BIO220H1 Lecture 6: Extended phenotypes

121 views9 pages
25 Jan 2019
School
Department
Course
Professor
Extended phenotypes
Outline
What is an extended phenotype?
Parasite extended phenotypes (altering behavior)
Criteria for determining if these phenotypes are really adaptations of the parasites
Examples of putative parasite extended phenotypes
What is a phenotype?
Any observable characteristic or trait of an organism.
Morphology
Physiology
Behavior
Phenotypes reflect both genetic and environmental effects
Z=G+E
We’ve been thinking about genes being contained’ in the same individuals as where
the phenotypes are expressed.
Extending the notion of phenotypes
The phenotypic expression of a gene can exist outside the cell in which the genes
exert their immediate biochemical influence”
Dawkins, 1999
Extending the notion of phenotypes
Things’ produced by individuals
E.g., dam building of beaver
(gene affects dam building behavior)
A gene for dam building or a gene for dams?
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 9 pages and 3 million more documents.

Already have an account? Log in
Evolution by natural selection...
Variation in a trait (e.g dam size)
Variation in fitness for the trait
Genetic basis for the trait
Things’ produced by individuals
E.g., bower building
Subject to genetic variation
Influences fitness
Could therefore be exposed to selection
Extending the notion of phenotypes
Things’ produced in other individuals
Dawkinsview: An animal’s behaviour tends to maximize
the survival of the genes for’ that behaviour, whether or
not those genes happen to be in the body of the particular
animal performing it.
What is fitness for a parasite?
𝑅0 The # of new infections generated by a single infected individual
(in a fully susceptible population).
This will depend on things like
Replication or growth within a host
Opportunities for transmission between hosts
(for new infections)
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 9 pages and 3 million more documents.

Already have an account? Log in
Parasite extended phenotypes
Three broad categories of extended phenotypes of parasites:
1. Host behavioural modification
2. Host morphological modification
3. Host molecular modification
In order to facilitate the growth, reproduction or transmission of the parasite.
= to increase the fitness of the parasite.
Toxoplasma gondii
When mice are infected:
More active
Explore more
Less likely to startle
More aggressive over territories
Slower reaction times
Is this the result of behavioural manipulation of the rodent by the parasite to increase
transmission to its definitive host?
Three hypotheses
1. Adaptive for the parasite
Generates a fitness benefit to parasites that led to natural selection for trait.
2. Adaptive for the host
Generates a fitness benefit to hosts that led to natural selection for trait
3. Coincidental by‐product of infection
(But, may have beneficial side effects.)
Non-adaptive explanation
Consequence of the infection
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 9 pages and 3 million more documents.

Already have an account? Log in

Get OneClass Notes+

Unlimited access to class notes and textbook notes.

YearlyBest Value
75% OFF
$8 USD/m
Monthly
$30 USD/m
You will be charged $96 USD upfront and auto renewed at the end of each cycle. You may cancel anytime under Payment Settings. For more information, see our Terms and Privacy.
Payments are encrypted using 256-bit SSL. Powered by Stripe.