E106 Quiz 4 (Lec 11-12)

Aging

Age-related loss of physiological integrity, impaired function, and increased vulnerability to death

• Growing older in some cases decreases vulnerability to death (young mortality as offspring)

Hallmarks of aging

• Genomic instability

• Telomere attrition

• Epigenetic alterations

• Loss of protein homeostasis

• Deregulated nutrient sensing

• Mitochondrial dysfunction

• Cellular senescence

• Stem cell exhaustion

• Altered intercellular communiction

Genomic instability

Accumulation of DNA damage & mutations

• As you age —> more DNA damages as it divides —> adverse effects

Telomere attrition

Telomere shortening each time cell divides/DNA replicated —> DNA Damage

Epigenetic alterations

Modifications that alter activity without changing DNA sequence

• Age —> epigenetic disruption disrupted —> changes in gene expression —> cells don’t function as well as before

Loss of protein homeostasis

Protein synthesis folding/degradation

• Age —> accumulate misfolded protein —> less protein quality

Deregulated nutrient sensing

Diff ways for cells to detect nutrient availabililty, regulation

• Systems break down —> metabolic imbalance

Mitochondria dysfunction

Aging declines function with mDNA —> decreased energy production and cell function

Cellular senescence

Cells enter G0 state (quiescence) —> no longer divides

• Issues with regeneration and healing

Stem cell exhaustion

Helps with tissue repair and regeneration

• Decline in function over time —> slow healing

Altered intercellular communication

Cells and tissues constantly communicate with each other —> less effective as we age

• Impair physiological responses (stimuli, wound healing, body)

Trade-offs

Live fast and die young vs. live slow and die old

• Rates of process = rate of chance

  • Faster an organism lives/reproduce — > faster it gains damage that leads to aging

• Age of reproduction can be selected for

4 Evolutionary explanations for aging

1. Senescence allows for new generations to thrive

2. Benign neglect - selection overlooks the old

3. Trade-off - live now, pay later

4. Body as a vehicle for reproduction

Senescence allows new generations to thrive (NOT EXPLANATION)

Senescence: biological process of aging

• Early explanation

• Programmed

• Limits population size, accelerates generational turnover

• Old ones have to die for the new ones to open up more resources for younger generations

• Senescence doesn’t contribute to mortality (external factors) - most species don’t die of old age

REASON: Mortality in wild is high & senescence rarelly occurs

• Programmed to reduce population size and maintain generational tunrover

1. Enhance survival of relatives

Adaptive suicide: older adults sacrifice themselves for the good of the rest of their lineage

• Senescent/diseased indvls leave the group

• E. coli, bees, aphids

• Prevents infection

Post-reproductive caregivers: indvls no longer can reproduce —> takes care of offspring/relatives

• Intergenerational care

• Enhances fitness of related indvls

• genes shouldn’t enhance aging (loss of function) through maintaining non-reproductive indvls can be beneficial, especially for humans

Adaptive suicide

older adults sacrifice themselves for the good of the rest of their lineage

• Senescent/diseased indvls leave the group

• E. coli, bees, aphids

• Prevents infection

Post-reproductive caregivers

indvls no longer can reproduce —> takes care of offspring/relatives

• Intergenerational care

• Enhances fitness of related indvls

2. Benign neglect - selection overlooks the old

• Selection maximizes reproductive output

• Weak selection on post-reproductive indvls —> so intensity of selection declines with age

  • Once indvls are post-reproduce —> things that kill them at old age not going to impact their fitness (reproduce)

• Selection shadow: Selection can’t see/affect deleterious mutations whose effects are confined to later ages

Selection shadow

Selection can’t see/affect deleterious mutations whose effects are confined to later ages

3. Tradeoff - live now, pay later

• Genes favor early survival and reproduction

• Early reproductive success at the cost of later success

• Not just different selective pressures for early vs. late reproduction - actual cost later in life related to early success

• Adaptive pleiotropy: a gene affecting more than one trait

Adaptive pleiotropy

a gene affecting more than one trait

• Ex. calcium helpful for developing bones when young but harmful for old in arteries

4. Body as a vehicle for reproduction

Goal of evolution is to pass on genetic material

• Fitness: the reproductive capability of an organism and its contribution to the gene pool

• Germ (reproductive) cells are what matter —> the body (somatic) is just a vehicle

• Meiosis: process that produces 4 haploid (N) cells from a diploid cell (2n)

• Allocation of energy/ resources towards reproductive, not maintenance of the body (DNA repair, radical oxygen species)

Resource allocation: Decline of DNA repair —> more mutations —> aging —> accumulation of mutations, genomic arrangements —> de-regulation of transcription impaired stress response

Meiosis

process that produces 4 haploid (N) cells from a diploid cell (2n)

Biodiversity

A contraction of biological diversity: variety of live at all levels of biological organization

• Ecosystem —> species —> genetic —> molecular

Biodiversity hotspots

• Covers only 2.3% of Earth’s surface

• Home to 42% of terrestrial vertebrate species and 50% of plants

Quantifying biodiversity

Species richness (S)

Evenness (J)

Shannon diversity index (H’) combines S & J (0 < H’ < ln[S])

Species richness (S)

number of species

Evenness (J)

Distribution of abundance across species (0 < J < 1)

Ex) Forest A: Contains 10 oaks, 10 maples, 10 birches, 10 pines, and 10 willows. This area has high species evenness because all species are represented equally.

• Forest B: Contains 46 oaks, 1 maple, 1 birch, 1 pine, and 1 willow. This area has low species evenness because the oak is heavily dominant, making the other species rare.

Shannon diversity index (H’)

combines species richness and evenness

Why are there so many species?

1. Consumers and trophic relationships

2. Plant diversity drives animal diversity

3. Complex food webs confer stability

4. Changes in diversity with latitude

5. Species-area relationships

6. Niche differences between species

Niche partitioning - how it affects biodiversity

Competitive exclusion: species use the same resources

Coexistence: can occur when species use different resources

Disturbance - how it affects biodiversity

Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment

ex) big boulders don’t roll as much as small ones —> crush species like se anemones, urchins

Consumers - how it affects biodiversity

• Starfish (keystone species)

  • Remove —> mussels accumulate —> less of other species

Productivity - how it affects biodiversity

Rate of generation of biomass in an ecosystem

• Productivity increase/more species can coexist (plant —> herbivores —> carnivores)

• Diversity within trophic levels

• Relationship between nutrients and diversity

Diversity affects productivity

Changes in biodiversity affect ecosystem processes such as biomass accumulation and resource use

• Ex) Plant root depth: Diff plant species have roots that reach diff depths. (Grass roots shallow + Dandelion roots deep)

  • Help reach nitrate

Complementarity: species complement each other with respect to their ecological roles

Sampling effect/ species identity effect: a more diverse community has a greater chance of containing a species with a big effect

Complementarity

species complement each other with respect to their ecological roles

Sampling effect/ species identity effect

a more diverse community has a greater chance of containing a species with a big effect