Life history and reproductive biology of a unique arboreal freshwater crab, Kani maranjandu Kumar, Raj & Ng, 2017 (Decapoda: Brachyura: Gecarcinucidae), from the Western Ghats, India.

We present the first comprehensive account of the reproductive biology of Kani maranjandu Kumar, Raj & Ng, 2017, a unique tree-dwelling gecarcinucid freshwater crab endemic to the southern Western Ghats of Kerala, India. As the only known exclusive arboreal freshwater crab, the species exhibits remarkable reproductive adaptations associated with a phytotelmic lifestyle. We investigated the mating patterns, gonadosomatic index (GSI), breeding seasonality, sex ratio, fecundity, gonadal maturation, size at first maturity, parental care, and life cycle through monthly sampling from September 2021 to August 2022. The available evidence suggests that K. maranjandu appears to exhibit a soft-female mating system, with mating occurring between post-moult females and intermoult males from January to February. Peak GSI values were observed in December for males (0.9059 ± 0.1235) and January for females (2.4102 ± 0.1641), indicating a distinct breeding season extending from December to May, coinciding with pre-monsoon rains. The overall sex ratio was 1F:0.79M. Mean fecundity was low (23.3 ± 5.61), consistent with phytotelmic habitat constraints, but increased significantly with female body size (R² = 0.91). Juvenile- carrying females appeared from March to June, peaking in April. Histological analyses identified five ovarian stages and three testicular stages, revealing typical gametogenic progression. Reproductive organs were compact and dorsolaterally arranged, possibly facilitating arboreal mobility. Size at first maturity was estimated at 29.97 mm CW in males, 32.57 mm CW in females. Females guarded the eggs and hatchlings within tree holes for 40 ± 4.5 days until juvenile release during the onset of monsoon rains in June. These reproductive traits appear to be adapted to the spatially isolated, predator-sheltered canopy microhabitats. The species’ relatively low fecundity, habitat specialization, and restricted distribution may increase its vulnerability to habitat disturbance and changing rainfall regimes, emphasizing the need for baseline data for conservation and long-term monitoring.