Deep inside Silent Valley National Park in Kerala, scientists examining a small freshwater crab made an unexpected discovery. Three adult specimens of Vela carli, a species found nowhere else in the world, had both male and female reproductive organs on the same body.
The finding, published on 10 March in the international journal Crustaceana, marks the first recorded case of gynandromorphy in the entire freshwater crab family Gecarcinucidae. The study was carried out by researchers from the Zoological Survey of India and MES Mampad College, Calicut.
Crabs are typically easy to tell apart by sex. Males have narrower abdomens, larger claws, and specialised organs called pleopods used to transfer sperm during reproduction. Females carry eggs and have wider abdomens with distinct reproductive openings called gonopores.
The three Vela carli specimens fit neither category cleanly.
Each had pleopods, the male reproductive structures but none had the full set of four that a developed male crab would carry. One specimen had three pleopods, another had three but two were poorly formed, and the third had only two. All three also had gonopores, the female reproductive opening, though none were fully developed either.
Taken together, the researchers concluded these were gynandromorphic individuals, organisms displaying both male and female biological traits on the same body due to anomalies during early development.
“These three anomalous specimens appear to represent the first known cases of gynandromorphism in the freshwater crab family Gecarcinucidae,” the study stated.
Why Silent Valley Makes This Discovery Unusual
Gynandromorphy in crustaceans has been linked to chemical pollutants in other cases. Substances such as tributyltin and copper, found in contaminated water bodies, have been shown to disrupt reproductive development in aquatic animals.
But Silent Valley sits at the core of the Nilgiri Biosphere Reserve, India’s first biosphere reserve, and is one of the last undisturbed tracts of tropical evergreen forest in the Western Ghats. The researchers ruled out chemical pollution as a cause precisely because of where the crabs were collected.
“Since the gynandromorphs of V. carli were collected from the Silent Valley National Park, chemical pollutants are unlikely to have influenced the reproductive system of this species,” the paper stated.
Three Other Possible Causes
With pollution eliminated, the researchers explored three alternative explanations.
The first is early developmental error. Errors in embryo formation or cell division during the crab’s earliest growth stages could produce mixed reproductive structures. The second is hormonal imbalance, which has already been documented as a cause of androgyny in other crustacean species.
The third possible cause requires more research: climate-related stress. Temperature fluctuations and rainfall variation are known to affect sex determination and reproductive development in some animal species. Scientists noted this could warrant further investigation, particularly given the pace of environmental change across the Western Ghats.
Why a Tiny Crab in a Kerala Forest Matters
Vela carli is endemic to India, meaning it exists nowhere else on Earth. It lives in tree holes and small water bodies within the forests of Palakkad and Malappuram districts. Because of its restricted range and limited population, any biological discovery involving the species carries weight for conservation science.
The study fills a documented gap in crustacean research. Gynandromorphy has been recorded in insects, birds, and some crustaceans, but never before in this crab family. Understanding how and why it occurs in an isolated, pristine habitat adds a new dimension to the study of reproductive biology in freshwater species.
Silent Valley itself has a history of scientific and conservation significance. In the 1970s, a proposed dam on the Kunthipuzha River, which flows through the park, triggered the Save Silent Valley movement, one of India’s earliest environmental campaigns. The dam was abandoned. The park was declared a national park in 1984 and was recognised as part of the Western Ghats UNESCO World Heritage Site in 2012.
The crabs the researchers were examining had been living, largely undisturbed, in those same forests ever since.
