Care sheet guide by DartFrogsAndGeckos.com

Observations on Sex Ratios in Dart Frogs

Over the years, I have noticed significant sex ratio skews in certain frog species. Dendrobates tinctorius populations tend to be heavily female, whereas many thumbnail dart frogs lean male-heavy. These trends are consistent across breeders in the U.S. and Europe, suggesting that they stem from natural biological factors rather than diet, temperature, water pH, or other environmental influences.

Unusual Sex Ratios in Vietnamese Mossy Frogs

My work with Theloderma corticale (Vietnamese Mossy Frogs) revealed a striking male bias in captive-bred populations:

• My original imported group had a fairly balanced sex ratio.
• However, captive-bred offspring frequently resulted in 7 to 10 males per female.
• Reports from other breeders showed entire groups composed entirely of males.
• Interestingly, my breeding setup mirrored dart frog husbandry, with water temperatures around 72-74°F.

Discovery of Possible Temperature-Dependent Sex Determination (TSD)

While researching their natural history, I came across a Russian study on wild Theloderma corticale. The researchers observed:

• These frogs inhabit the highlands of Northern Vietnam, where temperatures are much cooler.
• The study proposed that mossy frogs might be temperature sex-determined (TSD)—a phenomenon well-documented in reptiles but rarely considered in amphibians.

Similar Findings in Cinnamon Frogs

I observed a similar male bias in Nyctixalus pictus (Cinnamon Frogs):

• Groups raised at standard temperatures (mid-70s°F) resulted in all-male offspring.
• Since this species also occurs at varying elevations, the exact environmental conditions of their wild populations remain uncertain.

Experimenting with Lower Temperatures

To test the TSD hypothesis, I intentionally lowered water temperatures during tadpole development:

Vietnamese Mossy Frog Experiment (2014-2015)

• Tadpoles raised in a cool basement closet (mid-to-upper 60s°F).
• Slower development: Up to one year to metamorphose.
• Preliminary results: 50% male, 50% undetermined (no calling males yet).

Cinnamon Frog Experiment (2015-2016)

• Tadpoles moved to a cooler area (70-72°F water temps).
• Results: Froglets matured in 4-5 months and successfully bred that fall.
• Significant increase in females in breeding groups.

Future Plans & Availability

Given these findings:

• I am raising a portion of my mossy frog tadpoles in cooler conditions to increase the female population.
• Due to longer development times, these individuals will be more expensive.
• While sex cannot be guaranteed, I am confident that cooler-reared juveniles will yield more females.

If further research confirms this trend, temperature-dependent sex determination in amphibians could have major implications for breeding programs worldwide.