Lecture 14 Flashcards
What is altruistic behaviour and give an example
- self-sacrificing behaviour
- helping others at personal cost
ex.
- birds feeding or protecting offspring from another nest
- warning calls in birds or mammals to alert others of a predator approaching
- helping to attack and “mob” a predator to drive it away
How can you explain the existence of altruistic behaviours in some animals?
- most cases in animal studies determine that altruism usually happens in support of CLOSE GENETIC RELATIVES (also known as “kin”)
What is inclusive fitness?
- direct fitness + infirect fitness
WILLIAM HAMILTON redefined fitness based on both components
What is the concept of “Kin selection”
- selection arising from the indirect benefits of helping relatives raise offspring, rather than reproducing yourself is often the result of altruistic behaviour
What is the Hamilton RUle
- an altruistic allele can increase in frequency when: relatedness*benefit is greater than the cost
- rB > C
where:
r = the coefficient of relatedness
B = the benefit to the recipient
C = the cost to the altruist
Review the coefficient of relatedness
- fraction of genes shared
r = 0.5 with offsprings and full siblings
r = 0.25 with grandchildren and half siblings, nephews and nieces
r = 0.125 with great-grandchildren and cousins
- identical twins are close to 1.0 (100%) genomically the same, but will change over time due to mutations, and other genetic (epigenetic) and environmental factors
Why is the frequency of alarm calling the highest in females of reproductive age?
- the males migrate to other areas when they mature
- the females stay close to the area of the offsprings therefore they protect them with the alarm callings
that is why many “neighbours” are their own offspring and other close genetic relatives (kin)
Do black-tailed prairie dogs prefer to help relatives when they give an alarm call? - answer the conclusion of the experiment
Hypothesis: individuals give an alarm call only when close relatives are near
Null Hypothesis: the presence of relatives has no influence on the probability of alarm calling
Experimental setup:
1. Determine relationships among individuals in prairie dog coterie
2. Drag stuffed badger across territory of coterie
3. From observation tower, record which members of coterie give an alarm call
4. Repeat experiment 698 times. Each prairie dog coterie is tested 6-9 times over a 3-year period
Prediction of Kin-selection Hypothesis : indivudlas in coteries that contain a close genetic relative are more likely to give an alarm call than individuals in coteries that do not contain a close genetic relative
Prediction of null hypothesis: the presence of relatives in coteries will not influence the probability of alarm calling
Conclusion: Alarm calling usually benefits relatives. More callings with relatives or offsprings around
What does the Hamilton’s rule do and does not do?
- does NOT help animals make decisions consciously
- DOES provide a model for understanding how genes that contribute to altruism can increase through kin selection
Define fitness
- an individual’s contribution of genes to the next generation, relative to other individuals in the population
What are the direct and indirect ways an individual can maximize his or her own fitness?
Directly
- by contributing to the survival and reproductive success of one’s own offspring
Indirectly
- by contributing to the survival and reproductive success of close relatives or kin with shared genes
NOTE: fitness is relative. An individual or group’s fitness is always compared with other individuals or groups
Give an example of inclusive fitness
two male turkeys displaying together to attract femals. Even if only 1 brother (r=0.5) mates, the non-mating male still gets a genetic benefit in the next population from genes shared with brother’s offspring (nephews and nieves) : each with r=0.25
review the florida scrub jays defending their nest (helper research)
Florida scrub jays defending their nest (which contains four young hidden under the mother). The father is crouched on top of the mother. Their helper is two-year-old bachelor at the right. Most helpers are prior offspring of the mated couple, but this one is a brother of the breeding male.
What is genetic drift?
- genetic drift is a change in allele frequencies due to CHANCE events (random sampling errors)
ex. changes in allele frequency that are random and are not the result of fitness advantages/disadvantages
does genetic drift affect small or large populations more
- the effects of genetic drift are strongest in very small populations
Does genetic drift reduce or increase genetic diversity
- reduces genetic diversity population because it can fix alleles or eliminate them
When is an allele fixed?
- an allele is fixed when it has a frequency of 1,0 or 100% (and the other allele is now 0=lost)
- the overall effect is to REDUCE GENETIC DIVERSITY, which has conservation implications
When does the founder effect occur?
- occurs when a few individuals become isolated from a larger population and start a new small population
- ex. finches blown onto small islands
- allele frequencies in the small founder population can be DIFFERENT (“sampling error” like drift) form those in the larger parent population (reduced number of alleles due to small founder population)
- reduced genetic diversity and new gene pool is the result
What is the likely fate of most founder populations?
local EXTINCTION (extirpation)
What happens when a large population becomes small very quickly and what is the population called?
allele frequencies may change due to chance events (sampling errors again)
- remember the diagram (rare yellow balls (alleles) are more rare compared to blue, and the whites are more likely to be “missed” by sampling error)
What is the bottleneck effect
- a sudden reduction in population size due to a change in the environment (disease, parasites, climate, etc)
- the resulting smaller gene pool may have lost some rare alleles
- if the population remains small, it may be further affected by genetic drift and inbreeding
how were cheetahs affected through the bottleneck effect?
- cheetahs went though bottleneck, very low genetic variability, and more prone to extinction, leads to CONSERVATION CONCERNS
Explain the bottleneck effect using the exmaple with Northern Elephant Seals at the Pacific Coast
- pop reduced to perhaps 20 individuals in 1890s due to hunting
- current population ranges from 30000 to 100000
- scientists examined 24 genes but found no allelic variation (each gene had only 1 allele)
- this is HIGH HOMOZYGOSITY (fixed and lost alleles) as would be predicted by genetic drift theory and bottlenecking
What is mutation
Ultimate source of heritable variations
What are the 3 things that mutation can be
- Deleterious (genetic diseases)
- Neutral (MN blood alleles and many others)
- Beneficial (may produce adaptive change)
What are the 3 different levels that mutation can act on?
- point mutations of DNA (change in nucleotides)
- gene duplication (chromosome pieces copied)
- genome duplication (polyploidy, multiple copies of whole genomes)
What is an important point about mutation?
- only mutations that occur in germ lines (ex. cells that produce gametes and offsprings) are passed onto the next generation
What is an error of meiosis?
- if homologous chromosomes fail to separate, the gametes may be diploid (2N) instead of haploid (n)
- failure of cell division after chromosome duplication gives rise to tetraploid tissue
