Host shifting and host specificity Flashcards
range of hosts
a parasite infects - similar to the ‘ecological niche’ of other species - crucial determinant of potential to shift hosts
shifting hosts can…
- promote parasite diversification
- trigger EID events
- increase selective pressures on hosts
Plasmodium - not always intimate host relationships
1. Plasmodium falciparum
2. Plasmodium knowlesi
- highly host specific and infects humans only and associated with single genus of mosquito species (Anopheles)
- mostly found in macaques in SE Asia, first human record in 1965, now the dominant cause of malaria in Borneo
what parasite is likely to be most risky and dangerous?
generalist parasites - infect whoever = more spread
Rabies (Rabies lyssavirus)
1. host range?
2. affecting what?
3. what are different strains associated with?
4. may circulate in what animal with absence of what?
5. what is spread of rabies heavily influenced by?
- broad host range - not host specific
- affecting many mammalian species (bats, racoons, foxes, doges, etc.) - affect wide of mammals but not all are good hosts
- different strains associated with specific hosts (better adapted to certain immune systems)
- may circulate in bats with the absence of clinical symptoms - makes them a good reservoir for disease
- spread is heavily influenced by environmental factors (dog-human contact, bat migration and habitat use)
Borrelia (bacteria causing Lyme disease)
1. host range and what for?
2. what are vectors?
3. what has bacteria optimised in some hosts?
4. what does transmission strongly depend on?
- broad host range of mammals and birds
- specific Ixodes ticks as vectors (Ixodes scapularis in N-America, I. ricinus in Europe)
- bacteria has optimised reproduction in some hosts (e.g. white-footed mice) to optimise transmission
- transmission strongly depend on environmental conditions and host presence and diversity
Host specificity of multi-host parasites
1. strong similarities between what?
2. broad vs specific?
- strong similarities in ecological and evolutionary patterns of host-parasite and insect-plant interactions
- most species rather specific in resource use but some are generalist using broad range of resources
Host specificity of multi-host parasites
1. what does host evolutionary history impact?
2. what are traits allowing infection?
3. use branch length…?
- host evolutionary history impacts parasite specificity
- traits allowing infection are conserved (‘phylogenetic relatedness’ and/ or ‘ecological fitting’)
- uses branch length ‘distances’ (can compute pair-wise similarity and community-level average similarity)
(Poulin et al., 2011)
Host specificity of multi-host parasites
1. two aspects that make host specificity?
2. low both
3. high both
4. high basic specificity, low phylogenetic specificity
5. low basic specificity, high phylogenetic specificity
- basic specificity and phylogenetic specificity
- four (two on one branch, two on the other) close related on phylogenetic tree on two branch
- two close on phylogenetic tree on one branch
- two further away related - on separate branches
- four closely related on same branch
Host specificity of multi-host parasites
1. shared ecological traits?
2. shared evolutionary history?
- live in same environment; do they overlap in niche for what they eat -> and T/F parasites too
- infected species on different branches of the phylogenetic tree - more closely related = more likely to share parasites
- infected species on same branch of phylogenetic tree
(Agosta et al., 2008)
what is ecological fitting?
the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition
(Agosta et al., 2008)
Ecological fitting
1. ecological fitting via resource tracking
2. ecological fitting via adaptive plasticity
3. ecological fitting via nonadaptive plasticity
- pathogen readily able to infect new host because of similarity in traits between old and new host, facilitates subsequent pathogen adaptation to the new
- with limited similarity in traits between hosts, pathogen becomes more compatible to new host only via adaptive plasticity
- allows parasite to shift to host species - pathogen changes phenotype via nonadaptive plasticity, which initially low compatibility. Hidden genetic variation, previously shielded from natural selection may facilitate subsequent pathogen adaptation to the new host
- if parasite cannot fit to host, it will not shift to the host
Barriers to parasite sharing and spillover
(Clark et al., 2018)
avian malaria
1. what may prevent parasite transmission between species?
geographic (e.g. distance, mountain range), environmental (e.g. between-region = macroclimate, elevation; within region = habitat and microclimate) and inter-species barriers
Barriers to parasite sharing and spillover
1. when are parasites phylogenetically more distinct?
2. when are parasites less distinct?
- parasites phylogenetically more distinct when infecting locally distinct hosts
- less distinct with increased host diversity and community connectivity
fundamental niche
the ideal conditions in which an organism can survive and reproduce
realized niche
the space an organism actually occupies in the environment, taking into account the effects of competition and other limiting factors
Host specificity in variable environments
1. what do regional observations reflect?
2. what does this suggest?
- regional observations only reflect a ‘realized’ host range, ‘fundamental’ range of host specificity is typically not approached
- host shifting through ecological opportunity rather than evolutionary history?
Wells & Clark (2019)
Barriers to parasite sharing: realised niche matching
(Estrada-Peña et al., 2014)
1. pathogens/disease can only be present and transmitted where?
2. may involve?
- environmental conditions enable species presence
- the distribution of vital vector species (e.g. ticks - Lyme disease caused by Borrelia)
Barriers to parasite sharing: realised niche overlap
(Estrada-Peña et al., 2014)
1. what may facilitate pathogen spread?
- several host and vector species with distinct ecological niches may facilitate pathogen spread if species overlap in some portions of their environmental space
- deer not replace mice -> different life stages of tick feed on mice and other one feed on deer
Abundance-occupancy relationships
Gaston etal. (2000)
Wells etal. (2025)
Cebrián-Camisón et al. (2025)
“Is there any trade-off of being specialist versus generalist and does host specificity (‘occupancy’) affect abundance?”
1. trade-off hypothesis
2. niche breadth hypothesis
- broader host-specificity can result in less optimal adaptation to the main host species
- broader host range amplifies prevalence through increasing ecological opportunities
Abundance-occupancy relationships
1. if host species is abundant, what happens to parasite?
2. what happens if parasite is specific to host species?
- parasite potentially can have high abundance
- negative for infecting other host species -> parasite may not be very generalist
Modelling parasite sharing risk
1. which traits predict zoonotic spillover from mammals to humans?
- environmental conditions, host traits, host phylogeny, pathogen traits
Analysing parasite sharing risk
1. what can pathogen present-absence be linked to?
- traits in regression models
ecological filters and spillover risk
(Olival et al., 2017)
1. what is the proportion of zoonotic viruses in mammal species predicted by?
phylogenetic relatedness to humans, host taxonomy, and human population within a species range - which may reflect human-wildlife contact
Ecological filters and spillover risk
(Olival et al., 2017)
1.what do mammals with different taxonomic groups carry?
- zoonotic viruses, with a prominent role of domestic species
