Lucilia blowflies

: their ecology, taxonomy and the evolution of obligate amphibian parasitism

Abstract

Blowflies (Diptera: Calliphoridae) are of evolutionary, ecological and economic importance, performing essential ecosystem services in the consumption, recycling and dispersion of carrion and acting as facultative agents of livestock myiasis. The interspecific ecological differences that facilitate coexistence within the diverse blowfly community are not fully understood. To quantify differences in habitat use by calliphorid species (Chapter 2), thirty flytraps were distributed within three habitats at two sites in south west England during March–August 2016. A total of 17,246 specimens were caught and identified, Lucilia sericata (Meigen) was the dominant species in open habitats, whereas Lucilia caesar (Linnaeus) was the most abundant species in shaded habitats. The results demonstrate that Calliphora and Lucilia species show strong tempo,ral and spatial segregation, mediated by temperature, and that species of the genus Lucilia show differences in habitat use which are likely to be driven by differences in humidity tolerance and light intensity. These factors in combination result in effective niche partitioning. Within the genus Lucilia only one species is generally recognized as an obligate agent of myiasis in Europe, Lucilia bufonivora (Moniez). This species is a specialist parasite of amphibians. However, it has been suggested that a second species Lucilia silvarum (Meigen) may also act as a facultative parasite of amphibians. Their morphological similarity has led to misidentification, taxonomic ambiguity and a paucity of studies of L. bufonivora. To resolve this question (Chapter 3), larvae were analysed from toad myiasis cases from the U.K., The Netherlands and Switzerland, together with adult specimens of fly species that are thought to be implicated in amphibian parasitism: L. bufonivora, L. silvarum and the strictly Nearctic Lucilia elongata (Shannon). Partial sequences of two genes, COX1and EF1α, were amplified. Bayesian inference trees of COX1and EF1α and a combined-gene dataset were constructed. All larvae isolated from toads were identified as L. bufonivora and no specimens of L. silvarum were found implicated in amphibian myiasis. This study confirms L. silvarum and L. bufonivora as distinct sister species, however there is not clear resolution on the relationships of L. silvarum and L. elongata using the nuclear marker EF1α. The evolution of obligate toad parasitism is of particular interest and to investigate this (Chapter 5), molecular clock-dating was performed with a concatenated data set of 3 genes: COX1 (mtDNA), ITS2 (non-coding) and per (nDNA). Unlinked substitution and relaxed clock models were implemented to allow evolution to vary amongst lineages. Obligate amphibian parasitism probably evolved just once around 4 mya. It is likely that this occurred after the niche displacement of a saprophagous ancestor from the carrion-fly community. Evidence from nDNA phylogenies suggest that, although with slow nuclear evolution rates, L. elongata is a distinct species to L. silvarum. Consistent paraphyly of L. bufonivora across single-gene phylogenies and high mtDNA sequence divergence between Palearctic and Nearctic lineages suggest on-going cryptic speciation of L. bufonivora in these two regions for at least 2mya. Thus, due to its relative rarity, it has remained unrecorded by taxonomists until recent studies. Since the ecology of L. bufonivora is poorly understood, ecological studies were undertaken in the Netherlands (Chapter 5). These demonstrated the low abundance of adult L. bufonivora in the field and showed that it was more frequently encountered in open and wet habitats where its hosts are abundant rather than in woodland habitats. The broad issues surrounding the evolution of diversity within the calliphorid blowflies are discussed (Chapter 6) and it is suggested that it is the patchy and ephemeral nature of carrion that is the key to understanding the ecology and evolution of this family of flies, since this drives the evolution of niche partitioning and specialisation.

Date of Award	1 Oct 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Eric Morgan (Supervisor) & Richard Wall (Supervisor)