Abstract
Elucidating the impacts of demographic history and genomic selection on species evolution is a central topic in phylogeography and evolutionary biology. Black walnuts (Juglans section Rhysocaryon) are native nut trees of the NEW WORLD, with a broad distribution ranging from southern Canada to northern Argentina. The demographic history and genomic dynamics of Rhysocaryon species remain poorly understood. Here, we employed population genomics and chloroplast data to construct a high-density map of genomic variation across 108 Rhysocaryon accessions. Despite gene introgression, these accessions were clearly delimited into four groups. Evolutionary scenarios analysis showed that the diversification of black walnuts might have occurred approximately 28.74 million years ago during the late Oligocene, with the clade comprising Juglans hindsii and Juglans californica diverging earliest. The gene introgression and hybridization analysis indicated that Juglans microcarpa might be a hybrid descendant of Juglans nigra and J. hindsii. As the climate oscillated, these ancestral populations kept diverging, laying the basis for their colonization of South America. Quaternary climatic oscillations also exerted a profound influence on black walnut population size, which exhibited sensitive fluctuations in response to alternation of glacial and interglacial periods. The selection sweeps analysis unveiled highly divergent genomic regions in the economic species J. nigra, which were associated with development, reproduction, disease resistance, and stress tolerance. The genes WRKY41 and ERF012 were identified as potential drivers of J. nigra's adaptation. Our findings illuminated the demographic history and selective signatures of black walnuts, thereby providing a genetic foundation for future breeding, conservation, and genomic studies.
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Claims 10
Claim · model-written summary
The study constructed a high-density map of genomic variation across 108 Rhysocaryon accessions.
Verbatim
e0“construct a high-density map of genomic variation across 108 Rhysocaryon accessions.”
Claim · model-written summary
The 108 Rhysocaryon accessions were delimited into four groups despite introgression.
Verbatim
e0“Despite gene introgression, these accessions were clearly delimited into four groups.”
t0“108 Rhysocaryon accessions”
Claim · model-written summary
Black walnuts may have diversified about 28.74 million years ago in the late Oligocene.
- Taxon
- black walnuts
Juglans nigrae0 - Outcome
- diversification of black walnutse0
- Value
- approximately 28.74 million years agoe0
- Qualifier
- might have occurrede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the diversification of black walnuts might have occurred approximately 28.74 million years ago during the late Oligocene”
Claim · model-written summary
The clade containing Juglans hindsii and Juglans californica diverged earliest.
- Taxon
- Juglans hindsii and Juglans californica
Juglans californica
Juglans hindsiie0 - Outcome
- diverging earlieste0
- Direction
- earlieste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the clade comprising Juglans hindsii and Juglans californica diverging earliest.”
Claim · model-written summary
Juglans microcarpa may be a hybrid descendant of Juglans nigra and J. hindsii.
- Taxon
- Juglans microcarpa
Juglans microcarpae0 - Outcome
- hybrid descendant of Juglans nigra and J. hindsiie0
- Qualifier
- might bee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Juglans microcarpa might be a hybrid descendant of Juglans nigra and J. hindsii.”
Claim · model-written summary
Ancestral black walnut populations kept diverging as climate oscillated, preceding South American colonization.
- Taxon
- black walnutsJuglans nigrat0
- Outcome
- ancestral populations kept diverginge0
- Direction
- diverginge0
- Qualifier
- climate oscillatede0
- Setting
- South Americae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“As the climate oscillated, these ancestral populations kept diverging, laying the basis for their colonization of South America.”
t0“black walnuts”
Claim · model-written summary
Black walnut population size fluctuated with Quaternary glacial and interglacial periods.
- Taxon
- black walnutJuglans nigrae0
- Outcome
- black walnut population sizee0
- Qualifier
- alternation of glacial and interglacial periodse0
- Setting
- Quaternary climatic oscillationse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Quaternary climatic oscillations also exerted a profound influence on black walnut population size, which exhibited sensitive fluctuations in response to alternation of glacial and interglacial periods.”
Claim · model-written summary
J. nigra contained highly divergent genomic regions associated with development, reproduction, disease resistance and stress tolerance.
- Taxon
- J. nigraJuglans nigrae0
- Gene
- genomic regionse0
- Outcome
- highly divergent genomic regionse0
- Qualifier
- development, reproduction, disease resistance, and stress tolerancee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“highly divergent genomic regions in the economic species J. nigra, which were associated with development, reproduction, disease resistance, and stress tolerance.”
Claim · model-written summary
WRKY41 was identified as a potential driver of J. nigra adaptation.
- Taxon
- J. nigraJuglans nigrae0
- Gene
- WRKY41e0
- Outcome
- potential drivers of J. nigra's adaptatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The genes WRKY41 and ERF012 were identified as potential drivers of J. nigra's adaptation.”
Claim · model-written summary
ERF012 was identified as a potential driver of J. nigra adaptation.
- Taxon
- J. nigraJuglans nigrae0
- Gene
- ERF012e0
- Outcome
- potential drivers of J. nigra's adaptatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The genes WRKY41 and ERF012 were identified as potential drivers of J. nigra's adaptation.”