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Phenotypic plasticity is the capacity for an individual genotype to produce different phenotypes in response to environmental variation (1). Most traits are plastic, but the degree to which plasticity is adaptive or non-adaptive depends on whether environmentally induced phenotypes are closer or further away from the local optimum (2-4). Existing theories make conflicting predictions about whether plasticity constrains or facilitates adaptive evolution (4-12). Debate persists because few empirical studies have tested the relationship between initial plasticity and subsequent adaptive evolution in natural populations. Here we show that the direction of plasticity in gene expression is generally opposite to the direction of adaptive evolution. We experimentally transplanted Trinidadian guppies (Poecilia reticulata) adapted to living with cichlid predators to cichlid-free streams, and tested for evolutionary divergence in brain gene expression patterns after three to four generations. We find 135 transcripts that evolved parallel changes in expression within the replicated introduction populations. These changes are in the same direction exhibited in a native cichlid-free population, suggesting rapid adaptive evolution. We find 89% of these transcripts exhibited non-adaptive plastic changes in expression when the source population was reared in the absence of predators, as they are in the opposite direction to the evolved changes. By contrast, the remaining transcripts exhibiting adaptive plasticity show reduced population divergence. Furthermore, the most plastic transcripts in the source population evolved reduced plasticity in the introduction populations, suggesting strong selection against non-adaptive plasticity. These results support models predicting that adaptive plasticity constrains evolution (6-8), whereas non-adaptive plasticity potentiates evolution by increasing the strength of directional selection (11,12). The role of non-adaptive plasticity in evolution has received relatively little attention; however, our results suggest that it may be an important mechanism that predicts evolutionary responses to new environments., A long-standing problem in evolutionary biology is to understand the relationship between environmentally induced variation observed within a generation, and genetically-based evolutionary changes between generations (1-5). It has long been [...]

Theory suggests evolutionary change can significantly influence and act in tandem with ecological forces via ecological-evolutionary feedbacks. This theory assumes that significant evolutionary change occurs over ecologically relevant timescales and that phenotypes have differential effects on the environment. Here we test the hypothesis that local adaptation causes ecosystem structure and function to diverge. We demonstrate that populations of Trinidadian guppies (Poecilia reticulata), characterized by differences in phenotypic and population-level traits, differ in their impact on ecosystem properties. We report results from a replicated, common garden mesocosm experiment and show that differences between guppy phenotypes result in the divergence of ecosystem structure (algal, invertebrate, and detrital standing stocks) and function (gross primary productivity, leaf decomposition rates, and nutrient flux). These phenotypic effects are further modified by effects of guppy density. We evaluated the generality of these effects by replicating the experiment using guppies derived from two independent origins of the phenotype. Finally, we tested the ability of multiple guppy traits to explain observed differences in the mesocosms. Our findings demonstrate that evolution can significantly affect both ecosystem structure and function. The ecosystem differences reported here are consistent with patterns observed across natural streams and argue that guppies play a significant role in shaping these ecosystems. ecological--evolutionary feedbacks | intraspecific variation | ecosystem function doi/10.1073/pnas.0908023107

Evolutionary biologists have long sought to understand the relationship between microevolution (adaptation), which can be observed both in nature and in the laboratory, and macroevolution (speciation and the origin of the divisions of the taxonomic hierarchy above the species level, and the development of complex organs), which cannot be witnessed because it occurs over intervals that far exceed the human lifespan. The connection between these processes is also a major source of conflict between science and religious belief. Biologists often forget that Charles Darwin offered a way of resolving this issue, and his proposal is ripe for re-evaluation in the light of recent research., Charles Darwin and Alfred Russel Wallace based their insight that organisms evolve by natural selection on four principles (1,2): first, that organisms have 'individual variations' that are faithfully transmitted from [...]

The ecological impacts of the indirect effects of predators are well established, but the evolutionary consequences are unknown. Predators often decrease prey density, which indirectly increases the resources available to surviving prey. This ecological effect could provide a link to evolution because it is generally assumed that resource availability influences life history evolution. Yet, predictions from theory that consider food availability are inconsistent, and evidence for an important role of resources in shaping life history evolution is absent. We compared life history traits in a Trinidadian killifish, Rivulus hartii, from fish communities that differ in predation intensity; predators are associated with lower population density and faster growth rates. To determine whether the indirect effects of predators influence evolutionary change, we reared second-generation-born fish under two food levels that approximated natural differences in resources between communities. Rivulus from sites with predators are younger and smaller at maturity. They have increased reproductive investment and produce many small eggs and smaller hatchlings. Such divergence is predicted as a direct effect of predation. We also found significant interactions between predator community and food level for age and size at maturity, fecundity, and egg size. These interactions, whereby the differences between communities were more pronounced at high-food levels, argue that evolution in Rivulus has been influenced by the indirect effects of predators mediated through resource availability. Rivulus from sites with predators better exploit the higher resources in those habitats. Therefore, both direct and indirect effects of predators have evolutionary consequences. density | guppy | resource availability | trophic cascade

Despite abundant examples of both adaptation at the level of phenotype and Darwinian selection at the level of genes, correlations between these two processes are notoriously difficult to identify. Positive Darwinian selection on genes is most easily discerned in cases of genetic conflict, when antagonistic evolutionary processes such as a Red Queen race drive the rate of nonsynonymous substitution above the neutral mutation rate. Genomic imprinting in mammals is thought to be the product of antagonistic evolution coincident with evolution of the placenta, but imprinted loci lack evidence of positive selection likely because of the ancient origin of viviparity in mammals. To determine whether genetic conflict is a general feature of adaptation to placental reproduction, we performed comparative evolutionary analyses of the insulin-like growth factor II (IGF2) gene in teleost fishes. Our analysis included several members of the order Cyprinodontiformes, in which livebearing and placentation have evolved several times independently. We found that IGF2 is subject to positive Darwinian selection coincident with the evolution of placentation in fishes, with particularly strong selection among lineages that have evolved placentation recently. Positive selection is also detected along ancient lineages of placental livebearing fishes, suggesting that selection on IGF2 function is ongoing in placental species. Our observations provide a rare example of natural selection acting in synchrony at the phenotypic and molecular level. These results also constitute the first direct evidence of parent-offspring conflict driving gene evolution. genomic imprinting | parent-offspring conflict | placentation | positive selection | sexual antagonism

Where the fish are greener? One of the trickiest problems in evolutionary biology is to explain how natural populations maintain an element of genetic diversity. Of all the proposed mechanisms, theory shows that frequency-dependent selection can be the most potent, yet there is only indirect evidence for its importance in natural populations. An experimental manipulation in natural populations of guppies now shows that there is a significant survival advantage for rare genotypes (exotic colouring in males) in natural populations of guppies. This is perhaps the best experimental evidence yet that frequency-dependent selection can be a potent mechanism maintaining genetic variation in natural populations. Results from an experimental manipulation showed a significant survival advantage for rare genotypes in natural populations of guppies, confirming that frequency-dependent selection can act as a potent mechanism in maintaining genetic variation in natural populations. The maintenance of genetic variation in traits under natural selection is a long-standing paradox in evolutionary biology.sup.1,2,3. Of the processes capable of maintaining variation, negative frequency-dependent selection (where rare types are favoured by selection) is the most powerful, at least in theory.sup.1; however, few experimental studies have confirmed that this process operates in nature. One of the most extreme, unexplained genetic polymorphisms is seen in the colour patterns of male guppies (Poecilia reticulata).sup.4,5. Here we manipulated the frequencies of males with different colour patterns in three natural populations to estimate survival rates, and found that rare phenotypes had a highly significant survival advantage compared to common phenotypes. Evidence from humans.sup.6,7 and other species.sup.8,9 implicates frequency-dependent survival in the maintenance of molecular, morphological and health-related polymorphisms. As a controlled manipulation in nature, this study provides unequivocal support for frequency-dependent survival--an evolutionary process capable of maintaining extreme polymorphism., Author(s): Robert Olendorf [sup.1] , F. Helen Rodd [sup.3] , David Punzalan [sup.3] , Anne E. Houde [sup.4] , Carla Hurt [sup.5] , David N. Reznick [sup.6] , Kimberly A. [...]

Numerous studies have documented evolution by natural selection in natural populations, but few are genuine selection experiments that are designed and then executed in nature. We will focus on these few cases to illustrate what can be learned from field selection experiments alone or field and laboratory selection experiments together that cannot be learned from laboratory experiments alone. Both types of study allow us to evaluate cause and effect relationships because a planned experiment can be accompanied by a more direct evaluation of the factors that cause evolution. A unique benefit of field experiments is that they give us the opportunity to measure the rate and magnitude of selection in nature. We have found that this rate is far greater than one might imagine based on observations of the fossil record. A combination of field and laboratory selection experiments has revealed the importance of population size and structure in shaping the genetics of adaptation. For example, laboratory selection experiments on insecticide resistance tend to attain resistance though polygenic inheritance. The evolution of insecticide resistance in nature often eventually yields to single genes of large effect that are rare but, once they arise, represent a higher fitness solution to resistance and spread among populations. Finally, field studies enable us to test evolutionary theory in a context in which all of the tradeoffs associated with a trait are realized; in the laboratory, organisms may be shielded from the fitness tradeoffs associated with the evolution of a trait. For example, we have compared the patterns of senescence in guppies from high and low mortality rate environments in the laboratory and in the field. In the laboratory, guppies from high predation environments had delayed senescence relative to those from low predation environments. In the field the apparent relationship is the opposite. One hypothesis for this difference is that a tradeoff associated with the evolution of the high predation life history is a decrease in the investment in the immune system. Such a sacrifice would be evident in nature where there is exposure to disease and parasites but less so in the laboratory, which is relatively disease and parasite free.

Author(s): David N. Reznick (corresponding author) [1]; Michael J. Bryant [1, 2]; Derek Roff [1]; Cameron K. Ghalambor [3]; Dionna E. Ghalambor [3] Classical theories [1, 2] for the evolution [...]

Whole organism performance represents the integration of numerous physiological, morphological, and behavioral traits. How adaptive changes in performance evolve therefore requires an understanding of how selection acts on multiple integrated traits. Two approaches that lend themselves to studying the evolution of performance in natural populations are the use of quantitative genetics models for estimating the strength of selection acting on multiple quantitative traits and ecological genetic comparisons of populations exhibiting phenotypic differences correlated with environmental variation. In both cases, the ultimate goal is to understand how suites of traits and trade-offs between competing functions respond to natural selection. Here we consider how these two complimentary approaches can be applied to study the adaptive evolution of escape performance in fish. We first present an extension of Arnold's (1983) quantitative genetic approach that explicitly considers how trade-offs between different components of performance interact with the underlying genetics. We propose that such a model can reveal the conditions under which multiple selection pressures will cause adaptive change in traits that influence more than one component of fitness. We then review work on the Atlantic silversides and Trinidadian guppies as two case studies where an ecological genetics approach has been successfully applied to evaluate how the evolution of escape performance trades-off with other components of fitness. We conclude with the general lesson that whole organism performance is embedded in a complex phenotype, and that the net outcome of selection acting on different aspects of the organism will often result in a compromise among competing influences.

A fundamental goal of population ecology is to quantify how spatial and temporal variation in life history traits translates into variation in population-level parameters such as vital rates and projected growth rate ([lambda]). Further emphasis has been on the sensitivity of [lambda] to absolute variation (sensitivities) and relative variation (elasticities) in vital rates, because [lambda] can be related to the evolutionary fitness of a life history phenotype (r = ln[lambda]). Furthermore, because density regulation can affect the expression and evolution of life history traits, which in turn can feed back on population dynamics, correctly incorporating the relationship between the two is critical to understanding the evolution and evolvability of life history strategies. Here we ask how life history variation affects projected population growth and evolutionary fitness dynamics in the long-term study system of the Trinidadian guppy (Poecilia reticulata). There are striking differences in the life history traits of guppies that co-occur with two different assemblages of predators and so these populations are a model natural system for examining the fitness consequences of, and selective pressures on, traits that covary predictably. We found that populations experiencing high rates of predation had lower estimates of growth and fitness than did those experiencing low rates of predation (pooled r = 0.02 and 0.17, respectively). But when we incorporated density regulation in low predation sites, observed with field manipulations and modeled with simulations, this difference became negligible. Furthermore, for all populations irrespective of predators, growth rate was most sensitive to changes in neonatal growth and was contributed to maximally by early adult survival. Particularly in light of growing concerns on correctly identifying sensitive life stages in overharvested fauna, addressing these questions in a long-term natural experimental system may provide guidance. Key words: density regulation; elasticity; guppy; life history trait; population growth rate; sensitivity.

Natural populations of guppies were subjected to an episode of directional selection that mimicked natural processes. The resulting rate of evolution of age and size at maturity was similar to rates typically obtained for traits subjected to artificial selection in laboratory settings and up to seven orders of magnitude greater than rates inferred from the paleontological record. Male traits evolved more rapidly than female traits largely because males had more genetic variation upon which natural selection could act. These results are considered in light of the ongoing debate about the importance of natural selection versus other processes in the paleontological record of evolution., Natural populations of guppies in Trinidad are found in simple communities replicated in a series of drainages (1) that can be characterized as either high or low predation. In high-predation [...]

Key words.--Adaptation, life-history evolution, mark-recapture, mortality, selection, size-selective predation. Received September 26, 1995 Accepted September 26, 1995 Testing evolutionary theories in natural populations requires identifying the agent of selection, evaluating [...]

Author(s): David N. Reznick (corresponding author) [1]; Joseph Travis (corresponding author) [2] Adaptive evolution causes populations to evolve towards a body form that is best suited to the local environment. [...]

The evolution of complex organs is a source of controversy because they require the contributions of many adaptations to function properly. We argue that placentas are complex, that they have evolved multiple times in Poeciliopsis, and that there are closely related sister taxa that have either no placentas or intermediate stages in the evolution of a placenta. Furthermore, placentas can evolve in 750,000 years or less, on the same time scale as suggested by theoretical calculations for the evolution of complex eyes. Independent origins of such complexity, accompanied by sister taxa that either lack or have intermediate stages in the evolution of the trait, present an opportunity to study the evolution of novelty and complexity from a comparative, evolutionary perspective., Darwin addressed the conceptual difficulty of complex adaptations, or 'organs of extreme perfection,' with his treatment of the evolution of the eye: 'To suppose that the eye with all its [...]

Author(s): Cameron K. Ghalambor; Kim L. Hoke; Emily W. Ruell; Eva K. Fischer; David N. Reznick; Kimberly A. Hughes Nature 525, 372375 (2015); doi:10.1038/nature15256 There are several errors in this [...]

Author(s): Cameron K. Ghalambor (corresponding author) [1, 2]; Kim L. Hoke [1, 2]; Emily W. Ruell [1]; Eva K. Fischer [1]; David N. Reznick [3]; Kimberly A. Hughes [4] REPLYING [...]

Experimental studies on the southern clade of Poeciliopsis were conducted to distinguish between the alternatives that placental species either sacrifice body condition to maintain reproduction when resources are restricted or that the documented pattern of resource allocation is a function of other life-history correlates of placentation rather than placentation alone. The obtained results provide support to hypotheses which suggested parent-offspring conflict in utero drives the evolution of the placenta.

The genetic basis of trait variation between Rivulus/guppy and Rivulus-only communities were examined by comparing life-history differences after two generations of laboratory rearing for Rivulus from sites with and without guppies under two food levels that match natural differences in growth. Rivulus from localities with guppies on high food which were found to mature earlier, produced many small eggs, and exhibited increased reproductive investment compared to low food indicated that indirect effects mold Rivulus evolution and highlighted link between community processes and evolutionary change.

Several analyses are conducted to explain the phenotypic and life-history differences observed in different species across an environmental gradient. The evolution of the life histories is shown to be extremely affected by the predators, as well as the availability of resources in the environment.

A study to disentangle the effects of fish predation in color evolution from the potential effects of physical habitat features and predation by prawns on male guppies is presented. Predatory fishes do impose the strongest selection in the color pattern of male guppies but other factors also play an important role.

The differences in larval habitats and life history of three species of spadefoot toads are examined. The genetic basis of the differences in development and controlled comparisons of phenotypic plasticity is discussed.

Life history traits in guppies (Poecilia reticulata) vary geographically along a predator assemblage gradient, and field experiments have indicated that the association may be causal; guppies introduced from high predation sites to low predation sites have evolved the phenotype associated with low predation in as few as seven generations. It has long been recognized, however, that low predation sites tend to have greater forest canopy cover than high predation sites. Stream differences in canopy cover could translate into stream differences in resource availability, another theoretically potent agent of selection on life history traits. Moreover, new computer simulations indicate that the high predation phenotype would outcompete the low predation phenotype under both mortality regimes. Thus, predation alone may not be sufficient to explain the observed life history patterns. Here we show that food availability for guppies decreases as forest canopy cover increases, among six low predation streams in the Northern Range of Trinidad. Streams with less canopy cover received more photosynthetically active light and contained a larger standing crop of algae (the primary food of guppies), as measured by algal pigments (chlorophylls and carotenoids) on both natural cobble and artificial tile substrates, but did not contain a greater biomass of guppies (per square meter of streambed). Consequently, algae availability for guppies (in micrograms of algal pigments per milligram of guppy) increased with decreasing canopy cover. The biomass of guppies and algae both decreased after a series of floods, with no net effect on algae availability. Field mark--recapture studies revealed that female and juvenile guppies grew faster, and that the asymptotic size of mature males was larger, in streams with less canopy cover. Canopy cover explained 84% of the variation among streams in algae availability which, in turn, explained 93% of the variation in guppy growth rates. Laboratory 'common garden' experiments indicated that the stream differences in growth and adult male size in the field were largely environmental (non-genetic). These results strongly suggest that stream differences in canopy cover result in consistent stream differences in food availability, independent of predation. Our preliminary data indicate that some life history traits (offspring size and litter size) vary genetically along the canopy cover gradient, among low predation streams, in the same direction as along the predation gradient. Another recent study shows that food availability is higher at high predation sites than at low predation sites, partly as an indirect effect of predators reducing guppy densities. Further research is required to disentangle the direct effects of predation from those of resource availability in the evolution of life histories. Key words: canopy cover; density-dependent selection; environmental gradient; growth rate; life history evolution; periphyton; Poecilia reticulata; predation; primary productivity; resource availability; tropical stream; Trinidad, West Indies.

Inexorable facts of life in Western society are birth, death, and taxes. For organisms in nature, life's trinity is instead birth, death, and reproduction. It is the task of evolutionary [...]

Natural population of guppies that co-occur with the pike cichlid Crenicichla alta and associated predators mature at smaller body sizes, produce more and smaller offspring per litter, reproduce more frequently, and have higher reproductive allotments (weight of developing embryos/total body weight) than guppies that co-occur with just the killifish Rivulus harti (Reznick and Endler, 1982). I here consider three forms of repeatability in these life-history patterns: i) among replicate samples colleceted on the same day from the same locality, ii) between Crenicichla and Rivulus communities among a new series of localities, and iii0 among a smaller series of Crenicichla and Rivulus localities sampled in two yet and two dry seasons. In the analysis of replicate collecetions from two localities, seven of eight statistical comparisons revealed no significant difference. The usual methodology for estimating these variables therefore accurately represents guppy life-history patterns at a given locality. Differences among guppies from Rivulus and Crenicichla localities, covering a wider geographical area than considered by Reznick and Endler (1982), were virtually identical to the previous comparison. Wet-season samples were associated with significant decreases in reproductive allotment and fecundity and significant increases in the size of mature males and the minimum size of reproducing females. Differences between guppies from Rivulus and Crenicichla localities persisted across all samples and were consistent with all other observations, although they tended to be smaller during the wet season. Discriminating analyses on female reproductive traits showed that fecundity and offspring size made strong, independent contributions to discriminating between guppies from the two types of localities. The contribution from reproductive allotment was considerably smaller. There was moe overlap between predator treatments during the wet season. Only 8.5% of the individuals were misclassified during the dry season, but 19.5% were misclassified during the wet season.

Guppies show great variation in the coloring of the males. A study has assessed how far mate selection may be requency dependent. Females were familiarized to males which had one type of color pattern, and then exposed to different types of males. The females were found to selected mates more often if they had novel color patterns, rather than familiar color patterns. The finding back up the hypothesis that mate selection may be frequency dependent.The size of females or males does not appear to be important in mate selection.