Premise of the study: Habitat fragmentation generates molecular genetic divergence among isolated populations but few studies have assessed phenotypic divergence and fitness in populations where the genetic consequences of habitat fragmentation are known. Phenotypic divergence could reflect plasticity, local adaptation, and/or genetic drift.

Methods: We examined patterns and potential drivers of phenotypic divergence among 12 populations of jewelweed (Impatiens capensis Meerb.) that show strong molecular genetic signals of isolation and drift among fragmented habitats. We measured morphological and reproductive traits in both maternal plants within natural populations and their self-fertilized progeny grown together in a common garden. We also quantified environmental divergence between home sites and the common garden.

Key results: Populations with less molecular genetic variation expressed less maternal phenotypic variation. Progeny in the common garden converged in phenotypes relative to their wild mothers but retained among-population differences in morphology, survival, and reproduction. Among-population phenotypic variance was 3-10x greater in home sites than in the common garden for 6 of 7 morphological traits measured. Patterns of phenotypic divergence paralleled environmental gradients in ways suggestive of adaptation. Progeny resembled their mothers less as the environmental distance between their home site and the common garden increased.

Conclusions: Despite strong molecular signatures of isolation and drift, phenotypic differences among these Impatiens populations appear to reflect both adaptive quantitative genetic divergence and plasticity. Quantifying the extent of local adaptation and plasticity and how these covary with molecular and phenotypic variation help us predict when populations may lose their adaptive capacity. 

Detailed methods are available in the README for this data package.

Briefly - Morphological data (height, stem diameter, leaf size and shape traits) and reproductive output data were collected on 96 Impatiens capensis plants in each of 12 remote home field sites in southern/central Wisconsin. Cleistogamous seeds were collected from a subset of these mother plants, germinated in a greenhouse, and grown in a common garden for their lifetime.  In the common garden, the same morphological data were collected as on the mothers and lifetime reproductive output was recorded.  Climate, soils, and canopy openness environmental data were collected or downloaded for each of the 12 remote home field sites and the common garden.

impatiens_phenotypic_diversity.zip