Experimental evidence that host choice by parasites is age-dependent in a fish-monogenean system

Abstract

Host age is known to influence the risk of parasite infection, but there is very little experimental evidence on whether parasites show preference towards potential hosts of a specific age. To investigate how host age affects host choice by parasites, we used the Nile tilapia (Oreochromis niloticus) as a fish parasite model and manipulated its gill ectoparasitic monogeneans in mesocosm experiments. Our experimental setting combined three age classes (juvenile, subadult, and adult) of both infected donor hosts and uninfected potential target hosts assigned to each treatment. We predicted that adult target hosts would be more susceptible to parasites than juveniles and adults because they represent high-quality habitat patches. Contrary to our prediction, we found that subadults were more susceptible to parasites than juvenile and adult target hosts. Our models confirmed that variation in target host age influenced parasite choice, suggesting that subadults might represent the most favourable option for parasites regarding a balance between host quality and susceptibility. We provide experimental evidence that host choice by parasites is age-dependent, and that this life-history trait can play a major role in structuring parasite populations.

Season, size, and sex: factors influencing monogenean prevalence and intensity on Gambusia affinis in New Zealand

“…Fish that have reached 50 mm in length are likely to represent particularly mature individuals (McDowall 1990 ), and should therefore be more immunologically competent (Izhar and Ben-Ami 2015 ; Izhar et al, 2020 ). In fact, for this reason, younger fish are expected to be parasitized more than older fish (Ashby and Bruns 2018 ; Wunderlich et al 2022 ). It is thus difficult to be certain why the larger fish had the greatest prevalence and intensity of S. seculus .…”

“…On this basis, G. affinis individuals that are large and old would be expected to see greater parasite prevalence and intensity. However, patterns in host age and parasite infection are not universal and younger individuals may possess more parasites than their older counterparts (Wunderlich et al 2022 ). In parasitic interactions, the immune system of the host is an important factor, and this is not an exception for monogeneans infesting either the skin or gills (Buchmann 1999 ; Buchmann and Lindenstrøm 2002 ).…”

Temporal changes in streamflow regime and host-related factors affect parasitism of freshwater prawn in Southeast Brazil

“…Although this rule has been reported in several taxa (Poulin, 2007), we still lack knowledge on whether Harrison's rule holds among seasons and between host sex, and also for cymothoid isopods (Welicky et al 2019). Other host characteristics such as host age, sex, and molt are also correlated with parasite variations between individuals within populations (Christe et al 2007;Ben-Ami, 2019, Izhar et al 2020, which can be agedependent (Wunderlich et al 2022) or sex-biased (Poulin and Forbes, 2012). In crustaceans, the molting stage is a key growth factor, while it can expose hosts to parasite infections (Duneau and Ebert, 2012) or reduce the likelihood of parasite penetration (Izhar et al 2020).…”

Geographic range, distribution patterns and interactions of Monogenea Van Beneden 1858, with species of native host freshwater fishes from Brazil

“…Analysis of the monogeneans-host interactions is an important way to evaluate the local adaptation of these parasites with heterogeneous distribution in host because infection rates vary between host fish populations. Studies provided evidence that host choice by monogeneans is age-dependent of hosts, and that this life-history trait can play a major role in structuring populations of parasites (Wunderlich et al, 2022). We detected the following patterns within monogenean-host fish interactions in the different basins in Brazil: (a) prevalence ranging from low to high, with abundance and intensity ranging from low to moderate; (b) association with other ectoparasites infracommunities on gills; (c) distribution pattern typically aggregated; (d) occasionally positive correlation of abundance with body size of hosts at the infracommunity level and (e) are usually ectoparasites, infecting mainly gills and tegument.…”