Topic 5: Origin of Species

Question 1

Microevolution

Answer 1

-evolution that happens at the population level, it occurs mainly through selection (results in adaptations) or drift (changes in allele frequencies over time)

Question 2

Macroevolution

Answer 2

• evolution that occurs above the species level

- results in origin of new traits in a population, higher taxa, mass extinctions, speciation

Question 3

What is the biological species concept?

Answer 3

A species is a group of actually or potentially interbreeding individuals that are reproductively isolated from other such groups (they can breed together and make viable offspring that can also reproduce)

Question 4

What are the problems with the biological species concept?

Answer 4

1. Only applies to sexually reproducing species, what about asexual species? (This is why we use morphological, phenotypic, and chemical processes similarities to classify)
2. It suggests that two different species would never mate and produce offspring, but what about successful hybrids? (these are often rare occurrences, so we just say generally they are different species)

Question 5

What is the ecological species concept (under the biological species conceot) and what are the issues relating to it?

Answer 5

-species is a set of organisms adapted to a particular set of resources, called a niche, in the environment
Issue: species will differ at the extremes of the distribution (eg: some individuals who live in the same region but different parts of the region will have different adaptations to better suit their particular environment)

Question 6

What is the phylogenetic species concept (under the biological species concept) and the issues relating to it?

Answer 6

-species are classified based on their evolutionary history
Issue: some populations are more unique than others (have special characteristics depending on where they live, so though they are capable of interbreeding, they will never come into contact and actually do so)

Question 7

What is reproductive isolation?

Answer 7

-when species only mate with those of their own species (are separated from each other and maintain their differences)

Question 8

What is a pre-zygotic isolating mechanism?

Answer 8

It is a pre-reproductive isolating mechanism that prevents two individuals from forming a zygote

Question 9

What is a postzygotic reproductive mechanism?

Answer 9

It is a post-reproductive isolating mechanism that ours after a zygote has been formed

Question 10

What are some prezygotic isolation mechanisms?

Answer 10

• ecological (habitat selection)
• temporal isolation (different time of day/season)
• behavioral isolation (courtship patterns, mating calls)
• mechanical and morphology isolation (anatomically incompatible or look different)
• gamete isolation (sperm and egg fusion)

Question 11

What are some postzygotic isolation mechanisms

Answer 11

• zygote death
• hybrid infertility (offspring cannot reproduce)
• hybrid inviability (lower fitness and or reproduction)

Question 12

What is speciation?

Answer 12

• The formation of new and distinct species in the course of evolution
• the process where one genetically cohesive population splits into 2 or more reproductively-isolated populations

Question 13

What is cladogenesis?

Answer 13

The branching or splitting of a lineage (species becomes 2)

Question 14

What is anagenesis?

Answer 14

Evolutionary change within a lineage, resulting in differences between sister lineages (changes over time)

Question 15

Allopatric Speciation

Answer 15

• when a single population becomes subdivided by a geographical barrier
• when they come back together they are no longer able to mate (different species)
• eg: mountains, water, natural disasters, habitat fragmentation

Question 16

Sympatric Speciation

Answer 16

• subgroups that can form within a continuous habitat (like cliques)
• if individuals in the subgroup stop mating with individuals of the larger population, they may eventually become a new species
• based on factors like selection of habitat, temporal isolation, and assortative mating

Question 17

Describe the Steps of Speciation

Answer 17

1. population becomes subdivided (geographically/physically or within a habitat)
2. more likely to mate with those in their subgroup and gene flow is reduced (pre-and/or postzygotic isolation)
3. microevolution independently acts on the subgroups
4. separate groups evolve and adapt to their local environment and become different from each other, mating no longer occurs between them (reproductive isolation)

Question 18

What is a Hybrid?

Answer 18

-the offspring formed when two genetically differentiated populations or species mate

Question 19

What characteristics of hybrids tell us that the two species that made it are distinct

Answer 19

Hybrid individuals being less viable or less reproductively successful

Question 20

Explain the different outcomes of hybridization in terms of how it affects speciation

Answer 20

1. Reinforcement- hybrids are crappy (inviable), therefore the behavioral, mechanical, and ecological isolation will be selected for and the species will remain separate (anagenesis goes into overdrive)
2. Fusion- hybrids are more fit than the original population, therefore they will form their own species and the parent species will disappear (two species become 1)
3. Stability-hybrids are meh (differences are not much better or much worse), the 2 species and the fit hybrids will remain stable and keep their differences because of lack of gene flow between them

Question 21

What evidence do we have of hybrids?

Answer 21

Introgression-incorporation of the genes from other species into the gene pool (movement of genes from one species to another species)

Question 22

What is gradualism and who supported this theory?

Answer 22

• slow differentiation by natural selection over many generations
• supported by Charles Darwin

Question 23

What is punctuated equilibrium and who supported this theory?

Answer 23

• speciation happens rapidly, followed by relatively long periods of stasis (no change)
• rapid changes in phenotypes and genetics can create many new species from one type
• happens under certain conditions like climate change
• shown on fossil record (one layer shows one morphology while the next shows another)
• supported by Stephen J Gould and Wiles Eldeledge