Origin of Species and Macroevolution PPT 1, 2, 3

Macroevolution

occurs at or above the species level

Speciation

the process of species formation

Species

a group of organisms that maintains a distinctive set of attributes in nature

• genus (capitalized) + specific epithet (uncapitalized) [italisized or underlined]

Subspecies

groups of the same species that have somewhat different traits but not different enough to be called a separate species

Ecotypes

bacterial species

• genetically distinct population adapted to local environment

5 Characterization factors of species

• characteristcs that a biologist uses to identify a species

1. morphological traits are most commonly used

2. ability to interbreed (biological concept)

3. molecular features

4. eco factors

5. evolution relationships

Morphological species concept

• all individuals of a species share measureable traits that distinguish them from individuals of other species

• Linnaeu’s classification system

  • genus + specific epithet

what is a downside for determining species using morphology alone?

• members of the same species can look very different

• members of different species can look very similar

Biological species concept

• a biological species is a group of interbreeding individuals that is reproductively isolated from other such groups

• developed by ernst mayr

• example: group with potential to interbreed produce viable offspring, but cannot interbreed with other species

what is a downside of the biological species concept

• difficult to determine in nature

• can interbreed and don’t

• doesn’t apply to asexual organisms or extinct organisms

molecular traits concept

• compares features to identify similarities and differences among different population

  • dna within genes

  • genes along chromosomes

  • chromosome number and structure

downside to molecular traits concept?

may be difficult to draw the line when separating groups

Ecological factors concept

• variety of factors of organism’s habitat can be used to distinguish species

• bacterial species have been organized based on eco factors

what is the downside to ecological factors concept?

different groups of bacteria sometimes display similar growth characteristics, and even the same species may show great variation in the growth conditions it will tolerate

Evolutionary relationships concept

• based on phylogenies

• evolutionary trees describe relationships between ancestral species and modern species

  • fossil record

  • dna sequences

intraspecific mating

intra = within

Reproductive isolating mechanisms

• prevent interbreeding between different species

• consequence of genetic changes as species adapt to environment

Interbreeding

inter = between

interspecies hybrid

when 2 different species are able to produce offspring (often w/reduced fitness)

reproductive isolating mechanisms

prevent gene pools mixing

1. prezygotic

2. postzygotic

prezygotic isolating mechanisms

occur before zygote formation

• zygotic = 2n

postzygotic isolating mechanisms

occur after zygote formation

5 types of prezygotic isolating mechanisms

1. ecological isolation

2. temporal isolation

3. behavioural

4. mechanical

5. gametic

ecological prezygotic isolation

from habits

• geographic barrier prevents contact

• example: northern vs southern squirrels

temporal prezygotic isolation

• from mating timing

• reproduce at different times of day or year

• example; spring and fall field crickets

behavioural prezygotic isolation

• from mating signals

• s3xual selection

• behaviours important in mate choice

• example: changes in bird song

mechanical prezygotic isolation

• from reproductive structures

• size or incompatible g3nitalia prevents mating

• example; shell shapes of snails

gametic prezygotic isolation

• from gamete incompatibility

• gametes fail to unite successfully

• important in species that release gametes into water or air

3 Postzygotic isolating mechanisms

1. hybrid inviability

2. hybrid sterility

3. hybrid breakdown

• interspecies offspring reproductively isolted if less fit than intraspecies offspring

Hybrid inviability

species hybrids not surviving

Hybrid sterility

• species hybrids not producing functional gametes

• example: mating a female horse and a male donkey produce a mule, which have a short life span

Hybrid breakdown

• reduced fitness of F2

• example; tiglons and ligers (crossing male/female lions and tigers)

Speciation

formation of a new species

• underlying cause of speciation

  • the accumulation of genetic changes that ultimately promote enough differences so that we judge a population to constitute a unique species

Why does life often diversify into species?

1. abrupt events, like changes in chromosome number, causing reproductive isolation

2. consequence of adaptation to different ecological niches

2 patterns of speciation

1. cladogenesis

2. allopatric speciaiton

Cladogenesis

division of a species into 2+ species

• requires gene flow between populations to be interrupted

Allopatric speciation

• most prevelent method for cladogensis

• occurs when some members of a species become geographically separated

Allopatric Speciation

• physical barrier dividing a large population or when a small population becomes separated from a species’ main geo. distribution

• species cluster

• hybrid zones

• can also occur when a small population moves to a new location that is geographically separated from main population

Species cluster - allopatric speciation

group of closely related species

• founder effect

• genetic drift

Hybrid zones - allopatric speciation

from secondary contact

natural selection affecting allopatric speciation

• may rapidly alter the genetic composition of the population, leading to adaptation to the new environment

adaptive radiation affecting allopatric speciation

• single species evolves into array of descendants that differ greatly in habitat, form or behaviour

Sympatric Speciation

• occurs when members of a species that are within the same range diverge into 2+ different species though there are no physical barriers to interbreeding

• 4 mechanisms

what are the 4 mechanisms of sympatric speciation?

1. polyploidy

2. hybrid speciation

3. adaptation to local environments

4. sexual selection

Genetic diverage in allopatric speciation

• genetic differences from allopatric populations can lead to speciation

• in the absence of gene flow, geographically separated populations inevitably accumulate genetic differences through the action of mutation, genetic drift and natural selection

reproductive isolation:

1. postzygotic

2. prezygotic

3. s3xual

Sympatric speciation

• occurs when members of a species within the same range diverge into 2+ species even though there are no physical barriers to interbreeding

• sym = same

• patric = homeland

mechanisms:

1. polyploidy

2. hybrid speciation

3. adaptation to local environments

4. s3xual selection

Polyploidy

• organism has 2+ sets of chromosomes

• plants are more tolerant of polyploidy than animals

• nondisjunction

2 types

1. autopolyplouds

2. allopolyploids

Autopolyploids

increased number of sets of chromosomes from the same parental species

• auto = same

Allopolyploids

contains chromosomes from 2+ different species

• formation can abruptly lead to reproductive isolation and speciation

• 2 or more sets of chromosomes from 2+ different species

• allo = different

hybrid speciation

• interspecies plants that have become polyploid may be fertile and reproductively isolated from the original populations

• interspecies hybrids may become a new species even if they’re not polyploid

  • galeopsis tetrahit

Adaptation to local environments

• geographic area may have variation so that some members of a population may diverge and occupy different local environments that are continuous with each other

• eg; microhabitat partitioning

  • the division of precise, small-scale environments (e.g., specific spots on a tree, under rocks) by coexisting species to reduce competition for resources like food or shelter

S3xual selection

• females choose which male to mate

• related to courtship behaviours, songs, colouration

• certain females prefer males w/one colour pattern, while other females prefer males w/different colour pattern

influences to the pace of speciation

influenced by 2 things

1. gradualism

2. punctuated equilibrium

Gradualism

• each new species evolves continuously over long spans of time

• large phenotypic differences that produce new species are due to the accumulation of many small genetic changes

Punctuated equilibrium

• tempo more sporadic

• species in equilibrium for long periods and then short rapid bursts of changes

the pace of speciation

• large animals with long generation times evolve much more slowly than microbial species w/short generations

• many new species of bacteria will come into existence during our lifetime; new species arise on longer timeline

• important because bacteria have great environmental effects

Evo-devo: evolutionary developmental biology

• compares the development of different organisms to understand

• ancestral relationships between organisms

• developmental mechanisms that bring about evolutionary change

involves the discovery of genes that control development and how their roles vary in different species

Key developmental genes in the role of development

1. cell division

2. cell migration

3. cell differentiation

4. cell death / apoptosis

• interplay makes organisms with specific body pattern (pattern formation)

• developmental genes are very important to the phenotypes of individuals

chicken vs. duck feet

• changed expression of BMP4

• nonwebbed feet are favoured in terrestrial settings

• webbed feet are favoured in aquatic settings

Developmental genes that affect growth rate

• genetic variation can influence morphology by controlling relative growth rate of different parts of the body during development

• heterochrony - evolutionary changes in the rate or timing of developmental events

  • compare head growth between humans and chimp.

  • at the fetal state they are similar

  • after, growth rates become different