Long-Distance Travellers: Phylogeography of a Generalist Parasite, Pholeter gastrophilus, from Cetaceans

• Published in: PloS one Vol. 12; no. 1; p. e0170184
• Main Authors: Fraija-Fernández, Natalia, Fernández, Mercedes, Lehnert, Kristina, Raga, Juan Antonio, Siebert, Ursula, Aznar, Francisco Javier
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 13.01.2017; Public Library of Science (PLoS)
• Subjects: Analysis; Analysis of Variance; Animal behavior; Animals; Atlantic Ocean; Biodiversity; Biology and Life Sciences; Cetacea; Cetacea - parasitology; Clustering; Coasts; Cryptic species; Delphinidae; Demographics; Demography; Diseases and pests; Dispersal; DNA, Helminth - chemistry; Dolphins & porpoises; Earth Sciences; Ecological effects; Ecology and Environmental Sciences; Equator; Equatorial regions; Evolutionary biology; Exploitation; Gene flow; Genetic aspects; Genetic diversity; Genetic Speciation; Genetic Variation; Haplotypes; Likelihood Functions; Marine; Medicine and Health Sciences; Mediterranean Sea; Mitochondria; Mitochondrial DNA; Parasites; Pholeter gastrophilus; Phylogeography; Physiological aspects; Population; Population Dynamics; Population growth; Population structure; Populations; Reproductive Isolation; Research and Analysis Methods; Sequence Analysis, DNA; Studies; Travellers; Troglotrematidae - classification; Troglotrematidae - genetics; Troglotrematidae - physiology; Veterinary medicine; Whales; Germany; Spain; Mediterranean Sea
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0170184

We studied the phylogeography and historical demography of the most generalist digenean from cetaceans, Pholeter gastrophilus, exploring the effects of isolation by distance, ecological barriers and hosts' dispersal ability on the population structure of this parasite. The ITS2 rDNA, and the mitochondrial COI and ND1 from 68 individual parasites were analysed. Worms were collected from seven oceanic and coastal cetacean species from the south western Atlantic (SWA), central eastern Atlantic, north eastern Atlantic (NEA), and Mediterranean Sea. Pholeter gastrophilus was considered a single lineage because reciprocal monophyly was not detected in the ML cladogram of all individuals, and sequence variability was <1% for mtDNA and 0% for ITS2. These results rule out a recent suggestion that P. gastrophilus would actually be a cryptic-species complex. The genetic cohesion of P. gastrophilus could rely on the extensive exploitation of wide-ranging and highly mobile cetaceans, with a putative secondary role, if any, of intermediate hosts. Unique haplotypes were detected in SWA and NEA, and an AMOVA revealed significant population structure associated to the genetic variation in these regions. The Equator possibly acts as a significant geographical barrier for cetacean movements, possibly limiting gene flow between northern and southern populations of P. gastrophilus. A partial Mantel tests revealed that the significant isolation of NEA populations resulted from geographic clustering. Apparently, the limited mobility of cetaceans used by P. gastrophilus as definitive hosts in this region, coupled with oceanographic barriers and a patchy distribution of potential intermediate hosts could contribute to significant ecological isolation of P. gastrophilus in NEA. Rather unexpectedly, no genetic differentiation was found in the Mediterranean samples of this parasite. Historical demographic analyses suggested a recent population expansion of P. gastrophilus in the Atlantic Ocean, perhaps linked to initial association and subsequent spreading in cetaceans.