BIOL 2390 - Topic 5 (part 4)

Species (old definition)

They are defined by similar characters

Species (modern definition)

Groups of interbreeding populations that produce fertile offspring

Speciation

1.) The formation of a new species from evolutionary processes

2.) Usually occurs when different populations change over time, until reproductive isolation occurs

Adaptive radiation

Speciation where one species gives rise to many new species, who exploit the environment in unique ways

Adaptive radiation example

Salamanders are at this point, but have not yet fully speciated

Reproductive isolation

It is caused by isolating mechanisms/reproductive barriers that restrict the flow of genes between populations

Reproductive isolating mechanisms examples

1.) Morphological (different reproductive parts)

2.) Behavioural (different courtship rituals)

3.) Ecological conditions (reproduce in different places)

4.) Genetic incompatibility (different number of chromosomes)

Mechanisms may be _________ or __________.

Pre-mating (morphological, behavioural, and ecological conditions) or post-mating (genetic incompatibility)

Horse + Donkey =

Infertile mule

What kind of isolating mechanism does horse+donkey have?

Post-mating mechanism caused by genetic incompatibility

How are donkey’s and horses able to reproduce in the first place?

It was only recently that they speciated, therefore they only have the one barrier between them (i.e. the genetic incompatibility)

Types of speciation

1.) Allopatric speciation

2.) Sympatric speciation

Allopatric speciation

1.) It occurs when a geographical barrier separates a population into isolated subpopulations with no gene flow

2.) The different local environments create different selective pressures, causing them to diverge, until reproductive isolation and speciation eventually occur

Example of allopatric speciation

London Underground mosquito, who are in the process of allopatric speciation as they only produce fertile offspring in the lab

Sympatric speciation

Speciation occurs due to the formation of a reproductive barrier within the same geographic location (i.e. there is no geographic barrier)

Sympatric speciation is caused by…

1.) Polyploidy

2.) Disruptive selection

Polyploidy

1.) Refers to the doubling of the number of chromosomes, resulting in genetic incompatibility

2.) It occurs when errors happen during meiotic cell division

Disruptive selection

1.) Selection that favours the extremes, caused by multiple selection forces at the same time, such as sexual selection, habitat and food source specialization, etc

2.) It is difficult to observe in progress

Disruptive selection example

Arctic charr

Hybridization

The mating of two closely related species that can lead to hybrids, which may or may not be sterile or fertile

Fertile hybrids

They blur the lines between two species and challenges the species concept definition

Are hybrids new species

No

Number of fertile hybrids

An estimated 6% of animals and up to 70% of insects/plants can form fertile hybrids

Junco

1.) Prefers coniferous forest habitats across North America, giving it a wide distribution

2.) Eats mostly ground-level insects and seeds and nests near the ground, low in trees, or on the ground itself

3.) Its evolutionary history and speciation fascinates scientists