Hamilton's inclusive fitness in finite-structured populations

Hamilton''s formulation of inclusive fitness has been with us for 50 years. During the first 20 of those years attention was largely focused on the evolutionary trajectories of different behaviours, but over the past 20 years interest has been growing in the effect of population structure on the evolution of behaviour and that is our focus here. We discuss the evolutionary journey of the inclusive-fitness effect over this epoch, nurtured as it was in an essentially homogeneous environment (that of ‘transitive’ structures) having to adapt in different ways to meet the expectations of heterogeneous structures. We pay particular attention to the way in which the theory has managed to adapt the original constructs of relatedness and reproductive value to provide a formulation of inclusive fitness that captures a precise measure of allele-frequency change in finite-structured populations.     

Direct fitness or inclusive fitness: how shall we model kin selection?

Two standard mathematical formulations of kin-selection models can be found. Inclusive fitness is an actor-centred approach, which calculates the fitness effect on a number of recipients of the behaviour of a single actor. Direct fitness is a recipient-centred approach, which calculates the fitness effect on the recipient of the behaviour of a number of actors. Inclusive fitness offers us a powerful heuristic, of choosing behaviour to maximize fitness, but direct fitness can be mathematically easier to work with and has recently emerged as the preferred approach of theoreticians. In this paper, we explore the fundamental connection between these two approaches in both homogeneous and class-structured populations, and we show that under simple assumptions (mainly fair meiosis and weak selection) they provide equivalent formulations, which correspond to the predictions of Price's equation for allele frequency change. We use a couple of examples to highlight differences in their conception and formulation, and we briefly discuss a two-species example in which we have a class of 'actor' that is never a 'recipient', which the standard direct fitness method can handle but the usual inclusive fitness cannot.     

Genetic Markers in Primate Studies: Elucidating Behavior and Its Evolution

The application of genetic techniques has provided valuable new insights into primate evolution and behavior. Important techniques include the polymerase chain reaction (PCR), where in exponential amounts of a target DNA sequence are produced via enzymatic amplification. This allows DNA to be analyzed from fecal droppings, which is particularly beneficial in field studies. Fragments containing hypervariable microsatellites can be amplified and subsequently typed. Also parts of the mitochondrial DNA can be amplified and subsequently sequenced. These methods have been applied with great success to determine familial relationships and, on a smaller scale, relationships among lineages and social groups, and the redefinition of the interface between social behavior, social structure and population genetics. Moreover, it has become possible, to a degree, to study genetic variation as it relates directly to adaptive evolution, as the maintenance of genetic variation has become accessible to analysis.     

In vitro gametogenesis and reproductive cloning: Can we allow one while banning the other?

In vitro gametogenesis (IVG) is believed to be the next big breakthrough in reproductive medicine. The prima facie acceptance of this possible future technology is notable when compared to the general prohibition on human reproductive cloning. After all, if safety is the main reason for not allowing reproductive cloning, one might expect a similar conclusion for the reproductive application of IVG, since both technologies hold considerable and comparable risks. However, safety concerns may be overcome, and are presumably not the sole reason why cloning is being condemned. We therefore assess the non‐safety arguments against reproductive cloning, yet most of these can also be held against IVG. The few arguments that cannot be used against IVG are defective. We conclude from this that it will be hard to defend a ban on reproductive cloning while accepting the reproductive use of IVG.     

Decompositions of Price’s formula in an inhomogeneous population structure

The central tool for the study of allele frequency change due to selection is the remarkably simple but powerful formula of Price [Nature 227 (1970) 520] . Here, I provide what might be called a structural analysis of this formula. The formula essentially accumulates the average allele frequency change over many instances of a fitness‐determining interaction, but there are different ways of organizing this average and these lead to quite different computational algorithms. I present three of these: an analysis by population state, an analysis by recipient and an analysis by actor. A comparison of these can lead to a heightened understanding of the different factors behind selective allele frequency change. In particular, I pay attention to the effects of structural inhomogeneity on reproductive value (RV) and emphasize that Price’s formula measures RV‐weighted allele frequency change. I examine in detail a simple example as a crucial way of cementing the different theoretical pathways. My aim was to produce a simple transparent presentation and therefore I work with a simple population structure and have omitted a number of technical details that are found elsewhere.     

Colony genetic structure in a facultatively eusocial hover wasp

The degree of genetic heterogeneity among the individuals inan animal society depends on the society's genetic structure.Genetic heterogeneity, in turn, means that group members willdiffer in their reproductive objectives and conflicts over reproductionmay arise. The resolution of these conflicts may be reflectedin the way that reproduction is partitioned between potentialreproductives. We used 5 microsatellite loci to investigategenetic structure and reproductive skew in 17 nests of the Malaysianhover wasp, Parischnogaster alternata. Parischnogaster alternatacolonies are small (1–10 females), and all adult colonymembers are capable of mating and producing offspring. We foundthat colonies tended to consist of closely related individualsand that at any one time the production of both female and maleoffspring was nearly always monopolized by a single dominantfemale, despite considerable variation between nests in parameterspredicted to affect skew. Subordinate females that remainedin their natal colonies obtained indirect fitness benefits byhelping to raise offspring to which they were related. Subordinatefemales also appeared to be positioned within an age-based queuefor inheritance of the dominant egg-laying position. We suggestthat the high skew in P. alternata may result from strong ecologicalconstraints on solitary nesting, high relatedness, and a relativelyhigh probability that subordinates will eventually inherit theposition of dominance.     

Life history interactions with environmental conditions in a host–parasite relationship and the parasite's mode of transmission

The microsporidian parasite Edhazardia aedis is capable of vertical or horizontal transmission among individuals of its host, the mosquito Aedes aegypti, and either mode of transmission may follow the other. We show that following the horizontal infection of host larvae, the parasite's subsequent mode of transmission largely depends on host life history traits and their responses to different environmental conditions. In two experiments the intensity of larval exposure to infection and the amount of food available to them were simultaneously manipulated. One experiment followed the dynamics of host development and the parasite's production of spores while the other estimated the outcome of their relationship. Host life history traits varied widely across treatment conditions while those of the parasite did not. Of particular importance was the host's larval growth rate. Horizontal rather than vertical transmission by the parasite was more likely as low food and high dose conditions favoured slower larval growth rates. This pattern of transmission behaviour with host growth rate can be considered in terms of reproductive value: the potential vertical transmission success that female mosquitoes offer the parasite decreases as larval growth rates slow and makes them more attractive to exploitation for horizontal transmission (requiring host mortality). However, the lack of variation in the parasite's life history traits gave rise in some conditions to low estimates for both its vertical and horizontal transmission success. We suggest that the unresponsive behaviour of the parasite's life history traits reflects a bet-hedging strategy to reduce variance in its overall transmission success in the unpredictable environmental conditions and host larval growth rates that this parasite encounters in nature.     

Philopatry and reproductive success in Bornean orang-utans (Pongo pygmaeus)

Behavioural observations suggest that orang-utans are semi-solitary animals with females being philopatric and males roaming more widely in search of receptive partners, leading to the prediction that females are more closely related than males at any given site. In contrast, our study presents evidence for male and female philopatry in the orang-utan. We examined patterns of relatedness and parentage in a wild orang-utan population in Borneo using noninvasively collected DNA samples from animals observed to defecate, and microsatellite markers to assess dispersal and mating strategies. Surprisingly, resident females were equally as related to other resident females (mean r(xy) = 0.303) as resident males were to other resident males (mean r(xy) = 0.305). Moreover, resident females were more related to each other and to the resident males than they were to nonresident females, and resident males were more related to each other (and resident females) than they were to nonresident males. We assigned genetic mothers to 12 individuals in the population, while sires could be identified for eight. Both flanged males and unflanged males achieved paternity, similar to findings reported for Sumatran orang-utans.     

太白红杉种群的生殖对策研究Ⅱ．生殖力和生殖值

研究了太白红杉种群的年龄结构、生殖年龄结构、生殖力和生殖值,分析了太白红杉种群的生殖适合度和生殖对策.结果如下(1)北坡和南坡两个种群的低龄级个体数都非常少,种群间的生育力差异不显著(P>0.05),但北坡太白红杉的生殖年龄比南坡大,平均生殖时间比南坡长,平均寿命也比南坡长.(2)北坡各龄级的生殖值比南坡高,剩余生殖值随年龄下降的速度比南坡小,北坡的生殖适合度比南坡高.(3)北坡第Ⅰ～Ⅶ龄级的剩余生殖值比南坡高,第Ⅶ龄级后由于下降速度较快,其值要比南坡小.     

Coevolution at multiple spatial scales: Linum marginale–Melampsora lini – from the individual to the species

Coevolutionary processes are intrinsically spatial as well as temporal, and occur at many different scales. These range from single populations dominated by demographic and genetic stochasticity, to metapopulations in which colonisation/extinction dynamics have a large influence, and larger geographic regions where phylogenetic patterns and historical events become important. We present data for the genetically and demographically well-characterised plant host–pathogen interaction, the Linum marginale–Melampsora lini system, and use this to demonstrate the varying nature of resistance and virulence structure across these spatial scales. At the within population level, our results indicate considerable variability in resistance and virulence, but little evidence of coordinated changes in host and pathogen. Studies involving comparisons among multiple demes within a single metapopulation show that adjacent populations often have asynchronous disease dynamics and large differences in diversity and frequency of resistance and virulence phenotypes. Nevertheless, at this scale, there is also evidence of spatial structure in that more closely adjacent host populations are significantly more likely to have similar resistance phenotypes and mean levels of resistance. At larger scales, comparisons among adjacent metapopulations indicate that quantitative differences in host mating system and other life history features can have further major consequences for how host and pathogen variation is packaged. Finally, comparisons at continental and among host-species levels show variation consistent with specialisation and speciation in the pathogen. This revised version was published online in July 2006 with corrections to the Cover Date.     

“超级真菌”耳念珠菌研究进展

耳念珠菌Candida auris也被称为“超级真菌”,是近年来出现的一种人体病原真菌新物种,临床分离株通常具有多重耐药和高致死率等特征。2009年日本首次报道耳念珠菌之后,其感染病例在多个国家呈现出爆发式增长。目前已报道的病例分布在全球五大洲27个国家,包括中国。耳念珠菌感染给临床诊断和防控以及人类健康带来了巨大的挑战。本文从该菌临床分离菌株的生物学、遗传变异分化及耐药特征等方面入手,围绕分子流行病学、基因组特征、毒性因子和耐药性等方面系统地综述了近年来国内外取得的相关进展,并探讨了我国耳念珠菌感染的诊断、治疗和预防的措施。     

Within-host parasite cooperation and the evolution of virulence

Infections by multiple genotypes are common in nature and are known to select for higher levels of virulence for some parasites. When parasites produce public goods (PGs) within the host, such co-infections have been predicted to select for lower levels of virulence. However, this prediction is based on simplifying assumptions regarding epidemiological feedbacks on the multiplicity of infections (MOI). Here, we analyse the case of parasites producing a PG (for example, siderophore-producing bacteria) using a nested model that ties together within-host and epidemiological processes. We find that the prediction that co-infection should select for less virulent strains for PG-producing parasites is only valid if both parasite transmission and virulence are linear functions of parasite density. If there is a trade-off relationship such that virulence increases more rapidly than transmission, or if virulence also depends on the total amount of PGs produced, then more complex relationships between virulence and the MOI are predicted. Our results reveal that explicitly taking into account the distribution of parasite strains among hosts could help better understand the selective pressures faced by parasites at the population level.