Biomedical subjects

C Weinig

Publications and source records attributed to C Weinig.

5 recordsLinked to original sources

PubMed2006

Local and global costs of adaptive plasticity to density in Arabidopsis thaliana.

Although phenotypic plasticity is demonstrably adaptive in a range of settings, organisms are not perfectly plastic. Costs of plasticity comprise one factor predicted to counter the evolution of this adaptive strategy, yet evidence of costs is rare. Here, we test the fitness effects of plastic life-history and morphological responses to density and costs of this plasticity in recombinant inbred lines of Arabidopsis thaliana. Several costs of plasticity and homeostasis were detected. Of particular relevance, there was a significant cost of plasticity to active stem-elongation responses, an adaptive trait in many species. There was also a cost of plasticity to apical branch production at both high and low density, which resulted from the greater suppression of basal branching in genotypes with plastic apical branch production relative to genotypes with fixed apical branch production. The presence of a cost in multiple environments (i.e., a global cost) is predicted to counter the evolution of plasticity. Experimental segregating progenies such as the one used here are expected to have higher genetic costs of plasticity than arrays of genotypes sampled from natural populations because selection should remove genotypes with costs resulting from linkage disequilibrium or epistasis. The use of experimental progeny arrays therefore increases the ability to evaluate genetic costs.

Adaptation, Physiological↗

PubMed2001

Phenotypic plasticity early in life constrains developmental responses later.

Plastic stem-elongation responses to the ratio of red:far-red (R:FR) wavelengths enable plants to match their phenotype to local competitive conditions. However, elongation responses early in the life history may occur at the cost of reduced plasticity later in the life history, because elongation influences both allocation patterns and structural integrity. A common-garden experiment was performed to test whether seedling responses to R:FR affect biomass allocation. biomass accumulation, and subsequent plasticity to the cue. Seedlings of Abutilon theophrasti were stimulated to elongate by low R:FR treatments, and subsequent growth and plasticity was compared with nonelongated individuals. Elongated seedlings were less responsive than nonelongated ones to a second bout of low R:FR. Thus, seedling plasticity to R:FR reduces subsequent responsiveness to this cue. This negative association across life-history stages suggests an important constraint on the evolution of plastic stem responses, because selection in A. theophrasti has previously been shown to favor increases in early elongation in combination with increased later elongation. The reduced responsiveness of elongated seedlings to R:FR appeared to result from a structural feedback mechanism, indicating that the opportunity cost of early responses may be lower in environments providing structural support.

Biological Evolution↗

PubMed2000

Differing selection in alternative competitive environments: shade-avoidance responses and germination timing.

Under competitive conditions, stem elongation in plants is thought to enhance fitness by increasing light interception. However, the onset of competition should vary with the species of competitor due to interspecific differences in timing of emergence and plant growth form. The fitness benefits of elongation may therefore depend on the timing of this plastic response. Phenotypic selection analyses and path analysis were used to evaluate selection acting on stem elongation at early and late life-history stages and the combination of germination timing and elongation in an annual plant. Velvetleaf (Abutilon theophrasti) were raised in one of three environments experienced by natural populations (cornfields; soybean fields; and disturbed, weedy sites). Due to the rapid growth rate and high density of plants in disturbed areas, selection to increase seedling-stage elongation was expected in weedy sites. Due to the wide spacing of crop plants, competition for light is initially low in cultivated fields, but intensifies as the season progresses. Selection for increased elongation at later nodes was expected in soybean fields because velvetleaf can often overtop soy and thereby increase leaf exposure. In contrast, selection against late elongation was expected in cornfields because velvetleaf are incapable of overtopping corn. Individuals that elongate would experience the carbon cost of allocating to structural tissue, but fail to experience a carbon return through increased light interception. The phenotypic selection analyses were consistent with these predictions and therefore support the role of stem elongation as an adaptation to interspecific competition. Selection also acted on the combination of germination timing and elongation. In the weedy environment, early emergence in conjunction with enhanced stem elongation conveyed the highest fitness. Reduced elongation was favored among individuals that emerged late, potentially because these individuals were unable to overtop neighbors. The results of this study demonstrate that the timing of stem elongation strongly affects competitive success. Environments that differ in the timing of competition for light select for elongation at different life-history stages, and this selection depends on the timing of emergence.

Biological Evolution↗

PubMed2000

Plasticity versus canalization: population differences in the timing of shade-avoidance responses.

The reliability of environmental cues and costs of a fixed phenotype are two factors determining whether selection favors phenotypic plasticity or environmental specialization. This study examines the relationship between these two factors and the evolution of plant competitive strategies (plastic vs. fixed morphologies). In natural plant populations, shifts in light quality associated with foliar shade reliably indicate the presence of neighbors. These cues mediate plastic stem-elongation responses that often increase competitive ability and access to light. Using experimental light treatments (full sun, neutral shade, and foliar shade), genetic differences among populations of Abutilon theophrasti (velvetleaf) in average elongation and plasticity to foliar-shade cues were examined. Six populations, two from each of three site types (fields in continuous corn cultivation, fields undergoing corn-soy rotation, and weedy sites), were exposed to the light treatments at two stages in their life history. At the seedling stage, populations derived from cornfield sites exhibited higher, average elongation than populations from either rotating corn-soy fields or weedy areas. Because seedling elongation may delay shading of velvetleaf by corn, population differences may reflect adaptive responses to directional selection imposed by competitive conditions. However, the effects of simulated foliar shade on elongation were three times as great as the average population differences, and these comparatively higher levels of elongation were associated with an allocation cost. These results are consistent with the hypothesis that phenotypic plasticity may limit the evolution of specialists; reliable environmental cues enable individuals to facultatively adopt highly elongated, costly phenotypes in crowded patches while avoiding the costs of that phenotype in less crowded microsites. At later life-history stages, populations experiencing competition with corn exhibited lower plasticity to light quality than populations derived from weedy areas. Elongation at later nodes is maladaptive in cornfields because velvetleaf is ultimately incapable of overtopping corn; individuals that elongate therefore experience the cost of allocating to stems but fail to improve leaf exposure. The decreased responsiveness of cornfield populations to light quality is consistent with theoretical predictions in which reduced plasticity is favored when environmental cues fail to mediate an adaptive response.

Biological Evolution↗

PubMed2000

Limits to adaptive plasticity: temperature and photoperiod influence shade-avoidance responses.

In plants, the ratio of red to far-red wavelengths (R:FR) reliably indicates neighbor proximity and influences stem elongation. Enhanced elongation increases light interception and fitness under crowded conditions. However, many environmental factors vary simultaneously such that responses to R:FR may be affected by abiotic conditions or maternal environmental conditions. This study examines the effects of temperature, photoperiod, and maternal environment on stem-elongation responses to R:FR. Four populations of Abutilon theophrasti (two from disturbed, weedy areas and two from cornfields) were used in factorial common-garden experiments of temperature × R:FR × population and photoperiod × R:FR × population. Seedling growth of greenhouse- and field-derived seed was compared to evaluate maternal effects. Maternal environment did not alter seedling elongation. Higher temperatures resulted in both a twofold increase in average elongation and increased responsiveness to R:FR. Significant three-way interactions in both experiments demonstrate that population responses to R:FR differ depending on temperature and photoperiod conditions. These results indicate that elongation responses to R:FR are more variable than previously realized. The observed variability in elongation also suggests that the outcome of competitive interactions in the natural environment will depend on ambient temperature, photoperiod length, and population origin.

Journal Article↗