Fitness - Lecture 5 Flashcards
What is the definition of fitness?
The relative probability of survival and reproduction of a given phenotype
What is the fitness of an individual who does not reproduce (generally)?
zero
What causes fitness to vary?
○ Survival and reproduction - both will vary according to environmental conditions (which change in time and space)
○ Number of copies of an allele
Why does the sickling variant still exist?
○ Is advantageous in malarial zones - but only heterozygotes are “fitter”
○ Homozygotes are unwell
What is selected?
○ Complicated to say what the level of selection is
○ Species are not selected - individuals within populations are
What is hitchhiking?
Genes can be linked together - possible to have increased of deleterious (harmful) gene - physically close to a selected gene
What is sexual selection?
○ Explains why some characters appear to be maladaptive and to reduce fitness e.g. big antlers, peacock feathers
○ Increases an individual’s chances of attracting a mate (generally female) so that they can reproduce even if it could be disadvantageous to their survival
What is runaway sexual selection?
When a trait that is initially favored by mate preference becomes exaggerated over time
What is altruism?
The behaviour of an animal that benefits another at its own expense
What are some examples of altruism?
○ Most social insects are sterile - only the queen reproduces
○ Bee stings and dies
What did Bill Hamilton come up with?
○ Direct fitness = survival and production of offspring
○ Inclusive fitness = direct fitness + indirect fitness (fitness of related offspring)
What is the equation for Hamilton’s rule?
○ Natural selection of genes that lead to social actions via the sharing of these genes between performer and recipient
○ Being altruistic has a cost (c) to the performer
○ Receiving altruism has a benefit (b) to the recipient
○ Depending on the degree of relatedness (r), you get altruism as long as: rb>c
What is Hamilton’s rule?
○ Highly unlikely that there is a gene for altruism
○ Altruistic effects can be produced by responding to individuals with similar genotype
○ Particularly likely to occur when r is high e.g. social insects
Hamilton’s rule applied to Hymenoptera (wasps, ants, bees)
○ Females = diploid, Males = haploid
○ In offspring: r = 0.5 (mom) and r = 1 (dad)
r = 1/2(mother’s contribution) + 1/2(father’s contribution)
○ r between to sisters: 1/2(0.5) + 1/2(1) = 0.75
○ Sisters are more closely related to each other than their own offspring
○ Genes more likely to be passed down to the next generation if rear sisters than if have own offspring
Problems with Hymenoptera
○ Queen may mate with more than one male
- Answer: ancestral form mated with only one male - explains how system got going
○ Many hymenoptera with haplodiploid sex determination are not eusocial (sawflies, solitary bees, parasitoid wasps)
- Answer: close relatedness is a precondition, not a determining factor
○ Termites have XY sex determination
- Answer: Still based on close relatedness of individuals
