By John P. Roche
Acanthiophilus is a genus of fruit flies that infest plants of the tribe Cardueae (thistles) within the family Asteraceae. Members of this genus live in Africa, the Canary Islands, Europe, and Asia. Some species of Acanthiophilus are potential biological control agents of weeds, and others are serious pests to economically important crop plants. For example, the safflower fly, A. helianthi, is a significant pest to safflower in Europe and the Middle East.
There is little previous research on the life history of this group, and the phylogeny of the Acanthiophilus has never before been systematically studied. In 1999, Allen Norrbom and colleagues performed a morphological investigation of Acanthiophilus and assigned ten species to the genus, but this study was preliminary. Now a new study published in the Annals of the Entomological Society of America by Elizabeth Morgulis, Amnon Freidberg, and Netta Dorchin of Tel Aviv University helps to fill this gap in knowledge by investigating the phylogeny of Acanthiophilus using morphological data, and also the science of cladistics, which infers evolutionary relationships statistically based on the number of characters shared among groups. The authors performed an extensive analysis using individuals collected throughout the wide geographic range of the genus, and they provide a revision of the genus and a detailed, illustrated key to all of the members of the genus. In addition, they describe the host plants for three species for which host information was not previously known.
In their study, Morgulis and her colleagues found cladistic evidence that supports a monophyletic origin for Acanthiophilus. Their data suggest that the genus originated in Africa, and then dispersed to Europe and Asia in response to climate change and the dispersal of their host plants.
When asked why the authors chose Acanthiophilus for a phylogenetic revision, Morgulis said, “The revision of Acanthiophilus is a part of a bigger project, which is a revision of both Acanthiophilus and the fruit fly genus Tephritomyia. When we began our research, our hypothesis was that Acanthiophilus and Tephritomyia form a monophyletic group. Based on our previous knowledge, some of the species that were assigned to Acanthiophilus actually belonged to other genera, and we also recognized three undescribed species of Acanthiophilus. These data led us to revise the genus Acanthiophilus.”
The three undescribed species assigned to Acanthiophilus are A. minor, A. summissus, and A. unicus. The five species they reassigned to other genera are A. astrophorus, A. coarctatus, A. kohleri, A. melanoxanthus, and A. trypaneodes. Thus, based on their phylogenetic revision, the genus now includes eight species.
One of the most fascinating parts of the new study is the information it provides about the potential biogeography of members of the genus over time. The biogeographic analysis concluded that Acanthiophilus probably arose in middle Africa, and then spread to other regions. The researchers propose that the hosts of these fruit flies, members of the thistle tribe (Cardueae), arose first in Asia in the Eocene Epoch (between 34-56 million years ago) and then dispersed to Africa in the Pleistocene Epoch (11,000 years to 2.5 million years ago). The Cardueae then dispersed to the Canary Islands, which could have allowed Acanthiophilus to disperse there and could have led to the evolution of A. walkeri, which currently lives in the Canary Islands. The dispersal of Acanthiophilus to India could have occurred through the Arabian Peninsula in the middle of the Pleistocene when the Peninsula had a wet climate. When the Arabian Peninsula later became arid in the late Pleistocene, this formed a barrier between Acanthiophilus in Africa and in India. This could have led to the speciation of A. lugubris, which lives in India. The species A. helianthi is found throughout much of Europe and Asia, and the authors suggest that it may have dispersed so widely via international trade of safflower plants.
When asked about the most important next steps for the study of Acanthiophilus, Morgulis said, “What is needed is a larger-scale cladistic analysis and a molecular phylogenetic analysis, which will include Acanthiophilus and related genera, and which can enhance our understanding of the phylogeny of this group as a whole. It will also be important to find and verify the status of additional host plants, and to search for additional Acanthiophilus species, which no doubt exist.”
Morgulis and colleagues significantly advanced our understanding of the phylogeny of the genus Acanthiophilus. Additional research, particularly an analysis using molecular data, will further expand our knowledge of the phylogeny of this group, and could potentially add new insights into the intriguing biogeographical history of the genus.
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John P. Roche is a science writer and author with a PhD and a postdoctoral fellowship in the biological sciences. He has served as editor-in-chief of university research periodicals at Indiana University and Boston College, has published more than 150 articles, and has written and taught extensively about science and science writing. Dr. Roche also directs Science View Productions™, which provides technical writing and developmental editing for clients in academia and industry.