title: Characterizing Local Adaptation and Gene Flow in the Patagonian tree species Nothofagus pumilio
title: Charakterisierung lokaler Anpassung und Genfluss Genflusses bei der patagonischen Baumart Nothofagus pumilio
titleType: AlternativeTitle
Creators: name: Sekely, Jill Terese
Publisher: name: Philipps-Universität Marburg
Year: 2024
Subjects: Local adaptation
Südbuchen
Life sciences
Biowissenschaften, Biologie
Patagonia
Climate change
lokale Anpassung
Patagonien
Nothofagus pumilio
genetische Vielfalt
genomische Verschiebung
Southern beeches
Klimawandel
gene flow
Genfluss
Genetic diversity
genomic offset

description: Contemporary changes in climate and land use pose great potential threats to Earth’s forest
ecosystem biodiversity. While biodiversity is often discussed at the species scale, genes are
the most basic building block of diversity. Genetic variation provides the raw material for
specific adaptations to local conditions, makes speciation possible, and confers evolvability,
meaning organisms’ potential for rapid genetic change when they are exposed to sudden or
severe change. Whether trees’ extant genetic diversity and adaptations are sufficient for
them to survive and thrive under future climactic conditions is actually a multifaceted host
of questions that, in the case of most species, remains unanswered.
The southernmost forested ecosystem on Earth resides in the Patagonian Andes region of
South America, which is an ecologically fascinating yet understudied region. Sharp climactic
gradients in temperature and precipitation are created by the Andes’ predominantly North-
South orientation, and the resultant heterogeneous environments exert divergent selection
pressures upon local populations of forest tree species. Therefore, those populations likely
exhibit local adaptation patterns, but the genetic basis of that adaptation remains largely
undescribed. Patagonian forests are predominantly comprised of seven species from the
Nothofagus genus, which are collectively called the southern beeches, and these forests
provide invaluable ecosystem services yet face increasing challenges. The most widespread
of these species is Nothofagus pumilio [Poepp. et Endl.] Krasser, a cold-adapted and
deciduous species with a continuous range stretching across more than 2,000 kilometers. Its
common name “lenga” comes from the indigenous Mapuche language, suggesting that this
species has long been of interest to humanity. Lenga has also been called a foundation
species, since it physically creates the local forest structure and regulates ecosystem
functioning.
While prior studies have investigated N. pumilio population structure and neutral genetic
diversity patterns, questions remain about its adaptive genetic diversity, patterns of gene
flow, and climate change risk. Characterizing these parameters is critical to understanding
how the species might respond to coming change, either through further adaptation,
migration, or local extinction. In the following Chapters, I address local adaptation knowledge
gaps for Nothofagus pumilio. Specifically, I asked the following questions: i) do signatures of
local adaptation exist within its genome, and if so, which climactic conditions may have
played a role in shaping those signatures? ii) what are the spatial characteristics of gene flow,and how might they affect natural selection? and iii) based on these evolutionary
characteristics, what risk might future climate change pose for this species?
The following chapters encompass my work in addressing these questions. Chapter I is a
general introduction that outlines existing research and relevant knowledge gaps for N.
pumilio. Chapter II addresses question i) via a landscape genomics approach, using genetic
markers (SNPs) and climactic data to characterize spatial patterns of population structure,
genetic diversity, and signatures of adaptation. I found evidence of local adaptation, with
many candidate genes showing signatures of selection that were associated with
temperature and day length gradients and, to a lesser extent, precipitation. I also found
latitude-oriented genetic diversity and population structure patterns, with greater genetic
diversity in the North. To illuminate how gene flow may be interacting with natural selection
and thereby affecting local adaptation, I addressed question ii) in Chapter III by analyzing
gamete dispersal distances and fine-scale spatial genetic structure with neutral genetic
markers obtained from adult and seedling cohorts. My work shows that gamete dispersal
distances are largely spatially restricted, but with some immigration especially among pollen,
which aligns with my population structure results from Chapter II. These results also suggest
strong selection pressures. Short migration distances could have implications for migration
capacity under coming climate change, which plays into the major question about how
anthropogenic climate change will affect species. To characterize risk based on the observed
evidence of local adaptation (Chapter II), I addressed question iii) in Chapter IV using the
genomic offset method, which is an extension of the landscape genomics approach. This
relatively new approach takes the relationships between allele and climate gradients and
projects them across time and space, to predict how maladapted different populations might
be under altered climate conditions in the future. I assessed projected risk in context of
natural selection and gene flow results from Chapters II &amp; III to illuminate possible species
responses. Finally, Chapter V is a synthesis of main results from my research, including
possible management applications, and in Chapter VI, I suggest future research avenues
based on my findings. Overall, my results suggest that Nothofagus pumilio exhibits signatures
of local adaptation to current climate conditions (Chapter II) but has limited gene flow and
migration (Chapter III), and it may therefore face an uncertain future under climate change
(Chapter IV).