Parasite escape through trophic specialization in a species flock

Abstract

24In adaptive radiations species diversify rapidly to occupy an array of ecological niches. In these 25 different niches, species might be exposed to parasites through different routes and at different 26 levels. If this is the case, adaptive radiations should be accompanied by a turnover in parasite 27 communities. How the adaptive radiation of host species might be entangled with such a turnover of 28 parasite communities is poorly documented in nature. In the present study, we examined the 29 intestinal parasite faunas of eleven species belonging to the tribe Tropheini, one of several adaptive 30 radiations of cichlid fishes in Lake Tanganyika. The most parsimonious ancestral foraging strategy 31 among Tropheini is relatively unselective substrate ingestion by browsing of aufwuchs. Certain 32 lineages however evolved more specialized foraging strategies, such as selective combing of 33 microscopic diatoms or picking of macro-invertebrates. We found that representatives of such 34 specialized lineages bear reduced infection with intestinal acanthocephalan helminths. Possibly, the 35 evolution of selective foraging strategies entailed reduced ingestion of intermediate invertebrate 36hosts of these food-web transmitted parasites. In Tropheini, trophic specialization is therefore 37 intertwined with divergence in parasite infection. We conclude that the study of parasite 38 communities could improve our understanding of host evolution, ecological speciation and the origin 39 of adaptive radiations. 40 41

Sick of eating: Eco‐evo‐immuno dynamics of predators and their trophically acquired parasites

“…In short, there is little fitness benefit in maintaining an immunity to a parasite rarely encountered, but there is significant benefit to maintaining a morphology suitable to consume multiple prey even when they contain parasites that confer significant fitness drawbacks. This theoretical result runs contrary to suggestions that parasite infection risk drove the evolution of a narrower diet in Tropheini cichlids (Hablützel et al 2017).…”

“…Hosts can evolve avoidance behaviors to reduce parasite encounter rates (Behringer et al 2018;Weinstein et al 2018), leading to diet shifts that then favor new morphological adaptations. Hablützel et al (2017) argue that this avoidance process may have driven the evolution of diatom-specialization in Tropheini cichlids, which harbor fewer parasites than their more generalist relatives. In an opinion article, Britton and Andreou (2016) argue that parasites may often favor the evolution of host diet specialization.…”

Divergent parasite infections in sympatric cichlid species in Lake Victoria

“…This may be related to the habitat specialization of the former, being confined to crevices in both islands, which may provide a refuge from infections (see also Hablutzel et al . ()). Alternatively, it could be related to the more insectivorous feeding habits, which could limit exposure to limnetic parasites compared to the more planktivorous P. nyererei and P. sp.…”

“…The first prerequisite of parasite‐mediated divergent selection in natural populations is that infections differ between diverging host populations. Currently, there is a growing body of literature describing differentiated parasite infections in ecotypes or closely related species particularly in freshwater fishes (Knudsen et al ., , ; MacColl, ; Eizaguirre et al ., ; Natsopoulou et al ., ; Karvonen et al ., ,b, ) including cichlid fishes (Blais et al ., ; Maan et al ., ; Raeymaekers et al ., ; Hablutzel et al ., , ). Overall, these studies suggest that conditions for parasite‐mediated divergent selection between ecological niches are not uncommon.…”

Patterns of ectoparasite infection in wild-caught and laboratory-bred cichlid fish, and their hybrids, implicate extrinsic rather than intrinsic causes of species differences in infection

“…A large number of species has rapidly diverged through niche partitioning (Turner, 2007) resulting in a large diversity of macro-habitat, micro-habitat and trophic specializations (Sturmbauer & Meyer, 1992;Bouton et al, 1997;Genner et al, 1999). In several African cichlid lineages, species differences in ecology are associated with differences in the community composition of the parasites infecting them (Hablützel et al, 2017;Hayward et al, 2017;Karvonen et al, 2018), suggesting that variation in exposure contributes to variation in infection. Variation in immune response may have evolved as well: among closely related and sympatric cichlid species of Lake Malawi, differentiation in parasite community composition is correlated with differentiation at the MHC locus (Major Histocompatibility Complex, coding for proteins that recognize pathogens) (Blais et al, 2007).…”