Abstract
Increased human activity and climate change are driving numerous tree species to endangered status, and in the worst cases extinction. Here we examine the genomic signatures of the critically endangered ironwood tree Ostrya rehderiana and its widespread congener O. chinensis. Both species have similar demographic histories prior to the Last Glacial Maximum (LGM); however, the effective population size of O. rehderiana continued to decrease through the last 10,000 years, whereas O. chinensis recovered to Pre-LGM numbers. O. rehderiana accumulated more deleterious mutations, but purged more severely deleterious recessive variations than in O. chinensis. This purging and the gradually reduced inbreeding depression together may have mitigated extinction and contributed to the possible future survival of the outcrossing O. rehderiana. Our findings provide critical insights into the evolutionary history of population collapse and the potential for future recovery of the endangered trees.
Highlights
Increased human activity and climate change are driving numerous tree species to endangered status, and in the worst cases extinction
Comparisons between the old and young O. rehderiana trees allowed us to contrast the very recent impacts of inbreeding on genomic diversity to longer-scale demographic impacts. Based on these genomic data, we addressed the following questions: (1) do these two species show similar demographic histories in response to the Quaternary climate change? If not, when did their demographics begin to diverge? (2) Have deleterious variations accumulated in the endangered species at a greater rate than in the widespread tree, and have they impacted the potential to recover? and (3) have more highly recessive deleterious variations been purged by drift in the endangered species? The answers to these questions will aid in identifying plant genomes that are on the cusp of demographic collapse
A total of 243 unique and 526 expanded gene families were present in O. rehderiana, whereas 434 unique and 880 expanded gene families were present in O. chinensis (Supplementary Figs. 8 and 9, Supplementary Tables 14–17)
Summary
Increased human activity and climate change are driving numerous tree species to endangered status, and in the worst cases extinction. We examine the genomic signatures of the critically endangered ironwood tree Ostrya rehderiana and its widespread congener O. chinensis Both species have similar demographic histories prior to the Last Glacial Maximum (LGM); the effective population size of O. rehderiana continued to decrease through the last 10,000 years, whereas O. chinensis recovered to Pre-LGM numbers. The close relative O. chinensis (=O. multinervis), has relatively large wild populations, which are distributed from southeastern China to the high mountains of southwestern China[30], an area that was only recently colonized by humans and remains sparsely populated[31,32] Wood produced by both species is extremely hard and is highly prized for construction of boats and religious temples[33]. Based on these genomic data, we addressed the following questions: (1) do these two species show similar demographic histories in response to the Quaternary climate change? If not, when did their demographics begin to diverge? (2) Have deleterious variations accumulated in the endangered species at a greater rate than in the widespread tree, and have they impacted the potential to recover? and (3) have more highly recessive deleterious variations been purged by drift in the endangered species? The answers to these questions will aid in identifying plant genomes that are on the cusp of demographic collapse
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