True polyandry and pseudopolyandry: why does a monandrous fly remate?

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Genetics

Background:

• Female remating rates significantly influence species dynamics, including family conflict, population viability, and gene flow.
• Accurate determination of polyandry is challenging, with mating system data often limited or based on single experiments.
• Contradictory reports on Drosophila subobscura mating systems (monandrous vs. polyandrous) necessitate further investigation.

Purpose of the Study:

• To investigate the mating system of Drosophila subobscura, specifically female remating propensity under various laboratory conditions.
• To differentiate between true polyandry (remating after successful insemination) and pseudopolyandry (remating after failed insemination).
• To compare mating behaviors between English and Greek populations of Drosophila subobscura.

Main Methods:

• Laboratory experiments assessed female Drosophila subobscura willingness to remate under controlled conditions.
• Distinction was made between true polyandry and pseudopolyandry based on the success of the initial mating.
• Male responses to prior exposure to rivals were analyzed, comparing copulation duration in English and Greek populations.

Main Results:

• A low rate of true polyandry (4%) was observed, unaffected by population origin (England vs. Greece) but influenced by temperature.
• Pseudopolyandry was three times more frequent than true polyandry, often occurring after the first mating opportunity post-insemination failure.
• Male responses to rivals differed between populations; English males increased copulation duration after one rival, while Greek males required four or more, suggesting non-sperm competition drivers.

Conclusions:

• Determining a species' mating system, even in well-studied organisms like Drosophila subobscura, is complex and highly dependent on experimental conditions and population origin.
• Observed male responses to rivals in Drosophila subobscura are unlikely to be driven by sperm competition due to the rarity of polyandry and population-specific responses.
• The study underscores the variability in mating behaviors and the challenges in generalizing findings across populations and experimental setups.