Chapter

7.1. Although very few insect species have been evaluated, 72 per cent of those that have are classified as threatened. This, in conjunction with the high proportion of evaluated species that are threatened in other taxonomic groups, suggests that the demise of many species may be imminent.

7.2. A reduction in population size leads to an increase in the rate of genetic drift. Genetic drift reduces the diversity of populations through the loss of alleles. A reduction in alleles leads to an increase in homo-zogygosity, which in turn is a reflection of increased inbreeding because individuals will be more likely to share two copies of an allele that is identical by descent.

Polygynous

Population

Gene

mating

bottleneck

flow

system*

Small Ne

i

i

4

iNe 1

1 î Ne 1

| T VRS 1

4 Selection

4

i

4

i He 1

1 î He 1

1 4 Ne 1

| T Drift |

4

i

4

4

î AF 1

i AF

1 T AF 1

T AF

7.4. When inbreeding depression results from dominance, deleterious alleles are increasingly likely to be homozygous and therefore expressed, in which case they may be eliminated following natural selection, i.e. purged. In over-dominance, heterozygotes are fitter than homozygotes. Overdominance therefore requires both relevant alleles to be maintained within the population, meaning that there is no scope for the purging of deleterious alleles.

7.6. Founder effect, genetic swamping and outbreeding depression.

7.7. The most conservative approach would be to move only those individuals with haplotype 3 from Seymour Norte to Baltra. Because haplotype 3 has been found nowhere other than these two islands, it is reasonable to conclude that the Seymour Norte haplotype 3 individuals are direct descendants of the Baltra population that we introduced to that island in the 1930s. The individuals on Seymour Norte with haplotype 2, on the other hand, could have come from nearby Santa Cruz instead of Baltra and therefore may be less suitable for repopulating isla Baltra.

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