Sex determination in the common marmoset (Callithrix jacchus)

Area of Science:

• Primate Morphology
• Comparative Anatomy
• Reproductive Biology

Background:

• The external genitalia of non-human primates often present challenges for accurate sex determination.
• Morphological variations in primate genitalia can be subtle, particularly in younger individuals.
• Understanding these differences is crucial for research and conservation efforts involving common marmosets.

Purpose of the Study:

• To describe the morphological development of external genitalia in common marmosets (Callithrix jacchus) from birth to adulthood.
• To identify reliable external indicators for differentiating male and female common marmosets.
• To highlight the difficulties and provide accurate methods for sex determination in this species.

Main Methods:

• Gross morphological examination of external genitalia in 43 common marmosets of varying ages.
• Detailed observation and comparison of male and female genital structures.
• Documentation of key differentiating features for sex identification.

Main Results:

• At birth, male and female genitalia show superficial similarities, leading to potential misidentification.
• Testes descend into the scrotum between 8-11 months of age in males.
• Adult males have furless, nodule-covered scrotums, while females have pendulous pudendal pads with similar nodules; preputial and vestibular openings differ significantly.

Conclusions:

• Casual observation of common marmoset external genitalia can lead to significant errors in sex determination.
• Accurate sexing relies on specific morphological differences, including the preputial opening, presence of the glans penis, and testes palpation.
• These findings provide essential criteria for reliable sex identification in Callithrix jacchus research and management.