Spatial and temporal patterns in the population genomic structure of the European cockchafer Melolontha melolontha in the Alpine region

The European cockchafer Melolontha melolontha is an agricultural insect pest in many European countries. Populations have a synchronised three or four year life cycle (i.e., individuals are in the same developmental stage), leading to temporally isolated populations. Despite the economic importance and availability of comprehensive historic as well as current records on cockchafer occurrence, population genetic analyses of M. melolontha are missing. For example, the effects of geographic separation caused by the mountainous terrain in the Alpine region and of temporal isolation on the genetic structure of M. melolontha still remain unknown. In this study, we established collections of M. melolontha from 35 sites in the central Alpine area during three years and genotyped the 475 adults with double-digest Restriction site Associated DNA sequencing (ddRADseq). Subsequent population structure analyses discriminated the South Tyrol collections, located south-east of the Alpine mountain range as compared to all the other collections, reflecting evolutionary history and geographic barriers. A general mixed model confirmed that both geographic distance and, to a lower extend, also temporal isolation had a significant effect on the genetic distance among M. melolontha collections. This study contributes to the understanding of the phylogeography of an organism that is recognised as agricultural problem, and provides significant information on the population genetic structure of insect species with prolonged temporally shifted and synchronised life-cycles.