Testing the Adaptive Sterilization Hypothesis in Mice Inoculated with Chlamydia muridarum

Area of Science:

• Evolutionary Biology
• Microbiology
• Reproductive Biology

Background:

• The adaptive sterilization hypothesis proposes that sexually transmitted infections (STIs) causing infertility may be evolutionary adaptations.
• Some STIs induce tubal occlusion, leading to infertility and potentially increasing mating frequency in affected females.

Purpose of the Study:

• To investigate if female mice infected with Chlamydia muridarum exhibit increased mating frequency compared to controls.
• To test if tubal occlusion caused by Chlamydia infection influences mating behavior to enhance pathogen transmissibility.

Main Methods:

• Female mice were inoculated with Chlamydia muridarum or sterile saline.
• Infected mice were monitored for reproductive tract damage, infertility, and mating behavior over 90 days.
• Mating frequency and litter sizes were compared between infected and control groups.

Main Results:

• Female mice with Chlamydia-induced tubal infertility mated significantly more frequently than fertile females and saline controls.
• Chlamydia infection led to oviductal damage and infertility, while ovarian function and mating activity were maintained.
• Fertile infected females with unilateral tubal occlusion showed reduced litter sizes and a tendency for fewer weaned pups.

Conclusions:

• Chlamydia-induced tubal infertility in mice is associated with increased mating frequency, consistent with the adaptive sterilization hypothesis.
• These findings suggest that STIs might evolve mechanisms to increase host mating behavior, thereby enhancing their own transmission.
• Further research is needed to confirm increased sexual transmissibility and promiscuity in freely breeding populations.