Lecture 6 - Ecology and Evolution of Harvested Populations 2

how is harvesting determined?

by size thresholds and trophy ornaments

size threshold example

if larger than X it gets caught in the net and if its smaller it swims through the holes

trophy ornaments

the bigger a specific characteristic is the better, for example antler racks or horns in sheep

quantitative traits

phenotypes that vary continuously like size, mass, length, time to maturity and behavior

mendelian traits

traits that have discrete qualitative categories like eye color, tongue rolling, ear lobed ness and blood groups

quantitative traits architecture

• they are influenced by lots of genes and each one has a very small individual effect on the phenotype

• influenced by environment

discrete mendelian traits architecture

• cant infer genotype of a given gene from phenotype

• frequency of individual SNPs or alleles wont predict phenotypic values

how are quantitative traits medically relevant?

every health outcome is a quantitative trait because they are influenced by a lot of genes and have strong environmental influences (nature and nurture)

truncation/directional selection

a strong form of directional selection where individuals with phenotypes above the threshold die and those below it live

how is the intensity of selection measured?

by comparing the mean before and after selection

Atlantic cod

fish selected to be smaller and less abundant despite better growth conditions

what should we expect low density and warmer to promote?

• faster population growth

• larger sizes of individuals

because there is less competition for food source for the fish so more resources to go around per fish

why were the smaller fish harvest selected?

maybe due to fishing so overtime all the big fish have been caught already

fecundity

egg production

why was faster growth not observed in light of low density and warmer temperatures?

because the environmental forces pushing towards larger fish counteracted the evolutionary harvesting selection forces for smaller fish causing no net difference in fish size cause effects balance out

why was there no recovery in fish after a crash in growth due to selection?

because the continued fishing trapped the population in the region where smaller and less fecund fish are dominant slowing recovery of the population

what was the effect of the Mozambique civil war on elephants?

caused a dramatic reduction in elephants with tusks because of poaching where their tusks were removed and the overall decline in elephant population size ( abt 20K per year)

what is the main difference in tusks between males and females?

males tusks are larger than females

before war tusk percentages

70% females had 2 tusks and 18.5% no tusks

immediate survivors tusk percentages

41% have 2 tusks and 51% have no tusks

offspring of survivors tusk percentages

58% have 2 tusks and 33% have no tusks

why do tuskless individuals have a strong selective advantage?

because they don’t get poached so trait is better for survival, selective advantage not the result of a bottleneck

why are males 100% tusked?

because having tusks or no tusks is a dominant X-linked locus that is lethal in males so XY males (tuskless) are never observed because they die in utero

• female-biased sex ratio

x

tusks

X

no tusks

why are XX (no tusks) females never observed?

because it requires an X from a male but that is not possible because if they have that genotype they die in utero