The Ratchet and the Red Queen: the maintenance of sex in parasites

The adaptive significance of sexual reproduction remains as an unsolved problem in evolutionary biology. One promising hypothesis is that frequency‐dependent selection by parasites selects for sexual reproduction in hosts, but it is unclear whether such selection on hosts would feed back to select for sexual reproduction in parasites. Here we used individual‐based computer simulations to explore this possibility. Specifically, we tracked the dynamics of asexual parasites following their introduction into sexual parasite populations for different combinations of parasite virulence and transmission. Our results suggest that coevolutionary interactions with hosts would generally lead to a stable coexistence between sexual parasites and a single parasite clone. However, if multiple mutations to asexual reproduction were allowed, we found that the interaction led to the accumulation of clonal diversity in the asexual parasite population, which led to the eventual extinction of the sexual parasites. Thus, coevolution with sexual hosts may not be generally sufficient to select for sex in parasites. We then allowed for the stochastic accumulation of mutations in the finite parasite populations (Muller's Ratchet). We found that, for higher levels of parasite virulence and transmission, the population bottlenecks resulting from host–parasite coevolution led to the rapid accumulation of mutations in the clonal parasites and their elimination from the population. This result may explain the observation that sexual reproduction is more common in parasitic animals than in their free‐living relatives.     

The natural selection of metabolism explains curvature in allometric scaling

I simulate the natural selection of metabolism and mass to explain the curvature in the metabolic allometry for placental and marsupial mammals. The simulation model starts with a single ancestor in each clade at the Cretaceous–Palaeogene boundary 65 million years ago. The release of inter‐specific competition by the extinction of dinosaurs make it possible for each clade to diversify into a multitude of species across a wide range of empty niches. The selection of mass in these species depends on the net assimilated energy that depends on 1) the handling of the resources in the different niches, and on 2) mass‐specific metabolism that defines the pace of the handling process. The model is fitted to explain the maximum observed body masses over time and the current inter‐specific allometry for metabolism. The selection of mass‐specific metabolism is found to bend the metabolic allometry over time, even when all species have the same selection on the per‐generation time‐scale of natural selection. This is because the smaller species evolve over a larger number of generations than the larger species. The strongest curvature is in the placental clade, where the estimated rate of exponential increase in mass‐specific metabolism is 9.3 × 10^?9 (95% CI: 7.3 × 10^?9 – 1.1 × 10^?8) on the per‐generation time‐scale. This is an order of magnitude larger than the estimate for marsupials, in agreement with an average metabolism that is 30% larger in placentals relative to marsupials of similar size.     

From survivors to replicators: evolution by natural selection revisited

For evolution by natural selection to occur it is classically admitted that the three ingredients of variation, difference in fitness and heredity are necessary and sufficient. In this paper, I show using simple individual-based models, that evolution by natural selection can occur in populations of entities in which neither heredity nor reproduction are present. Furthermore, I demonstrate by complexifying these models that both reproduction and heredity are predictable Darwinian products (i.e. complex adaptations) of populations initially lacking these two properties but in which new variation is introduced via mutations. Later on, I show that replicators are not necessary for evolution by natural selection, but rather the ultimate product of such processes of adaptation. Finally, I assess the value of these models in three relevant domains for Darwinian evolution.     

Evolution of male age‐specific reproduction under differential risks and causes of death: males pay the cost of high female fitness

Classic theories of ageing evolution predict that increased extrinsic mortality due to an environmental hazard selects for increased early reproduction, rapid ageing and short intrinsic lifespan. Conversely, emerging theory maintains that when ageing increases susceptibility to an environmental hazard, increased mortality due to this hazard can select against ageing in physiological condition and prolong intrinsic lifespan. However, evolution of slow ageing under high‐condition‐dependent mortality is expected to result from reallocation of resources to different traits and such reallocation may be hampered by sex‐specific trade‐offs. Because same life‐history trait values often have different fitness consequences in males and females, sexually antagonistic selection can preserve genetic variance for lifespan and ageing. We previously showed that increased condition‐dependent mortality caused by heat shock leads to evolution of long‐life, decelerated late‐life mortality in both sexes and increased female fecundity in the nematode, Caenorhabditis remanei. Here, we used these cryopreserved lines to show that males evolving under heat shock suffered from reduced early‐life and net reproduction, while mortality rate had no effect. Our results suggest that heat‐shock resistance and associated long‐life trade‐off with male, but not female, reproduction and therefore sexually antagonistic selection contributes to maintenance of genetic variation for lifespan and fitness in this population.     

Cheats as first propagules: A new hypothesis for the evolution of individuality during the transition from single cells to multicellularity

The emergence of individuality during the evolutionary transition from single cells to multicellularity poses a range of problems. A key issue is how variation in lower‐level individuals generates a corporate (collective) entity with Darwinian characteristics. Of central importance to this process is the evolution of a means of collective reproduction, however, the evolution of a means of collective reproduction is not a trivial issue, requiring careful consideration of mechanistic details. Calling upon observations from experiments, we draw attention to proto‐life cycles that emerge via unconventional routes and that transition, in single steps, individuality to higher levels. One such life cycle arises from conflicts among levels of selection and invokes cheats as a primitive germ line: it lays the foundation for collective reproduction, the basis of a self‐policing system, the selective environment for the emergence of development, and hints at a plausible origin for a soma/germ line distinction.     

Reproduction alters oxidative status when it is traded‐off against longevity

Oxidative stress has been proposed to mediate one of the most important aspects of life‐history evolution: the trade‐off between reproduction and self‐maintenance. However, empirical studies have cast doubt on the generality of this intriguing notion. Here, we hypothesize that reproduction alters oxidative status only when a trade‐off between reproduction and self‐maintenance occurs. Accordingly, in female Bicyclus anynana butterflies, we found that reproduction affected oxidative markers only under challenging thermal conditions that made the trade‐off between reproduction and longevity emerge. Interestingly, under such conditions, butterflies favored longevity over reproduction, suggesting that self‐maintenance mechanisms were activated. Accordingly, butterflies reproducing under challenging thermal conditions exhibited enhanced antioxidant defenses and stable oxidative damage. Altogether, our results indicate that a trade‐off between reproduction and self‐maintenance is indeed a necessary condition for reproduction to alter oxidative status, and that the effects of such a trade‐off on oxidative status depend on whether priority is given to self‐maintenance or reproduction. Assessing the existence of the trade‐off between self‐maintenance and reproduction, and whether self‐maintenance is prioritized relative to reproduction is therefore crucial for understanding variation in oxidative status in reproducing animals, which may clarify the general implication of oxidative stress in the resolution of life‐history trade‐offs.     

One cell, two cell, red cell, blue cell: The persistence of a unicellular stage in multicellular life histories

As developmental biologists come closer to understanding at the molecular and genetic levels how a zygote becomes an adult, it is easy to forget that the very phenomenon that gives them an occupation remains a vexing problem to evolutionary biologists: why do unicellular stages persist in life histories of multicellular organisms? There are two explanatory hypotheses. One is that a unicellular stage purges multicellular organisms of deleterious mutations by exposing offspring that are each uniformly of one genotype to selection. Another is that a one-cell stage reduces conflicts of interest among genetically different replicators within an organism.     

Viral sex, levels of selection, and the origin of life.

Several issues in Chao's related paper J. theor. Biol. (1991, 153, 229-246) are revisited. It is argued that mixes of segments from different viral coinfection groups cannot be regarded as sex, unless one is willing to accept that these groups are replicators and individuals. But, because selection in coinfection groups is dynamically analogous to that in trait groups in structured demes, one should also regard these latter groups as replicators. This approach is unacceptable since the groups in question have irregular ploidies, an unfixed number of parents, and no rules analogous to those of meiosis. It is emphasized, however, that the effective presence of neighbour-modulated fitness can ensure dynamical coexistence of covirus segments, even if the equal net reproduction rate within groups is not warranted. It seems that during the origin of coviruses from complete viruses, a higher-level evolutionary unit has become disintegrated, whereas during the origin of life a higher-level unit, the protocell, has emerged from lower-level ones, i.e. unlinked, replicating genes. These two gene-level systems are not homologous, but analogous. Although it is true that the resistance to parasites and the need to avoid a mutational collapse of the genome are likely to have called for some compartmentation in precellular stages of evolution, no clear demonstration, that the proposed mechanisms (the compartmentalized hypercycle and the stochastic corrector model) do in fact solve the error threshold problem, exists. Neither has a plausible mode of protocellular sex been suggested.     

Genetic improvement of production while maintaining fitness

Selection for production tends to decrease fitness, in particular, major components such as reproductive performance. Under an infinitesimal genetic model restricted index selection can maintain reproductive performance while improving production. However, reproductive traits are thought to be controlled by a finite number of recessive alleles at low frequency. Culling for low reproduction may weed out the negative homozygous genotypes for reproduction in any generation, thus controlling the frequencies of alleles negative for reproduction. Restricted index selection, culling for low reproduction and a new method called empirical restricted index selection were compared for their efficiency in improving production while maintaining reproduction. Empirical restricted index selection selects animals that have on average the highest estimated breeding values for production and on average the same estimated breeding values for reproduction as the base population. An infinitesimal genetic model and models with a finite number of loci for reproduction with rare deleterious recessive alleles, which have additive, dominant or no pleiotropic effects on production, were considered. When reproduction was controlled by a finite number of loci with rare recessive alleles, restricted index selection could not maintain reproduction. The culling of 20% of the animals on reproduction maintained reproduction with all genetic models, except for the model where loci for reproduction had additive effects on production. Empirical restricted selection maintained reproduction with all models and yielded higher production responses than culling on reproduction, except when there were dominant pleiotropic effects on production.     

Reproductive biology of Clintonia udensis

To clarify the life history of Clintonia udensis, we investigated its reproductive systems and spatio‐temporal population structure. Pollination experiments and the observation of floral visitors revealed that C. udensis was compatible with both self‐ and outcross‐pollen, and it potentially produces seeds by insect‐mediated outcrossing in natural conditions. In addition, propagation by clonal reproduction from rhizomes was evident. In this study, it was clarified that C. udensis potentially propagates by sexual and asexual reproduction and maintains its population through a stable frequency of flowering. The differences in the dependence on each reproduction mode could be one of the contributing factors for creating a variety of population sizes and distribution patterns of ramets in populations.     

A model for the origin of group reproduction during the evolutionary transition to multicellularity

During the evolution of multicellular organisms, the unit of selection and adaptation, the individual, changes from the single cell to the multicellular group. To become individuals, groups must evolve a group life cycle in which groups reproduce other groups. Investigations into the origin of group reproduction have faced a chicken-and-egg problem: traits related to reproduction at the group level often appear both to be a result of and a prerequisite for natural selection at the group level. With a focus on volvocine algae, we model the basic elements of the cell cycle and show how group reproduction can emerge through the coevolution of a life-history trait with a trait underpinning cell cycle change. Our model explains how events in the cell cycle become reordered to create a group life cycle through continuous change in the cell cycle trait, but only if the cell cycle trait can coevolve with the life-history trait. Explaining the origin of group reproduction helps us understand one of life''s most familiar, yet fundamental, aspects—its hierarchical structure.     

Feed‐backs among inbreeding,inbreeding depression in sperm traits,and sperm competition can drive evolution of costly polyandry

Ongoing ambitions are to understand the evolution of costly polyandry and its consequences for species ecology and evolution. Emerging patterns could stem from feed‐back dynamics between the evolving mating system and its genetic environment, defined by interactions among kin including inbreeding. However, such feed‐backs are rarely considered in nonselfing systems. We use a genetically explicit model to demonstrate a mechanism by which inbreeding depression can select for polyandry to mitigate the negative consequences of mating with inbred males, rather than to avoid inbreeding, and to elucidate underlying feed‐backs. Specifically, given inbreeding depression in sperm traits, costly polyandry evolved to ensure female fertility, without requiring explicit inbreeding avoidance. Resulting sperm competition caused evolution of sperm traits and further mitigated the negative effect of inbreeding depression on female fertility. The evolving mating system fed back to decrease population‐wide homozygosity, and hence inbreeding. However, the net overall decrease was small due to compound effects on the variances in sex‐specific reproductive success and paternity skew. Purging of deleterious mutations did not eliminate inbreeding depression in sperm traits or hence selection for polyandry. Overall, our model illustrates that polyandry evolution, both directly and through sperm competition, might facilitate evolutionary rescue for populations experiencing sudden increases in inbreeding.     

Contributions of animal nutrition research in rostock to energetic feed evaluation

The Rostock research in animal nutrition has underlain in continuation and progressive development of Kellner's starch value system, net energy fat as measuring unit for energetic feed evaluation. Net energy‐fat was used as an uniform unit of measure for all farm animals with different performances. The scientific basis for the net energy‐fat system was created by numerous studies on energy retention and utilisation efficiency of pure nutrients and nutrients of feedstuffs and rations. For the estimation the energy content of feedstuffs and rations, multiple regression equations were derived on the basis of experimental results of the energy research group. The regressions for the estimation of energy values are used directly and modified in feed evaluation systems for practical use. The Rostock research group in energy metabolism created also essential contributions to factorial derivations of energy requirement of farm animals. In the presented paper selected results on maintenance energy requirement in relation to partial energy requirement values and utilisation efficiencies in growing, pregnant and lactating animals, especially cattle and pigs, are comprised. The Rostock results are compared to those from literature.     

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.     

生物多样性的自组织、起源和演化

生命系统是典型的自组织系统,系统中的多样性和复杂性存在着涨落,巨涨落在生物多样性上表现为生物的大规模爆发和灭绝,微涨落则为常规发生和背景灭绝,不断增加多样性是生命系统的内在属性,而实际多样性由自然选择决定,低选择压有利于生物多样性的产生,系统中过于优势的单一成分抑制多样性,系统的复杂性相变存在临界点,临界点定,低选择压有利于生物多样性的产生,系统中过于优势的单一成分抑制多样性,系统的复杂性相变存在临界点,临界点之上可自发产生正反馈的繁荣,临界点之下会发生趋于简单性的相变。上述原理可应用在生物多样性研究和保护中,例如研究特定系统的相变临界点,以便在配置系统组分时使复杂性超过其相变临界点,促使多样性的维持和增长由“被组织”进入“自组织”的可持续发展。     

Evolution of indefinite generation lengths

Intrinsic mortality at relatively advanced age results from natural selection favouring early reproduction. When individuals produce many and early offspring, costs are incurred due to the accumulation of pleiotropic mutations with adverse effects late in life, which make senescence an inevitable result of evolution. However, a few organisms exist with seemingly indefinite generation lengths. This paper identifies conditions of life history and ecology under which natural selection favours continually reducing intrinsic mortality. The analysis considers the particular case of populations held at carrying capacity by density dependence suppressing net fertility, acting either on fecundity equally across fecund ages or on juvenile mortality up to the first fecund age. This broad category of density dependence increases the susceptibility of populations to invasion by mutations that extend net fertility into later life. Whether a population then evolves longer generation times depends on the relative timing of period benefit to onset of senescent cost amongst antagonistic pleiotropisms that arise to confront the selection process. Simulations show that if the onset of senescent costs either precedes the benefit, is concurrent with it, or is postponed by a fixed interval, then natural selection will favour those pleiotropisms that increase generation length. The selection on generation-lengthening pleiotropisms continues indefinitely and regardless of current generation length, for as long as the environment remains constant. The wide range of life histories encompassed by these conditions leads to the conclusion that many species may have evolved generation lengths considerably longer than the minimum set by developmental constraints.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 269–280.     

Current views on insect feed and its future

Population growth and the subsequent increased demand for food, along with the rise in cost of feed, have led insect feed to be considered as an alternative to conventional animal feed. Insect feed is a sustainable and nutritious option; however, it does carry the risk of lower microbiological safety than conventional feed. Although there is some hesitancy from farmers in adapting insect feed due to fear of market rejection of insect‐fed animals, surveys seem to show positive attitudes of people towards insect feed when they informed of the benefits. Traditional methods of harvesting insects is not a sustainable method of production, and therefore further research will be needed to access appropriate methods of mass‐producing insects without putting a strain on the natural ecosystem. This review discusses the benefits and risks of using insect feed, its acceptance, type of animals that can be fed by insects, and future directions of insect feed.     

Energy,Nitrogen, and Farm Surplus Transitions in Agriculture from Historical Data Modeling. France, 1882–2013.

This article addresses agricultural metabolism and transitions for energy, nitrogen, farm production, self‐sufficiency, and surplus from historical data since the nineteenth century. It builds on an empirical data set on agricultural production and production means in France covering 130 consecutive years (1882–2013). Agricultural transitions have increased the net production and surplus of farms by a factor of 4 and have zeroed self‐sufficiency. The energy consumption remained quasi‐stable since 1882, but the energy and nitrogen structure of agriculture fully changed. With an EROI (energy return to energy invested) of 2 until 1950, preindustrial agriculture consumed as much energy to function as it provided in exportable surplus to sustain the nonagricultural population. The EROI doubled to 4 over the last 60 years, driven, on the one hand, by efficiency improvements in traction through the replacement of draft animals by motors and, on the other hand, by the joint increase in crop yields and efficiency in nitrogen use. Agricultural energy and nitrogen transitions shifted France from a self‐sufficiency agri‐food‐energy regime to a fossil‐dependent food export regime. Knowledge of resource conversion mechanisms over the long duration highlights the effects of changing agricultural metabolism on the system's feeding capacity. Farm self‐sufficiency is an asset against fossil fuel constraints, price volatility, and greenhouse gas emissions, but it equates to lower farm surplus in support of urbanization.     

Density‐dependent,central‐place foraging in a grazing herbivore: competition and tradeoffs in time allocation near water

Optimal foraging theory addresses one of the core challenges of ecology: predicting the distribution and abundance of species. Tests of hypotheses of optimal foraging, however, often focus on a single conceptual model rather than drawing upon the collective body of theory, precluding generalization. Here we demonstrate links between two established theoretical frameworks predicting animal movements and resource use: central‐place foraging and density‐dependent habitat selection. Our goal is to better understand how the nature of critical, centrally placed resources like water (or minerals, breathing holes, breeding sites, etc.) might govern selection for food (energy) resources obtained elsewhere – a common situation for animals living in natural conditions. We empirically test our predictions using movement data from a large herbivore distributed along a gradient of water availability (feral horses, Sable Island, Canada, 2008–2013). Horses occupying western Sable Island obtain freshwater at ponds while in the east horses must drink at self‐excavated wells (holes). We studied the implications of differential access to water (time needed for a horse to obtain water) on selection for vegetation associations. Consistent with predictions of density‐dependent habitat selection, horses were reduced to using poorer‐quality habitat (heathland) more than expected close to water (where densities were relatively high), but were free to select for higher‐quality grasslands farther from water. Importantly, central‐place foraging was clearly influenced by the type of water‐source used (ponds vs. holes, the latter with greater time constraints on access). Horses with more freedom to travel (those using ponds) selected for grasslands at greater distances and continued to select grasslands at higher densities, whereas horses using water holes showed very strong density‐dependence in how habitat could be selected. Knowledge of more than one theoretical framework may be required to explain observed variation in foraging behavior of animals where multiple constraints simultaneously influence resource selection.