Nath A., Priya T.A.J., Kappalli S.* 2023. On sexual maturity in male fiddler crab, Gelasimus hesperiae (Crane, 1975) (Brachyura: Ocypodidae) // Invertebrate Zoology. Vol.20. No.4: 417–432 [in English].

Marine Zoology Laboratory, Department of Zoology, School of Biological Sciences, Central University of Kerala, Kasaragod 671316, India.

* Corresponding author. E-mail:

doi: 10.15298/invertzool.20.4.07

ABSTRACT: Determining the sexual maturity of male fiddler crabs based on morphological observations is a challenging task. In this study, we attempted to determine the onset of sexual maturity in the male fiddler crab, Gelasimus hesperiae, by considering body morphometry and the morphological and histological characteristics of the reproductive system. Crabs with carapace lengths (CL) from 2.0 to 22.0 mm were randomly sampled from the field and measured for carapace widths (CW) and major propodus lengths (MPL). The onset of morphological sexual maturity (CL50) was determined to be CL 11.0 mm using a Lysack’s model, and accordingly, those crabs below CL 11.0 mm were designated as immature. Allometric growth estimation and regression analysis between the body morphometry of the immature and mature groups revealed a positive allometry between CL and MPL. Since, the reproductive system is not visible in immature stage 1 crabs (with CL < 7.0 mm), they were not considered for the analysis of physiological sexual maturity. Between the immature stage 2 (CL 7.1–11.0 mm) and mature groups (CL > 11.0 mm), there was a significant difference (p < 0.05) in the width of the testes, length and width of vas deferens, and length and width of the tubules of accessory sex gland. However, principal component analysis (PCA), revealed no discrete cluster formation between these groups, especially for the immature stage 2 crabs (CL 8.0–11.0) close to CL50. Further, histologically, the testes of these immature stage 2 crabs showed signs of spermatogenesis and spermiogenesis similar to that found in mature crabs, indicating the fulfilment of physiological sexual maturity. Overall, our results indicate that the commencement of physiological sexual maturity in male G. hesperiae precedes morphological sexual maturity, and hence, the external morphology cannot be considered as the sole criterion for determining the sexual maturity in this species.

KEY WORDS: Gelasimus hesperiae, morphometry, allometry, sexual maturity, male reproductive system.

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