Greenhead ants Rhytidoponera metallica make trade‐offs between food temperature and food concentration

1. Foraging animals are often faced with foods that vary in several important attributes, some of which may be in conflict with one another. For ectothermic animals, food temperature can be an important characteristic, as the consumption of cold foods is metabolically costly. 2. Here, the effect of food temperature on food preferences in the green‐headed ant Rhytidoponera metallica (Smith, 1858) was investigated. The first aim of the study was to determine how food concentration (caloric value) and relative food temperature influenced colony‐level preferences. We found that, all else being equal, green‐headed ant colonies preferred warmer food solutions over colder solutions, and more concentrated food solutions over less concentrated ones. 3. Next, the question of whether green‐head ant colonies could make trade‐offs between temperature and food concentration was tested. It was found that ant colonies switched their preferences in favour of a colder food solution when the colder food solution was 10 times more concentrated than the warmer food solution. 4. These experiments show that temperature is an important characteristic shaping food preferences in ants. Moreover, we show that colonies can make trade‐offs between food concentration and food temperature.     

Ecology shapes the evolutionary trade‐off between predator avoidance and defence in coral reef butterflyfishes

Antipredator defensive traits are thought to trade‐off evolutionarily with traits that facilitate predator avoidance. However, complexity and scale have precluded tests of this prediction in many groups, including fishes. Using a macroevolutionary approach, we test this prediction in butterflyfishes, an iconic group of coral reef inhabitants with diverse social behaviours, foraging strategies and antipredator adaptations. We find that several antipredator traits have evolved adaptively, dependent primarily on foraging strategy. We identify a previously unrecognised axis of diversity in butterflyfishes where species with robust morphological defences have riskier foraging strategies and lack sociality, while species with reduced morphological defences feed in familiar territories, have adaptations for quick escapes and benefit from the vigilance provided by sociality. Furthermore, we find evidence for the constrained evolution of fin spines among species that graze solely on corals, highlighting the importance of corals, as both prey and structural refuge, in shaping fish morphology.     

A distance–performance trade‐off in the phenotypic basis of dispersal

Across taxa, individuals vary in how far they disperse, with most individuals staying close to their origin and fewer dispersing long distances. Costs associated with dispersal (e.g., energy, risk) are widely believed to trade off with benefits (e.g., reduced competition, increased reproductive success) to influence dispersal propensity. However, this framework has not been applied to understand variation in dispersal distance, which is instead generally attributed to extrinsic environmental factors. We alternatively hypothesized that variation in dispersal distances results from trade‐offs associated with other aspects of locomotor performance. We tested this hypothesis in the stream salamander Gyrinophilus porphyriticus and found that salamanders that dispersed farther in the field had longer forelimbs but swam at slower velocities under experimental conditions. The reduced swimming performance of long‐distance dispersers likely results from drag imposed by longer forelimbs. Longer forelimbs may facilitate moving longer distances, but the proximate costs associated with reduced swimming performance may help to explain the rarity of long‐distance dispersal. The historical focus on environmental drivers of dispersal distances misses the importance of individual traits and associated trade‐offs among traits affecting locomotion.     

The competition–dispersal trade‐off exists in forbs but not in graminoids: A case study from multispecies alpine grassland communities

Much theoretical evidence has demonstrated that a trade‐off between competitive and dispersal ability plays an important role in facilitating species coexistence. However, experimental evidence from natural communities is still rare. Here, we tested the competition–dispersal trade‐off hypothesis in an alpine grassland in the Tianshan Mountains, Xinjiang, China, by quantifying competitive and dispersal ability using a combination of 4 plant traits (seed mass, ramet mass, height, and dispersal mode). Our results show that the competition–dispersal trade‐off exists in the alpine grassland community and that this pattern was primarily demonstrated by forbs. The results suggest that most forb species are constrained to be either good competitors or good dispersers but not both, while there was no significant trade‐off between competitive and dispersal ability for most graminoids. This might occur because graminoids undergo clonal reproduction, which allows them to find more benign microenvironments, forage for nutrients across a large area and store resources in clonal structures, and they are thus not strictly limited by the particular resources at our study site. To the best of our knowledge, this is the first time the CD trade‐off has been tested for plants across the whole life cycle in a natural multispecies plant community, and more comprehensive studies are still needed to explore the underlying mechanisms and the linkage between the CD trade‐off and community composition.     

Sick plants in grassland communities: a growth‐defense trade‐off is the main driver of fungal pathogen abundance

Aboveground fungal pathogens can substantially reduce biomass production in grasslands. However, we lack a mechanistic understanding of the drivers of fungal pathogen infection and impact. Using a grassland global change and biodiversity experiment we show that the trade‐off between plant growth and defense is the main determinant of infection incidence. In contrast, nitrogen addition only indirectly increased incidence via shifting plant communities towards faster growing species. Plant diversity did not decrease incidence, likely because spillover of generalist pathogens or dominance of susceptible plants counteracted negative diversity effects. A fungicide treatment increased plant biomass production and high levels of infection incidence were associated with reduced biomass. However, pathogen impact was context dependent and infection incidence reduced biomass more strongly in diverse communities. Our results show that a growth‐defense trade‐off is the key driver of pathogen incidence, but pathogen impact is determined by several mechanisms and may depend on pathogen community composition.     

An appraisal of the enzyme stability‐activity trade‐off

A longstanding idea in evolutionary physiology is that an enzyme cannot jointly optimize performance at both high and low temperatures due to a trade‐off between stability and activity. Although a stability‐activity trade‐off has been observed for well‐characterized examples, such a trade‐off is not imposed by any physical chemical constraint. To better understand the pervasiveness of this trade‐off, I investigated the stability‐activity relationship for comparative biochemical studies of purified orthologous enzymes identified by a literature search. The nature of this relationship varied greatly among studies. Notably, studies of enzymes with low mean synonymous nucleotide sequence divergence were less likely to exhibit the predicted negative correlation between stability and activity. Similarly, a survey of directed evolution investigations of the stability‐activity relationship indicated that these traits are often uncoupled among nearly identical yet phenotypically divergent enzymes. This suggests that the presumptive trade‐off often reported for investigations of enzymes with high mean sequence divergence may in some cases instead be a consequence of the degeneration over time of enzyme function in unselected environments, rather than a direct effect of thermal adaptation. The results caution against the general assertion of a stability‐activity trade‐off during enzyme adaptation.     

The form of a trade‐off determines the response to competition

Understanding how populations and communities respond to competition is a central concern of ecology. A seminal theoretical solution first formalised by Levins (and re‐derived in multiple fields) showed that, in theory, the form of a trade‐off should determine the outcome of competition. While this has become a central postulate in ecology it has evaded experimental verification, not least because of substantial technical obstacles. We here solve the experimental problems by employing synthetic ecology. We engineer strains of Escherichia coli with fixed resource allocations enabling accurate measurement of trade‐off shapes between bacterial survival and multiplication in multiple environments. A mathematical chemostat model predicts different, and experimentally verified, trajectories of gene frequency changes as a function of condition‐specific trade‐offs. The results support Levins' postulate and demonstrates that otherwise paradoxical alternative outcomes witnessed in subtly different conditions are predictable.     

Quality–quantity trade‐off of human offspring under adverse environmental conditions

A central paradigm in life‐history theory is the trade‐off between offspring number and quality. Several studies have investigated this trade‐off in humans, but data are inconclusive, perhaps because prosperous socio‐cultural factors mask the trade‐off. Therefore, we studied 2461 offspring groups in an area under adverse conditions in northern Ghana with high fertility and mortality rates. In a linear mixed model controlling for differences in age and tribe of the mother and socioeconomic status, each additional child in the offspring group resulted in a 2.3% (95% CI 1.9–2.6%, P < 0.001) lower proportional survival of the offspring. Furthermore, we made use of the polygamous population structure and compared offspring of co‐wives in 388 households, thus controlling for variation in resources between compounds. Here, offspring survival decreased 2.8% (95% CI 2.3–4.0%, P < 0.001) for each increase in offspring number. We interpret these data as an apparent quality–quantity trade‐off in human offspring.     

Discovery–dominance trade‐off among widespread invasive ant species

Ants are among the most problematic invasive species. They displace numerous native species, alter ecosystem processes, and can have negative impacts on agriculture and human health. In part, their success might stem from a departure from the discovery–dominance trade‐off that can promote co‐existence in native ant communities, that is, invasive ants are thought to be at the same time behaviorally dominant and faster discoverers of resources, compared to native species. However, it has not yet been tested whether similar asymmetries in behavioral dominance, exploration, and recruitment abilities also exist among invasive species. Here, we establish a dominance hierarchy among four of the most problematic invasive ants (Linepithema humile, Lasius neglectus, Wasmannia auropunctata, Pheidole megacephala) that may be able to arrive and establish in the same areas in the future. To assess behavioral dominance, we used confrontation experiments, testing the aggressiveness in individual and group interactions between all species pairs. In addition, to compare discovery efficiency, we tested the species' capacity to locate a food resource in a maze, and the capacity to recruit nestmates to exploit a food resource. The four species differed greatly in their capacity to discover resources and to recruit nestmates and to dominate the other species. Our results are consistent with a discovery–dominance trade‐off. The species that showed the highest level of interspecific aggressiveness and dominance during dyadic interactions.     

Parasites and competitors suppress bacterial pathogen synergistically due to evolutionary trade‐offs

Parasites and competitors are important for regulating pathogen densities and subsequent disease dynamics. It is, however, unclear to what extent this is driven by ecological and evolutionary processes. Here, we used experimental evolution to study the eco‐evolutionary feedbacks among Ralstonia solanacearum bacterial pathogen, Ralstonia‐specific phage parasite, and Bacillus amyloliquefaciens competitor bacterium in the laboratory and plant rhizosphere. We found that while the phage had a small effect on pathogen densities on its own, it considerably increased the R. solanacearum sensitivity to antibiotics produced by B. amyloliquefaciens. Instead of density effects, this synergy was due to phage‐driven increase in phage resistance that led to trade‐off with the resistance to B. amyloliquefaciens antibiotics. While no evidence was found for pathogen resistance evolution to B. amyloliquefaciens antibiotics, the fitness cost of adaptation (reduced growth) was highest when the pathogen had evolved in the presence of both parasite and competitor. Qualitatively similar patterns were found between laboratory and greenhouse experiments even though the evolution of phage resistance was considerably attenuated in the tomato rhizosphere. These results suggest that evolutionary trade‐offs can impose strong constraints on disease dynamics and that combining phages and antibiotic‐producing bacteria could be an efficient way to control agricultural pathogens.     

Life histories of closely related amphidromous and non‐migratory fish species: a trade‐off between egg size and fecundity

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Evaluating the life‐history trade‐off between dispersal capability and reproduction in wing dimorphic insects: a meta‐analysis

A life‐history trade‐off exists between flight capability and reproduction in many wing dimorphic insects: a long‐winged morph is flight‐capable at the expense of reproduction, while a short‐winged morph cannot fly, is less mobile, but has greater reproductive output. Using meta‐analyses, I investigated specific questions regarding this trade‐off. The trade‐off in females was expressed primarily as a later onset of egg production and lower fecundity in long‐winged females relative to short‐winged females. Although considerably less work has been done with males, the trade‐off exists for males among traits primarily related to mate acquisition. The trade‐off can potentially be mitigated in males, as long‐winged individuals possess an advantage in traits that can offset the costs of flight capability such as a shorter development time. The strength and direction of trends differed significantly among insect orders, and there was a relationship between the strength and direction of trends with the relative flight capabilities between the morphs. I discuss how the trade‐off might be both under‐ and overestimated in the literature, especially in light of work that has examined two relevant aspects of wing dimorphic species: (1) the effect of flight‐muscle histolysis on reproductive investment; and (2) the performance of actual flight by flight‐capable individuals.     

Evolutionary innovation and diversification of carotenoid‐based pigmentation in finches

The ornaments used by animals to mediate social interactions are diverse, and by reconstructing their evolutionary pathways we can gain new insights into the mechanisms underlying ornamental innovation and variability. Here, we examine variation in plumage carotenoids among the true finches (Aves: Fringillidae) using biochemical and comparative phylogenetic analyses to reconstruct the evolutionary history of carotenoid states and evaluate competing models of carotenoid evolution. Our comparative analyses reveal that the most likely ancestor of finches used dietary carotenoids as yellow plumage colorants, and that the ability to metabolically modify dietary carotenoids into more complex pigments arose secondarily once finches began to use modified carotenoids to create red plumage. Following the evolutionary “innovation” that enabled modified red carotenoid pigments to be deposited as plumage colorants, many finch species subsequently modified carotenoid biochemical pathways to create yellow plumage. However, no reversions to dietary carotenoids were observed. The finding that ornaments and their underlying mechanisms may be operating under different selection regimes—where ornamental trait colors undergo frequent reversions (e.g., between red and yellow plumage) while carotenoid metabolization mechanisms are more conserved—supports a growing empirical framework suggesting different evolutionary patterns for ornaments and the mechanistic innovations that facilitate their diversification.     

A trade‐off between antipredatory behavior and pairing competition produced by male‑male tandem running in three Reticulitermes species

Due to the omnipresent risk of predation, termites have evolved many antipredatory behaviors. The two related species Reticulitermes speratus and R. chinensis have been demonstrated to use homosexual tandem running to decrease individual predation risk after shedding their wings. In this study, we tested risk of predation in the termite R. flaviceps, which is distantly related to the above two species. We determined that homosexual tandem running also led to low individual predation risk in dealates of R. flaviceps. Moreover, by combining a predation model with a competition model, we observed a typical trade‐off phenomenon between antipredatory behavior and pairing competition produced by male?male tandem running in the above three Reticulitermes species. Our results indicated that male?male tandem running could effectively protect disadvantaged individuals from being caught, but disadvantaged individuals would be easily eliminated in pairing competition after male?male tandem running, suggesting that male?male tandem running can promote population evolution in termites by repeatedly removing the relatively inferior male individuals.     

The trade‐off to macroptery in the cricket Gryllus firmus: a path analysis in males

Among the Orthoptera, wing dimorphism, where one morph is long‐winged and flight capable while the other is short‐winged and flight incapable, is common and believed to be maintained in populations due to trade‐offs to flight capability. In males, macropterous individuals call less than micropterous individuals and as a consequence obtain fewer matings. This trade‐off is hypothesized to be mediated by the energetic costs of calling. In this paper we report results for a path analysis examining lipid weight and DLM (dorso longitudinal muscle) condition of male Gryllus firmus. We found that as DLM condition changes from a nonfunctional to a functional state, call duration decreases, and as lipid weight increases, call duration increases. The most important linked path was wing morph → DLM condition → call duration. This model is consistent with the prediction that the trade‐off between wing morph and call duration is mediated via DLM and lipid stores.     

How zooplankton feed: mechanisms,traits and trade‐offs

Zooplankton is a morphologically and taxonomically diverse group and includes organisms that vary in size by many orders of magnitude, but they are all faced with the common problem of collecting food from a very dilute suspension. In order to maintain a viable population in the face of mortality, zooplankton in the ocean have to clear daily a volume of ambient water for prey particles that is equivalent to about 10⁶ times their own body volume. While most size‐specific vital rates and mortality rates decline with size, the clearance requirement is largely size‐independent because food availability also declines with size. There is a limited number of solutions to the problem of concentrating dilute prey from a sticky medium: passive and active ambush feeding; feeding‐current feeding, where the prey is either intercepted directly, retained on a filter, or individually perceived and extracted from the feeding current; cruise feeding; and colonization of large particles and marine snow aggregates. The basic mechanics of these food‐collection mechanisms are described, and it is shown that their efficiencies are inherently different and that each of these mechanisms becomes less efficient with increasing size. Mechanisms that compensate for this decline in efficiency are described, including inflation of feeding structures and development of vision. Each feeding mode has implications beyond feeding in terms of risk of encountering predators and chance of meeting mates, and they partly target different types of prey. The main dichotomy is between (inefficient) ambush feeding on motile prey and the more efficient active feeding modes; a secondary dichotomy is between (efficient) hovering and (less efficient) cruising feeding modes. The efficiencies of the various feeding modes are traded off against feeding‐mode‐dependent metabolic expenses, predation risks, and mating chances. The optimality of feeding strategies, evaluated as the ratio of gain over risk, varies with the environment, and may explain both size‐dependent and spatio‐temporal differences in distributions of various feeding types as well as other aspects of the biology of zooplankton (mating behaviour, predator defence strategies).     

A genotypic trade‐off between the number and size of clonal offspring in the stoloniferous herb Potentilla reptans

A negative, genetic correlation between the total number and average size of progeny is a classical life‐history trade‐off that can greatly affect the fitness of organisms in their natural environments. This trade‐off has been investigated for animals and for sexually reproducing plants. However, evidence for a genetical size‐number trade‐off for clonal progeny in plants is still scarce. This study provides experimental evidence for such a trade‐off in the stoloniferous herb Potentilla reptans, and it studies phenotypic plasticity to light availability for the involved traits. Genotypes of P. reptans were collected from distinctively different environments, clonally replicated and exposed to high light and to shaded conditions. We found a significant negative correlation between the average size and the total number of offspring across genotypes for both light environments. Shading reduced ramet numbers, but hardly affected average ramet size.     

Above‐ and belowground herbivory jointly impact defense and seed dispersal traits in Taraxacum officinale

Plants are able to cope with herbivores by inducing defensive traits or growth responses that allow them to reduce or avoid the impact of herbivores. Since above‐ and belowground herbivores differ substantially in life‐history traits, for example feeding types, and their spatial distribution, it is likely that they induce different responses in plants. Moreover, strong interactive effects on defense and plant growth are expected when above‐ and belowground herbivores are jointly present. The strengths and directions of these responses have been scarcely addressed in the literature. Using Taraxacum officinale, the root‐feeding nematode Meloidogyne hapla and the locust Schistocerca gregaria as a model species, we examined to what degree above‐ and belowground herbivory affect (1) plant growth responses, (2) the induction of plant defensive traits, that is, leaf trichomes, and (3) changes in dispersal‐related seed traits and seed germination. We compared the performance of plants originating from different populations to address whether plant responses are conserved across putative different genotypes. Overall, aboveground herbivory resulted in increased plant biomass. Root herbivory had no effect on plant growth. Plants exposed to the two herbivores showed fewer leaf trichomes than plants challenged only by one herbivore and consequently experienced greater aboveground herbivory. In addition, herbivory had effects that reached beyond the individual plant by modifying seed morphology, producing seeds with longer pappus, and germination success.     

How traits shape trees: new approaches for detecting character state‐dependent lineage diversification

Biologists have long sought to understand the processes underlying disparities in clade size across the tree of life and the extent to which such clade size differences can be attributed to the evolution of particular traits. The association of certain character states with species‐rich clades suggests that trait evolution can lead to increased diversification, but such a pattern could also arise due other processes, such as directional trait evolution. Recent advances in phylogenetic comparative methods have provided new statistical approaches for distinguishing between these intertwined and potentially confounded macroevolutionary processes. Here, we review the historical development of methods for detecting state‐dependent diversification and explore what new methods have revealed about classic examples of traits that affect diversification, including evolutionary dead ends, key innovations and geographic traits. Applications of these methods thus far collectively suggest that trait diversity commonly arises through the complex interplay between transition, speciation and extinction rates and that long hypothesized evolutionary dead ends and key innovations are instead often cases of directional trends in trait evolution.