Summary
1The role of phenotypic plasticity in evolution has historically been a contentious issue because of debate over whether plasticity shields genotypes from selection or generates novel opportunities for selection to act. Because plasticity encompasses diverse adaptive and non-adaptive responses to environmental variation, no single conceptual framework adequately predicts the diverse roles of plasticity in evolutionary change.
2Different types of phenotypic plasticity can uniquely contribute to adaptive evolution when populations are faced with new or altered environments. Adaptive plasticity should promote establishment and persistence in a new environment, but depending on how close the plastic response is to the new favoured phenotypic optimum dictates whether directional selection will cause adaptive divergence between populations. Further, non-adaptive plasticity in response to stressful environments can result in a mean phenotypic response being further away from the favoured optimum or alternatively increase the variance around the mean due to the expression of cryptic genetic variation. The expression of cryptic genetic variation can facilitate adaptive evolution if by chance it results in a fitter phenotype.
3We conclude that adaptive plasticity that places populations close enough to a new phenotypic optimum for directional selection to act is the only plasticity that predictably enhances fitness and is most likely to facilitate adaptive evolution on ecological time-scales in new environments. However, this type of plasticity is likely to be the product of past selection on variation that may have been initially non-adaptive.
4We end with suggestions on how future empirical studies can be designed to better test the importance of different kinds of plasticity to adaptive evolution.

/pdf/adaptive-versus-non-adaptive-phenotypic-plasticity-and-the-55680hih4y.pdf

Adaptive versus non‐adaptive phenotypic plasticity and the potential for contemporary adaptation in new environments

The pace-of-life syndrome (POLS) hypothesis specifies that closely related species or populations experiencing different ecological conditions should differ in a suite of metabolic, hormonal and immunity traits that have coevolved with the life-history particularities related to these conditions. Surprisingly, two important dimensions of the POLS concept have been neglected: (i) despite increasing evidence for numerous connections between behavioural, physiological and life-history traits, behaviours have rarely been considered in the POLS yet; (ii) the POLS could easily be applied to the study of covariation among traits between individuals within a population. In this paper, we propose that consistent behavioural differences among individuals, or personality, covary with life history and physiological differences at the within-population, interpopulation and interspecific levels. We discuss how the POLS provides a heuristic framework in which personality studies can be integrated to address how variation in personality traits is maintained within populations.

/pdf/personality-and-the-emergence-of-the-pace-of-life-syndrome-537mg1fify.pdf

Personality and the emergence of the pace-of-life syndrome concept at the population level

The current paper synthesizes theory and data from the field of life history (LH) evolution to advance a new developmental theory of variation in human LH strategies. The theory posits that clusters of correlated LH traits (e.g., timing of puberty, age at sexual debut and first birth, parental investment strategies) lie on a slow-to-fast continuum; that harshness (externally caused levels of morbidity-mortality) and unpredictability (spatial-temporal variation in harshness) are the most fundamental environmental influences on the evolution and development of LH strategies; and that these influences depend on population densities and related levels of intraspecific competition and resource scarcity, on age schedules of mortality, on the sensitivity of morbidity-mortality to the organism’s resource-allocation decisions, and on the extent to which environmental fluctuations affect individuals versus populations over short versus long timescales. These interrelated factors operate at evolutionary and developmental levels and should be distinguished because they exert distinctive effects on LH traits and are hierarchically operative in terms of primacy of influence. Although converging lines of evidence support core assumptions of the theory, many questions remain unanswered. This review demonstrates the value of applying a multilevel evolutionary-developmental approach to the analysis of a central feature of human phenotypic variation: LH strategy.

https://cals.arizona.edu/fcs/sites/cals.arizona.edu.fcs/files/HN%20Ellis%20et%20al%202009.pdf

Fundamental Dimensions of Environmental Risk : The Impact of Harsh versus Unpredictable Environments on the Evolution and Development of Life History Strategies.

Under what conditions might organisms be capable of rapid adaptive evolution? We reviewed published studies documenting contemporary adaptations in natural populations and looked for general patterns in the population ecological causes. We found that studies of contemporary adaptation fall into two general settings: (1) colonization of new environments that established newly adapted populations, and (2) local adaptations within the context of a heterogeneous environments and metapopulation structure. Local ecological processes associated with colonizations and introductions included exposure to: (1) a novel host or food resource; (2) a new biophysical environment; (3) a new predator community; and (4) a new coexisting competitor. The new environments that were colonized often had depauperate communities, sometimes because of anthropogenic disturbance. Local adaptation in heterogeneous environments was also often associated with recent anthropogenic changes, such as insecticide and herbicide resistance, or industrial melanism. A common feature of many examples is the combination of directional selection with at least a short-term opportunity for population growth. We suggest that such opportunities for population growth may be a key factor that promotes rapid evolution, since directional selection might otherwise be expected to cause population decline and create the potential for local extinction, which is an ever-present alternative to local adaptation. We also address the large discrepancy between the rate of evolution observed in contemporary studies and the apparent rate of evolution seen in the fossil record.

/pdf/the-population-ecology-of-contemporary-adaptations-what-u8kr5h9brc.pdf

The population ecology of contemporary adaptations: What empirical studies reveal about the conditions that promote adaptive evolution

The theory of r- and K-selection was one of the first predictive models for life-history evolution. It helped to galvanize the empirical field of comparative life-history and dominated thinking on the subject from the late 1960s through the 1970s. Large quan- tities of field data were collected that claimed to test predictions of the theory. By the early 1980s, sentiment about the theory had changed so completely that a proposal to test it or the use of it to interpret empirical results would likely be viewed as archaic and naive. The theory was displaced by demographic models that concentrated on mortality patterns as the cause of life-history evolution. Although demographic models are known for their density-independent approach and focus on extrinsic mortality, these models can incorporate many ecological features captured by r- and K-selection, such as density-dependent pop- ulation regulation, resource availability, and environmental fluctuations. We highlight the incorporation of these factors in recent theory, then show how they are manifest in our research on life-history evolution in Trinidadian guppies (Poecilia reticulata). Explanations of the repeatable suites of life-history differences across populations of guppies originate from demographic models of predator-driven age-specific mortality. Recently, careful ex- amination of guppy demography and habitat has revealed that density-dependent regulation and resource availability may have influenced the evolution of guppy life histories. In the field, these factors covary with predation risk; however, they can be uncoupled experi- mentally, providing insight into how they may have synergistically driven guppy life-history evolution. Although life-history theory has shifted away from a focus on r- and K-selection, the themes of density-dependent regulation, resource availability, and environmental fluc- tuations are integral to current demographic theory and are potentially important in any natural system.

/pdf/r-and-k-selection-revisited-the-role-of-population-2cpn09qm9m.pdf

r- AND K-SELECTION REVISITED: THE ROLE OF POPULATION REGULATION IN LIFE-HISTORY EVOLUTION

In earlier publications, we reported an association between the life-history patterns of guppies and the types of predators with which they co-occur. We contrasted guppies from high-predation sites (Crenicichla localities) with those from low-predation sites (Rivulus localities) found on the south slope of the Northern Range Mountains of Trinidad. Guppies from high-predation localities attain maturity at an earlier age and smaller size, produce more and smaller offspring per litter, and have higher reproductive allotments than their counterparts from low-predation sites. Here we present a parallel series of analyses for guppies from a new series of localities on the north slope of the Northern Range. These fish are also found in what appear to be high- and low-predation communities, but, with one exception, the species of predators are entirely different from those on the south slope. The larger predators are derived from marine families (gobies and mullets) that have invaded freshwater rivers; the south ...

Michael Cardenas

Papers

Life-history evolution in guppies (poecilia reticulata: poeciliidae). iv. parallelism in life-history phenotypes