Abstract
BackgroundCurrent data about Pseudaliidae show contrasting patterns of host specificity between congeneric species. We investigated how both contact and compatibility between hosts and parasites contributed to the patterns of lungworm infection observed in a community of five species of cetaceans in the western Mediterranean.MethodsThe lungs of 119 striped dolphins Stenella coeruleoalba, 18 bottlenose dolphins Tursiops truncatus, 7 Risso’s dolphins Grampus griseus, 7 long-finned pilot whales Globicephala melas, and 6 common dolphins Delphinus delphis were analysed for lungworms. Parasites were identified by morphology and analysis of ITS2 sequences using both maximum likelihood and Bayesian inference methods. Body length was used as a proxy for lungworm species fitness in different hosts and compared with Kruskal-Wallis tests. Infection parameters were compared between cetacean species using Fisher’s exact tests and Kruskal-Wallis tests. Phylogenetic specificity was explored by collating the overall lungworm species prevalence values in hosts from previous surveys in various localities. To explore the relative importance of vertical and horizontal transmission, Spearman’s rank correlation was used to look for an association between host size and lungworm burden. A Mantel test was used to explore the association between lungworm species similarity and prey overlap using dietary data.ResultsHalocercus delphini had higher infection levels in striped dolphins and common dolphins; Stenurus ovatus had higher infection levels in bottlenose dolphins; and Stenurus globicephalae had higher infection levels in long-finned pilot whales. These results are congruent with findings on a global scale. Morphometric comparison showed that the larger nematodes were found in the same host species that had the highest parasite burden. Lungworms were found in neonatal striped dolphins and a Risso’s dolphin, and there was a weak but significant correlation between host size and parasite burden in striped dolphins and bottlenose dolphins. There was also a weak but significant association between prey overlap and lungworm species similarity.ConclusionsData indicate that phylogenetic specificity has an important role in governing host–parasite associations, as indicated by the higher infection levels and larger nematode size in certain hosts. However, diet can also influence infection patterns in these preferred hosts and contribute to less severe infections in other hosts.Graphical
Highlights
Current data about Pseudaliidae show contrasting patterns of host specificity between congeneric species
Since direct detection of intermediate or paratenic hosts has proven unsuccessful to date, we investigated the probability of parasite exchange among host species through dietary overlap analysis, assuming that the greater the overlap in the consumption of infected prey species, the higher the probability that the hosts share the same parasites [12,13,14]
Sample collection Pseudaliid lungworms were collected from the carcasses of 119 striped dolphins Stenella coeruleoalba, 18 bottlenose dolphins Tursiops truncatus, 7 Risso’s dolphins Grampus griseus, 7 long-finned pilot whales Globicephala melas, and 6 short-beaked common dolphins Delphinus delphis that were found stranded along the Mediterranean coast of Spain (Valencian Community, between 40°31′00′′N, 0°31′00′′E and 37°50′00′′N, 0°45′42′′W) between 1982 and 2019
Summary
Current data about Pseudaliidae show contrasting patterns of host specificity between congeneric species. We investigated how both contact and compatibility between hosts and parasites contributed to the pat‐ terns of lungworm infection observed in a community of five species of cetaceans in the western Mediterranean. Adults of all but one of the 29 currently valid species of lungworms of the family Pseudaliidae typically infect the lungs, middle ear and air sinuses of odontocetes worldwide [1, 2]. Direct evidence on the use of intermediate or paratenic hosts is limited to a single species. Evidence for trophic transmission is only implied by the absence of infection in unweaned hosts, coupled with the increase in prevalence with host age [1]. There is evidence for vertical transmission from mother to calf at least for three species of Halocercus infecting bottlenose dolphins Tursiops truncatus, orcas Orcinus orca, and striped dolphins Stenella coeruleoalba [5,6,7]
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