The Falkland fritillary: biological and ecological factors in the conservation of Yramea cytheris cytheris (Drury 1773).

Abstract

This thesis aims to address gaps in the knowledge of the Falkland Islands' only resident butterfly, Yramea cytheris cytheris (Drury 1773), and thereby to contribute to an evidence-based approach to its conservation. Sightings had been infrequent, and its distribution, life cycle, habitat requirements and relationship to its Latin American cosubspecies Y. c. siga (Geyer 1832) little studied. Research set out here showed it to be an obligate Viola-feeder, most commonly on Viola maculata, which was widely, but sparsely, spread around the islands in small (< 1 ha) patches around the coast, particularly amongst dwarf shrub heath. Y. c. cytheris had a wide geographic spread, but records of only 21 populations had been recorded. For oviposition, it favoured mediumsized Viola in warm, sheltered locations, for example north-east facing slopes within a matrix of dwarf shrub heath, grass and patches of bare ground. There was evidence that it chose plants with above-average chlorophyll content. It appeared to be univoltine, laying its eggs singly, with a preference for warmer leaves; the larvae were not gregarious. Female adults were on the wing for an average of four days, the males five, over a flying season from December to February. It showed little mobility, even between adjacent patches. Populations were small, generally <10 on a given day, though catch rates varied considerably. Y. c. cytheris and Y. c. siga differed little genetically: the commonest haplotypes for each of the genes COI, EF-1α, wingless, as well as a concatenation of all three, were shared by both. Latin American butterflies were larger than those from the Falklands, with a lower wing aspect ratio. Morphometric analyses showed Latin American butterflies had more scalloped outer margins to their forewings. Y. c. cytheris showed local adaptation in claw shape, with those from the windiest sites being more curved. A draft species action plan sets out recommendations. There are still knowledge gaps in the life cycle, particularly diapause and pupation, and in population sizes and dynamics. An integrated morphometric and molecular approach is advocated in approaching relationships between populations. Viola conservation is important, especially in the light of climate change, with greater understanding needed of the role of grazing. Urgent consideration should be given to ensuring reintroductions can be made in response to extinctions. A case is made for Y. c. cytheris to become a flagship for insect conservation in the Falklands.