Global Changes in Lepidopteran Phylogenetic Diversity Across Space and Time

Amidst increasing reports of insect declines, it is ever more important to understand spatial and temporal insect diversity patterns and processes. Phylogenetic diversity (PD) is an important biodiversity metric in that it relates strongly to ecosystem processes, and it can be estimated more accurately from opportunistic occurrence data than other elements of biodiversity. Here, we assess recent changes across global variation in Lepidopteran PD, to discover overall patterns, their repeatability across regions and environmental drivers. We assess global, spatiotemporal variation in PD, as compared to null expectations given sampling effort, determining how such variation relates to region, space, time and environment. Our analysis is based on 374,749 gene sequence accessions from the barcode of life database (BOLD), representing 3158 species assemblages, spanning 62 years. We find that global variation in PD of Lepidopteran species assemblages has significantly increased over time at high latitudes while remaining relatively unchanged near the equator. This pattern exhibits parallelism across global regions, with the strongest increases in PD towards the present observed in high-latitude communities in North America and Asia, in lowland sites in Europe, and across the African continent. In contrast, PD has declined through time in wetter portions of Australasia and in Africa and South America. Our reported patterns likely reflect changes in Lepidopteran responses to tropical habitat loss and widespread range expansions to higher latitudes. However, changing clines in DNA barcoding strategies could also play a role. Detecting spatiotemporal patterns of change in PD at the global scale is enabled by the increasing use of genetic markers in taxonomy. Our replicated findings provide confidence in biogeographic interpretation, yet increased metadata on sub-sampling decisions would aid future interpretation of biodiversity trends using ecological genomics synthesis.