Freeman Biological Science Chapter 24 Speciation

What is speciation?

creates 2+ distinct species from a single ancestral species

An evolutionary independent population or group of populations is known as_________?

species

What is a clade?

another name for a monophyletic group; an ancestral population and all of its descendants, and only those descendants

What is a monophyletic tree?

a section of a phylogenetic tree where a synapomorphy occurred, making all descendants to the left of this synapomorphy related

What criteria are used to determine organisms in a monophyletic tree?

synapomorphies, DNA

Why is sexual vs. asexual reproduction an issue?

Sexual reproduction allows variation while asexual reproduction produces copies of the parents

Why won't the biological species concept work with the fossil record?

It is hard to determine if there was reproductive isolation occurring in fossils.

Compare and contrast the biological, morphospecies, and phylogenetic species concepts.

Biological - relies on reproductive isolation between populations

Morphospecies - relies on morphologically distinct populations and is widely applicable

Phylogenetic - relies on smallest monophyletic group on the phylogenetic tree and is widely applicable; also based on testable criteria

How does speciation actually occur?

it begins when gene flow between populations is reduced or eliminated, causing genetic isolation

What is the difference between allopatric and sympatric speciation?

~ Allopatric speciation is when a population becomes geographically separated.
~ Sympatric speciation is when a new species appears in the same geographical species, even if there is already a population living there (ex: new trees just popped up in population of existing trees).

What mechanisms or methods contribute to allopatric speciation? Which contribute to sympatric speciation?

Allopatric =
1) DISPERSAL - some individuals disperse from popu. and colonize to form new habitat.
2) VICARIANCE - a chance event seperates popu. into subgroups
ex.) shrimp and isthmus of Panama
Sympatric =
1) EXTERNAL EVENTS, such as disruptive selection for extreme phenotypes based on diff. niches
2) INTERNAL EVENTS, such as chromosomal mutations

Explain why gene flow has to stop in order for speciation to occur.

When a pop. splits and becomes geographically isolated, gene flow must stop in order to allow each group to evolve in order to suit it's new, restricted environment.

Why is geographical isolation mentioned? How is it achieved?

This is the MAIN reason for why allopatric speciation occurs. It can occur by either dispersal or vicariance.

What does the founder effect have to do with allopatric speciation?

When a few members of a population cross a major geographical barrier (ex mountains) is is known as a founder event. If the few members that crossed have to evolve to better suit their environment, then it becomes known as allopatric speciation.

Can you have more than one evolutionary processes occurring at once (ex: genetic drift and natural selection)?

yes; beetle with genetic drift and natural selection example

Compare and contrast all of the different mechanisms of pre zygotic isolation.

-TIMING - one fly mates in the morning while the other fly mates at night
-HABITAT - 1 frog likes pond but other likes muddy water
-BEHAVORIAL - male fireflies recognize certain female flash
-GENETIC BARRIER - sperm and egg have certain proteins
-MECHANICAL - snails = physically impossible

Compare and contrast all of the different mechanisms for post zygotic isolation.

HYBRID VIABILITY - offspring are abnormal and do not survive

HYBRID STERILITY - offspring are sterile

Draw a diagram illustrating the apple and hawthorn maggot example. What do you think this represents?

Apple flies and hawthorn flies live in the same area, however, they do not breed together because they prefer to breed with flies on the same fruit as them.

In what ways can allopatric and sympatric speciation occur? Give examples of each.

(Allopatric)
dispersal - popu. of coyotes move from high up in mountains, down into desert and evolve to suit hotter climate

vicariance - closing of isthmus of panama, causing 6 species of shrimp to become 12 (6 caribbean, 6 pacific)

What is a cryptic species?

differ in traits other than morphology

What is the difference between cladogenesis and anagenesis?

Anagenesis = now branching or splitting, just a gradual change into a new species

Cladogenesis = splitting into two new species

How do new species arise?

~ gene flow ends between populations
~ mutation, selection, genetic drift cause isolated populations to diverge

The Biological Species Concept

~ population members, interbreed and produce viable, fertile offspring
~ no gene flow occurs between populations that are reproductively isolated from each other

True/False: Criterion of reproductive isolation can't be evaluated in fossils or in species that reproduce asexually.

true

What are morphospecies concept disadvantages?

1) may lead to naming of 2+ species when there's only 1 polymorphic species with differing phenotypes
2) can't id cryptic species, differ in traits other than morphology
3) morphological features used to distinguish species are subjective (debatable)

What does phylogenetic species concept identify species base on?

evolutionary history of populations

What is a monophyletic group also known as?

clades or lineage

What are monophyletic groups identified by?

traits called synapomorphies

What is a synapomorphy?

trait found in certain groups of organisms and their common ancestor, but missing in more distant ancestors

Explain why the criteria invoked by the biological species, morphospecies, and phylogenetic species concepts allow biologists to identify evolutionary independent groups.

BSC: Reproductive isolation means that no gene flow is occurring.
MSC: If populations are evolving independently, they may have evolved morphological differences.
PSC: If populations are evolving independently, they should have synapomorphies that identify them as independent twigs on the tree of life.

Describe the disadvantages of the biological species, morphospecies, and phylogenetic species concepts.

BSC: It cannot be used to evaluate fossils, species that reproduce asexually, or species that do not occur in the same area and therefore never have the opportunity to mate.
MSC: It cannot identify species that differ in traits other than morphology and is subjective - it can lead to differences of opinion that can't be resolved by data.
PSC: Reliable phylogenetic information exists only for a small number of organisms.

Hypothesize why natural selection would favor divergence based on the observation that apple fruits drop about 3-4 weeks earlier in the fall than hawthorn fruits.

The difference in timing of ripening of apples and hawthorns causes divergence by separating apple flies and hawthorn flies not only in space but also in time. The earlier the ripening of apples means that apple maggots develop in relatively warm conditions in the fall compared to hawthorn maggots. Natural selection may favor traits in apple maggots that make them adapted to warmer temperatures and traits in hawthorn maggots that make them adapted to cooler temperatures.

Explain whether human populations would be considered separate species under the biological species, morphospecies, and phylogenetic species concepts.

Human populations would not be considered separate species under the biological concept, because human pop can successfully interbreed. They would not be considered separate species under the MSC, because all human pop have the same basic morphology. Although human races differ in minor superficial attributes such as skin color and hair texture, they have virtually identical anatomy and physiology in all other regards. Nor would human pop by separate species under PSC, because they all arose from a very common ancestor.

What distinguishes a morphospecies?

it has distinctive characteristics, such as size, shape, or coloration

Describe vicariance?

a population is fragmented into isolated subpopulations

Why are genetic isolation and genetic divergence occurring in apple maggot flies, even though populations, occupy the same geographic area?

different populations feed and mate on different types of fruit

The biological species concept can be applied only to which of the following groups?

*bird species living today
dinosaurs and bird species living today
dinosaurs
bacteria

Why is "reinforcement" an appropriate name for the concept that natural selection should favor divergence and genetic isolation if populations experience post zygotic isolation?

the selected traits reinforce differences that evolved while the populations were isolated from one another

Which studies in this chapter represent direct observation of speciation? which are indirect studies of historical speciation events?

Direct observation: Galapagos finch colonization, apple maggot flies.
Indirect Studies: snapping shrimp, sunflowers

Gene flow increases the divergence of populations.

False