Plastic and constant developmental traits contribute to adaptive differences in co‐occurringPolygonumspecies

Abstract

Adaptive differences among species are often thought to result from developmentally constant trait differences that enhance fitness in alternative environments. Species differences in patterns of individual phenotypic plasticity can also have ecological consequences. Indeed, functionally related constant and plastic traits may interact to determine the phenotype's adaptive value in particular conditions. We compared juvenile shade avoidance traits (height and its components, internode length and node number) across two field density treatments in Polygonumpersicaria and P. hydropiper, annual plant species that co‐occur in pastures comprised of a mosaic of plant densities. We used selection analyses to test trait contributions to fitness in alternative density treatments. Seedlings of both species expressed plasticity for internode elongation in response to density; P. persicaria plants increased internode length and consequently height significantly more in high density than did those of P. hydropiper. As predicted by the shade avoidance hypothesis, increased height was adaptive for both species in high density stands, so P. persicaria plants had higher fitness in this environment. By contrast, node numbers were relatively constant across density treatments in both species: P. hydropiper seedlings consistently produced more nodes than did those of P. persicaria. This constant trait difference contributed to P. hydropiper's greater relative fitness at low density, where more nodes and hence leaves enable plants to better exploit available light. Differences between species in these juvenile shade‐avoidance traits did not result from the evolutionary constraints of lack of heritable variation or costs of plasticity. We discuss how these interspecific trait differences may have been generated by divergent selective histories resulting from differences in herbivore resistance. These results illustrate how adaptive differences in both plastic and constantly expressed traits may jointly contribute to ecological distribution, including coexistence in patchy habitats.

Environmental correlates of growth traits of the stoloniferous plant Potentilla palustris

“…Numerous other studies report increased internode length as a plant response to various unfavorable conditions such as shading (Gonzalez and Gianoli 2004;Niva et al 2006), crowding van Kleunen et al 2005;Griffith and Sultan 2006) or flooding (Lenssen et al 2004). Studies reporting a change in internode number are rather scarce (but see Griffith and Sultan 2006). Therefore, it is likely that internode length is a plastic trait, while internode number is a more constant trait, of horizontal stolon growth in P. palustris.…”

“…As this species is able to alter its phenotype, it has the potential to grow in a wide range of habitats (comp. Griffith and Sultan 2006).…”

The role of developmental plasticity in evolutionary innovation

“…(c) Developmental plasticity creates novel trait interactions Patterns of phenotypic correlation among developmentally or functionally related traits vary from one environment to another when some or all of the constituent traits express plasticity [56,57]. As a result, plastic developmental systems can give rise to new trait interactions, trait covariances and fitness trade-offs that contribute to evolutionary diversification, as reported for learning ability in cabbage white butterflies [58] and diet-induced horn expression in beetles [59].…”

Variation in petiole and internode length affects plant performance in Trifolium repens under opposing selection regimes

“…Long vertical structures allow for the positioning of leaves in more favourable light conditions thereby increasing light harvesting and reducing the negative effects of low light availability (Aphalo and Ballare 1995;de Kroon and Hutchings 1995;Donohue et al 2000;Geber and Griffen 2003;Huber et al 1998;Sultan 1995). In competitive sites plants capable of producing long vertical structures perform better than smaller or less plastic plants (Ballare et al 1994;Dudley and Schmitt 1996;Griffith and Sultan 2006;Schmitt et al 1995;Weijschede et al 2006;Weinig 2000a). However, plants with longer vertical structures can be at a disadvantage in grazed or mown sites, because they lose relatively more biomass than plants with shorter vertical structures.…”