Life-history trade-offs in a generalist digenean from cetaceans: the role of host specificity and environmental factors

Abstract

BackgroundAdults and larvae of generalist parasites are exposed to diverse hosts and local environmental conditions throughout their life cycles, thus local adaptation is expected to occur through phenotypic plasticity and/or natural selection. We investigated how the combined effect of cryptic host specificity and local selective pressures could shape reproductive traits of a putative generalist parasite in the oceanic realm.MethodsThe LSU rDNA, ITS2 and the mt-COI of individuals of the digenean Pholeter gastrophilus (Kossack, 1910) Odhner, 1914 (Heterophyidae Leiper, 1909) from oceanic striped dolphins, Stenella coeruleoalba Meyen, and coastal bottlenose dolphins, Tursiops truncatus Montagu, in the western Mediterranean were used to elucidate whether worms were conspecific. Infection parameters were compared between both dolphin species. General Linear Mixed Models were used to analyse the influence of host species on four reproductive traits of P. gastrophilus: body size, maturity stage (non-gravid/gravid), egg size, and number of eggs in utero. AIC values were used to rank competing models, and p-values to assess the effect of specific predictors.ResultsEvidence indicated that worms collected from both dolphin species were conspecific. All worms collected were gravid and infection parameters did not differ between dolphin species. However, body size and egg size of individuals of P. gastrophilus were significantly larger in striped dolphins. The number of eggs in utero did not significantly differ between dolphin species but, for a given body size, worms in bottlenose dolphins harboured more eggs. A trade-off between egg size and egg number was found in worms from both dolphin species, with a higher slope in striped dolphins.ConclusionsApparently, striped dolphin is a more suitable host for P. gastrophilus, but reproductive investment seems to be adapted to the habitat where the life-cycle develops. Worms from striped dolphins likely face the problem of finding intermediate hosts in the oceanic realm and apparently invest into offspring size to enhance the early survival of larvae and the potential to multiply asexually within the first intermediate host. The small-sized worms from bottlenose dolphins would be adapted to reproduce early because of higher adult mortality, generating smaller and numerous eggs in a coastal habitat where chances of transmission are presumably higher.

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

“…Evidence indicates that P . gastrophilus readily infects both sympatric coastal and oceanic dolphins that have largely non-overlapping diets, which would suggest that this parasite is able to extensively exploit the food web to reach its definitive hosts [19]. …”

ARGENTINEAN ORCA (ORCINUS ORCA) AS AN UMBRELLA SPECIES: CONSERVATION & MANAGEMENT BENEFITS

“…MATTIUCCI and NASCETTI, 2008). However, FRAIJA-FERNÁNDEZ et al (2015b; did not detect significant genetic divergence between specimens from different cetacean species, or between populations geographically apart (south western vs. north eastern Atlantic). This apparently suggests that there is ample genetic flow between populations and P. gastrophilus represent a single species.…”

“…This hypothesis assumes that a larger egg translates in both longer times for hatching and larger hatched miracidia, and these two factors would increase the chances of initial survival in a harsh environment. However, the study by FRAIJA-FERNÁNDEZ et al (2015b) was based on just two host species, and replication using other coastal and oceanic cetaceans is peremptory to confirm this pattern.…”

Increasing the Understanding of Multispecies Feeding Events in Marine Hotspots by Medium Term Instrumentation and Tracking

“…Although the number of eggs in utero does not seem to differ between worms infecting an oceanic cetacean, the striped dolphin (Stenella coeruleoalba), and a coastal cetacean, the common bottlenose dolphin (Tursiops truncatus), eggs are significantly larger in the former. Apparently, worms infecting the oceanic cetacean would make a greater 42 provision of resources per capita for their offspring to withstand their lower probability of contacting the first intermediate host (FRAIJA-FERNÁNDEZ et al 2015b). Conversely, in a costal habitat with more intermediate hosts available it would be wiser to divide the investment into more offspring.…”