Weak impact of fine-scale landscape heterogeneity on evolutionary potential in Arabidopsis lyrata

Microhabitat heterogeneity can lead to fine-scale local adaptation when gene flow is restricted, which may be important for the maintenance of genetic variation within populations. This study tested whether microhabitat heterogeneity was associated with trait differences in a population of Arabidopsis lyrata and studied its impact on the genetic variance-covariance (G) matrix. Maternal seed families were collected from dune tops and bottoms, two microhabitats known to vary significantly in water availability. In a common garden experiment, replicate individuals per family were raised under wet and dry conditions, and physiological, morphological and life-history traits were assessed. Plants from the two microenvironments differed in their response to treatment in two performance components, in stomata density and most strongly in flowering time. Under wet conditions, plants originating from dune bottoms flowered 4 weeks earlier than those from dune tops. Only one of three G-matrix comparisons revealed that habitat heterogeneity and evolutionary potential were positively linked. The number of independent trait dimensions was larger in the entire population than within subpopulations separated by microhabitat under wet conditions. However, the size of the G-matrix was no larger in the entire population than within subpopulations separated by microhabitat, and trait correlation structure between microhabitats and treatments was not significantly different. These results indicate that fine-scale habitat heterogeneity likely led to local adaptation, which weakly affected levels of across-trait genetic variation.