Evolution & Speciation

Evolution

a cumulative change in heritable characteristics of a population over generations

• heritable characteristics are determined by alleles of genes

  • random mutations change alleles —  either advantageous, disadvantageous or no effect

Dawinism

theory of evolution by natural selection

• wide range of variation due to random mutations

• populations compete for survival due to selection pressures

• most adapted characteristics = higher chance of survival and more likely to repoduce

Lamarkism

organisms acquired characteristics through their lifetime and passed them on to their offsprings

Homologous Structures(morphological)

Allopatric Speciation

• occurs as a result of geographical isolation

• when the population of a species becomes separated from each other by a geographical barrier

Sympatric Speciation

• new species form from existing species living in the same geographical location

  • temporal/behavioural reasons lead to sympatric speciation

• random changes in alleles & phenotypes prevent individuals from successfully breeding with other inviduals

• may live in same habitat but do no interbreed

Temporal Isolation: Seasonal Changes

• refers to incompatible time frames that prevent populations or their gametes from encountering each other 

  • Reproductive timings no longer match up

Behavioural Isolation

• when individuals in a population develop changes in their courtship behaviours — no longer attract individuals of the opposite sex for mating

  • methods of attracting a mate are no longer effective

Adaptive Radiation

natural selection results in the rapid evolution of multiple species from a common ancesto

• variation allows certain members of to occupy different ecological niches

  • reproductive isolation leads to speciation

  • e.g., Darwin’s finches, Hawaiaan honeycreepers

Hybridization

• “hybrid” — offspring of individuals of two different species

  • hybridization: mating, fertilization and development processes

    • rare and usually infertile

Hybridization: Incompatible Chromosomes

fusiion of games from different species often leads to non-viable zygotes

• occurs if chromosomes of different species don’t match

  • result is either viable zygotes or infertile hybrid

  • e.g., mule chromosomes cannot pair up during meiosis — mules cannot produce gametes of their own

Incompatible Courtship Behaviours

• courship behavioru in animals isa ritual—results in mating & reproduction

• if courtship rituals don’t match— no mating will occur/hybridization is prevented

Abrupt Speciation: Plants

refers to a situation when a cell contains three or more sets of chromosomes

• can occur during meiosis(incomplete sepration) — when two plants fuse their genetics

• production of offspring with the original population becomes impossible, leading to speciation

  • extra set of chromosomes(fatal) in animals

  • more vigorous plants that produce bigger fruits/food storage organs & are more resistant to disease

Autopolyploidy

4n individuals can arise within a 2n plant population

• occurs when the separation of homologous pairs doesn’t happen correctly — one daughter cell may contain two sets of chromosomes

  • chromosome nondisjunction

Allelopatric Speciation: Trees

• population of trees is divided by a new mountain range that divides the species into two geographically isolated populations

  • selection pressures and geentic drift cause divergence

  • barrier prevents populations from interbreeding — no gene flow — speciation occurs

Sympatric Speciation: Fruit Flies

• A species of fruit flies is divided into two populations due to a random mutation (e.g., food preference)

  • difference in phenotype — prevents two populations from interbreeding — no gene flow

Allelopolyploidy

• diploid gametes from different species fuse to produce a polyploid zygote

  • polyploid zygote

Speciation due to polyploidy

• 4n population produces 2n gametes — unable to breed with original population

  • resulting offspring is infertile

Polyploidy: Persicaria

• Plant genus Persicaria(smartweeds) contians a range of polyploidy types

• Persicaria foliosa(2n)

• Persicaria japonica(4n)

• Persicaria puritanorum(6n)

Natural Selection

process where organisms better adapted to their environment are more likely to survive breed