Direct fitness benefits explain mate preference,but not choice,for similarity in heterozygosity levels

Under sexual selection, mate preferences can evolve for traits advertising fitness benefits. Observed mating patterns (mate choice) are often assumed to represent preference, even though they result from the interaction between preference, sampling strategy and environmental factors. Correlating fitness with mate choice instead of preference will therefore lead to confounded conclusions about the role of preference in sexual selection. Here we show that direct fitness benefits underlie mate preferences for genetic characteristics in a unique experiment on wild great tits. In repeated mate preference tests, both sexes preferred mates that had similar heterozygosity levels to themselves, and not those with which they would optimise offspring heterozygosity. In a subsequent field experiment where we cross fostered offspring, foster parents with more similar heterozygosity levels had higher reproductive success, despite the absence of assortative mating patterns. These results support the idea that selection for preference persists despite constraints on mate choice.     

Stern-judging: A simple, successful norm which promotes cooperation under indirect reciprocity

We study the evolution of cooperation under indirect reciprocity, believed to constitute the biological basis of morality. We employ an evolutionary game theoretical model of multilevel selection, and show that natural selection and mutation lead to the emergence of a robust and simple social norm, which we call stern-judging. Under stern-judging, helping a good individual or refusing help to a bad individual leads to a good reputation, whereas refusing help to a good individual or helping a bad one leads to a bad reputation. Similarly for tit-for-tat and win-stay-lose-shift, the simplest ubiquitous strategies in direct reciprocity, the lack of ambiguity of stern-judging, where implacable punishment is compensated by prompt forgiving, supports the idea that simplicity is often associated with evolutionary success.     

Relatedness does not explain geographic variation in queen cooperation in the seed-harvester ant Messor pergandei

The desert seed-harvester ant Messor pergandei shows sharp regional differences in social structure: in central Arizona, queens initially form group nests but become aggressive following worker emergence and reduce to a single queen (secondary monogyny). In much of the rest of the species range, however, co-founding queens do not display aggression and retain multiple queens throughout the colony lifecycle (primary polygyny). One hypothesis to explain why queen behavior differs between regions is that relatedness among co-foundresses and, therefore, the potential for kin-selected cooperation, varies geographically. To test whether primary polygyny is associated with greater kin association, we used highly polymorphic microsatellites to estimate within-group relatedness for co-foundress associations in the field at two secondarily monogynous sites and five primarily polygynous sites. To determine whether queens can potentially use nestmate identity as a proxy for genetic relatedness, we compared these values to similarly sized samples of worker nestmates from adult colonies at the same sites. We found that foundresses do not preferentially form groups with relatives regardless of the ultimate fate of foundress groups. Mean relatedness values for co-foundresses did not differ significantly from zero irrespective of social structure. In contrast, adult colony worker nestmates were significantly positively related at all sites. These results indicate that kin-selected benefits are not likely to be responsible for the absence of fatal competition in the polygynous region; instead, the cause of geographic variation in queen cooperation must lie in ecological factors that alter the costs and benefits of retaining additional queens into colony maturity.     

Parsimony analysis of endemicity describes but does not explain: an illustrated critique

Aim To demonstrate that parsimony analysis of endemicity (PAE) is not analogous to a cladistic biogeographical analysis. Location We used six data sets from previously published studies from around the world. Methods In order to test the efficiency of PAE in recovering historical relationships among areas, we performed an empirical comparison of nodes recovered with PAE, primary Brooks parsimony analysis (BPA), and an event‐based method using three models (maximum codivergence, reconciled trees, and the default model of the treefitter program) for six data sets. We measured the performance of PAE in recovering historical area relationships by counting the number and examining the content of nodes recovered by PAE and by historical methods. The dispersal/vicariance ratio was calculated to assess the prevalence of dispersal or vicariance in each reconstruction and its relationship to the performance of PAE. Results Our results show that PAE recovers an average of 17.25% of historical nodes. PAE and BPA tend to provide similar results; however, in relation to the event‐based models, PAE performance was poor under all the tested scenarios. Although in some cases PAE reconstructions are more resolved than historical reconstructions, this does not necessarily mean that PAE produces more informative answers. These additional nodes correspond to unsupported statements that are based solely on the distributional data of taxa and not on their phylogenetic history. In other words, these nodes were not found by the historical methods, which take phylogenetics into account. The number of historical nodes recovered using PAE was in general negatively correlated with the dispersal/vicariance ratio. Main conclusions Our results show that PAE is unable to recover historical patterns and therefore does not fit into the current paradigm of historical biogeography. These findings raise doubts regarding conclusions derived from biogeographical studies that interpret PAE trees as area cladograms. We acknowledge that PAE aims to describe but does not explain the current distribution of organisms. It is therefore a useful tool in other biogeographical or ecological analyses for exploring the distribution of taxa or for establishing hypotheses of primary homology between areas.     

Correlational selection does not explain the evolution of a behavioural syndrome

Correlated suites of behaviours, or behavioural syndromes, appear to be widespread, and yet few studies have explored how they arise and are maintained. One possibility holds that correlational selection can generate and maintain behavioural syndrome if certain behavioural combinations enjoy greater fitness than other combinations. Here we test this correlational selection hypothesis by comparing behavioural syndrome structure with a multivariate fitness surface based on reproductive success of male water striders. We measured the structure of a behavioural syndrome including dispersal ability, exploration behaviour, latency to remount and sex recognition sensitivity in males. We then measured the relationship between these behaviours and mating success in a range of sex ratio environments. Despite the presence of some significant correlational selection, behavioural syndrome structure was not associated with correlational selection on behaviours. Although we cannot conclusively reject the correlational selection hypothesis, our evidence suggests that correlational selection and resulting linkage disequilibrium might not be responsible for maintaining the strong correlations between behaviours. Instead, we suggest alternative ways in which this behavioural syndrome may have arisen and outline the need for physiological and quantitative genetic tests of these suggestions.     

Temperature alone does not explain phenological variation of diverse temperate plants under experimental warming

Anthropogenic climate change has altered temperate forest phenology, but how these trends will play out in the future is controversial. We measured the effect of experimental warming of 0.6–5.0 °C on the phenology of a diverse suite of 11 plant species in the deciduous forest understory (Duke Forest, North Carolina, USA) in a relatively warm year (2011) and a colder year (2013). Our primary goal was to dissect how temperature affects timing of spring budburst, flowering, and autumn leaf coloring for functional groups with different growth habits, phenological niches, and xylem anatomy. Warming advanced budburst of six deciduous woody species by 5–15 days and delayed leaf coloring by 18–21 days, resulting in an extension of the growing season by as much as 20–29 days. Spring temperature accumulation was strongly correlated with budburst date, but temperature alone cannot explain the diverse budburst responses observed among plant functional types. Ring‐porous trees showed a consistent temperature response pattern across years, suggesting these species are sensitive to photoperiod. Conversely, diffuse‐porous species responded differently between years, suggesting winter chilling may be more important in regulating budburst. Budburst of the ring‐porous Quercus alba responded nonlinearly to warming, suggesting evolutionary constraints may limit changes in phenology, and therefore productivity, in the future. Warming caused a divergence in flowering times among species in the forest community, resulting in a longer flowering season by 10‐16 days. Temperature was a good predictor of flowering for only four of the seven species studied here. Observations of interannual temperature variability overpredicted flowering responses in spring‐blooming species, relative to our warming experiment, and did not consistently predict even the direction of flowering shifts. Experiments that push temperatures beyond historic variation are indispensable for improving predictions of future changes in phenology.     

Competition does not explain the absence of a carnivorous pitcher plant from a nutrient-rich marsh

Plant and Soil - Why is the carnivorous pitcher plant, Sarracenia alata Wood, largely absent from eutrophic habitats? Two hypotheses are addressed: (1) Sarracenia alata is competitively excluded by...     

Mate limitation does not explain the lack of capsules in a Pseudocalliergon trifarium population

Abstract

(1) Net assimilation and respiration rates were measured at intervals after re-moistening, following various periods of desiccation, in Hookeria lucens, Hylocomium splendens, Neckera crispa, Plagiochila spinulosa, Plagiothecium undulatum, Rhacomitrium lanuginosum, Rhytidiadelphus loreus, Saccogyna viticulosa, Scorpiurium circinatum and Tortula ruraliformis.

(2) Rhacomitrium lanuginosum was extremely resistant, recovering apparently normally after 239 days' desiccation at 32% R.H.; Plagiochila spinulosa and Hookeria lucens were the most sensitive.

(3) Rhacomitrium lanuginosum and Tortula ruraliformis were most quickly damaged at the highest humidity (76%) and Plagiothecium undulatum at the lowest humidity tested (32%).

(4) Saccogyna viticulosa and Scorpiurium circinatum combined relatively rapid impairment and slow recovery of assimilation with the capacity to survive long dry periods.

(5) Dark respiration was relatively slow (commonly c. 5–20% of net assimilation). It usually showed a slight initial stimulation and a longer-term build-up following moderate or prolonged desiccation.

(6) Desiccation responses of bryophytes can be characterized in terms of parameters defining rate of loss of photosynthetic capacity with desiccationtime, rate of recovery after short periods of desiccation, and survival.     

Size variation facilitates population divergence but does not explain it all: an example study from a widespread African monkey

Subspecific variation is widespread in vertebrates. Within Africa, several mammals have extensive geographic distributions with attendant morphological, ecological, and behavioural variations, which are often used to demarcate subspecies. In the present study, we use a primate species, the vervet monkey, Cercopithecus aethiops, as a case study for intraspecific divergence in widespread mammals, assessed through hard tissue morphology. We examine intraspecific differences in size, shape, and non‐allometric shape from a taxonomic perspective, and discuss the macroevolutionary implications of findings from microevolutionary analyses of geographic variation. A geometric morphometric approach was used, employing 86 three‐dimensional landmarks of almost 300 provenanced crania. Many of the taxonomic differences in skull morphology between vervet populations appear to be related to geographic proximity, with subspecies at opposite extremes of a west‐to‐east axis showing greatest divergence, and populations from central and south Africa being somewhat intermediate. The classification rate from discriminant analyses was lower than that observed in other African primate radiations, including guenons as a whole and red colobus. Nonetheless, taxonomic differences in shape were significant and not simply related to either geography or size. Thus, although shifts in size may be an important first step in adaptation and diversification, with size responding more quickly than shape to environmental change, the six vervet taxa currently recognized (either as species or subspecies) are not simply allometrically scaled versions of one another and are probably best viewed as subspecies. Holding allometry constant when examining inter‐population differences in shape may thus help to reveal the early stages of evolutionary divergence. The vervet case study presented here hence has relevance for future studies examining intraspecific differentiation in other large mammals, particularly through the methods used to identify small but biologically meaningful divergence, with attendant implications for conservation planning. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 823–843.     

Direct observation of fat crystallization in a living fly by X-ray diffraction: fat crystallization does not cause the fly's instantaneous death, but ice formation does

A cool-temperate fly, Drosophila triauraria, stores fat, triacylglycerol (TAG), primarily in the fat storage organ, the fat body, and then diapauses to pass the winter in imago stage. TAG crystallization and ice formation taking place in a living fly by lowering temperatures were studied, in order to clarify the relationship between crystallizations and the fly’s death at lower temperatures. X-ray diffraction, a direct non-invasive method, was used to detect the liquid-to-crystal transformations of TAG and water. During cooling, TAG crystallization preceded ice formation. It was also found that ice formation causes the fly to die instantaneously whereas the TAG crystallization does not.     

A study of indirect reciprocity involving a reputation system or a simple tag system in a one-shot, multi-player game

The possibility of the evolution of cooperation backed by indirect reciprocity (IDR) in a one-shot, multi-player game is investigated focusing on two mechanisms. First of all, the reputation system with image score (RS with IS), as proposed by Nowak and Sigmund [Nowak, M.A., Sigmund, K., 1998. Evolution of indirect reciprocity by image scoring. Nature 393, 573–577], is investigated in various game structures. A numerical experiment demonstrates that the RS with IS is a robust mechanism for the support of IDR in various dilemma games, but whose effectiveness decreases with an increase in the number of players in a game. It is fair to say that the RS is an information mapping function to relate between player's cooperative fraction on his action and IS. As the second mechanism, a simple tag system which could be applicable to animals having no cognitive complexity is considered to support IDR. Computer simulations of the tag system's strategy for invading a population initially consisting of AllD, AllC, and Random strategies suggest several novel facts. The Tag strategy with plausible crossover and mutation probabilities can only invade to settle down if the game structure is not Trivial and contains a moderate dilemma. The Tag strategy's evolutionary competition takes place mainly in the presence of the AllD strategy. During the competition, the Tag strategy frequently metamorphoses to shake off the AllD strategy, but stops after winning in order to avoid a shrinking payoff due to fragmentation.     

Load minimization of the genetic code: history does not explain the pattern

The average effect of errors acting on a genetic code (the change in amino-acid meaning resulting from point mutation and mistranslation) may be quantified as its ''load''. The natural genetic code shows a clear property of minimizing this load when compared against randomly generated variant codes. Two hypotheses may be considered to explain this property. First, it is possible that the natural code is the result of selection to minimize this load. Second, it is possible that the property is an historical artefact. It has previously been reported that amino acids that have been assigned to codons starting with the same base come from the same biosynthetic pathway. This probably reflects the manner in which the code evolved from a simpler code, and says more about the physicochemical mechanisms of code assembly than about selection. The apparent load minimization of the code may therefore follow as a consequence of the fact that the code could not have evolved any other way than to allow biochemically related amino acids to have related codons. Here then, we ask whether this ''historical'' force alone can explain the efficiency of the natural code in minimizing the effects of error. We therefore compare the error-minimizing ability of the natural code with that of alternative codes which, rather than being a random selection, are restricted such that amino acids from the same biochemical pathway all share the same first base. We find that although on average the restricted set of codes show a slightly higher efficiency than random ones, the real code remains extremely efficient relative to this subset P = 0.0003. This indicates that for the most part historical features do not explain the load- minimization property of the natural code. The importance of selection is further supported by the finding that the natural code''s efficiency improves relative to that of historically related codes after allowance is made for realistic mutational and mistranslational biases. Once mistranslational biases have been considered, fewer than four per 100,000 alternative codes are better than the natural code.     

Strong reciprocity, human cooperation, and the enforcement of social norms

This paper provides strong evidence challenging the self-interest assumption that dominates the behavioral sciences and much evolutionary thinking. The evidence indicates that many people have a tendency to voluntarily cooperate, if treated fairly, and to punish noncooperators. We call this behavioral propensity “strong reciprocity” and show empirically that it can lead to almost universal cooperation in circumstances in which purely self-interested behavior would cause a complete breakdown of cooperation. In addition, we show that people are willing to punish those who behaved unfairly towards a third person or who defected in a Prisoner’s Dilemma game with a third person. This suggests that strong reciprocity is a powerful device for the enforcement of social norms involving, for example, food sharing or collective action. Strong reciprocity cannot be rationalized as an adaptive trait by the leading evolutionary theories of human cooperation (in other words, kin selection, reciprocal altruism, indirect reciprocity, and costly signaling theory). However, multilevel selection theories of cultural evolution are consistent with strong reciprocity.     

6-hydroxydopamine does not reduce molecular oxygen directly, but requires a coreductant

The autoxidation of 6-hydroxydopamine (6HODA) was virtually blocked (k2 less than 10(-15) M-1 S-1 at pH 8.0, ionic strength 0.04) by the simultaneous presence of diethylenetriaminepentaacetic acid (DTPA), catalase, and superoxide dismutase (SOD). No quinone product or oxygen consumption was detectable after 12 min under these conditions. Thus, if 6HODA is to react with molecular oxygen at a measurable rate, some other redox species is required as a coreductant. The subsequent addition of formate or mannitol proved capable of overcoming the total inhibition induced by the mixture of catalase, SOD, and DTPA. The simplest interpretation of the data is that most of the autoxidation of 6HODA, as commonly observed, involves successive reduction of a series of metal-bound species of oxygen; the actual transfer of electrons occurring within a ternary reductant-metal-oxygen transition state.     

Evolution of social learning does not explain the origin of human cumulative culture

Because culture requires transmission of information between individuals, thinking about the origin of culture has mainly focused on the genetic evolution of abilities for social learning. Current theory considers how social learning affects the adaptiveness of a single cultural trait, yet human culture consists of the accumulation of very many traits. Here we introduce a new modeling strategy that tracks the adaptive value of many cultural traits, showing that genetic evolution favors only limited social learning owing to the accumulation of maladaptive as well as adaptive culture. We further show that culture can be adaptive, and refined social learning can evolve, if individuals can identify and discard maladaptive culture. This suggests that the evolution of such "adaptive filtering" mechanisms may have been crucial for the birth of human culture.     

Virulence not only costs but also benefits the transmission of a fungal virus

Current theory suggests that cost-benefit relationships govern the evolution of parasite virulence. The cost of virulence is expected to be high for fungal viruses, which are obligate parasites and completely dependent on their hosts. The majority of fungal viruses infect their hosts without any apparent symptoms. Cryphonectria hypovirus 1 (CHV-1), in contrast, is virulent and debilitates its host, Cryphonectria parasitica. However, the virulence of CHV-1 is associated with high costs for virus transmission, such as an attenuated fungal growth and reduced production of the fungal spores spreading the virus. In this study, we tested the hypothesis that virulence may not only have costs but also benefits for transmitting CHV-1 across vegetative incompatibility barriers between fungi. We investigated viruses with low, medium, and high virulence, and determined their transmission rate per host-to-host contact (transmissibility). The average transmission rate across all combinations tested was 53% for the most virulent virus, 37% for the virus with intermediate virulence, and 20% for the virus with lowest virulence. These results showed that increased virulence was strongly correlated with increased transmissibility, potentially counterbalancing virulence costs. This association of virulence and transmissibility may explain why CHV-1 spread widely and evolved higher virulence than most other fungal viruses.     

Seasonality provokes a shift of thermal preferences in a temperate lizard,but altitude does not

1. We compared the mean, limits and breadth of the preferred thermal range (PTR) of two Iberian populations of the lizard Psammodromus algirus separated by 700 m altitude in May and July.