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Phenotypic variations between populations often correlate with climatic variables. Determining the presence of phenotypic plasticity and local adaptation of a species to different environments over a large spatial scale can provide insight on the persistence of a species across its range. Amphibians, and in particular their larvae, are good models for studies of phenotypic variation as they are especially sensitive to their immediate environment. Few studies have attempted to determine the mechanisms that drive phenotypic variation between populations of a single amphibian species over a large spatial scale especially across contrasting climatic regimes. The African clawed frog, Xenopus laevis, occurs in two regions with contrasting rainfall regimes in southern Africa. We hypothesised that the phenotypic variation of life-history traits of X. laevis tadpoles emerges from a combination of plastic and genetic responses. We predicted that plasticity would allow the development of tadpoles from both regions in each environment. We also predicted that local adaptation of larval traits would drive the differentiation of reaction norms between populations and lower survival in tadpoles reared away from their home environment. We measured growth, time to metamorphosis, and survival in a reciprocal transplant experiment using outdoor mesocosms. Supporting our prediction, we found that the measured variation of all traits was explained by both adaptation and plasticity. However, the reaction norms differed between populations suggesting adaptive and asymmetric plasticity. All tadpoles experienced lower survival when translocated, but only translocated tadpoles from the winter rainfall region matched survival of local tadpoles. This has implications for the dynamics of translocated X. laevis into novel environments, especially from the winter rainfall region. Our discovery of their asymmetric capacity to overcome novel environmental conditions by phenotypic plasticity alone provides insight into their invasion success. [ABSTRACT FROM AUTHOR]

Ontogeny has been identified as a main source of variation in the expression of plant phenotypes. However, there is limited information on the mechanisms behind the evolution of ontogenetic trajectories in plant defense. We explored if risk of attack, herbivore damage, heritability, and phenotypic plasticity can promote or constrain the evolutionary potential of ontogenetic trajectories in three defensive traits. We exposed 20 genotypes of Turnera velutina to contrasting environments (shadehouse and field plots), and measured the cyanogenic potential, trichome density, and sugar content in extrafloral nectar in seedlings, juveniles and reproductive plants. We also assessed risk of attack through oviposition preferences, and quantified herbivore damage in the field. We estimated genetic variance, broad sense heritability, and evolvability of the defensive traits at each ontogenetic stage, and of the ontogenetic trajectories themselves. For plants growing in the shadehouse, we found genetic variation and broad sense heritability for cyanogenic potential in seedlings, and for trichome density at all ontogenetic stages. Genetic variation and heritability of ontogenetic trajectories was detected for trichome density only. These genetic pre-requisites for evolution, however, were not detected in the field, suggesting that environmental variation and phenotypic plastic responses mask any heritable variation. Finally, ontogenetic trajectories were found to be plastic, differing between shadehouse and field conditions for the same genetic families. Overall, we provide support for the idea that changes in herbivore pressure can be a mechanism behind the evolution of ontogenetic trajectories. This evolutionary potential, however, can be constrained by phenotypic plasticity expressed in heterogeneous environments. [ABSTRACT FROM AUTHOR]

Polygonum aviculare subsp. aviculare is an annual selfing weed common in abandoned arable fields where it occurs as a widespread hexaploid cytotype (6 x=60) and a rarer tetraploid cytotype (4 x=40). The basis of phenological differentiation between the two cytotypes observed in a natural population where they coexist was examined in a greenhouse experiment comprising six soil conditions consisting of factorial combinations of two levels of fertility and three pot sizes. The environmental and genetic component of variation in 11 life history and morphological traits was quantified. Even though all traits except life span were plastic the two cytotypes appear to have evolved contrasting life history strategies and it is inferred that this can account for the temporal niche differentiation observed in the abandoned field during the first year of dereliction. Tetraploids are short-lived plants allocating a high proportion of their biomass to reproduction and completing their life cycle before July when the plant cover is sparse. Hexaploids are larger, later flowering, longer lived, plants with a lower reproductive effort and a higher final seed yield; it is inferred that these traits enable the hexaploids to compete successfully with the dense herbaceous layer of summer annuals that develops in the course of the first year of secondary succession. Differentiation in phenotypic plasticity between the two cytotypes was interpreted as indicative of higher opportunism and lower tolerance of poor soils and restricted rooting space in the hexaploid compared to the tetraploid cytotype. [ABSTRACT FROM AUTHOR]