Abstract
Colonial hosts offer unique opportunities for exploitation by endoparasites resulting from extensive clonal propagation, but these interactions are poorly understood. The freshwater bryozoan, Fredericella sultana, and the myxozoan, Tetracapsuloides bryosalmonae, present an appropriate model system for examining such interactions. F. sultana propagates mainly asexually, through colony fragmentation and dormant propagules (statoblasts). Our study examines how T. bryosalmonae exploits the multiple transmission routes offered by the propagation of F. sultana, evaluates the effects of such transmission on its bryozoan host, and tests the hypothesis that poor host condition provokes T. bryosalmonae to bail out of a resource that may soon be unsustainable, demonstrating terminal investment. We show that infections are present in substantial proportions of colony fragments and statoblasts over space and time and that moderate infection levels promote statoblast hatching and hence effective fecundity. We also found evidence for terminal investment, with host starvation inducing the development of transmission stages. Our results contribute to a growing picture that interactions of T. bryosalmonae and F. sultana are generally characterized by parasite persistence, facilitated by multiple transmission pathways and host condition-dependent developmental cycling, and host tolerance, promoted by effective fecundity effects and an inherent capacity for renewed growth and clonal replication.
Highlights
Colonial hosts offer unique opportunities for exploitation by parasites as a consequence of their extensive capacity for asexual reproduction that amplifies clonal genotypes over space and time
Infections of Buddenbrockia allmani Allman, 1856 are transmitted to some 99% of daughter colonies produced by fission of the bryozoan, Lophopus crystallinus Pallas, 1768 (Hill and Okamura, 2007) and preliminary evidence suggests that Tetracapsuloides bryosalmonae Canning et al 2002, undergoes transmission when colonies of its bryozoan host, Fredericella sultana Blumenbach, 1779, undergo fragmentation (Morris and Adams, 2006). Both B. allmani and T. bryosalmonae are able to infect asexual seed-like propagules produced by their bryozoan hosts (Hill and Okamura, 2007; Hartikainen et al 2013; Abd-Elfattah et al 2014) - a process that can be equated to vertical transmission since statoblast hatching effects recruitment when conditions improve
Covert infections of T. bryosalmonae have no apparent impact on host growth and are sustained when conditions are suboptimal for bryozoan hosts (Tops et al 2006; Hartikainen and Okamura, 2012). Despite recent insights, how myxozoans exploit opportunities for transmission offered by colonial hosts and the concomitant effects on hosts remain poorly understood
Summary
Colonial hosts offer unique opportunities for exploitation by parasites as a consequence of their extensive capacity for asexual reproduction that amplifies clonal genotypes over space and time. The material collected was retained in aerated river water at room temperature for 24h prior to examination of individual colony fragments (using a stereo-microscope at 10-40x magnification) to count the number of zooids (to characterise fragment size), to identify overt infection (requiring dissection to confirm the presence of T. bryosalmonae sacs), to determine if mature statoblasts were present, and if dead/moribund (no functional zooids). GLMs that assumed a Gaussian error distribution were used to test differences in the: mean infection severity of covertly infected fragments between rivers and months; mean infection intensity of infected statoblasts between rivers; mean fecundity of infected and uninfected maternal colonies; and mean covert infection severity and respective sampling dates in the host starvation study. A one-way ANOVA was used to test differences in mean chlorophyll-a concentrations per treatment
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
