temporal scale of density regulation are discussed. Finally, the results are applied to two biological cases in which local density regulation may be influencing the direction of phenotypic plasticity in group advantageous characters.     

Kin selection and the evolution of virulence

Social interactions between conspecific parasites are partly dependent on the relatedness of interacting parasites (kin selection), which, in turn, is predicted to affect the extent of damage they cause their hosts (virulence). High relatedness is generally assumed to favour less competitive interactions, but the relationship between relatedness and virulence is crucially dependent on the social behaviour in question. Here, we discuss the rather limited body of experimental work that addresses how kin-selected social behaviours affect virulence. First, if prudent use of host resources (a form of cooperation) maximizes the transmission success of the parasite population, decreased relatedness is predicted to result in increased host exploitation and virulence. Experimental support for this well-established theoretical result is surprisingly limited. Second, if parasite within-host growth rate is a positive function of cooperation (that is, when individuals need to donate public goods, such as extracellular enzymes), virulence is predicted to increase with increasing relatedness. The limited studies testing this hypothesis are broadly consistent with this prediction. Finally, there is some empirical evidence supporting theory that suggests that spiteful behaviours are maximized at intermediate degrees of relatedness, which, in turn, leads to minimal virulence because of the reduced growth rate of the infecting population. We highlight the need for further thorough experimentation on the role of kin selection in the evolution of virulence and identify additional biological complexities to these simple frameworks.     

Kin-directed altruism and the evolution of male androphilia among Istmo Zapotec Muxes

Male androphilia (i.e., sexual attraction and arousal to adult males) is considered an evolutionary puzzle because it reduces direct reproduction, but is influenced by genetic factors, reliably occurs across cultures, and has persisted over evolutionary time. The kin selection hypothesis states that genes for male androphilia can be maintained in a population if the costs of not reproducing directly are offset by enhancing the reproduction of kin. We tested this hypothesis among the Istmo Zapotec of Oaxaca, Mexico, where transgender and cisgender androphilic males are known as muxe gunaa and muxe nguiiu, respectively. We compared altruistic tendencies towards kin and non-kin children between muxe nguiiu (n = 106), muxe gunaa (n = 106), gynephilic men (i.e., men sexually attracted and aroused to adult females; n = 172), and androphilic women (n = 130). We also assessed whether the sisters of muxes (n = 96) reported receiving more childcare support from their muxe sibling compared to women with only gynephilic brothers (n = 65). The results showed that cisgender and transgender muxes reported more kin-directed altruistic tendencies than men. Muxe nguiiu also reported more kin-directed altruistic tendencies than women. When controlling for altruistic tendencies towards non-kin children, both muxe types exhibited more kin-directed altruistic tendencies than men and women. Women with muxe siblings reported receiving more childcare support from these relatives compared to women with only gynephilic brothers. These findings provide support for the kin selection hypothesis and highlight its potential role in elucidating the evolutionary paradox of male androphilia.     

Kin selection,species richness and community

Can evolutionary and ecological dynamics operating at one level of the biological hierarchy affect the dynamics and structure at other levels? In social insects, strong hostility towards unrelated individuals can evolve as a kin-selected counter-adaptation to intraspecific social parasitism. This aggression in turn might cause intraspecific competition to predominate over interspecific competition, permitting coexistence with other social insect species. In other words, kin selection—a form of intra-population dynamics—might enhance the species richness of the community, a higher-level structure. The converse effect, from higher to lower levels, might also operate, whereby strong interspecific competition may limit the evolution of selfish individual traits. If the latter effect were to prove more important, it would challenge the common view that intra-population dynamics (via individual or gene selection) is the main driver of evolution.     

Kin selection and natal dispersal in an age-structured population

We examine the effect of iteroparity on the evolution of dispersal for a species living in a stable but fragmented habitat. We use a kin selection model that incorporates the effects of demographic stochasticity on the local age structure and age-specific genetic identities. We consider two cases: when the juvenile dispersal rate is allowed to change with maternal age and when it is not. In the latter case, we find that the unconditional evolutionarily stable dispersal rate increases when the adult survival rate increases. Two antagonistic forces act upon the evolution of age-specific dispersal rates. First, when the local age structure varies between patches of habitat, the intensity of competition between adults and juveniles in the natal patch is, on average, lower for offspring born to older senescent mothers. This selects for decreasing dispersal with maternal age. Second, offspring born to older parents are on average more related to other juveniles in the same patch and they experience a higher intensity of kin competition, which selects for increasing dispersal with maternal age. We show that the evolutionary outcome results from a balance between these two opposing forces, which depends on the amount of variance in age structure among sub-populations.     

Kin selection,kin avoidance and correlated strategies

Summary Kin selection of correlated strategies is examined for both weak and strong altruism under simple haploid inheritance. While kin assortment enhances the range of evolutionary stability for (strongly altruistic) correlated strategies (defined herein), kin avoidance is possible under a weakly altruistic correlated strategy. When social competition induces role assignments of variable fitness, group mates may prefer association with non-relatives. Even when group life is mandatory, an individual may accept the risk of abandonment (and reproductive death) rather then associate with kin: a competitive superior may behave altruistically by permitting competitively inferior kin to emigrate. Thus, kin selection and social competition are not necessarily mutually supportive processes within groups. I conclude by interpreting dominance as a strongly altruistic correlated strategy in two social hymenopteran contexts.     

Kin selection and the evolution of sexual conflict

Males and females do not always share the same evolutionary interests. This is particularly true in the case of multiple mating, where male–male competition can often lead to adaptations that are harmful to the female, and females can evolve counter adaptations to reduce the benefits males gain from such traits. Although social evolution has made substantial progress from kin selection theory, most studies of sexual conflict have ignored the effects of genetic relatedness. Here, I use a model of male harm and female resistance to investigate how kin selection affects the evolution of sexual conflict. Building on models of social evolution, I show that relatedness inhibits sexual conflict, in terms of male harm, whereas it has no effect on the evolution female resistance. This study examines a previously neglected mechanism that can potentially help to resolve sexual conflict over mating and highlights the potential importance of considering relatedness in empirical studies of sexual conflict.