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Parasite/pathogen

Parasite specificity

QuestionAnswer
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: reub8n
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