Award details

Parasite persistence and local adaptation: selection in a limiting environment

Reference	BB/D523051/1
Principal Investigator / Supervisor	Professor Richard Tinsley
Co-Investigators / Co-Supervisors	Professor Mark Viney
Institution	University of Bristol
Department	Biological Sciences
Funding type	Research
Value (£)	244,956
Status	Completed
Type	Research Grant
Start date	05/12/2005
End date	04/02/2009
Duration	38 months

Abstract

The approach involves transfer of material from the natural experiment in the field to the laboratory, where trials can be replicated under precisely-controlled conditions (especially with regard to environmental factors, including temperature, and host factors including defined offspring lineages of lab-raised X. laevis). Laboratory infections will be set up using parasite eggs collected from wild-caught Welsh Xenopus and experimental exposures (using hatched swimming infective stages n=20 per host) will involve sibships of naïve hosts (offspring of the same parents, n-15 per parasite isolate). To address the effects of temperature, experimental infections will be maintained at 20, 15 10 and 6 degrees Centigrade, and parasite numbers, developmental stage and morphometric characters will be recorded at host dissection ranging from 100 days post infection (patency at 20 degrees Centigrade), 150 days (patency at 15 degrees Centigrade), up to 2 years p.i. (at low temperatures). Mature infections will be acclimated to these temperatures and egg output (eggs/worm/day) recorded. A major programme of controlled infections (at 20 degrees Centigrade) will investigate compatibility of host and parasite isolates. A series of lineages of naïve X. laevis will be bred from Welsh and S. African parents (initially 20 from both origins) and maintained separately for use throughout the 3 year project. Reciprocal cross-infections will involve Welsh parasites x Welsh hosts, Welsh parasites x S. African hosts, S. African parasites x Welsh hosts, S. African parasites x S. African hosts. Standard durations will be 100 days with counts of surviving worms, morphometric characters etc recorded at dissection. Data analysis will employ generalised linear models. Genetic diversity in the host population will be analysed by sequencing a 2Kb section of the D-loop region of mitochondrial DNA (with DNA extracted from tissues when a toe is clipped for bone growth ring analysis to determine age). Sequencing will be undertaken by the University of Bristol¿s transcriptomics facility. Transmission Electron Microscopy (in this School¿s E.M. Unit) will examine pathology evident in kidneys taken fro the experimentally-infected hosts maintained for various durations at 20,15,10 and 5 degrees Centigrade in studies on temperature effects on parasitic survival and development (above). The same TEM sections will demonstrate putative immune interactions at the interface of parasite tegument and host tissue. Short (overnight) visits to the Welsh site will provide all live material representing the introduced host-parasite population. Xenopus are caught in baited traps and parasite eggs are collected by temporary maintenance of hosts in containers of water; host sibships will be produced either from spawn at the field sites or from parents bred following gonadotrophin injection. X. laevis are individually-marked with freeze branded numbers, and 3mm of a digit removed for mtDNA and age analysis. Age is determined with standard wax section histological processing and haematoxylin and eosin staining. The population sampling simultaneously provides data on patent infections (eggs passed in urine) and changes in infection status with time (for marked individuals of, ultimately, known age, size, weight, reproductive condition, mitotype etc) contributing to documentation of episodes of infection etc. Water temperatures (recording field conditions and guiding the laboratory regime) are recorded with data loggers.

Summary

Xenopus laevis, an amphibian native to South Africa, has been used worldwide in laboratory research for many decades. In several regions, these aquatic toads have been released into the wild and feral populations are established in North and South America

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	Animal Health
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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