Human-impacted landscapes facilitate hybridization between a native and an introduced tree

Area of Science:

• Ecology
• Genetics
• Conservation Biology

Background:

• Hybridization dynamics are well-studied in sympatric species, but less so in native-introduced systems, particularly for long-lived trees.
• Understanding hybridization is critical for conservation, especially for declining species like butternut (Juglans cinerea).

Purpose of the Study:

• To investigate the influence of anthropogenic landscapes on the extent, direction, and spatial distribution of hybridization between native butternut and introduced Japanese walnut (Juglans ailantifolia).
• To assess the role of different landscape types in facilitating or hindering gene flow between these tree species.

Main Methods:

• Utilized microsatellite and chloroplast DNA markers to analyze genetic admixture in 1363 trees across 48 locations within the native range of butternut.
• Compared hybridization rates and parentage in anthropogenic sites versus fragmented and continuous forests.

Main Results:

• Admixture reached nearly 70% in anthropogenic sites, contrasting with minimal admixture (<8%) in fragmented and continuous forests.
• In anthropogenic sites, 95% of hybrids had Japanese walnut as the seed parent, compared to 69% and 59% in fragmented and continuous forests, respectively.
• Landscape type strongly influences the rate and direction of gene flow.

Conclusions:

• Anthropogenic landscapes dramatically increase hybridization rates and gene flow between butternut and Japanese walnut.
• Even small forested areas act as significant barriers to hybrid establishment, offering a crucial buffer for native butternut conservation.
• Findings are vital for butternut conservation planning and managing hybridization risks for other North American forest trees facing introduced congeners.