Lecture 8 Take Home Points
•
Genetic Stochasticity
-Random fluctuation in allele frequencies can lead to loss of particular genotypes and fixation of particular traits.
-Small founder populations inherently contain limited genetic diversity, and inbreeding and genetic drift can enhance the loss of diversity.
-Inbreeding: Populations that have a high frequency of closely related individuals can suffer from inbreeding. In inbred populations, deleterious alleles can be exposed in homozygous individuals, which may reduce fitness. The importance of inbreeding varies with species.
Potential Genetic Consequences of Invasion
Genetic Bottleneck and Founder Effect
Constrained genetic diversity – small population sample
Genetic Drift
Random loss of alleles in small populations
Inbreeding Depression
Consequences of deleterious recessive genes becoming apparent through inbreeding
Genetic Hotspots
Repeated introductions lead to hyperdiversity and the potential for novel invasive genotypes
Genetic Diversity and Invasion
Invasions often involve a small sample of the original population
Through random chance, can over or underrepresent particular genotypes
Are Bottlenecks Bad for Invaders?
Yes
Reduced genetic diversity
Less for selection to act on, thus less responsive to variable environments
Expression of deleterious alleles through inbreeding
Inbreeding depression and No
Genetic ‘purging’
Advantage of relatedness
Many invasive species are not really bottlenecked
Genetic purging – moderately inbred populations can shed deleterious alleles over several generations as selection acts against them. After a number of generations, the fitness increases to that of outbred populations.
Harmonia axyridis (Harlequin lady beetle)
Underwent a bottleneck of intermediate intensity
Related individuals had an increased probability of mating, increasing the homozygosity of the population.

Deleterious recessive alleles were then purged from the from population after ~15 generations because once exposed (as a homozygous recessive), natural selection eliminated them