Evolutionary Biology Test 3

Quantitative traits

• polygenic (multiple genes + alleles involved)

• additive genes underlie the traits

• environment affects also impact the phenotype observed

Modes of Selection for Quantitative Traits

• Directional: loss of variation, bell is moved to one direction

• Stabilizing: extremes are being selected against, bell is taller and skinnier

• Disruptive: 2 extremes are selected (happens with multiple niche polymorphisms)

Consequence of shifts (mean and variance)

• Directional: mean shifts, variance decreased

• Stabilizing: mean stays the same, variance decreased

• Disruptive: splitting of mean into 2, increased variance

Response to selection and Determinants/Characteristics

Alleles frequencies change in a predictable manner/fashion

Determinants/Characteristics:

• Relative fitness differential among/between genotypes (more off springs → allele transfer to next gen.)

• Heritability

• Starts fast and ends slow

Define Heritability

how much the trait of offspring is correlated to trait of parent

Components of phenotypes

P=G+E

P=G (Dom. & Additive effects) +E + GxE

Define adaptation

end result of natural selection… as a consequence the pop. has become better matched to its environment

Misconceptions about adaptation

not everything is an adaptation even though it may look so

• Exaptation: trait evolved for one reason but is advantageous for something else

• There are no perfect organism bc of constraints

Genetic constraints

• Conflicting selective pressures (environment is always changing)

• lack of genetic variation (has to be existing variation)

• negative genetic correlation

  • A single gen control 2 different traits but the effect on fitness is opposite

Frequency- Dependent Selection

the allele that is favored @ any given time is @ the lowest frequency as it increase the other traits is favored and the previous become less favored

Correlated Selection

traits that are beneficial, sometimes combinations of traits controlled by different genes, will confer together

Define group selection

sometimes used to explain altruistic (beneficial for others, not for the indiv.) traits/behaviors

group is what is being selected against/for based on the traits of the pop. compared to others

Consequences of Natural Selection

• Certain individuals with a lower fitness survive at a lower rate and have fewer off springs compared to the other groups of individuals

• Over time the “good” alleles increase in frequency and the “poor” alleles decrease

• Ultimately, most individuals in the pop. will have the “good” allele cause they are the only ones there

Basic Idea of group selection

• variation among groups in terms of fitness, that has to do with the presence of altruistic trait, becomes more predominant

• some groups propagate/survive at a higher rather than others

• ultimately all pops. with the favorable (altruistic trait) make up all groups across the entire landscape

• group level outpacing what’s happening on the individual level

Define species selection

• certain lineages go extinct or speciate/propagate at a faster rate than other species

Generalities of species distribution

Species biodiversity is not uniformly or randomly distributed across the world

• certain species exist in certain places and not in other places

Range distribution and Determinants

Where a particular species is known to exist geographically

• they can’t survive in other environments

• you are there because you could get there or originated there

Broad factors that determine species distribution

• Geography

  • Plate tectonics & continental drift

• Biological

Three main factors geologically that determines species distribution

• Plate tectonics/ Continental Drift

• Climate warming/cooling

• New land

Effects of Plate Tectonics/Continental Drift on geographic distribution

• Pangea → Laurasia + Gondwana → Current 7 Continents (cause rise to diff. species)

• Biological realms: centers of evolution, areas where the flora and fauna experience similar evolutionary histories in which characteristics flora and fauna evolve (similar characteristics)

Effects of climate warming/cooling on geographic distribution

Earth overtime has gotten much cooler/warmer over time

• Glaciation/glacial retreat

  • land mass → sea level relationships

    • as cool→ ice sheets at the poles get larger and cover areas that are not usually covered

    • sea levels drops → land mass increase (underwater lands become exposed)

• Land bridges: previous under water land is exposed, landmasses become connected (can change during warm periods)

  • Great American Exchange: NA & SA were connected allowing exchanging of mammals, more moved down because it was less hostile, and mammals did not have the cold or change in temp.

• Glacial refugia: as ice sheets covered areas that organisms lived, it caused them to go extinct, so these were areas where animals could go an still exist and is not have to worry about the ice sheets — they were pushed to habitable areas

Effects of climate new land on geographic distribution

caused by volcanic eruption

how animals get to the land

• birds

• rafting

• wind/storms

Three main factors (biologically) that determine species distribution

• Traits of species/adaptation

  • if you can exist in certain areas + continue to be there

  • would die if you can’t withstand the area

• Extinction

• Dispersal/Vicariance

Vicariance v. Dispersal

Vicariance: formerly connected area and animals occupied get split into section (naturally) → eventually diverge and become different species

Dispersal: organisms disperse and colonize a new spot disconnected from the original & eventually diversifies into a new species

List the common distribution patterns

• Endemic species

• cosmopolitan & ubiquitous

• disjunct

Describe endemic species

species that exits in one particular areas -scale dependent

• not random/islands tend to to have a larger # of endemic species

Determinants of endemic species

• Originated there and can’t go elsewhere

  • low dispersal ability (feeble disperser or barrier)

  • generalist/specialist (have very narrow ecological niches)

• Range collapse/shrinkage

  • due to changes to the landscape

Describe cosmppolitan & ubiquitous

• ubiquitous species is globally distributed in all kinds of habitats

• cosmopolitan species is globally distributed through only particular habitats (wherever the habitat occur)

Describe disjunct

species that are not-connected

What are the three other important concepts relating to species distribution

• Latitudinal gradients (relating to # of species)

  • # of species diversity inc. as you come towards the equator but decreases as you move away

    • may be because of a more benign climate

• Species Area/Distance

  • more species in a larger area and more if it is in an area that is a short distance from the mainland

• Theory of Island Biogeography

  • # of species on an island is a function of 2 balancing factors→ rate of immigration and rate of extinction

Define species and number of identified and believed species

means “kind”

1.8-2 million (currently named species)

8-10 million (# of believed species)

What does the majority of species consists of ?

2/3 are insects (~67%)

How were early species grouped and what were the caveats?

Grouped based off of resemblance, morphology and features

Problem

• They way things look does not represent same/different species

Ideas of species concepts & Consensus characteristics

Idea on how to group species

Shared elements:

• genetic cohesion separate from other populations

• share a gene pool separate from other groups and gene pools

• evolutionarily independent

Morphological Species concept aka morphospecies

Group them on similarity/dissimilarity of their morphology

• oldest form

• fast & easy approach

• useful for taxa that is very specious (lot of species)

• very straight fowards

Issues with morphological species concept

• lack of soft bodied fossils

• organisms can look alike but be different species

• organisms can look different but be the same species

• don’t necessarily fall into separate clusters

Biological Species Concept

reproductive isolation: organisms are different if they are reproductively isolated who can not hybridize/reproduce, if they do they are inviable

Issues with BSC

• some species hybridize yet still maintain their own unique gene pool

• doesn’t fit asexually reproducing organisms

• time specific → can only access reproductive isolation over a short time period

• problem of geography →

  • allopatric populations

  • sometimes yes/ sometimes no (occur in some spots and they hybridize/ other times they do not hybridize but occur together)

  • ring species: ancestral population exits, it expands in both directions around a barrier, gene flow, and when hey come back together they can no longer mate with each other

Phylogenetic Species Concept

Irreducible monophyletic groups: after grouping these species came to belong to one monophyletic group= a species

species are based off genetics, as long as they show up as their own monophyletic group

Issues with PSC

• Don’t have enough phylogenetic information for the vast number of species

• few species have bene identified down to an irreducible monophyly

• costly and time consuming

Novel/New approach of grouping species

Using a combination of data to identify species

Difficulty with grouping microbes

Change so readily, difficult to differentiate

Describe reproduction isolation prezygotic and postzygotic

Prezyogotic

• Pre-mating

  • Behavior isolation/different mating calls and strategies

  • Ecologically isolated

  • Mechanical Isolation

Postzygotic

• Instrinsic: internally → hybrid sterility or inviable

• Extrinsic: hybrid is sterile and inviable → they don’t mate or fit the environment (because they can’t)

Allopatric Speciation

gene pool is separated into sections by some barriers that prevents gen flow→ leading to them evolving independently & they become genetically + physically distinct

Vicariant vs. Dispersal (=Peripatict)

pat of the original gene pool goes off into an new area, there is no gene flow and they change genetically

nearly population that eventually changes

Parapatric Speciation

thing of that ring species where there is gene flow but speciation

less gene flow as geographic distance increases

IBD + natural selection outweighs the gene flow

Sympatric Speciation

when a population of individuals in the same area diverge (they split while occurring together)

Role of Assortative Mating

assortative mating can lead to sympatric speciation

Role of polyploidy

can result in instantaneous speciation → the individuals are no longer compatible with each other (if they are reproductively isolated)

Secondary contact & hybrid zone

previously separated species come in contact with each other again (secondary contact) which forms hybrid zones if there is hybridization

Outcomes of secondary contact and hybrid zones

• hybrids are less viable → marrow hybrid zones are

• hybrids do really well → gene pools come together → melded gene pool → new hybrid species

• hybrids are doing better than other species→ they’re on their own evolution tajectory → leading to 3 gene pools

Adaptive Radiation

“burst” of divergence/speciation over a short period of time

• short period of time involved

• production of many divergent lineages/species

• “ecological opportunity”

  • new niche spaces become available after extinction

  • new land forming

What is the rate of change across different taxa?

They have different rates

• rate of evol. changes across species/lineages varies

• speciation rate are not constant across taxa

Punctuated equilibrium vs Gradualism

Punc: evolutionary change and speciation occur simultaneously

Grad: evolutionary change is ongoing → by product change in species

Major order of primates

• Haplorrhini → Dry nose

• Strepsirrhini → Wet nose

55-110 mya

Major groups of Haplorrhines

• Tarsierformers

• Platyrrhinis (New World Monkey)

• Catyrrhinis (Old World Monkey and Apes)-humans are part of

Families of Hominoids

Hylabatidae

Hominidae

Polgidae → now a subfamily

Subfamilies of Hominoids

• Ponginae -arangatangs

• Homininea- great apes

3 genera of homininae

• homo

• pan

• gorilla

Divergence time of modern humans

300,000 years

Major groups of modern humans

• ardipithicus

• australopithicus

• homo erectus