Does evolution lead to maximizing behavior?

A long‐standing question in biology and economics is whether individual organisms evolve to behave as if they were striving to maximize some goal function. We here formalize this “as if” question in a patch‐structured population in which individuals obtain material payoffs from (perhaps very complex multimove) social interactions. These material payoffs determine personal fitness and, ultimately, invasion fitness. We ask whether individuals in uninvadable population states will appear to be maximizing conventional goal functions (with population‐structure coefficients exogenous to the individual's behavior), when what is really being maximized is invasion fitness at the genetic level. We reach two broad conclusions. First, no simple and general individual‐centered goal function emerges from the analysis. This stems from the fact that invasion fitness is a gene‐centered multigenerational measure of evolutionary success. Second, when selection is weak, all multigenerational effects of selection can be summarized in a neutral type‐distribution quantifying identity‐by‐descent between individuals within patches. Individuals then behave as if they were striving to maximize a weighted sum of material payoffs (own and others). At an uninvadable state it is as if individuals would freely choose their actions and play a Nash equilibrium of a game with a goal function that combines self‐interest (own material payoff), group interest (group material payoff if everyone does the same), and local rivalry (material payoff differences).     

Does consanguinity lead to decreased incidence of breast cancer?

Background: In the Middle East region, consanguinity remains to be a central feature where it has shown an increasing trend. Breast cancer is an extremely complex disease, characterized by a progressive multistep process caused by interactions of both environmental and genetic factors. Aim: The aim of this study was to examine the possible effect of consanguinity on the risk of breast cancer in a population with a high rate of consanguinity and find the associated risk-modifying factors. Subjects and methods: The study included 167 Qatari and other Arab expatriates women with breast cancer and 341 age and ethnicity matched control women. A questionnaire that included the socio-demographic information, type of consanguinity, medical history, life style habits, dietary intake and tumor grade was designed to collect, the information of cases and controls. A total number of 214 breast cancer patients were approached and 167 cases completed the questionnaires with a response rate of 78%. Of the 417 healthy women who agreed to participate in this study, 341 responded to the questionnaire (81.8%). Results: The study revealed that the rate of parental consanguinity was lower in breast cancer patients (24%) than in controls (32.3%) (p = 0.062). Female controls were slightly younger (46.5 ± 11.9) than breast cancer patients (48.4 ± 10.7). Breast cancer incidence was significantly higher in Qatari women (34.1%) compared to other Arab women (65.9%) (p = 0.034). A significant difference was noted only in occupation of the studied women between cases and controls (p < 0.001). Overweight (46.7%) and obesity (32.9%) were significantly higher in female breast cancer patients compared to controls (p = 0.028). Overall, the mean coefficient of consanguinity was lower in breast cancer patients (0.014) than in controls (0.018) (p = 0.0125). Family history of breast cancer was significantly more often in breast cancer patients (14.4%) than in controls (6.2%) (p = 0.002). However, the family history of breast cancer was more often positive in cases of non-consanguineous parents (15.7%) than cases of consanguineous parents (10.0%). Conclusion: The present study revealed the lack of association between of breast cancer and the parental consanguinity in Arab women residing in Qatar. The family history of breast cancer and the body mass index (BMI) are highly associated with breast cancer.     

Does male-biased predation lead to male scarcity in viviparous fish?

Male predation risk due to ornaments seldom reduces female mating opportunities because males escape costs through alternative mating strategies and/or females cease to select for highly ornamented males. Males of the Amarillo fish Girardinichthys multiradiatus (Goodeidae) have large sexually selected fins that impair attack-avoidance manoeuvres. This fish was used to seek evidence that intersexual selection for handicapping traits can result in a deficit of acceptable mating partners. Also it was examined whether, under male scarcity, females remain choosy to the point of missing mating opportunities, and that they can exert effective control over matings, which is a pre-condition of effective female choice. It was found that snakes prey disproportionately on males, that it leads to female-biased sex ratios, and that highly ornamented males are more scarce after predation than males with small ornaments. Females can avoid being fertilized by unattractive males, and that missing one reproductive period can lead to infertility. Thus it appears that females have promoted the exaggeration of a male trait that increases predation risk, remain choosy even when acceptable males are scarce, and pay a large cost when missing mating opportunities. A prediction from these results is that females enjoy substantial fitness benefits from mating with highly ornamented males, which override the occasional fatal costs of refusing to mate with sub–optimal males. One potential consequence of female selectivity and control over matings when males are scarce may be a reduced capability to colonize new habitats.     

Does access to fast food lead to super-sized pregnant women and whopper babies?

Rise in the availability of fast-food restaurants has been blamed, at least partly, for the increasing obesity in the U.S. The existing studies of obesity have focused primarily on children, adolescents, and adults, and this paper extends the literature by raising a little-studied question and using nationally representative data to answer it. It examines the relationship between the supply of fast-food restaurants and weight gain of pregnant women and their newborns. I study prenatal weight gain because excessive weight gain has been linked to postpartum overweight/obesity and I study both tails of the birthweight distribution because the origin of obesity may be traced to the prenatal period and both tail outcomes have been associated with obesity later in life. I merge the 1998 and 2004 Natality Detail Files with the Area Resource File, and County Business Patterns, which provide data on the number of fast-food restaurants in the metropolitan area where the mother resides. The empirical model includes an extensive list of MSA characteristics and MSA fixed effects to control for factors that may be correlated with both health outcomes and restaurants’ location decision. Results reveal that the fast-food and weight gain relationship is robust to the inclusion of these controls but these controls greatly mitigate the fast food–infant health relationship. Greater access to fast-food restaurants is positively related to mothers’ probability of excessive weight gain but it does not share a statistically significant relationship with birthweight. These relationships hold in all the socioeconomic and demographic subgroups studied.     

Does long-term experimental antiorthostasis lead to cardiovascular deconditioning in the rat?

Microgravity or simulated microgravity induces acute and chronic cardiovascular responses, whose mechanism is pivotal for understanding of physiological adaptation and pathophysiological consequences. We investigated hemodynamic responses of conscious Wistar rats to 45? head-down tilt (HDT) for 7 days. Arterial blood pressure (BP) was recorded by telemetry. Heart rate (HR), spectral properties and the spontaneous baroreflex sensitivity (sBRS) were calculated. Head-up tilt (HUT) was applied for 2 h before and after HDT to assess the degree of any possible cardiovascular deconditioning. Horizontal control BP and HR were 112.5+/-2.8 mmHg and 344.7+/-10 bpm, respectively. HDT elicited an elevation in BP and HR by 8.3 % and 8.8 %, respectively, in less than 1 h. These elevations in BP and HR were maintained for 2 and 3 days, respectively, and then normalized. Heart rate variability was unchanged, while sBRS was permanently reduced from the beginning of HDT (1.01+/-0.08 vs. 0.74+/-0.05 ms/mmHg). HUT tests before and after HDT resulted in BP elevations (6.9 vs. 11.6 %) and sBRS reduction (0.44 vs. 0.37 ms/mmHg), respectively. The pressor response during the post-HDT HUT test was accompanied by tachycardia (13.7 %). In conclusion, chronic HDT does not lead to symptoms of cardiovascular deconditioning. However the depressed sBRS and tachycardic response seen during the post-HDT HUT test may indicate disturbances in cardiovascular control.     

Synaptic vesicle exocytosis. Does a lingering kiss lead to fusion?

Direct optical measurements of single synaptic vesicles undergoing exocytosis at a synapse reveal rapid and complete transfer of membrane marker from the vesicle to the plasma membrane (; this issue of Neuron). Contact between the two membranes is consistent with free lipid exchange, such as might result from full fusion of the vesicle and plasma membranes.     

Does spatial aggregation of total nectar production lead to genetic structure?

Spatial aggregation of plants of high nectar production, receiving an enhanced pollinator service is known to occur in Echium vulgare. Moreover, an emanating effect of nectar production on pollinator visits may occur, i.e. many pollinator visits may be observed around high nectar patches. Consequently, gene flow within patches of plants of high nectar production and their close neighbours may result in genetic structure. In this study, we investigated whether aggregation of total nectar production (nectar production per flower×number of flowers) and its emanating effect resulted in genetic structure in a natural E. vulgare population. We compared the spatial structure of total nectar production, pollinator visits and microsatellite markers using spatial autocorrelation analysis. Increased geitonogamy, caused by longer boutlengths in plants of high nectar production may generate genetic structure. We estimated selfing rates of plants of the highest and lowest total nectar production. Spatial aggregation of total nectar production occurred on a relatively small scale up to 2.83 m. A significant emanating correlation between total nectar production and pollinator visits was observed on a relatively large scale up to a 4.24 m. Thus, around patches of high nectar production numbers of pollinator visits were relatively high, while few visits were observed around patches of low nectar production. Weak genetic structure was present on a small scale up to 2.20 m. This corresponded with the scale of aggregation of total nectar production. High gene flow around the patches of high nectar production seems to weaken genetic structure. This is supported by the relatively low selfing rates. The average selfing rate of the plants of highest nectar production was 8.8% and that of the plants of lowest nectar production 5.0%. Low gene flow within and around low nectar patches sustain a weak genetic structure or, conversely, may have caused it in the first instance. Results indicate the importance of spatial structure of nectar production for pollinator movement.     

Does leaf ontogeny lead to changes in defensive strategies against insect herbivores?

Plants use different defense strategies throughout their ontogenetic development. In this study, three questions were proposed: (1) Is there a greater abundance of ants on young leaves, which possess active extrafloral nectaries, than on mature leaves? (2) Do ants exert an indirect defense that is effective against the attack of herbivorous insects? (3) Do mature leaves have a greater concentration of physical and chemical defense than young leaves? These questions were addressed through an ant-exclusion experiment in which two branches of Copaifera langsdorffii (n = 25) were marked and monitored throughout the entire foliar expansion and development period. A reduction in the abundance of ants throughout foliar development was observed. The ants exerted an effective defense against herbivores on C. langsdorffii: the branches where ants were excluded had a greater number of herbivores. The mature leaves possessed a greater index of leaf sclerophylly than young leaves, but the leaves did not differ in the concentration of tannins. The foliar ontogeny of C. langsdorffii promoted an inversion in the defense strategy against herbivores, and despite showing an opportunistic relationship, the interaction between ants and extrafloral nectaries appears to play an important role in structuring the interactions between herbivorous insects and their host plants.     

Does quasi-local competition lead to pattern formation in metapopulations? An explicit resource competition model

In metapopulations, competitive interactions may extend beyond the confines of the local population such that members of neighbouring habitat patches affect each other adversely (quasi-local competition). We derive a model for quasi-local competition from first principles, assuming that individuals compete for shared resources and members of a population spend a certain fraction of their foraging time in the adjacent populations. Contrary to the results of Doebeli and Killingback [2003. Theor. Popul. Biol. 64, 397-416], our model does not produce spatial patterns of population densities in homogeneous environments. Quasi-local competition nevertheless contributes to pattern formation by amplifying the effect of heterogeneities in the external environment, and this amplification can be extremely strong when dispersal is absent. We discuss why apparently similar models lead to contrasting results.     

Does evolutionary innovation in pharyngeal jaws lead to rapid lineage diversification in labrid fishes?

Background  

Major modifications to the pharyngeal jaw apparatus are widely regarded as a recurring evolutionary key innovation that has enabled adaptive radiation in many species-rich clades of percomorph fishes. However one of the central predictions of this hypothesis, that the acquisition of a modified pharyngeal jaw apparatus will be positively correlated with explosive lineage diversification, has never been tested. We applied comparative methods to a new time-calibrated phylogeny of labrid fishes to test whether diversification rates shifted at two scales where major pharyngeal jaw innovations have evolved: across all of Labridae and within the subclade of parrotfishes.     

Can climate change lead to gap formation?

Consider a situation where spatial heterogeneity leads to a cline, a gradual transition in dominance of two competing species. We first prove, in the context of a simplified competition–diffusion model, that there exists a stationary solution showing that the two species coexist in a transition zone. What happens then if, owing to climate change, the environmental profile moves with constant speed in space? We show here that, when the speed with which the environmental condition shifts exceeds the Fisher invasion speed of the advancing species, an expanding gap will form. We raise the question of whether such a phenomenon has been or can be observed.     

Does abnormal spinal reciprocal inhibition lead to co-contraction of antagonist motor units? A modeling study

It is suggested that co-contraction of antagonist motor units perhaps due to abnormal disynaptic I(a) reciprocal inhibition is responsible for Parkinsonian rigidity. A neural model of Parkinson's disease bradykinesia is extended to incorporate the effects of spindle feedback on key cortical cells and examine the effects of dopamine depletion on spinal activities. Simulation results show that although reciprocal inhibition is reduced in DA depleted case, it doesn't lead to co-contraction of antagonist motor neurons. Implications to Parkinsonian rigidity are discussed.     

Does social complexity lead to sex-biased dispersal in polygynous mammals? A test on ground-dwelling sciurids

Mating systems are well known to influence the dispersing sex,but the magnitude of the sex-biased dispersal has not actuallybeen measured, whereas many theoretical predictions have beenmade. In this study, we tested a new prediction about the coevolutionbetween natal dispersal and sociality from a recent evolutionarilystable strategy (ESS) approach. From a comparative approach,we showed that, in agreement with the model, the male-biaseddispersal increases with increasing level of sociality in polygynousground-dwelling sciurids. In addition, the increase in male-biaseddispersal with increasing sociality results from an increasein male dispersal rates, whereas female dispersal rates remainconstant, contrary to what is expected from the ESS model. Althoughthe mating system through the level of polygyny could act asa confounding factor, our results strengthen previous work thatstates that inbreeding avoidance plays a major role in the evolutionof dispersal for the most social mammalian species.     

Asymmetric segregation: the shape of things to come?

Yeast mother cells pay a sacrifice during budding: they keep the extrachromosomal rDNA circles (ERCs) so that their buds have a full lifespan ahead. Two new studies indicate that retention of ERCs in mother cells occurs not by tethering to the nuclear periphery but rather by the simple rules of diffusion in a time-limited and complex landscape.     

Do fitness-equalizing tradeoffs lead to neutral communities?

Neutral theory in ecology is aimed at describing communities where species coexist due to similarities rather than the classically posited niche differences. It assumes that all individuals, regardless of species identity, are demographically equivalent. However, Hubbell suggested that neutral theory may describe even niche communities because tradeoffs equalize fitness across species which differ in their traits. In fact, tradeoffs can involve stabilization as well as fitness equalization, and stabilization involves different dynamics and can lead to different community patterns than neutral theory. Yet the important question remains if neutral theory provides a robust picture of all fitness-equalized communities, of which communities with demographic equivalence are one special case. Here, I examine Hubbell’s suggestion for a purely fitness-equalizing interspecific birth–death tradeoff, expanding neutral theory to a theory describing this broader class of fitness-equalized communities. In particular, I use a flexible framework allowing examination of the influence of speciation dynamics. I find that the scaling of speciation rates with birth and death rates, which is poorly known, has large impacts on community structure. In most cases, the departure from the predictions of current neutral models is substantial. This work suggests that demographic and speciation complexities present a challenge to the future development and use of neutral theory in ecology as null model. The framework presented here will provide a starting point for meeting that challenge, and may also be useful in the development of stochastic niche models with speciation dynamics.