Species & Species formation Flashcards
Biological species concept
If you can reproduce - 1 species; cannot reproduce - considered another species
BASED ON ABILITY TO REPRODUCE
Biological Species Concept: Advantages
- Diagnose species that look the same
- Clear and easy; if they look the same, they are the same species
Biological Species Concept: Disadvantages
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
Allopatry “in a diff place”
two populations from same species geographically isolated, prevents inbreeding, leads to diff distinct species over time
= reproductive isolation
Morphological Species Concept
Group individuals morphologically distinct from other groups (look different)
- way most species described today
Morphological species: Advantages
- works on fossils
- easily identify species
- doesn’t require geographic overlap (when identifying physical appearance, doesn’t matter where lives)
Morphological species: Disadvantages
- 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)
Phylogenetic species concept
the smallest group of organisms that share a common ancestor and can be distinguished from other such groups on a phylogenetic tree
Phylogenetic species concept (Advantages)
- works on cryptic species (look the same)
- works on fossils
- works on asexual species
- works on species that do not have geographic overlap
Phylogenetic species concept (Disadvantages)
- 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)
General Lineage Concept
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
What makes general lineage concept different from evolutionary species concept
says that most major species concepts are
- not concepts they are all based on species as evolutionary lineages
- criteria for recognizing evolutionary lineages
General lineage concept (Advantages)
- effort at unification
- Darwinian view of what species are (eschewing essentialism: speciation does not require necessary criteria)
Evolutionary Species Concept
Species are evolutionary lineages; own evolutionary trajectory, separate from other species
Evolutionary Species concept: Advantages
- Applies to fossils, asexual species, allopatric taxa
- incorporates phylogenetic perspectives to distinguish species in lineages
Evolutionary Species concept: Disadvantages
- 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
Example of Allopatric speciation - Snapping Shrimp
One species; land mass in-between; different clades on tree (Snapping Shrimp - Isthmus of Panama)
Allopatric Example - Fruit Flies
every time disperse to new island; new species
Parapatric Speciation
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
Example parapatric speciation
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
Sympatric Speciation
Evolution of separate species within a shared geographic range
Example of Sympatric speciation
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…
Reproductive Isolation mechanisms
factors that cause individuals from different groups to either fail to mate; or fail to produce viable offspring
Behavioral isolation
(Prezygotic Isolation = pre-mating isolation)
Individuals of different species do not recognize each other as potential mates
Mechanical isolation
(Prezygotic Isolation = pre-mating isolation)
sex may occur but transfer of sperm does not take place
Temporal isolation
(Prezygotic Isolation = pre-mating isolation)
individuals don’t mate because theyre active at different times (diff seasons perhaps)
Pollinator isolation
(Prezygotic Isolation = pre-mating isolation)
Plants rely on different pollinators, or apply pollen to different parts of the same animal
Zygotic mortality
(Post-zygotic Isolation (intrinsic))
egg fertilized, zygotę does not develop
Hybrid inviability
(Post-zygotic Isolation (intrinsic))
hybrid embryo forms, but hybrid has developmental or physiological deficiency
Hybrid sterility
(Post-zygotic Isolation (intrinsic))
Hybrid viable, but resulting adult is sterile
*example - donkey and horse makes a mule; mules sterile cannot reproduce
Ecological inviability
(Post-zygotic Isolation (intrinsic))
Hybrids develop normally, but suffer low viability because they lack an ecological niche or do not make choices that confer high fitness
What is fundamental to sympatric and parapatric speciation? Why?
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
If gene flow is present, Natural selection must be strong. Why?
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
How does NS (usually) lead to speciation?
process of adaptation to diff environments —> evolution of reproductive isolation (by divergent traits between pop in diff environments) —> new species as a consequence
Ecological Speciation
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
Parallel Speciation
- 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
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
allopatry
own
reinforcement
reproductive isolation
