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

Henrich T, Benesh DP, Kalbe M - Parasit Vectors (2013)

Bottom Line: We used an in vitro breeding system to hybridize Schistocephalus solidus and S. pungitii; hybridization rate was quantified using microsatellite markers.We 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.Further studies are needed to find the reason for the maintenance of the species boundaries in wild populations.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Evolutionary Ecology, Max Planck Institute for Evolutionary, Biology, August-Thienemann-Strasse 2, Plön 24306, Germany.

ABSTRACT

Background: Many 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 F(1) 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).

Methods: We 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.

Results: We 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.

Conclusions: Although 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.

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Experimental design and measured parameters. A: Life cycle of S. solidus and S. pungitii and parameters measured in this study. B: Experimental breeding design for hybrid worms.
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Figure 1: Experimental design and measured parameters. A: Life cycle of S. solidus and S. pungitii and parameters measured in this study. B: Experimental breeding design for hybrid worms.

Mentions: The two species of parasite can be maintained in the lab for all stages of their life cycle. Plerocercoids are removed from the fish and can be bred in an in vitro system that mimics the bird’s gut [42,43]. Worms are usually size-matched for breeding, as this limits selfing [44]. After three weeks of incubation at 20°C in the dark, the coracidia start to hatch from eggs [26]. The coracidia can then be used to infect copepods (e.g. Macrocyclops albidus). After approximately two weeks of development in copepods, worms are infective to sticklebacks [45-47]. Figure 1 shows the life cycle of Schistocephalus, the most relevant traits measured in this experiment, as well as the breeding design for hybridizing the two parasite species.


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

Henrich T, Benesh DP, Kalbe M - Parasit Vectors (2013)

Experimental design and measured parameters. A: Life cycle of S. solidus and S. pungitii and parameters measured in this study. B: Experimental breeding design for hybrid worms.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3584927&req=5

Figure 1: Experimental design and measured parameters. A: Life cycle of S. solidus and S. pungitii and parameters measured in this study. B: Experimental breeding design for hybrid worms.
Mentions: The two species of parasite can be maintained in the lab for all stages of their life cycle. Plerocercoids are removed from the fish and can be bred in an in vitro system that mimics the bird’s gut [42,43]. Worms are usually size-matched for breeding, as this limits selfing [44]. After three weeks of incubation at 20°C in the dark, the coracidia start to hatch from eggs [26]. The coracidia can then be used to infect copepods (e.g. Macrocyclops albidus). After approximately two weeks of development in copepods, worms are infective to sticklebacks [45-47]. Figure 1 shows the life cycle of Schistocephalus, the most relevant traits measured in this experiment, as well as the breeding design for hybridizing the two parasite species.

Bottom Line: We used an in vitro breeding system to hybridize Schistocephalus solidus and S. pungitii; hybridization rate was quantified using microsatellite markers.We 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.Further studies are needed to find the reason for the maintenance of the species boundaries in wild populations.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Evolutionary Ecology, Max Planck Institute for Evolutionary, Biology, August-Thienemann-Strasse 2, Plön 24306, Germany.

ABSTRACT

Background: Many 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 F(1) 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).

Methods: We 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.

Results: We 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.

Conclusions: Although 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.

Show MeSH
Related in: MedlinePlus