Species & Species formation

Question 1

Biological species concept

Answer 1

If you can reproduce - 1 species; cannot reproduce - considered another species

BASED ON ABILITY TO REPRODUCE

Question 2

Biological Species Concept: Advantages

Answer 2

• Diagnose species that look the same
• Clear and easy; if they look the same, they are the same species

Question 3

Biological Species Concept: Disadvantages

Answer 3

1) Doesn’t apply to asexual species (def of species being if they can reproduce; if they are asexual they cannot reproduce)

2) Don’t work with fossils

3) Hybridization is common (individuals in diff pop interbreed/produce offspring)

4) Allopatry

Question 4

Allopatry “in a diff place”

Answer 4

two populations from same species geographically isolated, prevents inbreeding, leads to diff distinct species over time

= reproductive isolation

Question 5

Morphological Species Concept

Answer 5

Group individuals morphologically distinct from other groups (look different)
- way most species described today

Question 6

Morphological species: Advantages

Answer 6

• works on fossils
• easily identify species
• doesn’t require geographic overlap (when identifying physical appearance, doesn’t matter where lives)

Question 7

Morphological species: Disadvantages

Answer 7

• Geographic variation (species might be similar but genetically distinct due to isolation)
• Lack of variation (cryptic: look the same, genetically diff)
• Polymorphism within pop (diff phenotypes of same species)

Question 8

Phylogenetic species concept

Answer 8

the smallest group of organisms that share a common ancestor and can be distinguished from other such groups on a phylogenetic tree

Question 9

Phylogenetic species concept (Advantages)

Answer 9

• works on cryptic species (look the same)
• works on fossils
• works on asexual species
• works on species that do not have geographic overlap

Question 10

Phylogenetic species concept (Disadvantages)

Answer 10

• What characters should be used on phylogenetic tree? morphology? molecules? certain genes?
• What level of divergence? (what is the appropriate level of genetic divergence that constitutes a separate species)
• Incomplete lineage sorting (genetic variants aren’t always sorted from ancestral lineages to offspring - may throw off relationships of species)
• Gene tree/species tree conflict (“species tree” - a diagram representing the evolutionary relationships between different species, a “gene tree” depicts the evolutionary history of a specific gene across those species (gene tree may look diff due to gene flow, etc)

Question 11

General Lineage Concept

Answer 11

basically evolutionary species concept…
- species is defined as a single evolutionary lineage, meaning a group of organisms that share a common ancestry and are distinct from other lineages, essentially forming a separate branch on the tree of life

• lineage separation = the key factor in defining species boundaries, rather than relying solely on physical characteristics or reproductive isolation

Question 12

What makes general lineage concept different from evolutionary species concept

Answer 12

says that most major species concepts are

• not concepts they are all based on species as evolutionary lineages
• criteria for recognizing evolutionary lineages

Question 13

General lineage concept (Advantages)

Answer 13

• effort at unification
• Darwinian view of what species are (eschewing essentialism: speciation does not require necessary criteria)

Question 14

Evolutionary Species Concept

Answer 14

Species are evolutionary lineages; own evolutionary trajectory, separate from other species

Question 15

Evolutionary Species concept: Advantages

Answer 15

• Applies to fossils, asexual species, allopatric taxa
• incorporates phylogenetic perspectives to distinguish species in lineages

Question 16

Evolutionary Species concept: Disadvantages

Answer 16

• define appropriate criteria for lineage diagnosis
• If a single rat swims to an island and establishes a new population, according to the ESC, this could be considered a new species even if it is genetically very similar to the original population, raising questions about the practicality of applying this concept to such scenarios
• species are ephemeral “or short lived” if they are individual lineages; constant splitting/reemerging

Question 17

Example of Allopatric speciation - Snapping Shrimp

Answer 17

One species; land mass in-between; different clades on tree (Snapping Shrimp - Isthmus of Panama)

Question 18

Allopatric Example - Fruit Flies

Answer 18

every time disperse to new island; new species

Question 19

Parapatric Speciation

Answer 19

new species evolves from a continuous population; no geographic barrier

• individuals more likely to mate with geographic neighbors
  = leads to genetic divergence = reproductive isolation

***different parts of the population adapt to slightly different environmental conditions within their range, leading to the evolution of new species even though there is still some gene flow between them

Question 20

Example parapatric speciation

Answer 20

Sweet vernal grass:
- populations near mines (selection for tolerance to heavy metals)

• Populations in uncontaminated soil do not experience selection
• Both plants close enough to fertilize each other; but different flowering times (limits gene flow (interbreeding) between them) geographically overlapping, no completely separation, some gene flow
• overtime, selective pressures drive genetic divergence between pop (natural selection favors tolerance to heavy metals)
• could lead to reproductive isolation and speciation

Question 21

Sympatric Speciation

Answer 21

Evolution of separate species within a shared geographic range

Question 22

Example of Sympatric speciation

Answer 22

Apple maggot flies (Rhagoletis pomonella)
- R. pomonella originally fed on hawthorn fruits; apples introduced

• Host Plant shift: Segment of pop. adapted to using apples instead of hawthorns = two distinct groups
• Temporal Isolation: Hawfruits ripen later than apples – mate different times (reduces gene flow)
• Behavoral isolation: flies mate near host plan (reproductive isolation)
• Genetic divergence accumulated – smell their fruit, larvae survival on fruit
• two groups GEOGRAPHICALLY overlapping but REPRODUCTIVELY ISOLATED…

Question 23

Reproductive Isolation mechanisms

Answer 23

factors that cause individuals from different groups to either fail to mate; or fail to produce viable offspring

Question 24

Behavioral isolation
(Prezygotic Isolation = pre-mating isolation)

Answer 24

Individuals of different species do not recognize each other as potential mates

Question 25

Mechanical isolation
(Prezygotic Isolation = pre-mating isolation)

Answer 25

sex may occur but transfer of sperm does not take place

Question 26

Temporal isolation
(Prezygotic Isolation = pre-mating isolation)

Answer 26

individuals don’t mate because theyre active at different times (diff seasons perhaps)

Question 27

Pollinator isolation
(Prezygotic Isolation = pre-mating isolation)

Answer 27

Plants rely on different pollinators, or apply pollen to different parts of the same animal

Question 28

Zygotic mortality
(Post-zygotic Isolation (intrinsic))

Answer 28

egg fertilized, zygotę does not develop

Question 29

Hybrid inviability
(Post-zygotic Isolation (intrinsic))

Answer 29

hybrid embryo forms, but hybrid has developmental or physiological deficiency

Question 30

Hybrid sterility
(Post-zygotic Isolation (intrinsic))

Answer 30

Hybrid viable, but resulting adult is sterile
*example - donkey and horse makes a mule; mules sterile cannot reproduce

Question 31

Ecological inviability
(Post-zygotic Isolation (intrinsic))

Answer 31

Hybrids develop normally, but suffer low viability because they lack an ecological niche or do not make choices that confer high fitness

Question 32

What is fundamental to sympatric and parapatric speciation? Why?

Answer 32

Natural selection; it acts on variations within a population, allowing certain traits to become more prevalent in specific ecological niches, leading to reproductive isolation and the eventual formation of new species, even when populations are geographically close or overlapping

Question 33

If gene flow is present, Natural selection must be strong. Why?

Answer 33

Gene flow tries to homogenize genetic variation (or make it the same); Natural selection maintains distinct adaptations in different environments

• NS counteracts the mixing of genes and favors locally advantageous traits

Question 34

How does NS (usually) lead to speciation?

Answer 34

process of adaptation to diff environments —> evolution of reproductive isolation (by divergent traits between pop in diff environments) —> new species as a consequence

Question 35

Ecological Speciation

Answer 35

Barriers to gene flow evolve among populations as a result of ecologically-based divergent natural selection

different environments drive the evolution of traits that prevent individuals from different habitats from successfully breeding with each other, leading to the formation of new species

Question 36

Parallel Speciation

Answer 36

• two or more separate, closely related species independently evolve similar reproductive isolating mechanisms, essentially creating new species with similar traits due to facing similar environmental pressures in different geographic locations

Question 37

When two populations diverge in _______ (geographic isolation), and then come into secondary contact, forming a hybrid zone where hybrids are unfit, natural selection will favor individuals that choose mates from their ____ population, promoting the evolution of assortative mating, a process known as “_______” which further strengthens _______ between the species

Answer 37

allopatry

own

reinforcement

reproductive isolation