The process of adaptation of flour beetles to new environments

Five populations derived from a composite, genetically heterogeneous strain of the flour beetle, Tribolium castaneum, were selected on new diets (dog food, powdered rice, brewers' yeast, wheat flour and oats) for 13–16 generations. A control population was reared on the standard medium (flour + 5% brewers' yeast). Adaptedness was measured in terms of (1) fitness parameters (survival and developmental time), (2) amylase activity levels (amylase is an essential digestive enzyme in flour beetles) and (3) food preference behavior.There were significant temporal trends in fitness components in the selected populations. Survival was initially low but increased with time. Developmental time decreased in later generations of selection. The control population showed the smallest increase in survival and no decrease in developmental time. When tested at the end of the experiment, survival to adulthood of eggs from each selected population on its selective diet was higher than that of control eggs. On the standard medium, no differences in survival among populations were detected. These results suggest that the improvement in fitness may indicate adaptation to the new environments created by the different food media.Amylase activity also increased temporally in 4 selected populations but not in the control (nor on unenriched wheat flour). Tests at the end of the experiment, however, suggest that this increase was, in large part, environmentally induced. We found no evidence that an adaptive genetic change in amylase regulation took place.There were no temporal trends in food-preference behavior during the selection process.     

The evolution of environmental and genetic sex determination in fluctuating environments

Twenty years ago, Bulmer and Bull suggested that disruptive selection, produced by environmental fluctuations, can result in an evolutionary transition from environmental sex determination (ESD) to genetic sex determination (GSD). We investigated the feasibility of such a process, using mutation-limited adaptive dynamics and individual-based computer simulations. Our model describes the evolution of a reaction norm for sex determination in a metapopulation setting with partial migration and variation in an environmental variable both within and between local patches. The reaction norm represents the probability of becoming a female as a function of environmental state and was modeled as a sigmoid function with two parameters, one giving the location (i.e., the value of the environmental variable for which an individual has equal chance of becoming either sex) and the other giving the slope of the reaction norm for that environment. The slope can be interpreted as being set by the level of developmental noise in morph determination, with less noise giving a steeper slope and a more switchlike reaction norm. We found convergence stable reaction norms with intermediate to large amounts of developmental noise for conditions characterized by low migration rates, small differential competitive advantages between the sexes over environments, and little variation between individual environments within patches compared to variation between patches. We also considered reaction norms with the slope parameter constrained to a high value, corresponding to little developmental noise. For these we found evolutionary branching in the location parameter and a transition from ESD toward GSD, analogous to the original analysis by Bulmer and Bull. Further evolutionary change, including dominance evolution, produced a polymorphism acting as a GSD system with heterogamety. Our results point to the role of developmental noise in the evolution of sex determination.     

The effect of sex on the repeatability of evolution in different environments

The adaptive function of sex has been extensively studied, while less consideration has been given to the potential downstream consequences of sex on evolution. Here, we investigate one such potential consequence, the effect of sex on the repeatability of evolution. By affecting the repeatability of evolution, sex could have important implications for biodiversity, and for our ability to make predictions about the outcome of environmental change. We allowed asexual and sexual populations of Chlamydomonas reinhardtii to evolve in novel environments and monitored both their change in fitness and variance in fitness after evolution. Sex affected the repeatability of evolution by changing the importance of the effect of selection, chance, and ancestral constraints on the outcome of the evolutionary process. In particular, the effects of sex were highly dependent on the initial genetic composition of the population and on the environment. Given the lack of a consistent effect of sex on repeatability across the environments used here, further studies to dissect in more detail the underlying reasons for these differences as well as studies in additional environments are required if we are to have a general understanding of the effects of sex on the repeatability of evolution.     

Facilitated variation: how evolution learns from past environments to generalize to new environments

One of the striking features of evolution is the appearance of novel structures in organisms. Recently, Kirschner and Gerhart have integrated discoveries in evolution, genetics, and developmental biology to form a theory of facilitated variation (FV). The key observation is that organisms are designed such that random genetic changes are channeled in phenotypic directions that are potentially useful. An open question is how FV spontaneously emerges during evolution. Here, we address this by means of computer simulations of two well-studied model systems, logic circuits and RNA secondary structure. We find that evolution of FV is enhanced in environments that change from time to time in a systematic way: the varying environments are made of the same set of subgoals but in different combinations. We find that organisms that evolve under such varying goals not only remember their history but also generalize to future environments, exhibiting high adaptability to novel goals. Rapid adaptation is seen to goals composed of the same subgoals in novel combinations, and to goals where one of the subgoals was never seen in the history of the organism. The mechanisms for such enhanced generation of novelty (generalization) are analyzed, as is the way that organisms store information in their genomes about their past environments. Elements of facilitated variation theory, such as weak regulatory linkage, modularity, and reduced pleiotropy of mutations, evolve spontaneously under these conditions. Thus, environments that change in a systematic, modular fashion seem to promote facilitated variation and allow evolution to generalize to novel conditions.     

The evolution of an annual life cycle in killifish: adaptation to ephemeral aquatic environments through embryonic diapause

An annual life cycle is characterized by growth, maturity, and reproduction condensed into a single, short season favourable to development, with production of embryos (seeds, cysts, or eggs) capable of surviving harsh conditions which juveniles or adults cannot tolerate. More typically associated with plants in desert environments, or temperate‐zone insects exposed to freezing winters, the evolution of an annual life cycle in vertebrates is fairly novel. Killifish, small sexually dimorphic fishes in the Order Cyprinodontiformes, have adapted to seasonally ephemeral water bodies across much of Africa and South America through the independent evolution of an annual life history. These annual killifish produce hardy desiccation‐resistant eggs that undergo diapause (developmental arrest) and remain buried in the soil for long periods when fish have perished due to the drying of their habitat. Killifish are found in aquatic habitats that span a continuum from permanent and stable to seasonal and variable, thus providing a useful system in which to piece together the evolutionary history of this life cycle using natural comparative variation. I first review adaptations for life in ephemeral aquatic environments in killifish, with particular emphasis on the evolution of embryonic diapause. I then bring together available evidence from a variety of approaches and provide a scenario for how this annual life cycle evolved. There are a number of features within Aplocheiloidei killifish including their inhabitation of marginal or edge aquatic habitat, their small size and rapid attainment of maturity, and egg properties that make them particularly well suited to the colonization of ephemeral waters.     

The physiological basis of adaptation in goats to harsh environments

Goat living in harsh environments represents a climax in the capacity of domestic ruminants to adjust to such areas. This ability is multifactorial: low body mass, and low metabolic requirements of goats can be regarded as an important asset to them for it minimise their maintenance and water requirements, in areas where water sources are widely distributed and food sources are limited by their quantity and quality. An ability to reduce metabolism allows goats to survive even after prolonged periods of severe limited food availability. A skillful grazing behaviour and efficient digestive system enable goats to attain maximal food intake and maximal food utilisation in a given condition. There is a positive interaction between the better recycling rate of urea and a better digestion of such food in desert goats. The rumen plays an important role in the evolved adaptations by serving as a huge fermentation vat and water reservoir. The water stored in the rumen is utilised during dehydration, and the rumen serves as a container, which accommodates the ingested water upon rehydration. The rumen, the salivary glands and the kidney coordinately function in the regulation of water intake and water distribution following acute dehydration and rapid rehydration. Goats in the tropics, when possible, eat a diet composed of tree-leaves and shrubs (browse), which ensure a reliable and steady supply of food all year around, albeit, from a low to medium quality food. Some of the physiological features of ruminants defined as intermediate feeders like large salivary gland, the large absorptive area of their rumen epithelium, and the capacity to change rapidly the volume of the foregut in response to environmental changes are most likely responsible for the goat’s superior digestion capacity.     

Genomic insights into adaptation to high-altitude environments

Elucidating the molecular genetic basis of adaptive traits is a central goal of evolutionary genetics. The cold, hypoxic conditions of high-altitude habitats impose severe metabolic demands on endothermic vertebrates, and understanding how high-altitude endotherms cope with the combined effects of hypoxia and cold can provide important insights into the process of adaptive evolution. The physiological responses to high-altitude stress have been the subject of over a century of research, and recent advances in genomic technologies have opened up exciting opportunities to explore the molecular genetic basis of adaptive physiological traits. Here, we review recent literature on the use of genomic approaches to study adaptation to high-altitude hypoxia in terrestrial vertebrates, and explore opportunities provided by newly developed technologies to address unanswered questions in high-altitude adaptation at a genomic scale.     

Evolutionary traction: the cost of adaptation and the evolution of sex

The advantage of sexual reproduction remains a puzzle for evolutionary biologists. Everything else being equal, asexual populations are expected to have twice the number of offspring produced by similar sexual populations. Yet, asexual species are uncommon among higher eukaryotes. In models assuming small populations, high mutation rates, or frequent environmental changes, sexual reproduction seems to have at least a two-fold advantage over asexuality. But the advantage of sex for large populations, low mutation rates, and rare or mild environmental changes remains a conundrum. Here we show that without recombination, rare advantageous mutations can result in increased accumulation of deleterious mutations ('evolutionary traction'), which explains the long-term advantage of sex under a wide parameter range.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

Multiple adaptive substitutions during evolution in novel environments

We consider an asexual population under strong selection-weak mutation conditions evolving on rugged fitness landscapes with many local fitness peaks. Unlike the previous studies in which the initial fitness of the population is assumed to be high, here we start the adaptation process with a low fitness corresponding to a population in a stressful novel environment. For generic fitness distributions, using an analytic argument we find that the average number of steps to a local optimum varies logarithmically with the genotype sequence length and increases as the correlations among genotypic fitnesses increase. When the fitnesses are exponentially or uniformly distributed, using an evolution equation for the distribution of population fitness, we analytically calculate the fitness distribution of fixed beneficial mutations and the walk length distribution.     

The evolution of sex chromosomes

Mammalian sex chromosomes appear, behave and function differently than the autosomes, passing on their genes in a unique sex-linked manner. The publishing of Ohno's hypothesis provided a framework for discussion of sex chromosome evolution, allowing it to be developed and challenged numerous times. In this report we discuss the pressures that drove the evolution of sex and the mechanisms by which it occurred. We concentrate on how the sex chromosomes evolved in mammals, discussing the various hypotheses proposed and the evidence supporting them.     

The ecology and genetics of fitness in Chlamydomonas. VIII. The dynamics of adaptation to novel environments after a single episode of sex

According to classical evolutionary theory, sexual recombination can generate the variation necessary to adapt to changing environments and thereby confer an evolutionary advantage of sexual over asexual reproduction. Using the green alga, Chlamydomonas reinhardtii, we investigated the effect of a single sexual episode on adaptation of heterotrophic growth on different carbon sources. In an initial mixture of isolates, sex was induced and the resulting offspring constituted the sexual populations, along with any unmated vegetative cells; the unmated mixture of isolates represented the asexual populations. Mean and variance in division rates (i.e., fitness) were measured four times during approximately 50 generations of vegetative growth in the dark on all possible combinations of four carbon sources. Consistent with effects of recombination of epistatic genes in linkage disequilibrium, sexual populations initially had a higher variance in fitness, but their mean fitness was lower than that of asexual populations, possibly due to recombinational load. Subsequently, fitness of sexual populations exceeded that of asexual ones, but finally they regained parity in both mean and variance of fitness. Although recombination was not more effective on more complex substrates, these results generally support the idea that sex can accelerate adaptation to novel environments.     

Evidence for two types of Aquilegia ecalcarata and its implications for adaptation to new environmentsOA

Spurs have played an important role in the radiation of the genus Aquilegia,but little is known about how the spurless state arose in A.ecalcarata.Here we aim to characterize the genetic divergence within A.ecalcarata and gain insights into the origin of this species.A total of 19 populations from A.ecalcarata and 23 populations from three of its closest relatives(Aquilegia kansuensis,Aquilegia rockii and Aquilegia yabeana) were sampled in this study.We sequenced fifteen nuclear gene fragments a...     

Information processing in multigame environments modeling the evolution of sex via punctuated equilibria

Uncertain environments are properly described by probability distributions which, as usual, can be collapsed or conditioned into distributions with reduced uncertainty through the processing of environmental information. Organisms which force this collapse gain evolutionary advantage by being able to employ strategies in a known environment rather than in a merely probable one. The accrued benefit gained from processing information can be precisely quantified by comparing benefits returned using distributions prior to, and after collapse, and these often large and immediate benefits can amply justify the evolutionary cost of information processing systems. More importantly, the evolution of information processing systems must necessarily occur in a predictable evolutionary sequence from less complex to more complex. Practical applications include modeling the evolution of sex modeled here as a sequence from asexual reproduction, to single gene exchange, to gene packet exchange, to same species packet exchange, and finally to sexual reproduction, sexual selection, Red Queen contests and so on. Modeling this sequence requires extensions to game theory originally designed to model a single game, to allow the simultaneous operation of many games. This extension is called a multigame environment. The dynamical evolution of the development sequence shows punctuated equilibria.     

The evolution of viviparity in holocene islands: ecological adaptation versus phylogenetic descent along the transition from aquatic to terrestrial environments

Species that contain populations with different reproductive modes offer excellent opportunities to study the transition between such strategies. Salamandra salamandra (Linnaeus, 1758) is one of two species within the Salamandra – Lyciasalamandra clade which displays two reproductive modes simultaneously. Along the S. salamandra distribution, the common reproductive mode is ovoviviparity although the species also has viviparous populations in the northern Iberian Peninsula. The occurrence of viviparity has recently been reported in two small offshore island populations on the Atlantic coast (NW Iberia), which originated after the last glacial period (8000–9000 years ago). In this paper, we analysed ovoviviparous, hybrid and viviparous populations (inland and mainland) from 17 localities across the northern Iberian Peninsula using two mitochondrial markers (Cyt b and COI , c . 1100 bp). Phylogenetic and phylogeographic analyses highly support that viviparity arose as an evolutionary novelty in the S. salamandra island populations and that viviparous populations are therefore not monophyletic. The recent insularity of Atlantic island populations leads us to conclude that the transition from ovoviviparity to viviparity can happen in a very short-time span. Additionally, to determine the likely source of this evolutionary transition, we discuss how ecological pressures could have an effect on the maintenance of the ovoviviparous reproductive mode. Hence, taking into account the results of this study, we propose the consideration of the island populations as an evolutionary unit for conservation purposes.     

The long-term adaptation of multicellular model organisms to non-terrestrial and space environments

The main point in this presentation is the following: It is of crucial importance that the Space Agencies define and support the long-term directions for Space Biology Research. The development and upgrading of Facilities and Carriers should be coordinated with the preparatory activities of scientific groups interested in tackling major questions using the future opportunities in the Space Exploration Programs. The current effort in establishing larger Research Networks may lead the way to a successful Space Program in the XXI Century.