Abstract
Phenotypic plasticity is common in many taxa, and it may increase an organism's fitness in heterogeneous environments. However, in some cases, the frequency of environmental changes can be faster than the ability of the individual to produce new adaptive phenotypes. The importance of such a time delay in terms of individual fitness and species adaptability has not been well studied. Here, we studied gender plasticity of Alternanthera philoxeroides to address this issue through a reciprocal transplant experiment. We observed that the genders of A. philoxeroides were plastic and reversible between monoclinous and pistillody depending on habitats, the offspring maintained the maternal genders in the first year but changed from year 2 to 5, and there was a cubic relationship between the rate of population gender changes and environmental variations. This relationship indicates that the species must overcome a threshold of environmental variations to switch its developmental path ways between the two genders. This threshold and the maternal gender stability cause a significant delay of gender changes in new environments. At the same time, they result in and maintain the two distinct habitat dependent gender phenotypes. We also observed that there was a significant and adaptive life-history differentiation between monoclinous and pistillody individuals and the gender phenotypes were developmentally linked with the life-history traits. Therefore, the gender phenotypes are adaptive. Low seed production, seed germination failure and matching phenotypes to habitats by gender plasticity indicate that the adaptive phenotypic diversity in A. philoxeroides may not be the result of ecological selection, but of gender plasticity. The delay of the adaptive gender phenotype realization in changing environments can maintain the differentiation between gender systems and their associated life-history traits, which may be an important component in evolution of novel traits and taxonomic diversity.
Highlights
Phenotypic plasticity is the capacity of a single genotype to produce different phenotypes in response to varying environmental conditions [1]
We observed that after pistillody and monoclinous segments of A. philoxeroides were transplanted to pistillody, monoclinous and neutral habitats, their offspring maintained the maternal genders in the first year in all these habitats
From year 2 to 5, habitat dependent gender changes took place and the genders of the offspring were significantly influenced by the maternal genders
Summary
Phenotypic plasticity is the capacity of a single genotype to produce different phenotypes in response to varying environmental conditions [1]. Plasticity affects the adaptive rate of phenotypes to new environments through developmental processes [3] and may alter the interactions between individuals and their environments in ways that influence the stability and local biodiversity of populations and communities [4]. The role of phenotypic plasticity in adaptive diversity has historically been a contentious issue [5]. The conventional view on adaptive diversity focuses on the role of allelic substitution or quantitative genetic variation [6]. Diversity is considered a result of natural selection on the phenotypes that are affected by the genotypes, and the process of diversity is believed to be genes ‘leading’ and phenotypes ‘following’ [5]. Growing data indicate that attributing diversity to mutation and recombination fails to fully explain evolutionary routes of change [8], the contribution of plasticity to diversity through developmental processes has received little attention
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