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Evolutionary theory predicts that the capacity to acclimate should be favoured in variable environments. However, perfect compensation for thermal variation is rare and the capacity for thermal acclimation can vary considerably between individuals within natural populations. This variation may be explained by costs associated with acclimation, but it is not clear what these costs are.We tested the hypothesis that oxidative stress is a cost of acclimation that could explain the variation between individuals in acclimation capacity. We acclimated individual mosquitofish Gambusia holbrooki (n = 416) to 18 and 28°C sequentially, and determined swimming performance at each temperature to evaluate their acclimation capacity. Fish were then acclimated to either cold (18°C) or warm (28°C) conditions, and we increased antioxidant capacities of a subset of fish experimentally by administering N‐acetyl cysteine (NAC). We measured H2O2 production, catalase antioxidant activities and oxidative damage to proteins and membranes.We show that there is significant variation in acclimation capacity between individuals, and that there is a trade‐off between acclimation capacity and swimming performance in warm conditions. Mean swimming performance across both acclimation temperatures increased with increasing acclimation capacity, but the increase was small biologically. Hence, greater thermal plasticity (high acclimation capacity) resulted in only minor performance benefits across acclimation conditions. We verified this rather surprising result in replicate populations grown in outdoor mesocosms.Reactive oxygen species production, antioxidant activities and oxidative damage were higher in cold‐acclimated fish, and particularly in those fish with low capacity for acclimation. However, experimentally increasing antioxidant capacities with NAC alleviated these changes to oxidative status, suggesting a causal relationship. Hence, oxidative stress may be a cost that constrains the capacity for acclimation. Together, the performance trade‐off and oxidative cost indicate that phenotypic plasticity is not always advantageous in variable environments, and instead bet‐hedging may be a more beneficial strategy, particularly in short‐lived species. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Until recently, senescence was assumed to be a universal phenomenon. Evolutionary theories of senescence predict that no organism may escape the physiological decline that results in an increase in mortality risk and/or decline in fertility with age. However, evidence both in animals and plants has emerged in the last decade defying such predictions. Researchers are currently seeking mechanistic explanations for the observed variation in ageing trajectories.We argue that the historical view on the inevitability of senescence is due, in part, to the development of its classical theories, which targeted primarily unitary organisms. In unitary species, the integration of resources and functions is high, and adult size is determined. In contrast, the architecture of modular organisms is indeterminate and built upon repeated modules. The isolation of mortality risk in species like hydra (Hydra spp.) or creosote brush Larrea tridentata may explain their null or even negative senescence.Caleb Finch hypothesized three decades ago that species with the ability to compartmentalize risk may escape senescence. Here, we first review the evidence on organisms that slow down or even avoid senescence in the context of their architecture, along a continuum of unitarity‐modularity. Then, we use open‐access databases to comparatively analyse various moments of senescence and link longevity to the degree of anatomical modularity. Our analysis compares the pace of senescence across 138 plants and 151 animals, and the shape of senescence across a subset of these. Our comparative analysis reveals that plant species that are more modular do indeed tend to escape from senescence more often than those that are unitary. The role of modularity in animal senescence is less clear.In light of novel support for Finch's hypothesis across a large diversity of plant species, and with less conclusive findings in animals, we identify new research directions. We highlight the opportunities related to age‐dependent mortality factors. Other areas for further research include the role of modularity in relation to endocrine actions, and the costs of modular anatomies. [ABSTRACT FROM AUTHOR]

Evidence of reciprocal influences between ecological and evolutionary processes (eco‐evolutionary dynamics) is accumulating at different levels of biological organisation, ranging from populations to communities and even ecosystems.This special feature showcases the state‐of‐the art knowledge on eco‐evolutionary dynamics and dissects the feedback types, the biological and spatial scales as well as the agents of selection underlying the interactions between ecology and evolution.Theoretical approaches to eco‐evolutionary feedbacks can draw on a wide range of fields and have a long history within evolutionary ecology. The integration of theoretical approaches from quantitative genetics, evolutionary ecology, and metapopulation ecology is necessary to advance our understanding of rapid evolution and associated eco‐evolutionary dynamics.Empirical studies in this special feature focus on the evolution‐to‐ecology pathway by which evolutionary processes influence ecological dynamics (the direction in eco‐evolutionary dynamics less well studied). Advancing towards the study of complete (i.e. reciprocal) eco‐evolutionary feedbacks requires unravelling both the ecology‐to‐evolution and the evolution‐to‐ecology pathways in isolation and understanding how they are coupled. This endeavour will require a combination of laboratory, semi‐natural (e.g. mesocosm) and field studies.As the field of eco‐evolutionary dynamics matures, it moves from proof‐of‐principle studies to understanding increasingly complex biological systems. This Special Feature provides necessary tools and approaches, both theoretical and empirical, to achieve this new aim. [ABSTRACT FROM AUTHOR]

Species coexistence can be promoted by both equalizing mechanisms that increase fitness equivalence among species and stabilizing mechanisms that decrease niche overlap among species. Strength of the coexistence mechanisms can be altered by evolution. In particular, populations evolved in sympatry may show niche divergence due to competition-mediated selection, whereas populations evolved in allopatry have a chance to become ecologically equivalent competitors which, on secondary contacts, may form 'neutral communities'., We addressed how evolution may change ecological mechanisms of coexistence with experimental microcosms of Escherichia coli strains that reproduce asexually and can be considered as analogues of species. We obtained five pairs of bacterial strains, within each of which the two strains could coexist stably. We then allowed the bacterial strains to evolve in a chemically defined nutrient medium for ˜1100 generations, under sympatric (in two-strain mixtures) or allopatric scenarios (in monocultures). The strength of coexistence mechanisms was assessed based on reciprocal invasion assays and measurements of environmental carrying capacity., Our data confirmed that coexistence could be weaken by either fitness difference or niche overlap among competitors. In allopatrically evolved strain pairs, fitness difference among competitors became larger or unchanged; and the magnitude of niche overlap often showed an increase rather than a decline. Sympatrically evolved competitors showed no consistent changing trend in the strength of the coexistence mechanisms. Overall, sympatrically evolved competitor pairs did not differ from allopatrically evolved ones in the magnitude of fitness difference, but had lower levels of niche overlap., The results are consistent with the 'character displacement' view that allopatric populations of competing species occupy more similar niche space compared with sympatric populations. However, the pattern observed here resulted from allopatrically evolved competitors showing niche convergence, but not sympatrically evolved competitors consistently showing further niche divergence. The results also suggest that convergent evolution in allopatry followed by secondary contacts is an unlikely mechanism for the origin of 'neutral communities'. [ABSTRACT FROM AUTHOR]

Body condition indices, measures of body 'plumpness' or mass relative to frame size, are often used as a proxy for lipid reserves or fitness-related traits of animals and assumed to be positively related to fitness., The quantification and analysis of body condition indices has been the subject of debate for decades. Here, we summarize three additional concerns with the use of body condition indices., First, body condition index is often poorly correlated with lipid content in animals. Second, even if body condition index and lipid content are correlated, lipid content of an animal may not be the most important aspect of body composition influencing fitness. Finally, neither body condition index nor lipid reserves are likely to be directly positively related to fitness in animals, as many animals homeostatically regulate intermediate levels of condition index or lipid reserves, with both higher and lower values incurring fitness costs., A wide range of analytical methods, including some relatively inexpensive and simple measures, are available for more detailed measures of animal body composition or fitness-related traits. Replacing body condition indices with more direct measures of body composition - even relatively simple measures - can inform understanding of the physiological mechanisms underlying animal responses in a wide range of behavioural, ecological and evolutionary studies. [ABSTRACT FROM AUTHOR]

Predation plays a fundamental role in evolutionary processes, driving changes in prey morphology, physiology and behaviour. With organisms being increasingly exposed to rapid environmental changes, there is growing interest in understanding individual phenotypic plasticity in response to changes in predation pressure., Behavioural and physiological responses to predator exposure are of particular interest as differences in predation pressure are often reflected in correlated suites of behavioural and hormonal profiles across populations. Within populations, the association between endocrine profiles and behaviour is less understood and often lacking., Adopting a reaction norm approach and a repeated measures design, we assessed within-population effects of changes in perceived predation risk on endocrinology and behaviour in three-spined sticklebacks ( Gasterosteus aculeatus). We repeatedly exposed subjects to a robotic model predator and assessed their behavioural response. The fish showed consistent behavioural profiles and were less active and shyer when predation risk was higher., Using non-invasive waterborne hormone analysis, we assessed basal cortisol as well as the cortisol response to changes in predation risk. Individuals showed significantly higher cortisol levels following exposure to the model predator. Individual post-predator exposure cortisol was repeatable but unrelated to behavioural responses. Accounting for between versus within-subject effects, we found that basal cortisol and shyness were positively related within individuals, that is individuals overall were shyer on days they had higher cortisol levels. We also tested if basal testosterone predicted risky behaviour and found no evidence for this hypothesis., No individual differences in hormonal or behavioural responses to changes in predation risk were found, suggesting that individuals are not constrained by their personalities in their ability to cope with a potentially harmful threat., Overall, we show that individuals of different personalities are equally 'flexible' in their response to changes in predation pressure. Our study offers novel insight into consistent individual differences and plasticity in hormones and behaviour as well as their interplay within populations. Future studies should assess the applicability of these findings to other changes in the environment, as well as the effects of social context on endocrine and behavioural reaction norms. [ABSTRACT FROM AUTHOR]

The prevalence of phylogenetic niche conservatism ( PNC) in nature is still a conflicting issue. Disagreement arises from confusion over its precise definition and the variety of approaches to measure its prevalence. Recent work highlighted that common measures of PNC strongly depend on the assumptions of the underlying model of niche evolution. However, this warning has not been well recognized in the applied literature and questionable approaches are still frequently applied., The aim of this study is to draw attention to the assumptions underlying commonly applied simple measures of PNC. We used a series of simulations to illustrate how misleading results can be if assumptions of niche evolution are violated, that the violation of assumptions is a common phenomenon and that testing assumptions requires in-depth pretest., We conclude that the seemingly simple measures of PNC, such as phylogenetic signal (PS) and evolutionary rate, are not so easy to apply if one accounts for the necessity to test model assumptions. In addition, these measures can be difficult to interpret. The common assumption that strong PS indicates PNC will be often invalid. In addition, the interpretation of some measures, for example the conclusion that evolutionary rate is slow enough to indicate PNC, requires a comparison with another clade, another trait or well-developed null model assumptions and thus additional data., We suggest that studies investigating PNC should always compare alternative evolutionary models and that model comparisons should in particular include flexible niche evolution models such as multiple-optima OU models, although these are computational intensive. These models are directly inherited from the concept of macroevolutionary adaptive landscape and can indicate PNC either by relative few peak shifts or by narrow peaks in the adaptive landscape. A test of PNC thus requires comparing these parameters of the macroevolutionary landscape between clades or time periods., The general prevalence of PNC in nature should be evaluated only based on studies keeping up to the high standards of communicating the used definition of PNC, testing the assumptions made in the modelling approaches and including newly developed models in a model comparison approach. [ABSTRACT FROM AUTHOR]

How a symbiosis originates and is maintained are important evolutionary questions. Symbioses in myrmecophytes (plants providing nesting for ants) are believed to be maintained by protection and nutrients provided by specialist plant-ants in exchange for nesting spaces (called domatia) and nourishment offered by ant-plants. However, besides the benefits accrued from housing protective ants, the mechanisms contributing to the fitness advantages of bearing domatia have rarely been examined, especially because the domatia trait is usually constitutively expressed, and many myrmecophytes have obligate mutualisms with single ant species resulting in invariant conditions., In the unspecialized ant-plant Humboldtia brunonis (Fabaceae) that offers extrafloral nectar to ants, only some plants produce domatia in the form of hollow internodes. These domatia have a self-opening slit making them more prone to interlopers and are occupied mostly by non-protective ants and other invertebrates, especially arboreal earthworms. The protection mutualism with ants is restricted in geographical extent, occurring only at a few sites in the southernmost part of this plant's range in the Western Ghats of India., We examined nutrient flux from domatia residents to the plant using stable isotopes. We found that between 9% (earthworms) and 17% (protective or non-protective ants) of nitrogen of plant tissues nearest the domatium came from domatia inhabitants. Therefore, interlopers such as earthworms and non-protective ants contributed positively to the nitrogen budget of localized plant modules of this understorey tree. 15N-enriched feeding experiments with protective ants demonstrated that nutrients flowed from domatia inhabitants to nearby plant modules. Fruit set did not differ between paired hand-pollinated inflorescences on domatia and non-domatia bearing branches. This was possibly due to the nutrient flux from domatia to adjacent branches without domatia within localized modules., This study has demonstrated the nutritive role of non-protective ants and non-ant invertebrates, hitherto referred to as interlopers, in an unspecialized myrmecophyte. Our study suggests that even before the establishment of a specialized ant-plant protection mutualism, nutritional benefits conferred by domatia inhabitants can explain the fitness benefits of bearing domatia, and thus the maintenance of a trait that facilitates the establishment of a specialized ant-plant symbiosis. [ABSTRACT FROM AUTHOR]

1. Ecological interactions that involve aggressive confrontations between animals are important in shaping the evolution of morphology, behaviour and life history. However, as such confrontations are rarely witnessed, direct quantification of the intensity of these processes in natural populations is notoriously difficult. While the utilization of the frequency of non-lethal injuries is fraught with difficulties, it may provide information concerning different types of interaction, such as predation, intraspecific aggression and interspecific interference competition. 2. In this paper, we report on an exceptionally large difference in toe loss incidence between two populations of Podarcis sicula lizards living on small, neighbouring islands in the Adriatic Sea. We caught 900 lizards and recorded the number and location of missing toes. Subsequently, we investigated five non-mutually exclusive hypotheses concerning differences in bite force capacity, bone strength, predation intensity, average age and intraspecific aggression that may provide proximate explanations for the observed differences in injury frequencies. 3. Bite force differences differed considerably between the populations, but bone strength was found to be stronger in the populations with a higher frequency of natural scars. Predation pressure clearly differed between the populations, but we found higher injury rates under predation relaxation. 4. Our results indicate that density and consequently an increased intraspecific competition is the most likely explanation for the observed high frequencies of injuries. We suggest that the intensity of toe amputation between lizard populations may be a useable indirect indication for the intensity of intraspecific competition. 5. This study shows how a combination of morphological, physiological, behavioural and ecological measurements can be used to test assumptions implicit to alternative explanations of an observed phenomenon. Such tests can reveal how likely each of these explanations is, even if the processes leading to the phenomenon are difficult to observe directly. [ABSTRACT FROM AUTHOR]

1. Personality is highly relevant to ecology and the evolution of fast–slow metabolic and life-history strategies. One of the most important personality traits is exploratory behaviour, usually measured on an animal introduced to a novel environment (e.g. open-field test). 2. Here, we use a unique comparative dataset on open-field exploratory behaviour of muroid rodents to test a key assumption of a recent evolutionary model, i.e. that exploration thoroughness is positively correlated to age at first reproduction (AFR). We then examine how AFR and exploratory behaviour are related to basal metabolic rate (BMR). 3. Inter-specific variation in exploratory behaviour was positively correlated with AFR. Both AFR and exploration behaviour were negatively correlated with BMR. These results remained significant when taking phylogeny into account. 4. We suggest that species occupying unproductive and unpredictable environments simultaneously benefit from high exploration, low BMR and delayed AFR because exploration increases the likelihood of finding scarce resources, whereas low BMR and delayed reproduction enhance survival during frequent resources shortages. 5. This study provides the first empirical evidence for a link between personality, life-history, phylogeny and energy metabolism at the inter-specific level. The superficial-thorough exploration continuum can be mapped along the fast–slow metabolic and life-history continua. [ABSTRACT FROM AUTHOR]

1. Despite the obvious importance of spermatozoa to individual reproductive success a general explanation of variation in spermatozoan form and function is still lacking. In species with internal fertilization, sperm not only have to interact with the physical and biochemical environment of the female reproductive tract, but frequently face competition from the sperm of rival males. Both sperm competition theory and adaptation to the selective environment of the female reproductive tract have been implicated in the evolution of spermatozoan morphological diversity. 2. Using the comparative method, we examine variation in sperm length in relation to (i) sperm competition intensity (as measured by relative testis size) and (ii) female reproductive characters, across 15 species of beetle belonging to the family Bruchidae. 3. Stepwise multiple regression within a phylogenetic framework revealed sperm length to be positively correlated with female spermathecal duct length and negatively related to spermathecal volume, but not testes size, indicating that the female reproductive environment rather than sperm competition per se exerts selection on sperm length in this taxonomic group. 4. A positive association between testes volume and the volume of the female spermatheca was also evident suggesting correlated evolution of these traits. 5. A number of models of sexual selection could lead to the correlated evolution of male and female reproductive characters, although the underlying mechanisms of cause and effect remain elusive. Divergence between species (and populations) in primary reproductive traits is likely to present a significant barrier to hetero-specific fertilization, and thus contribute to reproductive isolation. [ABSTRACT FROM AUTHOR]

1. Classical evolutionary theory states that senescence should arise as a consequence of the declining force of selection late in life. Although the quantitative genetic predictions of hypotheses derived from this theory have been extensively tested in laboratory studies of invertebrate systems, relatively little is known about the genetics of ageing in the wild. 2. Data from long-term ecological studies is increasingly allowing quantitative genetic approaches to be used in studies of senescence in free-living populations of vertebrates. We review work to date and argue that the patterns are broadly consistent with theoretical predictions, although there is also a clear need for more empirical work. 3. We argue that further advances in this field of research might be facilitated by increased use of reaction norm models, and a decreased emphasis on attempting to discriminate between mutation accumulation and antagonistic pleiotropy models of senescence. We also suggest a framework for the better integration of environmental and genetic effects on ageing. 4. Finally, we discuss some of the difficulties in applying quantitative genetic models to studies of senescence outside the laboratory. In particular we highlight the problems that viability selection can cause for an accurate estimation of parameters used in the prediction of age-trajectory evolution. [ABSTRACT FROM AUTHOR]

1. Comparative studies of ageing address the evolutionary lability of the rate of ageing as an indication of potential for, and constraints on, the extension of life span. 2. Experimental studies on ageing have focused on damage induced by reactive oxygen species (ROS) and other stresses, and on the mechanisms to prevent or repair this damage. Research on animal models has revealed genes with large effects on life span. However, the relevance of some animal models to human ageing is unclear and it is not known whether evolved differences in ageing involve such major gene effects. 3. Studies on the demography of populations of vertebrates in the wild show that animals suffer from senescence in nature. Variation in the rate of ageing is consistent with evolutionary theory in that senescence is delayed in populations that suffer relatively low extrinsic mortality. 4. Populations of longer-lived individuals suffer a higher proportion of ageing-related mortality, and thus stronger selection against early ageing. The presence of ageing-related deaths in these populations suggests a lack of suitable mechanisms that would further extend life span. 5. Similar patterns of ageing-related mortality in wild and captive or domesticated populations indicate that most ageing-related death is caused by intrinsic factors, such as tumours and cardiovascular failure, rather than increasing vulnerability to extrinsic causes of mortality. 6. Studies of several wild populations of long-lived birds suggest that ageing-related mortality is often catastrophic, with individuals maintaining high levels of condition until shortly before their demise. 7. Comparative studies of many species suggest connections between early development and the pattern of ageing later in life, consistent with laboratory studies on variation within individual species. The physiological connections across the life span are not well understood. 8. Comparative studies have provided important insights into the ageing process. However, we still lack information on important issues, including the causes of death in natural populations, the relationship of within- and between-population variation in the rate of ageing, the genetic basis of variation in rate of ageing in natural populations, and detailed longitudinal studies of individual health and reproductive success in relation to age at death. [ABSTRACT FROM AUTHOR]

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Discusses the factors that contribute to the evolution of animals' body size. Role of skew in body size frequency distributions proposed in mathematical models; Inconsistency of parameters included in the evolutionary model; Test of whether reproductive power is the dominant determinant of the shape of the body.