BioDiversity Set 5 Exam 2 - SPECIES AND SPECIATION

When defining a species, what is the Morphospecies Approach?

It was the most common way of defining species throughout history; this approach used physical appearance/morphology to define a species.

What were the problems with the Morphospecies Apprach?

These problems were:

• Sexual Dimorphism - Females/Males look different from each other

• Cryptic species – two or more species that are nearly identical to each other. Yet they were NOT capable of successful reproduction with each other

• Polymorphic species – Individuals of the same species that look different, but can breed successfully with each other

What is the BIOLOGICAL SPECIES CONCEPT?

This concept defined species as groups of actively or potentially interbreeding natural populations that are reproductively isolated from other such groups (populations)

Who came up with the Biological Species Concept?

Ernest Mayr created this concept

What were the issues with the biological species concept?

• This concept can’t be applied to ASEXUAL organisms

• Does not apply to bacteria, archaea, hermaphrodites, and self-fertilizers

• Can’t be used to define species for EXTINCT FOSSILS of organisms

• Difficult to apply to populations that are separated geographically:

a.       No way to determine the potential to reproduce when they are separated by oceans, mountains, rivers, etc.

What concept is based upon the evolutionary history of individual populations?

It is the PHYLOGENETIC SPECIES CONCEPT - It considers common ancestry. Starting off with an ancestral population that derives descendant populations.

• Descendant populations/species are separated from each other based upon traits/alleles that differ

  a.       Those that share particular traits and alleles share synapomorphies

  Reproductive isolation can also be used

What are synapomorphies?

It is shared derived characteristics that are inherited from an ancestor

What happens when there is reproductive isolation of different portions of a given population?

SPECIATION is occurring. When there is a lack of reproduction, the two isolated portions of this population start to diverge genetically.

Developing respective genetic trajectories based upon differences in the MECHANISMS OF EVOLUTION

What is the defintion of Sexual Reproduction?

It is the union of sperm and egg - which in turn produced a zygote

Reproductive Isolation is defined as…

Factors that prevent successful reproduction AND gene flow

Is reproductive isolation required for speciation to occur?

YES!!! It is required, and it can occur in a broad range of ways, primarily through PRE-ZYGOTIC ISOLATION and POST-ZYGOTIC ISOLATION

What is PRE-ZYGOTIC ISOLATION?

It is isolation BEFORE the zygote forms (pre-fertilzation) in which:

• Mating CANNOT typically occur

• Mating can occur, but does NOT

• Mating can occur, but NO ZYGOTE FORMS (no fertilization)

What is POST-ZYGOTIC ISOLATION?

It is isolation AFTER the zygote forms (post-fertilization) in which:

• Offspring occurs, but does not survive

• Offspring survives, but they are sterile

What form of pre-zygotic isolation occurs when breeding is physically impossible to occur?

Mechanical Isolation has occurred.

1. Female/Male reproductive parts don’t match up. Ex: snail shell direction mutation)

2. Body-size mismatch – Ex: Great Dane with a chihuahua

3. “Lock and Key” mismatch – Ex: Ground beetle copulatory pieces (despite looking the same, reproductive parts only match up with individuals of the same species)

What form of pre-zygotic isolation occurs when organisms who can breed together, and live in the same location do not due to differing habitat/ecological factors?

HABITAT/ECOLOGICAL ISOLATION - Even though they have the potential to reproduce, they never encounter each other OR breed. This is the result of feeding or breeding to particular habitats.

What form of pre-zygotic isolation occurs when mating can occur, but does not due to differing behaviors?

BEHAVIORAL ISOLATION - Due to differences in calls, songs, or ritualized dances, interbreeding does not occur

What form of pre-zygotic isolation occurs when mating can occur, but does not due to no overlap of breeding patterns? (they happen at different times)

TEMPORAL ISOLATION - Breeding periods of closely related species do NOT overlap → Resulting in NO potential for interbreeding

• Ex: Wild lettuce (Lactuca canadensis (late spring) and Lactuca graminifolia (late summer)) No chance for cross-pollination/breeding

What form of pre-zygotic isolation exists when mating occurs, but no zygote forms (no fertilization) ?

ISOLATION BY PREVENTION OF GAMETE FUSION - Something prevents sperm from fertilizing the egg

Toxic uterine environment – uterus kills sperm from the wrong species

What form of post-zygotic isolation happens when mating occurs, fertilization occurs, a zygote forms, but there is an accumulation of genetic issues/differences resulting from a mismatched sperm/egg?

It is HYBRID INVAILIBILITY – These differences in genetics typically results in the death of the zygote/offspring

What form of post-zygotic isolation happens when mating occurs, fertilization occurs, a zygote forms, but the offspring produced is sterile?

It is HYBRID INFERTILITY/STERILITY – offspring produced by breeding of closed released species that survive to adulthood, but they cannot reproduce.

Ex: Mules, and Ligers

Is there usually more than more than one type of isolation occurring at a time during reproductive isolation, leading to genetic divergence?

YES!! Populations become reproductively isolated (NO gene flow), resulting in genetic divergence (resulting from population-specific differences in genetic drift, mutation, and natural selection)

- Can lead to new species

What factors support the idea of there being 4 distinct species of lepoard frog species

These frogs are different through:

1. Breeding calls (Behavioral isolation)

2. Breeding periods (Temporal isolation)

3. Separated by habitats (Habitat isolation)

Resulting in genetic divergence (enhanced by geographic distance) → increased potential for speciation

What happened when researchers tried to breed these respective species of leopard frogs together?

They saw…

NO FERTILIZATION (pre-zygotic)

and

HYBRID INVIABILITY (post-zygotic)

Supporting the idea of 4 distinct species!