Landscape Genomics of Angiosperm Trees: From Historic Roots to Discovering New Branches of Adaptive Evolution

Abstract

Landscape genomic studies analyze spatial patterns of genetic variation to test hypotheses about how demographic history, gene flow, and natural selection have shaped populations. For decades, angiosperm trees have served as outstanding model systems for landscape-scale genetic studies due to their extensive geographic ranges, large effective population sizes, abundant genetic diversity, and high gene flow. These characteristics were recognized early in the landscape genetics literature, and studies on angiosperm trees, particularly Populus and Quercus, tested hypotheses about how landscape features shaped neutral patterns of gene flow and population divergence. More recently, advances in sequencing and analysis methodologies have allowed for greater opportunities to directly test how natural selection acting locally across the landscape has shaped the genome-wide diversity of populations, often in the context of broad climatic gradients in growing season length. Despite, the methodological gains and successes of the last decade, landscape genomics studies face new challenges of study design, hypothesis testing, and validation. Here, we explore the development of landscape genetics and genomics in angiosperm trees and what we have learned from investigating the evolutionary consequences of life as a tree in heterogeneous landscapes. We outline the past, present, and potential future of landscape genomic studies in angiosperm trees, highlighting successes of the field, challenges to overcome, and ideas that scientists from all backgrounds engaged in landscape genomics should consider.