Where to draw the boundaries? Using landscape genomics to disentangle the scribbly gum species complex

Abstract

PremiseSpecies delimitation is an integral part of evolution and ecology and is vital in conservation science. However, in some groups species delimitation is difficult, especially where ancestral relationships inferred from morphological or genetic characters are discordant, possibly due to a complicated demographic history (e.g., recent divergences between lineages). Modern genetic techniques can take account of complex histories to distinguish species at a reasonable cost and are increasingly used in numerous applications. We focus on the scribbly gums, a group of up to five closely related and morphologically similar ‘species’ within the eucalypts.MethodsMultiple populations of each recognized scribbly gum species were sampled over a wide region across climates and genome‐wide scans used to resolve species boundaries.Key resultsWe found that none of the taxa were completely diverged, and there were two genetically distinct entities: the inland distributed Eucalyptus rossii and a coastal conglomerate consisting of four species forming three discernible, but highly admixed groups. Divergence among taxa was likely driven by temporal vicariant processes resulting in partial separation across biogeographic barriers. High interspecific gene flow indicated separated taxa reconnected at different points in time blurring species boundaries.ConclusionsOur results highlight the need for genetic screening when dealing with closely related taxonomic entities, particularly those with modest morphological differences. We show that the use of high throughput sequencing can be effective at identifying species groupings and processes driving divergence, even in the most taxonomically complex groups, and support it as a standard practice for disentangling species complexes.This article is protected by copyright. All rights reserved.