African Queens find mates when males are rare

Area of Science:

• Evolutionary biology
• Microbiology
• Insect ecology

Background:

• Male-killing endosymbionts in Lepidoptera are transmitted maternally.
• Successful parasite transmission depends on host mating success.
• Male-killing Spiroplasma in Danaus chrysippus can reduce male populations, potentially limiting transmission.

Purpose of the Study:

• To investigate if female mating success is a rate-limiting step for Spiroplasma transmission in Danaus chrysippus.
• To assess the impact of altered sex ratios on female mating success in the field.

Main Methods:

• Spermatophore counts were used to assess mating frequency in female Danaus chrysippus.
• Field studies were conducted at two East African sites with typically rare males.

Main Results:

• Mated females carried an average of 1.5 spermatophores, irrespective of male frequency.
• Only 10-20% of females remained unmated, even when males were scarce.

Conclusions:

• Female mating success in Danaus chrysippus is not significantly affected by male rarity.
• Spiroplasma transmission is likely not limited by mating opportunities for infected females.
• This finding helps explain the persistence of male-killing Spiroplasma in populations with skewed sex ratios.