Lecture 3 Evolutionary Processes & Speciation Flashcards
Mutation and gene flow between populations
Mutation leads to diversity
Mixing prevents differentiation
Isolation increases differentiation (e.g. Galapagos finches)
Bottle neck population
Recovering no. W/reduced and altered genetic diversity e.g. Florida puma - risk of inbreeding
Stochastic events
Random unexpected environmental events e.g. floods, can affect populations and community dynamics
Non random mating
E.g. pin and thrum forms of flowers of same specie prevent self pollination.
Non random mating: sexual selection
E.g. selection by colour or plumage as in long tailed Widow birds - females choose longer tailed mates as long tails make it harder to fly and more susceptible to predators so reaching maturity with a long tail proves male has high fitness
Adaptive change
Allele frequencies in populations change adapting individuals to environment
Selection types
Stabilising: maintain average form(stasis)
e.g. human birth weight
Directional: phenotype/ characteristics progress in a direction e.g. resistance to neurotoxin in garter snakes allowing them to consume toxic newts.
Disruptive: selects to both extremes away from norm e.g. Black bellied seed cracker finch large bill good to open hard seeds and small bill good for feeding on soft seeds therefore survival lower in normal sized beaked birds and both extremes selected for
Linnaeus’s Morphological species concept
selection of convenient (reliable) morphological characteristics and use of dichotomous key
Biological species concept
Ernest Mayr 1940 “ Groups of actually or potentially interbreeding populations that are reproductively isolated” conclusive and testable but not for daily use.
Issues: duck ‘species’ interbreed when artificially introduced from other continents.
Cladistic method to construct phylogenic trees
Interbreeding population (parent species) encounters a barrier. Population splits in two leading to genetically divergence but populations remain reproductively compatible. Over time reproductive incompatibility is established creating 2 daughter species.
Isolation methods
Ecological: Spatial as in habitat or temporal as in time e.g. migration related
Reproductive: Temporal relating to seasons or diurnal/nocturnality. Ethological (behavioural) e.g. courtship or mechanical as in lock+key genitals.
Prezygotic - prevents fertilisation see reasons above
Post zygotic - prevents formation of viable offspring e.g. inviable embryo resulting from two different species mating
Asexual breeding
No waste of energy in stable environment
Evolution via mutation
No recombination
Common in plants less so in animalsa
Sexual breeding
Meiosis of gametes leads to recombination and assembly of new Geno/phenotypes, selected for,. An result in rapid evolution - with high waste of poorly adapted types (individuals)
Outbreeding
Some plants self compatible choose to outbreed
Can still differentiate into local races if seed dispersal is short even in absence of selection - genetic drift
Outbreeding: polymorphs
Sub populations exposed to different enviro/selection pressures. Natural selection operates in conjunction w/ ‘sampling error’ inherent in small populations to change local gene frequencies
