Evolution Test 4 part 2

Cervical vertebrae in mammals example of development affecting the course of evolution

Birds and reptiles vary dramatically in number of cervical (neck) vertebrae b/c hox genes are just responsible for segment identity. Almost all mammals have seven cervical vertebrae b/c their hox genes are responsible for both segment identity and cell proliferation

Recurrent laryngeal nerve of giraffes example of development affecting the course of evolution

The laryngeal nerve always has to go behind part of the circulatory system, making the laryngeal nerve in giraffes very inefficient

Loss of eyes in cavefish example of development affecting the course of evolution

Surface fish got into caves and evolved to have no eyes b/c of a faulty lens. Pax6 expression is required for proper eye development but pax6 is expressed less in cave fish b/c Pax6 is inhibited by Shh expression. Shh is overexpressed in the cave fish b/c increasing Shh increases the number of olfactory receptors

Loss of denticles in Drosophila larvae example of development affecting the course of evolution

D. sechellia lost their denticles b/c they evolved to be resistant to acid in fruit, change is on X chromosome, used deficiency screening to see that it’s a change in shaven baby gene. Three different enhancers were modified to reduce expression of shaven baby gene, proving that it’s likely not because of drift, it’s because of positive selection

Denticles

hair-like structures that helped Drosophila larvae gain traction when they move around in their food

shaven baby gene

Shaven baby produces hairs, less shaven baby expression = less hairs

Deficiency screening

Uses gaps in chromosomes to locate the gene that controls a certain trait by observing whether a missing region reveals a recessive trait

Evolutionary hotspots

genes where mutations can produce large, visible changes in form while minimizing harmful side effects on other traits

Pleiotropy

when a gene (or an allele) has an effect on more than one developmental or physiological process, typically affecting more than one trait

reciprocal selection

selection occurring in two species based on their interactions

Coevolution requires

genetic variation

Why not just evolve resistance?

Resistance has a cost due to pleiotropy

Positive/Positive Mutualism

an interaction between two different species where both organisms benefit, increasing their survival, growth, or reproduction

examples of positive/positive mutualism

Pollination, Seed dispersal, Mycorrhizal associations (fungi and roots), Rhizobia bacteria in root nodules

Positive/Neutral Commensualism

one organism (the commensal) benefits while the other (the host) is neither helped nor harmed

examples of Positive/Neutral commensualism

Remora on a shark

Negative/Positive Antagonism

an interaction between organisms so that one organism benefits at the expense of another

examples of Negative/Positive Antagonism

Predators and prey, Deceptive pollination, Host and parasite

Coevolutionary alteration

a species (parasite or predator) evolves by shifting its interaction between several different host or prey species over generations

Negative frequency-dependent selection

common, relative fitness goes down because more parasites are attacking it; rare, relative fitness goes up because less parasites are after it

Balancing Selection

a polymorphism is maintained in the population by natural selection.

mechanisms of balancing selection

Negative frequency-dependent selection, Heterozygote Advantage

Deception pollination in Elderflower Orchids example of antagonistic interaction

Elderflower orchids can be yellow or purple, doesn’t produce nectar but mimics plants that do. By maintaining two different colors, the orchid prevents pollinators from quickly learning to avoid them

Coevolutionary arms race

antagonistic interactions lead to directional selection in each species

Rough-skinned newt example of coevolutionary arms race

newts have a warning coloration (aposematism), telling predators that the species is toxic, but predators (snakes) evolved resistance to the toxin. The cost is that the snakes that are resistant are slow

virulence

the degree of damage or severity caused by a microorganism (bacteria, virus, fungus, parasite) to its host

optimal virulence

intermediate level of harmfulness that maximizes transmission while balancing host mortality, ensuring the pathogen spreads effectively before the host dies or recovers, happens if Virulence and transmission are positively correlated

Myxoma virus eradication strategy of optimal virulence

Myxoma virus was used to kill invasive rabbits, was very lethal, but virus doesn’t want to kill host too quickly b/c that cuts down on the amount of transmission of the virus

plants

nonmotile, desiccation-resistant, structurally reinforced, photosynthetic organisms with cellulosic walls

Stomata

openings in a plant to regulate the water balance

Xylem

Water transport system in a plant

Lignin

Chemical reinforcement that strengthens cell walls and allows plants to resist forces

dangers of living on land for a plant

atmosphere is dry, can’t get CO2 without losing water, no more currents to aid dispersal, no more buoyancy to help stay up

Cuticle

wavy outer layer that keeps leaves and stems from drying out

Clades of land plants diversity levels

Most species angiosperms, then Bryophytes, Ferns, Lycophytes, least is Gymnosperms

First unambiguous spores (spores belonging to a land plant)

475Ma in Libya

First unambiguous sporophytes (sporophytes belonging to a land plant)

430Ma they were Cooksonia

First seeds

390Ma in West Virginia, they were Elkinsia

First trees

380Ma, they were Archaeopteris

Cambrian explosion for plants

Devonian

Rynie Chert

Early Devonian fossil deposit near Rhynie, Scotland. Discovered in 1912 by William Mackie, when he found strange rocks that were actually early plants preserved in Chert

things preserved in Rynie Chert

nonvascular plants with spores and vascular plants with small leaves, members of mosses/liverworts, lycopods, fungi, and animals (webless arachnid inside a plant stem)

Arborescent Lycopods

30m tall trees with very little wood and branching. Grew fast and didn’t live long, made coal

Extinction selectivity

the non-random, trait-based survival of species, where certain ecological, physiological, or morphological traits make taxa more likely to go extinct or survive

“Live fast die young” plants

Drought-vulnerable but could move lots of water, usually went extinct and safer plants survived

Bolide impact that killed dinosaurs made us …

an Angiosperm world

Evidence for angiosperms evolving during the Cretaceous

Mesofossils in material from the Cretaceous that was traditionally disregarded show angiosperms, and we found grass fossils in dinosaur poop

Mesofossils

small, fragmented plant or animal remains, typically measured in millimeters

Gnetales are not related to Angiosperm because

they’re conifers