Inbreeding depression across a nutritional stress continuum.

Area of Science:

• Evolutionary biology
• Population genetics
• Ecology

Background:

• Natural populations face inbreeding and genetic drift due to factors like nonrandom mating or small population size.
• Environmental challenges can interact with increased homozygosity, leading to synergistic fitness declines.
• Previous studies on inbreeding-environment interactions often used limited stress levels, restricting detailed analysis.

Purpose of the Study:

• To investigate the synergistic effects of inbreeding and nutritional stress on fitness in Drosophila melanogaster.
• To quantify the impact of varying population sizes on inbreeding depression under different nutritional conditions.
• To elucidate the relationship between inbreeding depression and nutritional stress gradients.

Main Methods:

• Established replicate Drosophila melanogaster populations at three sizes (10, 50, 500) for 25 generations.
• Imposed a nutritional stress gradient using 11 yeast concentrations in developmental media.
• Assessed egg-to-adult viability and adult body mass to measure fitness consequences.

Main Results:

• Confirmed significant inbreeding-environment interactions affecting viability and body mass, with depression worsening under higher stress.
• Observed a steeper increase in inbreeding depression with nutritional stress in smaller populations (size 10) compared to larger ones (size 50).
• Identified a nonlinear relationship between inbreeding depression and nutritional stress, and a faster accumulation of lethal equivalents in smaller populations.

Conclusions:

• Inbreeding depression is exacerbated by higher nutritional stress levels.
• Smaller population sizes amplify the negative fitness consequences of inbreeding-environment interactions.
• The study provides strong evidence for pronounced deleterious effects of inbreeding-environment interactions under increased stress and inbreeding.