The Origin and Diversification of Life on Earth (ch.12)

Diversity of life

Microevolution

Speciation

Macroevolution

What is Macroevolution:

The accumulated effect of microevolution over a long period of time

What is a microevolution?

A change in allele frequencies over one or a few generations

Fact about microevolution:

• Microevolution changes in allele frequencies in a population over time can lead to macroevolution, changes on a grand scale including vast diversification of species

Classification of species

• Systematics and Taxonomy

• Every species has a two-part scientific name: Genus species

• Hierarchical Classification:

Genera= Relates species are grouped together

Families= groups of genera

What is a species?

• Hybrids were difficult to classify

• Dawin laughed at these difficulties and argued that varieties were in the process of evolving to become different species

• species are the products of evolution

Speciation is the formation of one or more new species from a current species

Biological Species Concept:

• Coined by Ernst Mayr in 1942

• A group of “actually or potentially interbreeding populations which are reproductively isolated from other such groups”

• focuses on the process of how species form, not just recognizing a species once it is already present

• Also provided info on how populations might be kept apart

Barriers- stops gene flow

• A species divides into 2 when a geographical or behavioral barrier between populations prevents interbreeding

Reproductive Isolation:

1) Before sex barriers (prezygotic), species result from some form of isolation, which prevents two organisms from having offspring together that occur in the zygote

2) After Conception Barriers (postzygotic), mating occurs, but the  offspring are not fertile or viable

Habitat Isolation

• Elk (N.America) and Red deer (Europe, Russia)

• Considered 2 Populations of a single species

• They can interbreed when put into zoos

• Where they will mate, like a forest or mountain (Habitat)

• Habitats by members of a species differ, and breeding interactions differ

Temporal isolation/ gammete

• Interbreeding is not separated geographically but by time or biology

• These coral species are mass spawners

• This happens for different species, and at different times they breed: Spring breeding or fall breeding (temporal)

• they release gametes at different times

• minimizing changes of interbreeding between species

• only in aquatic animals, 2 gametes to form a zygote is impossible (gametic isolation)

Behavioral Isolation:

• Male fireflies use flashes of light for courtship

• females respond only to signals from males of their own species

• Flash behavior by males and recognition from females creates a barrier to prevent interbreeding

• Mate selection, where they choose who to mate with (who they find attractive or not)

• same species but behave differently. 

• Different mating behaviors that don't attract from a different group

Mechanical Isolation

• Egg producing and sperm producing parts of different species are anatomically incompatible

• Some species can't mate with others

• Mating is not possible (like an elephant and a mouse)

Reproductive Barriers after conception

1. Hybrid Embryos between 2 different species may fail to develop

2. Hybrids sometimes are deformed or healthy but steriles

• Mules are hybrid between horses and donkey

• Mules are viable but sterile

• Keep horses and donkeys separate species

1. Hybrids live and are fertile but their offspring are not

Other speciation concepts:

• Phylogenetic species concept

• Morphological species concept

Mechanisms of Speciation

• Allopatric Speciation

• Sympatric speciation

Allopatric speciation

• A river poses a geographical barrier to interbreeding

• mutations accumulate

• reproductive barriers evolve which minimize interbreeding when/if geographical barrier is removed

• Anoles

• Gene flow is interrupted by geographic isolation

Example of evidence of allopatric speciation

• Atlantic and Pacific shrimp are more closely related to each other than they are to shrimp in the same ocean

Sympatric speciation

• Fly selection for different fruits helps isolate the populations, allowing them to diverge in sympatry

• happen in the same area

• Gene flow is reduced by other means, such as geographically overlapping populations

what did Carl Linnaeus invent?

invented a system for classifying species based on shared traits

biological spec ies concept

• A species is a group of members that can interbreed and produce viable, fertile offspring.

• Must be reproductively compatible. 

Morphological species concept

A species is a group of members of the same body shape or features

• Pro: can apply to both azexual and sexual organisms

• Con: can be misleading (convergent evolution- members of different species appear similar); can be subjective 

ecological species concept:

• Members of the same species occupy the same ecological niches

• Interaction with biotic and abiotic parts of the environment (soil type, ability to tolerate cold climate, elevation)

•  Even if gene flow occurs between the two types of trees, they are different species because they occupy different ecological niches

Phylogenetic species concept:

• A species is a group of organisms that share a common ancestor

• A species forms one branch on a tree 

Posyzygotic:

Zygote mortality

Hybrid inability

Hybrid sterlity

zygote mortality

• 2 gametes and a zygote are formed, they will have a high mortality rate nd unable to develop into mature offspring 

1. Hybrid Inability:

- Can grow to a mature offspring, but will have a high mortality rate and not grow to a mature adult

1. Hybrid sterility:

• Can grow to mature adults, but not mate and reproduce offspring on their own

If none of these barriers isolates two organisms, they are members of the same species.

reduced hybrid viability

1. Development not successful or results in frail offspring

1. Reduced hybrid fertility:

1. Healthy offspring are produced, but offspring are not fertile. 

Hybrid Breakdown

1. Offspring is produced, offspring can reproduce, but the 2nd generation is weak or sterile. 

Asexual Reproduction: 

• One organism,m like a single bacterium, um will divide into two daughter cells that are genetically identical to the original cell. 

• Usually have low genetic diversity

Sexual Reproduction: 

• Two members of the same species will reproduce together in order to form genetically unique offspring. -Usually have high genetic diversity