Quiz 3 A1 Review Session PDF

Quiz 3 A1 Review Session Phylogenetics & Speciation 30 Qs with same usual format  Phylogeny & Evolutionary Inference Lineage: Series of ☆ Evolution: Descent with modification, ancestor & descendant meaning, modern species are d...

Quiz 3 A1 Review Session Phylogenetics & Speciation 30 Qs with same usual format  Phylogeny & Evolutionary Inference Lineage: Series of ☆ Evolution: Descent with modification, ancestor & descendant meaning, modern species are descended from populations ancestral species and change over time. ↳ We represent these evolutionary histories with Phylogenetic Trees utilizing any genetically Taxon: Any group determined trait (heritable trait) designated with a Key Terms: name 1. Root: Common ancestor of all species 2. Node: A splitting event: Speciation or Clade: Any taxon that consists of all gene duplication/divergence evolutionary descendants of a common ancestor Monophyletic: Contains an ancestor and all descendants of that ancestor; just a clade Polyphyletic: A group not including a common ancestor Paraphyletic: A group that does not include all the descendants of a common ancestor  Character & Character States Character & Character States: A character is a general structure/feature that may have different forms in different species. ↳ Ex: A character would be eye color, while the character state would be brown, blue, green. Or in this case, Present or Absent More closely related species share more characteristics with each other than other species Synapomorphies: Shared derived traits, providing evidence of common ancestry - Most are homologous structures Homologous Features are shared by two or more species and inherited from a common ancestor; they can be any heritable trait. ☆ All homologs are synapomorphies, but not always the other way around: EX: The absence of an anatomical feature, for example, can be an example of a synapomorphy but it’s not an example of a homologous feature because it must be a present anatomical part. Taxonomy & Principle of Parsimony Classification Levels: broad to specific Principle of Parsimony (Occam’s Razor): Best explanation for observed Domain - most broad observed data is the one with the Kingdom fewest evolutionary changes Phylum Typical reasoning used to make Class phylogenetic trees Order Family Genus Species - most specific Less evolutionary trait changes, more parsimonious More evolutionary trait changes Phylogenetic Trees 1. Choose a taxa - Ingroup: organisms of interest - Outgroup: similar organisms used to compare 2. Determine characters & characters states - Presence or absence of a selected derived trait 3. Organize and group taxa - Taxa that share derived character traits (synapomorphies) = more closely related - Taxa that lack derived character trait = less closely related 4. Build your tree - All taxa go on endpoints - Nodes = common synapomorphy for taxa above node - Synapomorphies appear only once on tree Building Phylogenetic Trees & Examples 1. Which synapomorphy unites pigeons and chimpanzees? A. Gizzard B. Claws or Nails C. Fur; mammary glands D. Feathers 2. Which of the following organisms is most closely related to the Pigeon in this tree? A. Lizard B. Crocodile C. Mouse D. Salamander  Species & Speciation ☆ What is a species? Groups of organisms that share genetic and morphological attributes and are reproductively isolated from other groups ↳ Speciation: Divergence in biological lineages and emergence of reproductive isolation between lineages Species Concepts are different ways of approaching the question of what 2. Lineage Species Concept: Conceptualizing species a species is by emphasizing different aspects of species or speciation: as branches on the tree of life - Each species has a 1. Morphological Species Concept: Grouping organisms based on history that starts with a speciation event: one lineage careful observations of phenotypic/morphological characteristics. is split in two and ends either at extinction or another - Benefits: Can be applied to individuals that are extinct or living. speciation event. a. Can be applied to organisms that reproduce sexually or asexually - Benefits: b. Importantly, it's the only concept that we can apply to fossils a. Accommodates asexual reproduction - Limitations: Difficult to apply to organisms which can be hard to b. Extends over evolutionary time observe or have few distinguishing features. - Limitations: a. As well, members of the same species don’t always look alike: a. Change is ongoing & some speciation events Polymorphisms can be slow b. Different species may look alike: Cryptic Species, two or more species that are morphologically indistinguishable but do not interbreed.  Species Concepts Cont. 3. Biological Species Concept: Groups organisms into groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups - Basically, individuals either live in the same area and breed, or don’t live in the same area, but if they did they would breed, but both ultimately produce viable, fertile offspring - Results in Reproductive Isolation: two groups of organisms that can no longer exchange genes. - Benefits: a. Confirms sustained lack of gene flow b. Provides mechanistic framework to assess evolutionary divergence in a meaningful way - Limitations: a. Only represents a single point in evolutionary time b. Does not apply to asexually reproducing organisms c. Impossible to test in fossils ☆ A feature shared by all three species concepts is that biological diversity does not vary incrementally. We have many ways to represent and understand species and speciation!  Species & Speciation Pt.2: ☆ First step of speciation process which leads to loss of gene flow between populations → Reproductive Isolation ↓ Dobzhansky-Muller Model: As a population becomes subdivided, as a consequence of an isolating event, the groups begin to evolve independently. ↳ In each new lineage, new alleles become fixed at new loci (ex: The red and black alleles in Group 1 vs. green and purple alleles in Group 2) ↳ The new alleles at the two loci are Genetically Incompatible with one another → This model suggests that while these new gene products are fine on their own, the proteins can no longer combine or interact meaning that Hybrids may be less fit.  How does the isolating event that leads to genetic divergence and reproductive isolation occur? 1. Allopatric Speciation: When a population becomes separated by a physical or geographic barrier (climatic, anthropogenic, etc.) to diverge into two species: ↳ Sister Species: Species that are each other's closest relatives may live on opposite sides of a geographic barrier due to this form of speciation! 2. Sympatric Speciation: Speciation without physical isolation ↳ Consider Disruptive Selection and how individuals with particular genotypes have preferences for microhabitats (still within the same environment) where mating occurs ↳ Polyploidy could also be a mechanism for this form of speciation, meaning gene duplications can lead to offspring that are reproductively isolated (often found in plants). Secondary Contact & Reproductive Isolation Species are geographically isolated (allopatric) Species come back into contact years after Leads to reproductive isolation - which can be reinforced or incomplete 2 Outcomes of reproductive isolation 1. If hybrid offspring are less fit than non hybrids, selection will favor no hybridization 2. Species can form hybrids Prezygotic Mechanisms Prezygotic Reproductive Isolation Mechanisms 1. Geographic isolation = same as allopatric speciation- populations isolated due to geographic barrier 2. Habitat isolation = 2 species or populations diverging live or prefer different habitats, they simply don't have the opportunity to encounter each other in their natural settings a. Dung beetles - specialize in different kinds of feces b. Tigers and lions - prefer very different habitats 3. Gametic Isolation = prevents reproduction, actual gametes do not fuse, viral chemical incompatibilities a. Sea urchins - release sperm and egg cells into the water and hopes they reproduce, important to have this trait of gametic isolation so ANY species can’t fertilize the gametes 4. Mechanical isolation = morphological variation in reproductive organs that does not allow them to come together a. Dragonflies - very different genitalia among species b. Plants - different structure prevents pollination from specific species 5. Temporal isolation = timing of reproduction for diff individuals or populations is different and so they cannot mate a. Coral species - live next to each other but release gametes at different times of the day 6. Behavioral isolation = individuals reject or fail to recognize mating behaviors of other species a. Bird mating patterns Postzygotic Mechanisms Postzygotic Reproductive Barriers - genetic differences in diverging lineages reducing fitness of hybrid offspring 1. Low hybrid zygote viability = hybrid zygote is not viable (does not survive) a. Sheep and goats - they can breed in the lab but they don't in natural populations and the zygote fails to develop 2. Low hybrid adult viability = zygote does develop into adult but hybrid offspring has developmental abnormalities but they don't typically survive into late adulthood 3. Hybrid infertility = hybrids may mature into infertile adults a. Mules - sterile due to number of chromosomes passed on from donkeys and horses breeding Q: Which mechanism, pre or post-zygotic is preferred for natural selection? Why? Q&A Time!