Hybridization between two cestode species and its consequences for intermediate host range

Tina Henrich,Daniel P Benesh,Martin Kalbe

doi:10.1186/1756-3305-6-33

Tina Henrich, Daniel P Benesh + Show 1 more

Open Access

https://doi.org/10.1186/1756-3305-6-33

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Abstract

BackgroundMany parasites show an extraordinary degree of host specificity, even though a narrow range of host species reduces the likelihood of successful transmission. In this study, we evaluate the genetic basis of host specificity and transmission success of experimental F1 hybrids from two closely related tapeworm species (Schistocephalus solidus and S. pungitii), both highly specific to their respective vertebrate second intermediate hosts (three- and nine-spined sticklebacks, respectively).MethodsWe used an in vitro breeding system to hybridize Schistocephalus solidus and S. pungitii; hybridization rate was quantified using microsatellite markers. We measured several fitness relevant traits in pure lines of the parental parasite species as well as in their hybrids: hatching rates, infection rates in the copepod first host, and infection rates and growth in the two species of stickleback second hosts.ResultsWe show that the parasites can hybridize in the in vitro system, although the proportion of self-fertilized offspring was higher in the heterospecific breeding pairs than in the control pure parental species. Hybrids have a lower hatching rate, but do not show any disadvantages in infection of copepods. In fish, hybrids were able to infect both stickleback species with equal frequency, whereas the pure lines were only able to infect their normal host species.ConclusionsAlthough not yet documented in nature, our study shows that hybridization in Schistocephalus spp. is in principle possible and that, in respect to their expanded host range, the hybrids are fitter. Further studies are needed to find the reason for the maintenance of the species boundaries in wild populations.

Highlights

Many parasites show an extraordinary degree of host specificity, even though a narrow range of host species reduces the likelihood of successful transmission
In interaction with their host organisms, many parasite taxa show an extraordinary degree of specificity, which is often regarded as indication of a long co-evolutionary history
For parasites with complex life cycles, a narrow host range can be very disadvantageous since it decreases the probability for transmission when suitable host species are rare

Summary

Introduction

Many parasites show an extraordinary degree of host specificity, even though a narrow range of host species reduces the likelihood of successful transmission. We evaluate the genetic basis of host specificity and transmission success of experimental F1 hybrids from two closely related tapeworm species (Schistocephalus solidus and S. pungitii), both highly specific to their respective vertebrate second intermediate hosts (three- and nine-spined sticklebacks, respectively) In interaction with their host organisms, many parasite taxa show an extraordinary degree of specificity, which is often regarded as indication of a long co-evolutionary history. One possibility for a rather fast expansion of the host range could be the introgression of host compatibility genes by hybridization between closely related parasites species [3] This might be a way to escape extinction, since specialization has been suggested as a one-way street [4,5]. Such a scenario is conceivable in macroparasites with complex life cycles, where two parental species are highly specific to different intermediate hosts, but share a common final host where sexual reproduction takes place

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