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

Abstract

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.

A Visitor of Tropical Waters: First Record of a Clymene Dolphin (Stenella clymene) Off the Patagonian Coast of Argentina, With Comments on Diet and Metazoan Parasites

“…Our phylogenetic analyses of the cox1 dataset for heterophyid trematodes (16 taxa; 20 sequences; 369 nt; Supplementary Table 1A) clustered our newly generated sequence of P. gastrophilus from the Clymene dolphin with published sequences of P. gastrophilus from a bottlenose dolphin, Tursiops truncatus (Montagu, 1821) (KT883857 and KX059405), a striped dolphin, Stenella coeruleoalba (Meyen, 1833) (KT883856) and a short-finned pilot whale, Globicephala macrorhynchus Gray, 1846 (KX059411) (Figure 3). Our novel cox1 sequence for P. gastrophilus was identical to the sequence of the adult of this trematode reported from a bottlenose dolphin (KX059405) from Patagonia by Fraija- Fernández et al (2017). Genetic divergence between isolates of P. gastrophilus from these odontocete species range between 0.0% and 0.3% (0-1 nt).…”

Causes of cetacean stranding and death on the Catalonian coast (western Mediterranean Sea), 2012-2019

“…Lung nematodes were also frequently detected in juvenile and adult individuals, but lesion severity was low, and they were considered of low pathogenicity. The trematodes of the secretory stomach, Pholeter gastrophilus, (Fraija-Fernández et al 2017) and of the hepatopancreatic ducts, Brachycladiidae, (Mateu et al 2011, Fraija-Fernández et al 2016 were also frequently found, causing nodular lesions in the secretory stomach chambers and inflammation in and around the hepatopancreatic ducts. In one pregnant striped dolphin (N-258/19), these parasitic lesions caused the perforation of the gastric wall, leading to peritonitis and death.…”

Stranding Monitoring Programmes on Brazilian Coast: Analysis of Reports

“…the family Brachycladiidae (FERNÁNDEZ et al 1998;FRAIJA-FERNÁNDEZ et al2016a). As noted above, P. gastrophilus is the most generalist and geographically widespread digenean species that infects cetaceans (FRAIJA-FERNÁNDEZ et al 2017).…”