Sexual activity is predicted by digit ratio in rats

Area of Science:

• Endocrinology
• Behavioral Neuroscience
• Morphological Markers

Background:

• The second to fourth digit ratio (2D:4D) is a recognized marker of fetal sex steroid hormone exposure.
• Sexual dimorphism in 2D:4D ratio is observed in humans, with males typically exhibiting lower ratios due to higher prenatal androgen exposure.
• The relationship between 2D:4D ratio and sexual orientation in rodents remains largely unexplored.

Purpose of the Study:

• To investigate the relationship between the 2D:4D ratio and sexual behavior in a rat model.
• To determine if 2D:4D ratio can serve as a morphological marker for sexual activity and preference in rats.

Main Methods:

• Measurement of the 2D:4D ratio in male and female rats.
• Observation and quantification of male rat sexual behavior, including ejaculation during mating tests.
• Classification of male rats into long-2D and short-2D groups based on digit length.
• Assessment of olfactory preference for female odors in different 2D:4D ratio groups.

Main Results:

• Male rats displayed a significantly lower 2D:4D ratio compared to females, consistent with human patterns.
• Male rats that ejaculated during mating tests had shorter 2D lengths (lower 2D:4D ratio).
• Short-2D males demonstrated higher sexual activity and a preference for female odors compared to long-2D males.

Conclusions:

• Digit length, specifically the 2D:4D ratio, serves as a morphological marker for sexual activity and preference in male rats.
• These findings support the potential utility of the 2D:4D ratio as a tool for investigating the biological underpinnings of sexual orientation and behavior in animal models.