Parallel evolution


16 November 2010
Studying fish and fish parasites simultaneously will allow science to better understand the co-evolution of species, says Charlotte Schoelinck, a PhD student at the Natural History Museum of Paris.
Charlotte is studying groupers – fish of the genera Epinephelus, Cephalopholis, Variola, Plectropomus and Mycteroperca – along with two families of parasites that infect groupers' gills.
The parasites Charlotte is studying are flatworms of the class Monogenea. There are about 50 known families, and thousands of described species of monogeneans. Charlotte is focusing on the Diplectanidae and Ancyrocephalidae families: small worms, half a millimetre long, found in the gills of groupers.
She is using morphology (the study of the shapes, structure and anatomy) and molecular biology (DNA analyses) to understand the evolution, distribution and biodiversity both of the fish and the parasites. She plans to construct a phylogeny for this group of parasite species: essentially a family tree showing the shared evolutionary history of these species, and their patterns of speciation.
"By comparing the grouper phylogeny and the parasite phylogeny, we can study co-evolution: how fish evolution and parasite evolution affect each other," Charlotte says.
"I am interested in both types of animals; not each in isolation, but how they interact," she says.
Charlotte has spent nine months over the past two years collecting samples from New Caledonia, where her PhD supervisor is conducting research. Charlotte has also been in contact with other researchers in South Africa. She expects to further expand her understanding of species diversity by collecting specimens from Heron Island.
"It's very interesting to study the parasitic fauna in one spot, but it's more interesting if we have some comparison," she says.
She estimates she has found 400 specimens of monogeans in groupers so far during this field trip.
Charlotte says there is great cryptic diversity among these parasites: this means there are many closely-related species that look almost identical but which are genetically different.
"Sometimes, we can't distinguish the species by the morphological characteristics, so I have to wait for the DNA analysis to be completed before I can classify the specimens and describe new species.
"I have found at least one new species from Heron Island," she says, "but I think I will find a lot of cryptic species as well."
Charlotte's model of the relationships between host and parasites may help scientists to understand the parasite transmission between groupers. It may also have applications for aquaculture, by assisting to locate sources of infection or to reduce the prevalence of infection in commercial sea-pens.
Charlotte's work will contribute to scientific understanding of the biodiversity of parasites in marine fish, and the understanding of host-parasite relationships.