Inbreeding and interbreeding in Darwin's finches

Area of Science:

• Evolutionary biology
• Population genetics
• Ecology

Background:

• Inbreeding and hybridization studies often use separate metrics, hindering integrated understanding of fitness variation.
• Fitness variation in populations is influenced by genetic and ecological factors, necessitating integrated research approaches.

Purpose of the Study:

• To integrate inbreeding and hybridization research by comparing their effects on Darwin's finch fitness using mean expected heterozygosity.
• To investigate the genetic and ecological basis of fitness variation in Geospiza scandens and Geospiza fortis.

Main Methods:

• Comparison of relative fitness of inbred finches and hybrids (backcrosses) against matched outbred controls.
• Utilizing mean expected heterozygosity as a metric to assess fitness across different genetic scenarios in Darwin's finches.

Main Results:

• Inbred finches exhibited relative fitness below one in both species (Geospiza scandens and Geospiza fortis).
• Inbreeding depression was more pronounced in Geospiza scandens, which has a smaller effective population size.
• Hybrids (backcrosses) of Geospiza scandens showed relative fitness greater than one, indicating heterosis, while Geospiza fortis showed mixed results.

Conclusions:

• Inbreeding negatively impacts Darwin's finch fitness, with severity linked to effective population size.
• Hybridization can enhance fitness by mitigating inbreeding depression and potentially through additive/nonadditive genetic effects or ecological adaptation.
• Different species exhibit distinct fitness responses to inbreeding and hybridization under similar environmental conditions.