Molecular delimitation of evolutionary significant units reveals hidden geographic drivers of extinction risk within island arthropods

Aim: Globally, arthropod biodiversity is under threat, with increased risk of species-level extinctions, and this threat is particularly acute on oceanic islands. A fundamental first step toward understanding extinction risk is to understand genetic connectivity among the constituent populations of a species. Our aim is to develop and implement a protocol to characterise genetic connectivity among island populations within arthropod species to reveal otherwise hidden range size drivers of extinction.

Location: Canary Islands, Spain.

Methods: We implement a protocol based on mtDNA sequence data for the delimitation of evolutionary significant units (ESUs) to evaluate extinction risk among species of beetle and spider distributed across multiple islands.

Results: Our results reveal that more than half of the species analysed are comprised of two or more ESUs. We also find that low dispersal ability was a significant predictor of ESUs within species of Coleoptera, but with no significant difference for Araneae.

Main conclusions: Most ESUs are consistent with early stage differentiation, or incipient speciation, with some exceeding a conservative interspecific threshold, thus indicative of cryptic species. We suggest that extending our approach with the integration of other species-level traits may provide for a more refined predictive framework for understanding extinction risks across island arthropod species.

Methods
Date of data collection: 2012-2021

Geographic location of data collection: Canary Islands, Spain. Specifically, laurel forests of Tenerife, La Gomera, La Palma and El Hierro.

This data set was generated to calculate the Nst index usign SPAGeDI software to delimited potential ESUs (Evolutionary Significant Units) of spider and beetle species through a specific workflow; and to calculate GLM and the Spearman Rank-Order Correlation.Genetic data include cytochrome oxidase I (COI) sequences of spiders and beetles obtained with Sanger sequencing.