Heterosis without selectional coadaptation inDrosophila ananassae.

Area of Science:

• Population Genetics
• Evolutionary Biology
• Genetics

Background:

• Understanding the genetic basis of fitness and adaptation is crucial in evolutionary biology.
• Heterosis, or hybrid vigor, is a well-documented phenomenon where outbred organisms show improved traits.
• The role of chromosomal inversions in adaptation and heterosis remains an active area of research.

Purpose of the Study:

• To investigate the relative viabilities of homozygous and heterozygous karyotypes in Drosophila ananassae.
• To determine if chromosomal heterozygosity, particularly due to inversions, contributes to heterosis in interpopulation crosses.
• To assess the impact of geographic origin and selectional coadaptation on heterosis.

Main Methods:

• Crossed strains of Drosophila ananassae homozygous for specific gene orders (ST or inverted) on second and third chromosomes.
• Utilized strains from diverse geographic locations: India, Malaysia (Kuala Lumpur, Kota Kinabaru), and Thailand (Chian Mai).
• Measured relative viabilities of offspring from both interpopulation and intrapopulation crosses.

Main Results:

• Heterosis was observed in many interpopulation crosses, particularly those involving inversion heterozygotes from distant populations.
• Heterosis was notably absent in two intrapopulation crosses.
• The findings suggest that heterozygosity for numerous genes and gene complexes can confer high fitness.

Conclusions:

• Geographic distance and chromosomal heterozygosity, specifically inversion heterozygotes, are key factors driving heterosis in Drosophila ananassae.
• High fitness can be achieved through heterozygosis without the necessity of prior selectional coadaptation.
• This study provides evidence supporting the role of heterozygosity in promoting fitness in outbred populations.