Conserving Syngameons: Thinking Outside the Species Box

Charles H. Cannon

Published May 2024 in International Oaks No. 35: 25–36

Abstract

Conservation assessments are typically conducted at the species level, with each species evaluated separately. This approach overlooks the potential role of interspecific gene flow, primarily introgressive hybridization (IH), in shaping species diversity and adaptation, particularly at the syngameon level. The genus Quercus, with the well-known interfertility of the species that compose it, offers an ideal case study for examining the impact of IH.

Here, I present a novel method developed with colleagues to quantify the potential for IH across all 84 oak species within the contiguous United States. Our technique uses geospatial data to assess sympatry (i.e., the overlap in geographic distribution among each species pairs), considered as a proxy for IH potential. Notably, only 12.6% of US counties harbor just one oak species, indicating that oak species are typically sympatric with other oak species. For instance, section Lobatae oaks (Red Oaks) typically coexist with 5.7 (up to 15) other Red Oak species, and section Quercus oaks (White Oaks) with 3.8 (up to 13) other White Oak species in a single county. By compiling sympatry through pairwise metrics, we explore the network properties of each sectional syngameon within the oak genus

This sheds light on potential gene flow within each section between interfertile species in sections Lobatae and Quercus. Some species share habitat with over approximately 20 other interfertile species across their range. Our findings underline the importance of considering species interactions and potential gene flow in conservation efforts. We argue that conservation strategies must evolve beyond the species level to incorporate these broader ecological and evolutionary dynamics.

Keywords

introgression, introgressive hybridization, interspecific gene flow, conservation management

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