Chapter 24: Speciation and Macroevolution (Part 1, Week 2)

Question 1

What are evolutionary changes that produce new species and groups of species?

Answer 1

Macroevolution

Question 2

What is a group of related organisms that share a distinctive set of attributes in nature and (for sexually reproducing species) are capable of interbreeding?

Answer 2

Species

Question 3

What do members of the same species share? This question does not refer to shared attributes,

Answer 3

Evolutionary history which makes them genetically similar. Two closely related species may almost look identical.

Question 4

What are two practical uses for species identification?

Answer 4

1. Allows biologists to plan for the preservation and conservation of endangered species.
2. Allows a physician to correctly identify the microorganism that is causing a disease in a patient so the proper medication can be prescribed.

Question 5

What is the formation of a new species?

Answer 5

Speciation

Question 6

[Start 24.1 Identification of Species]

What are the number of species that have been identified and catalogued to date?

Answer 6

1.8 million

A vast number has yet to be classified and this is especially true for bacteria and archaea which are difficult to categorize into distinct species.

Question 7

What is the common estimate range for the total amount of species?

Answer 7

5 to 50 million!

Question 8

What is a subdivision of a species; the designation is used when two or more geographically restricted groups of the same species differ, but not enough to warrant their placement into separate species?

Answer 8

Subspecies

Question 9

What are genetically distine populations adapted to their local environments?

This is especially common for many bacterial species in which they are dubdivided into.

Answer 9

Ecotypes

Question 10

What are the most commonly used characteristics for identifying species?

Answer 10

• Morphological traits
• Ability to interbreed
• Molecular features
• Ecological factors
• Evolutionary relationships

Question 11

What are some drawbacks when using morphological traits as a way to classify a species? (2)

Answer 11

• difficulty in deciding how many traits to consider Size and weight vary a lot.
• degree of dissimilarity that distingues different species may not show a simple relationship. Members of the same species may look very different while members of different species may look very similar.

Question 12

Why would biologists describe two types of organsims as being different species if they are morphologically similar?

Answer 12

One reason is that they have discovered that the two organisms are unable to breed with each other.

THEREFORE, the second way of identifying a species is by its ability of its members to interbreed.

Question 13

In the late 1920s, geneticist Theodosius Dobzhansky proposed what? And what is the term that describes this?

Answer 13

He proposed that each species is reproductively isolated from other species.

The term, reproductive isolation, is a criterion for identifying a species; the circumstances and mechanisms that collectively prevent a species from interbreeding with other species.

Question 14

Who expanded on the ideas of Dobzhansky to provide a definition of a species and said a key feauture of sexually reproducing species is that, in nature, the members of one species have the potential to interbreed with one another to produce viable, fertile offspring but cannot successfully interbreed with members of another species?

Answer 14

Ernst Mayr

Question 15

What are the four main problems of the criterion, reproductive isolation regarding the ability to interbreed?

Answer 15

1. In nature, two populations can be isolated because of no overlapping geographic ranges, not necessarily because they can’t interbreed.
2. There are cases where two different species can interbreed yet consistently maintain themselves as separate species. Ex yucca plants can interbreed but remain distinct.
3. Reproductive isolation does not apply to asexual species such as bacteria. Likewise, some species of plants and fungi reproduce asexually.
4. Reproductive isolation cannot be applied to extinct species.

Question 16

How is reproductive isolation used today primarily?

Answer 16

Reproductive isolation has been primarily used to distinguish closely related species of modern animals and plants.

Question 17

What is now commonly used to determine if two different population are different species?

Answer 17

Molecular features

Question 18

What do evolutionary biologists compare when using molecular features as a way to determine speciation? (4)

What might be the issue with using this characteristic?

Answer 18

• DNA sequences of genes
• Gene order along chromosomes
• Chromosome structure
• Chromosome number

How much difference in the genome is sufficinet for placement into a different species? 2%? 5%?

Question 19

What characteristic of speciation is largely determined by their environment in morphologically similar species that deals with how they forage for food, means of resources like vitamins or minerals, grow range, etc?

Answer 19

Ecological factors

However, a drawback for bacteria is that sometimes they display very similar growth characteristics, and even the same species may show great variation in the growth conditions it will tolerate.

Question 20

What are the two common ways the evolutionary relationships can be used to determine speciation?

Answer 20

Relationships can be determined by using fossil records to create an evolutionary tree.

By the analysis of DNA sequences. Researchers obtain samples of cells from different individuals and compare the genes within those cells to see how similar or different they are

Question 21

What is a way of defining the concept of a species and/or of providing an approach to distinguish one species from another?

Answer 21

Species concept

Question 22

How many different species concepts have been introduced since 1942?

Answer 22

20

Question 23

What is an approach used to distinguish species, which states that a species is a group of individuals whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring but cannot successfully interbreed with members of other species?

Answer 23

Biological species concept

Question 24

What is an approach used to distinguish species; states that a species is derived from a single distinct lineage and has its own evolutionary tendencies and historical fate?

Answer 24

Evolutionary lineage concept

Question 25

What is an approach used to distinguish species; considers a species within its native environment and states that each species occupies its own ecological niche?

Answer 25

Ecological species concept

Question 26

What is a widely accepted approach used to distinguish species; states that each species is a population of an independently evolving lineage?

Answer 26

General lineage concept

Question 27

What is the term that describes mechanisms that prevent interbreeding between different species?

Answer 27

Reproductive isolating mechanisms

Question 28

What are the two categories in which reproductive isolating mechanisms fall and what do they mean?

Answer 28

Prezygotic isolating mechanisms - A mechanism that blocks interbreeding by preventing the formation of a zygote.

Postzygotic isolating mechanisms - A mechanism that prevents interbreeding by blocking the development of a viable and fertile individual after fertilization has taken place.

Question 29

What is the offspring from the interbreeding of members of two different species called?

Answer 29

Interspecies hybrid

Question 30

What are the five types of prezygotic isolating mechanisms and what do they mean?

Answer 30

Habitat isolation - Different species never come into contact with each other. Usually involves a geographic barrier or large body of water.

Temporal Isolation - Species happen to reproduce at different times of the day or year. Like crickets in northeast U.S., two species are almost exact yet they reproduce at different times.

Behavioral Isolation - Example of meadowlarks, they are nearly identical in many ways and have overlapping geographic regions. In these regions, their interspecies mating is incredibly low largely due to the differences of their songs. These songs help each species identify potential mates of their own species.

Mechanical Isolation - Morphological features such as size or incompatible genitalia prevent two species from interbreeding. Male dragonflies use a pair of appendages to grasp females during copulation. When a male tries to mate with a female of a different species, his grasping appendages do not fit her body.

Gametic Isolation - This occues when two species attempt to interbreed, but the gametes fail to unite in a successful fertilization event. This is widespread among plant and animal species.

For example, this is especially important to closely related species of sea urchins as they may release sperm and eggs into the water at the same time.

Question 31

When it comes to gamete isolation, what did researchers discover that sea urchin sperm operates when it comes to fertilizing an egg in the water?

Answer 31

They have a protein on their surface called bindin, which mediates sperm-egg attachment and membrane fusion. The structure of bindin is significantly different among different sea urchin species, therey ensuring that fertilization occurs only between sperm and egg of the same species.

Question 32

When it comes to gamete isolation, how is it associated with plants and pollination?

Answer 32

• Fertilization is initiated when a pollen grain lands on the stigma of a flower and sprouts a pollen tube that ultimately reaches an egg cell.
• This pollen can reach many different plants. In most cases, when a pollen grain lands on the stigma of a different species, it either fails to generate a pollen tube or the tube does not grow properly and thus does not reach the egg cell.

Question 33

What are the three types of postzygotic isolating mechanisms and what do they mean?

Answer 33

Hybrid Inviability - This occurs when an egg of one species is fertilized by a sperm of another species, but the fertilized egg cannot develop pat the early embryonic stages.

Hybrid Sterility - This is when an interspecies hybrid may be viable but sterile.

Hybrid Breakdown - Even though hybrids may be viable and fertile, the subsequent generation(s) may harbor genetic abnormalities that are detrimental. This is caused by changes in chromosome structure.

Question 34

Why are mules typically sterile? (2)

Answer 34

1. Horse has 32 chromosomes per set and donkey has 31, a mule inherits 63 chromosomes. The chromosomes do not pair correctly
2. Chromosomes also have structural differences, which either prevent them from pairing correctly or lead to chromosomal abnormalities if crossing over occurs in meiosis.

Question 35

Why do biologists hypothesize about nature that has more prevalence of prezygotic isolating mechanisms over postzygotic isolating mechanisms?

Answer 35

Natural selection has favored prezygotic isolating mechanisms because they do not waste a lot of energy.

Question 36

[Start 24.2 Mechanisms of Speciation]

How is speciation, the formation of a new species, caused by?

Answer 36

Genetic changes in a particular group that make it different from the species from which it was derived.

Question 37

How are mutations in genes acted upon in nature?

Answer 37

By natural selection and other evolutionary mechanisms to alter the genetic composition of a population and this is how new species evolve.

Question 38

What are some other ways that contribute to the formation of a new species?

Answer 38

Interspecies breeding, changes in chromosome number, and horizontal gene transfer.

Question 39

What is the underlying cause of speciation?

Answer 39

The accumulation of genetic changes that ultimately promote enough differences that a population can be recognized as a unique species.

Question 40

Why does life often diversify into the more or less discrete populations that we recognize as species?

Answer 40

1. In some cases, speciation may occur due to abrupt events, such as changes in chromosome number, that cause reproductive isolation.
2. More commonly, species arise as a consequence of adaption to different ecological niches. For sexually reproducing organisms, reproductive isolation is typically a by-product of that adaptation.

Question 41

What is the splitting or diverging of one species into two or more species?

Answer 41

Cladogenesis

Question 42

What is the most prevalent way that cladogenesis occurs and is a form of speciation that occurs when a population becomes geographically isolated from other populations and evolves into one or more new species?

Answer 42

Allopatric speciation (allos meaning other, patria meaning homeland)

This form of speciation occurs whena population becomes isolated from the other populations and evolves into one or more species. Typically, this isolation may involve a geographic barrier such as a large area of land or body of water.

In some cases, geographic separation may be caused by slow geological events that eventually produce quite large geographic barriers. For example, a mountain range may emerge and split one species that occupies the lowland regions, or creeping glacier may divide a population.

Question 43

What is the process whereby a single ancestral species evolves into a wide array of descendant species that differ greatly in their habitat, form, or behavior?

AND what is a great example of this happening? Think Drosophila, the fruit fly.

Answer 43

Adaptive radiation.

The fruit fly has approximately 1,000 species dispersed throughout the Hawaiian Islands which originated from a common ancestral species.

Natural selection resulted in changes in body form and function that produced the amazing diversity of Drosophila species that are now found.

Question 44

What is an area where two populations can interbreed?

Answer 44

Hybrid zone

Question 45

Explain what Jeffrey Podos, an American biologist, discovered by analyzing the songs of Darwin’s finches on the Galapagos Islands to determine how envrionmental adaptation may contribute to reproductive isolation.

Answer 45

• The adaptions of different beak sizes and shapes in various species of finches are adaptations to different feeding strategies.
• Podos hypothesized that changes in beak morphology could also affect the songs that birds produce, thereby having the potential affect mate choice. They modify their voice tracts and beak movements are precise.
• Larger beak size, which is an adaptation to cracking open large, hard seeds, contrains vocal performance. This may affect mating song patterns and thereby promoto reproductive isolation, in turn, speciation.

Question 46

What is a form of speciation that occurs when members of a species that initially occupy the same habitat within the same range diverge into two or more different species even though there are no physical barriers to interbreeding?

Answer 46

Sympatric speciation

Question 47

What is a type of sympatric speciation where the condition in which a cell or organism has three or more sets of chromosomes?

Answer 47

Polyploidy.

This is a result of unequal separation or nondisjunction of chromosomes, which can increase the number of chromosome sets in a given species. This is much more tolerant in plants than it is in animals.

Question 48

What is another mechanism that leads to polyploidy?

Answer 48

Interspecies breeding.

An organism having at least one set of chromosomes from two or more different species (alloploid). This term refers to the occurence of chromosome sets (ploidy) from the genomes of different (allo) species.

Interbreeding between two different species may produce an allodiploid, an organism that has only one set of chromosomes from each species. Species that are close evolutionary relatives are most likely to breed and produce allodiploid offspring like grasses.

An organism containing two or more complete sets of chromosomes from two or moredifferent species is called an allopolyploid. This occurence can lead to reproductive isolation.

Question 49

Other than polyploidy, what are the other two means of sympatric speciation?

Answer 49

• Adaption to local environments like the apple maggot fly that fed on native hawthorn trees and the hawthron fruits. When apple trees were brought in, produced a new local environment, and then created apple feeding species since apples developmuch quicker than hawthorn fruit.
• Sexual selection. A possible outcome of such secual selection is that it can separate one large sympatric population into smaller populations that eventually become distinct species because they have selectively breed among themselves due to coloration of mates, etc.