Lesson 4: Speciation and Macroevolution

Microevolution

evolution on a small scale (in populations)

Macroevolution

Evolution on a larger scale (Now)

Speciation

the splitting of one species into two distinct species

Species

a group of organisms that can reproduce and create offspring that can also reproduce

4 Species Concepts

1. Morphological Species Concept

2. Evolutionary Species Concept

3. Phylogenetic Species Concept

4. Biological Species Concept

Morphology

study of an organism’s form and the relationship between their structures

Organisms are defined by their distinct ___ knowns as ____

physical characteristic, diagnostic traits

Cryptic Species

two different species that look identical but differ in some other way (courtship,etc.)

Morphological Species Concept is tough to use on some organisms like ____

bacteria

What does Evolutionary Species Concept rely on?

Relies on the identification of certain morphological traits in the fossil record to distinguish one species from another

What does Evolutionary Species Concept track?

Evolution as specific characteristics change over time

What is a Phylogeny used to identify?

(Family tree) used to identify species based on a common ancestor

Monophyletic

A branch that contains all the descendants of a common ancestor is said to be

Phylogenetic Species Concept is based on ___ not ___

DNA code; morphology

What does Biological Species Concept rely on?

reproductive isolation to identify species (location, behavior, anatomical, etc.)

Why is Biological Species Concept difficult to test in nature?

Can’t be applied to asexually reproducing organisms or fossils

For two species to remain seperate, population must be reproductively isolated and _____ must NOT occur between them

Gene flow

Isolating Mechanisms

Barriers that prevent successful reproduction

In Reproductive Isolation, typically they are grouped as isolation before or after the formation of a ___

zygote

Prezygotic v. Postzygotic Isolation

isolation before vs. after becoming a zygote

3 Forms of Premating (prezygotic) Isolating Mechanisms

1. Habitat Isolation

2. Temporal Isolation

3. Behavioral Isolation

Habitat Isolation

Species at same locale occupy different habitats (ones in the forest, ones in the pond)

Temporal Isolation

Species reproduce at different seasons or different times for day

Behavioral Isolation

Courtship behavior differs or indiviuals respond to different songs, calls, pheromones, or other signals

2 Forms of Mating (prezygotic) Isolating Mechanisms

1. Mechanical Isolation

2. Gamete Isolation

Mechanical Isolation

Genitalia between species are unsuitable for one another

Gamete Isolation

Sperm cannot reach or fertilize egg

2 Forms of Fertilization (postzygotic) Isolating Mechanisms

1. Zygote Mortality

2. Hybrid Sterility

Zygote Mortality

Fertilization occurs, but zygote does not survive

Hybrid Sterility

Hybrid offspring survive but are sterile and cannot reproduce

2 Modes of Speciation

1. Allopatric speciation (geographic barrier)

2. Sympatric speciation (no geographic barrier)

2 Ways that Speciation Occurs

1. Gradualism - slowly over time

2. Punctuated Equilibrium - periods of rapid change followed by periods of no change

Allopatric speciation

physical barrier separates the two species, adapts, and now they are two different species

Sympatric speciation

stay in the same place but seperate themselves over periods of time that they become distinct species

Divergent Evolution (adaptive radiation) shows ___

common ancestry to different offspring

Convergent Evolution shows ___

no common ancestors but similar offspring due to similar environments

Divergent Evolution (adaptive radiation)

• Occurs when a single ancestral species creates new species and each adapt to a specific environment

• Occurs in times of ecological release - competition is reduced

  • Following extinction events, ice ages, and migration to new area

Convergent Evolution

• Occurs when a biological trait evolves in two unrelated species as a result of exposure to similar environments

  • Analogous traits - similar due to similar lifestyle of habitat

  • Homologous traits - similar traits due to a comon ancestor

Phylogeny

Tree of life

HOX Genes

• Specify regions of the body plan of an embryo

• Create head/tail axis in animals

• Ensures the correct structures are in the correct places

• Found in Pre-Cambrian Age (like humans and jellyfish) have been around for a LONG time