W12 L3 conservation genetic

Question 1

Extinction vortex

Answer 1

Small populations are prone to:
* Inbreeding
* Random genetic drift
* Loss of genetic variation
Can manifest as inbreeding depression
Can decrease adaptive potential to current and future environmental change (e.g. climate change)
Further increases extinction risk

Question 2

Mutation load

Answer 2

-The reduction in fitness caused by recurrent deleterious mutations
-Many new mutations are deleterious
-In large populations, mutation-selection balance keeps these deleterious mutations at low frequencies
-Most populations will have a low number of deleterious mutations e.g.cystic fibrosis allele in humans (~ 0.025)
-Inbreeding and genetic drift can increase the frequency of rare deleterious alleles, increasing the Genetic load

Question 3

Inbreeding

Answer 3

-mating between related individual
-More likely to occur in small populations even if mating is random
-Inbreeding decreases heterozygosity because related individuals are more likely to share the same alleles mate with each other
-alter genotype frequency, not alleles frequency

Question 4

why is heterozygousity important

Answer 4

-Low heterozygousity is linked to reduction in fitness. Bad for gene that have heterozygous advantage (over dominance )
-reduction in fitness due to homozygouity is dues to exposing harmful recessive alleles

Question 5

Inbreeding depression

Answer 5

The reduced biological fitness as a result of inbreeding, or breeding of related individuals
The magnitude of inbreeding depression
depends on:
* the inbreeding coefficient (F)
* number of harmful alleles segregating in the
genome (mutation load)
* proportion of harmful alleles that are recessive
* environment in which individuals are located

Question 6

Stress can increase inbreeding depression

Answer 6

The expression of genetic load may increase the sensitivity of inbred individuals to the physiological effects of environmental stress
Exposure to stressful environments may alter the genetic architecture underlying inbreeding depression

Question 7

Heterozygousity and extinction risk experiment

Answer 7

Heterozygosity was assessed in 42 populations of Finland butterfly
35 populations persisted
7 went extinct
-population with lower heterozygousity are more likely to be extinct
They then placed butterflies that were outbred or inbred by brother–sister mating into the field
All six inbred populations went extinct within 1 generation, while 4/6 outbred populations persisted

Question 8

Genetic diversity and extinction risk

Answer 8

• create bottleneck event for shrimp and place in stressful/ control environment
  -Most of the low diversity lines went extinct in the stressful environment
  -20% of the lowest diversity populations went extinct before the end of the study in non-stressful conditions
  -No high diversity lines went extinct in the stressful or permissive environment
  -change in fitness after 3 week, lower in low diversity, no change in high diversity pop > show diversity = better adaptation

Question 9

Neutral genetic diversity predicts selection response to stress and lower diversity increases extinction risk

Answer 9

• bottleneck drosophila and place under stressful condition
  -measure evolutionary respond and use DNA sequencing to see if neutral genetic diversity can predict selection respond
  -higher genetic respond tend to respond better than lower diversity

Question 10

Population fragmentation

Answer 10

Fragmentation can result in small, isolated populations
* Genetic drift and inbreeding (lower fitness, lower adaptive potential, increased extinction risk)
* Decreased chance of adaptation, because lower movement of adaptive alleles
* Increased chance of adaptive variation being lost
* Increased differentiation between populations that isn’t adaptive

Question 11

How population genetic help with conservation

Answer 11

Information on genetic drift and inbreeding: genetic variability
(Heterozygosity, number of alleles)
Population structure
Genetic management

Question 12

Case study: mountain Pygmy possum

Answer 12

-Initially described from fossils in the late 1800s
-Re-discovered in 1966 in a ski-hut on Mt Hotham
-Restricted to alpine/sub-alpine zone of Australia
-Hibernates under a cover of snow
-Prime habitat occurs in ski resort areas, loss of habitat and habitat fragmentation
-Numbers less than 2000, listed as critically endangered under the EPBC Act, IUCN Red List

Question 13

Inbreeding problem of mountain possum

Answer 13

-little to no gene flow between sub population
-genetic data was collected in mount buller
-by 2005, the census size was less than 20

Question 14

Way that we have tried to help the mountain possum

Answer 14

-Artificial boulder field to link habitat
-predation control program
-ski resort development regulation to protect habitat
-lead to small population size

Question 15

Genetic rescue

Answer 15

-Improvement in reproductive fitness and increase in genetic diversity through outcrossing a population suffering low genetic diversity and inbreeding depression
-Involves moving individuals from another population to a small, isolated population that is showing signs of low genetic variation or inbreeding
-Aims to alleviate detrimental genetic effects that arise in small fragmented populations such as inbreeding depression and reduced genetic variation
-The introduction of new genes into a small population counters the expression of deleterious genes (genetic load)
-Can also lead to genetic restoration by increasing levels of genetic variation and adaptive potential
-The aim is not to introduce a large numbers of individuals that will swamp locally adaptive variation, but to introduce enough beneficial genetic variation from a small number of immigrants
~ 5 immigrants per generation

Question 16

Risk of genetic rescue

Answer 16

-Risks of disease, pest and parasite spread
-Disrupting social systems in some animals
-Moving biological material across political jurisdictions
-Regulatory barriers
-Cost
-Emotional attachment
-Outbreeding depression

Question 17

Outbreeding depression

Answer 17

-Reducrion in fitness when crossing two population
-Genetic incompatibility can lead to outbreeding depression
-co-adapted gene complexes, selection for positive epistasis may result in the development of inquest co-adapted gene complexes within each isolated population
-adaptive differences among population

Question 18

Outbreeding depression is often overstated

Answer 18

-The effects if outbreeding might not be as severe as inbreeding and in populations with a high risk of extinction and the benefits may outweigh the risks
-Effects may not be long term. Natural selection will likely act on this variation and remove it.
-The hybrid populations may only go through a temporary decline in fitness and then an increase as the effects of inbreeding depression are decreased

Question 19

Assessing outbreeding risk

Answer 19

Increased risk of outbreeding depression when populations are from
* Increasingly distant geographic locations
* Increasingly different habitats
Crosses under common garden or field conditions
* Not always possible for species of immediate conservation concern
Risk factors
* Genetic differentiation
* Adapted to different habitats
Benefits often outweigh risks

Question 20

When is genetic rescue viable

Answer 20

-small isolated population
-low genetic variation due to inbreed
-availability of donor population
-will it lead to outbreeding depression

Question 21

Genetic rescue of the Pygmy

Answer 21

Wild translocation
* Males from central region to Mt Buller (Southern Region)
* Translocated 6 males from Mt Higginbotham in October 2010
* Repeated again in September 2011
* 4 produced F1 hybrids
* 6 more males were translocated from the central region in 2014

Question 22

Higher fitness in hybrids

Answer 22

All F1 hybrid females had a full-complement (four) of pouch young, whereas many non-hybrid females had less than four pouch young
Hybrids lived longer (2.78 years) compared to 1.8 years for non-hybrids
Four of the eight F1 hybrid females were still alive in spring 2015, whereas none of the 16 F1 non-hybrid females were known to be alive
No evidence of outbreeding depression!