IB biology: A4.1 - Evolution and Speciation

species

organisms which can make fertile offsprings

evolution

 change in the heritable characteristics of a population 

evidence for evolution by natural selection

•  base sequences in DNA or RNA and amino acid sequences in proteins 

• selective breeding of domesticated animals and crop plants 

• homologous structures

speciation

when groups become separated in space or become different in form or behavior so that they do not regularly breed

3 types of reproductive isolation

• geographical isolation

• behavioral isolation

• temporal isolation

geographical isolation

separation by natural or human made barriers

behavioural isolation

organisms of the same species might develop different mating rituals over time; if the potential mates do not recognise these rituals, the individuals won’t interbreed

temporal isolation

differences in the timing of the reproductive cycles, like mating season or gamete production. This can prevent interbreeding despite the same geographical locations

reproductive isolation due to geographical barriers

• The formation of a new geographical barrier divides the original population into two smaller populations: A and B.

• The geographical barrier prevents members of the two populations from mixing and interbreeding.

• In different environments, evolutionary forces such as natural selection, mutation and genetic drift act independently on the gene pools of the two populations for many generations.

• natural selection leads to differential reproduction, eventually leading to genetic separation.

• The resulting behavioural and/or physiological changes prevent the populations from mating.

• Even if the barrier is now removed, the members of the two populations cannot interbreed. Two new species A and B are formed.

differential selection

when selection pressures are different, so natural selection leads to divergent evolution

case study differential selection

chimpanzees and bonobos, african apes close to each other

used to have common ancestor, but Congo river divided the population

chimpanzees are larger, more aggressive, and male dominated: north of congo river as resources are scarce

bonobos are smaller, more playful, and female dominated: south if congo river where resources are plentiful

temporal isolation

occurs when organisms produce gametes at different times or seasons. An example in animals is brown throut and rainbow trout

Behavioural isolation

organisms have different behaviour routines, e.g. courtship or mating which separates them from other individuals of the species. 

 

Allopatric speciation 

means 'different country' → refers to isolating mechanisms that involve spatial separation 

Sympatric speciation

means 'the same country'→ refers to isolating mechanisms that occur in the same location but are brought about by temporal or behavioural isolation. 

molecular phylogeny - evidence for evolution

the analysis if DNA and RNA base sequences, and amino acid sequences in proteins, with the purpose of dtermining how close 2 species are to each other. very powerful evidence

selective breeding of dogs and plants - evidence for evolution

selective breeding occurs, as we select to breed organisms with the desired characteristics. these rapid changes in the genetic make-up of a population, eventually leading to evolution. this illustrates how quickly evolutionary changes can occur

homologous structures

homologous structures that are physically similar and share a common ancestor, but perform different functions in different species.

Evidence for evolution from homologous structures 

• pentadactyl (five-fingered) limb of vertebrates

• shows how some body structures are fundamentally similar

• they indicate divergent evolution from similar structures

analogous structures

Biological structures that have evolved independently in two living organisms to serve the same function in similar environments.

analogous structures origin

• do not necessarily indicate evolutionary relationship

• unrelated groups of organism adapt in similar ways

• insect and bird wings

convergent evolution

Pattern of evolution where distantly related organisms evolve similar traits in response to environmental similarities.

molecular clock

The technique that uses the mutation rate of biomolecules to deduce the time since two species shared a common ancestor.

adaptive radiation

evolution of multiple new species from an ancestral species to occupy different ecological niches. this allows closely related species to exist without competing, increasing biodiversity.

barriers to hybridisation

prezygotic:

• variation in the courtship behavior, or behavioral isolation

postzygotic

• reduce viability of the zygote

• reduces viability of the adult

• decreases (or removes) fertility of hybrid and it’s offspring

prevents the mixing of alleles of parent species and subsequent transmission to future generations

polyploidy

A condition where an organism possesses more than two sets of chromosomes.

caused by non-disjunction of chromosomes during mitosis or meiosis

allopolyploidy

a hybrid with more chromosome sets originating from different species. Oftentimes more vigorous than parents.

allopolyploidy explained

normal species and polyploid gamete fuse, create infertile species, but when fused with a normal gemete, results in an allopolyloid

allopolyploidy example

Knotweed → many species of knontweed have been formed through this process