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Parasite/pathogen
Parasite specificity
| Question | Answer |
|---|---|
| A step back | - most hosts have some resistance (host resistance) even to foreign parasites - coevolution starts an arm race between hosts and parasites - host specifity: variation in resitance or tolerance towards parasites |
| - so specialised hosts are able to defend themselves from a small amount of parasites | |
| Specialist vs Generalist | - specialist: only infects a narrow host range, more infections in species, often cannot infect one without loosing efficiency to another - generalist: infects a large range |
| Trade off hypothesis | - good at infecting one, less at another (limiting resources) - in lab, infection of a range of hosts sees decreasing success the further the host is related to the original host |
| Advantages | Specialists: better host establishment, higher parasitemia (proxy for intensity of blood parasites), higher prevelance Generalists: can match/exceed prevalence of specialist, better insurance against host extinction (resevoirs/opportunity) |
| STD | - measure for taxonomic distinctness of all host species a parasite infects - measured as the mean number of steps back up a phylogeny to get to a taxon common to two species - work backwards to find ancestors, add, divide by 6 |
| Evolution of parasite specificity | two filters: - ecological: shared habitats increase likelihood of a parasite/pathogen meeting - physiological: suitability of host for infection, hosts phylogentically similar attract similar hosts |
| Defining host range pt.1 | - biogeographical factors: broadly distributed parasites come into contact with broader host ranges, and some may be specialised - evolving to generalism for better host exploitation - based on gene flow |
| Spacial heterogenity | - locally differentiated host populations may be more difficult for a parasite to adapt to specific population - favour a broad host range and generalist strategy - each location could also develop differing degrees of specificity via local adaptation |
| Host phylogeny | - common ancestry shapes physiological traits - parasites may not be able to establish an infection because it has never evolved the necessary traits - species rich taxonomic groups may have more parasites simply because of morphological similarity |
| Transmission | - more frequent transmissions lead to specialisation - helminths: some undergo this and only infect a single host species - those that use intermediate hosts are less specific - use of a vector shows intermediate specificity |
| Host life history | - larger hosts have more resources to exploit - some show great parasite richness as a result |
| What happens if the host goes extinct? | - may increase specificity of a parasite lineage |
Created by:
rose.coo
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