Population Ecology and Genetics of the Marsh Fritillary Butterfly Euphydryas aurinia

Abstract

The past two decades have witnessed an unprecedented decline in Lepidopteran species, with more than a third of the UK’s butterflies now either considered threatened, or already lost from the country. The vulnerable marsh fritillary, Euphydryas aurinia, after a long term loss in the UK of 73% in abundance, has become an almost iconic species as the target of many well-funded conservation projects across the UK. Despite extensive ecological studies, populations of E. aurinia are shown in Chapter 2 to still be declining in south-west UK even after recommended management strategies have been implemented. This necessitates the need for prompt research beyond that of management requirements and butterfly habitat preferences.

In Chapter 3, microsatellite markers (EST-SSRs) were developed for E. aurinia and using these markers in Chapter 4, it is shown that E. aurinia populations in southern UK and Catalonia, Spain, are severely genetically differentiated at all geographical scales, and genetically depauperate, causing huge concerns for the conservation of this enigmatic and ecologically important species.

Dispersal is fundamental to metapopulation existence and survival. Phosphoglucose isomerase (PGI – an enzyme in the glycolysis pathway) is a well-endorsed candidate gene for dispersal, extensively studied in the Glanville fritillary (Melitaea cinxia) and Orange Sulphur (Colias eurytheme). In Chapter 5, an analysis across 27 sites in the UK discovered six non-synonymous SNPs (single nucleotide polymorphisms) within PGI. A single charge-changing SNP of interest showed no evidence of balancing selection, contrary to findings in M. cinxia, instead appearing to be neutral when analysed alongside microsatellite markers developed in Chapter 3. No link was found between genotype and flight, morphology or population trend. These findings challenge the emerging perspective that PGI could be used as an adaptive molecular marker for arthropods.

Wolbachia are endosymbiotic bacteria capable of dramatically altering the reproductive system of their host. In Chapter 6, a PCR-based diagnostic in conjunction with MLST (multi-locus sequence typing) identified 100% prevalence of a single strain of Wolbachia across all sampled E. aurinia populations in the UK. Total prevalence suggests that Wolbachia probably has little phenotypic impact on its host, but the potential impacts of this endosymbiont on uninfected populations should be considered during any management plans for the conservation of E. aurinia.

Current management plans will need to incorporate all areas of research, from basic ecological requirements to molecular adaptation and unseen manipulators of host biology, to be able to fully and effectively conserve declining fragmented species.