Postglacial migration and adaptation for dispersal in pitch pine (Pinaceae)

Area of Science:

• Ecology
• Evolutionary Biology
• Forest Genetics

Background:

• Species variation arises from adaptive, random, and migratory factors.
• Pitch pine (Pinus rigida) is a highly variable conifer with a history of occupying glacial refugia.
• Harsh glacial conditions likely favored adaptations for dispersal and recolonization.

Purpose of the Study:

• To assess phenotypic diversity in pitch pine through long-term growth trials.
• To elucidate adaptations and identify likely glacial refugia of pitch pine.

Main Methods:

• Grown pitch pine progeny from 31 origins in common gardens across six locations.
• Analyzed survival, growth, reproductive traits, seed mass, cone characteristics, and disease/frost burn incidence.
• Utilized cluster analysis to identify population structure.

Main Results:

• Survival increased with source latitude; southern-origin seedlings initially grew taller, but this advantage faded.
• Northern-origin progeny exhibited precocious reproduction, smaller seeds, and more seeds per cone.
• Seed mass decreased with latitude; serotinous cones were common in specific New Jersey and Maine populations. Disease and frost burn showed nonlinear latitudinal trends, with a break around 40°N.
• Cluster analysis revealed distinct northern and southern groups, with unique outliers. Geographic structure was clearer in the southern group.

Conclusions:

• Pitch pine recolonized its current range from at least three glacial refugia.
• One refugium was likely on the continental shelf during the Last Glacial Maximum.
• Population structure reflects colonization patterns from these refugia.