Origin of Species

speciation

How new species originate and how populations evolve

Consists of changes in allele frequency in a population over time

Refers to broad patterns of evolutionary change above the species level

• Biological Species concept

• Morphological species concept

• Ecological species

• Phylogenetic species concept

The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

The offspring of crosses between different species

By whether factors act before or after fertilization

• Habitat Isolation

• Temporal Isolation

• Behavioral Isolation

• Mechanical Isolation

• Gametic Isolation

• Reduced Hybrid Viability

• Reduced Hybrid Fertility

• Hybrid Breakdown

Two related species can hybridize, and their F1 offspring are fertile.

• But successive generations (F2 and beyond) suffer lower viability or fecundity.

  • Thus, they cannot become an established population.

Rice cultivars

• Cultivars have been artificially selected and some are related enough to hybridize

• F1 = fertile and viable

• F2 = stunted and sterile

Tigers and Lions are sister taxa, but seperate for millions of years

• Their hybrid offspring are viable and robust, but sterile.

• Chromosomes are not homologous, so they don’t migrate during meiosis normally

Tigers and Lions are sister taxa

• Their hybrid offspring are viable and robust, but sterile

  • A mating between a lion and leopard will produce sterile hybrids

  • A mating between a tiger and leopard will produce inviable hybrids

    • Zygotes divide, but embryo miscarries or is stillborn

Fossils or asexual organisms (including all prokaryotes)

• The biological species concept emphasizes absence of gene flow

Yes; grizzly bears and polar bears can mate to produce “grolar bears”

• Morphological Species Concept

• Ecological Species Concept

• Phylogenetic Species Concept

Defines a species by structural features

• It applies to sexual and asexual species but relies on subjective criteria

Spheres (cocci), Rods (bacilli), Spirals

It views a species in terms of its ecological niche

• It applies to sexual and asexual species and emphasizes the role of disruptive selection

It defines a species as the smallest group of individuals on a phylogenetic tree

• It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species (DNA Evidence)

• Based on DNA similarities

1. Allopatric Speciation

2. Sympatric Speciation

A population forms a new species while geographically isolated from its parent population.

A subset of a population forms a new species without geographic separation.

• 15 pairs of sibling species of snapping shrimp (Alpheus) are separated by the Isthmus of Panama

• These species originated 9 to 13 million years ago, when the Isthmus of Panama formed and separated the Atlantic and Pacific waters

Barriers to reproduction are intrinsic; separation itself is not a biological barrier

Geographically overlapping populations

Courtship rituals and other behaviors unique to a species are effective barriers

The presence of extra sets of chromosomes due to accidents during cell division

• Polyploidy is much more common in plants than in animals

• Polyploidy conditions occur through meiosis errors

An individual with more than two chromosome sets, derived from one species

Seedless Watermelon = triploid

Banana = triploid

Blackberries = tetraploid

Peanuts = tetraploid

Sweet Potato = hexaploid

Wheat = hexaploid

Strawberry = octopoid

A species with multiple sets of chromosomes derived from different species

That a group of organisms that can successfully interbreed and produce fertile offspring

Macroevolution is broader, such as the evolution of lungs, or tetrapods.

They may look alike, but there is some issue that prevents them from interbreeding.

Where organisms may be in the same environment, but in slightly different habitats so they never interact

• In the water and on land

Different mating periods, such as the season, time of day, etc.

Different courtship rituals

• Dancing, singing

Reproductive organs don’t line up

• Such as when snail shells are in the opposite ways

They can mate, butter gametes aren't chemically compatible

• The sperm and egg don’t merge, which means no zygote is made

Nope

No, not all the time

The absence of gene flow (intermitting, immigration, emigration)

Allopatric speciation is when a geological barrier prevents a population from interacting, so they are not able to reproduce with each other

• The reproductive barriers cause speciation

Sympatric speciation is when a population’s organisms evolve into unique species by different evolutionary pathways in the same environment until they are reproductively isolated from each other

Plants, not animals bc they are too complex

Errors in meiosis

• Non normal meiosis

Both parents species are of the same species, and due to meiosis errors, their gametes have a full set of chromosomes. This then leads to an offspring with double the amount of chromosomes.

• Failure to reduce chromosome # during meiosis

One species(A) has a proper gamete and makes a zygote with a different species(B) whose gamete has had meiosis errors resulting in a gamete with a full chromosomal set. This hybrid then mates with an organism from species A. Species A again gives the proper gamete, and the hybrid has a meiosis error with a full chromosomed gamete. Together, they will make what the first mating should have properly had

• Hybridize between two species, and not reduce chromosome #

Sympatric Speciation

Sympatric because they are still in the same geographical area, just occupying slightly different habitats and niches

Behavioral isolation

• A fish species’s slight was affected, changing how they saw the colors of other fish

  • This impacted the attraction between the fish species, eventually causing speciation

Sympatric speciation

A model that contrast with the model of gradual change

• A long period of no change followed by rapid changes or vice-versa

Thousands of years vs. Millions of years

Examples of species from the fossil record that appear suddenly, persist essentially unchanged for some time, and then apparently disappear

The cumulative effect of many speciation and extinction events