Modelling problems in conservation genetics using Drosophila: consequences of fluctuating population sizes

Area of Science:

• Population genetics
• Conservation biology
• Evolutionary biology

Background:

• Natural populations frequently experience wide fluctuations in size.
• Such fluctuations are theoretically predicted to decrease effective population size, genetic variation, and fitness, while increasing inbreeding.

Purpose of the Study:

• To experimentally investigate the consequences of fluctuating population sizes (FPS) versus equal population sizes (EPS) on genetic diversity and fitness in Drosophila melanogaster.
• To compare empirical results with theoretical predictions regarding effective population size and genetic parameters.

Main Methods:

• Small populations of Drosophila melanogaster were maintained under two distinct size regimes: fluctuating (alternating between 7 and 1 pair) and equal (constant 4 pairs).
• Ten replicates of each treatment were maintained for eight generations.
• Genetic variation (allozyme heterozygosity), inbreeding coefficient, and relative fitness were measured.

Main Results:

• Fluctuating population size (FPS) resulted in significantly higher inbreeding coefficients (0.60) compared to equal population size (EPS) (0.38).
• FPS lines exhibited lower average allozyme heterozygosity (0.068) than EPS lines (0.131).
• Relative fitness was drastically reduced in FPS lines (0.03) compared to EPS lines (0.25).
• Estimated effective population sizes aligned with theoretical expectations for both FPS and EPS treatments.

Conclusions:

• Population size fluctuations significantly reduce genetic variation and fitness while increasing inbreeding.
• Management strategies for rare and endangered species should prioritize stable population sizes to mitigate negative genetic consequences.