Phenotypic plasticity to light intensity in Arabidopsis thaliana: invariance of reaction norms and phenotypic integration

Phenotypic plasticity (the pattern of response of organisms to changes in environmental conditions) and phenotypic integration (the pattern of character correlations) are important components of our understanding of the evolution of complex phenotypes. Most studies published so far in this area have been conducted within populations with the express aim of predicting future response to evolutionary forces. However, among-population differentiation for plasticity and trait correlations are important indicators of recent past events that have shaped the currently observable phenotypes. We investigated variation in the reaction norms of several traits in a large number of accessions of Arabidopsis thaliana exposed to different levels of light quantity as well as the environmental lability of the corresponding across-population character variance–covariance matrix. Our results show that there is an astounding degree of inter-population variation for character means and very little variation for plasticity, in agreement with the idea that A. thaliana is a light-specialist often occurring in open, disturbed habitats. However, this plant also shows patterns of plasticity that are predicted to be adaptive based on functional ecological considerations, such as an increase in either specific leaf area or leaf number (but not both) under low light. We also demonstrate that the set of character correlations in A. thaliana is extremely stable to changes in light availability, contrary to previous findings in the same species when different environmental factors were considered. Several processes that might have been responsible for the observed patterns are discussed as a prelude to follow-up research on these problems.     

Quantitative genetics of behavioural reaction norms: genetic correlations between personality and behavioural plasticity vary across stickleback populations

Behavioural ecologists have proposed various evolutionary mechanisms as to why different personality types coexist. Our ability to understand the evolutionary trajectories of personality traits requires insights from the quantitative genetics of behavioural reaction norms. We assayed > 1000 pedigreed stickleback for initial exploration behaviour of a novel environment, and subsequent changes in exploration over a few hours, representing their capacity to adjust their behaviour to changes in perceived novelty and risk. We found heritable variation in both the average level of exploration and behavioural plasticity, and population differences in the sign of the genetic correlation between these two reaction norm components. The phenotypic correlation was not a good indicator of the genetic correlation, implying that quantitative genetics are necessary to appropriately evaluate evolutionary hypotheses in cases such as these. Our findings therefore have important implications for future studies concerning the evolution of personality and plasticity.     

Revisit on the evolutionary relationship between alternative splicing and gene duplication

Gene duplications and alternative splicing (AS) isoforms are two widespread types of genetic variations that can facilitate diversification of protein function. A number of studies claimed that after gene duplication, two AS isoforms with differential functions can be 'fixed', respectively, in each of the duplicate copies. This simple 'functional-sharing' hypothesis was recently challenged by Roux and Robinson-Rechavi (2011). Instead, they proposed a more sophisticated hypothesis, invoking that less alternative splicing genes tend to be duplicated more frequently, and single-copy genes are younger than duplicate genes, or the 'duplicability-age' hypothesis for short. In this letter, we show that all these genome-wide analyses of AS isoforms actually did not provide clear-cut evidence to nullify the basic idea of functional-sharing hypothesis. After updating our understanding of genome-wide alternative splicing, duplicability and CNV (copy number variation), we argue that the foundation of the duplicability-age hypothesis remains to be justified carefully. Finally, we suggest that a better approach to resolving this controversy is the correspondence analysis of indels (insertions and deletions) between duplicate genes to the genomic exon-intron structure, which can be used to experimentally test the effect of functional-sharing hypothesis.     

Individual variation in parental care reaction norms: integration of personality and plasticity

Personality (consistent differences between individuals in behavior) and plasticity (changes within individuals in behavior) are often viewed as separate and opposing phenomena. We tested this idea by analyzing parental care reaction norms in a bird that exhibits biparental care. Personality in provisioning behavior existed ([Formula: see text]) and persisted despite being reduced after accounting for individual differences in environment. Plasticity was also evident and differed between the sexes. Male visit rate was associated with changes in brood size and time of day, but female visit rate was associated with changes in nestling age and date. In both sexes changes in visit rate were positively correlated with changes in their partner's visit rate. Both sexes also exhibited multidimensional reaction norms; interaction terms revealed that within-individual visit rates increased more steeply with brood size when nestlings were older, and the effect of the partner's visit rate was sensitive to variation in date, precipitation, and the focal bird's age. Individuals also varied in how they responded (reaction norm slope) to changes in nestling age and partner visits. Moreover, parental personality was interdependent with individual plasticity in several ways. Individuals of both sexes with a high visit rate also responded more positively to changes in nestling age, and males also showed this pattern with changes in partner visit rate. Explicit use of the behavioral reaction norm integrated personality and plasticity, revealed that these are not opposing concepts, and stimulated new hypotheses about sexual conflict over care and provisioning as a life-history trait.     

Idealization in evolutionary developmental investigation: a tension between phenotypic plasticity and normal stages

Idealization is a reasoning strategy that biologists use to describe, model and explain that purposefully departs from features known to be present in nature. Similar to other strategies of scientific reasoning, idealization combines distinctive strengths alongside of latent weaknesses. The study of ontogeny in model organisms is usually executed by establishing a set of normal stages for embryonic development, which enables researchers in different laboratory contexts to have standardized comparisons of experimental results. Normal stages are a form of idealization because they intentionally ignore known variation in development, including variation associated with phenotypic plasticity (e.g. via strict control of environmental variables). This is a tension between the phenomenon of plasticity and the practice of staging that has consequences for evolutionary developmental investigation because variation is conceptually removed as a part of rendering model organisms experimentally tractable. Two compensatory tactics for mitigating these consequences are discussed: employing a diversity of model organisms and adopting alternative periodizations.     

Phenotypic plasticity and reaction norms of abdominal bristle number inDrosophila melanogaster

The phenotypic plasticity of abdominal bristle number (segments 3 and 4 in females) was investigated in 10 isofemale lines from a French population, grown at 7 constant temperatures, ranging from 12‡ to 31‡C. Overall concave reaction norms were obtained with a maximum around 20‡-21‡C. Intraclass correlation (isofemale line heritability) was not affected by temperature. Correlations between segments 3 and 4 strongly contrasted a low within-line phenotypic correlation (r = 0.39 ± 0.04) and a high, between-line genetic correlation (r = 0.89 ± 0.03). A significant decrease of the genetic correlation was observed when comparing more different temperatures. Finally, among 7 other morphometrical traits which were measured on the same set of lines, 3 provided a significant positive genetic correlation with abdominal bristles: thoracic bristles, abdomen pigmentation and thoracic pigmentation.     

Fluorescence-based alternative splicing reporters for the study of epithelial plasticity in vivo

Alternative splicing generates a vast diversity of protein isoforms from a limited number of protein-coding genes, with many of the isoforms possessing unique, and even contrasting, functions. Fluorescence-based splicing reporters have the potential to facilitate studies of alternative splicing at the single-cell level and can provide valuable information on phenotypic transitions in almost real time. Fibroblast growth factor receptor 2 (FGFR2) pre-mRNA is alternatively spliced to form the epithelial-specific and mesenchymal-specific IIIb and IIIc isoforms, respectively, which are useful markers of epithelial–mesenchymal transitions (EMT). We have used our knowledge of FGFR2 splicing regulation to develop a fluorescence-based reporter system to visualize exon IIIc regulation in vitro and in vivo. Here we show the application of this reporter system to the study of EMT in vitro in cell culture and in vivo in transgenic mice harboring these splicing constructs. In explant studies, the reporters revealed that FGFR2 isoform switching is not required for keratinocyte migration during cutaneous wound closure. Our results demonstrate the value of the splicing reporters as tools to study phenotypic transitions and cell fates at single cell resolution. Moreover, our data suggest that keratinocytes migrate efficiently in the absence of a complete EMT.