Population structure and sexual maturity of Minuca vocator: insights from a Brazilian mangrove ecosystem

The population biology of the fiddler crab Minuca vocator was analysed in the mangroves of the Itanhaém Estuary (SP), Brazil, focusing on population structure, sex ratio, handedness, and morphological maturity. A total of 407 individuals were collected, with a male-biased sex ratio of 1:0.6 (M:F), significantly different from the expected 1:1 ratio (χ2 = 26.1; p < 0.05). Specimens were sexed and measured (CW: carapace width; AW: abdominal width of the 5th somite; and PL: propodus length of the major chela), using precision callipers or an image analysis system. The morphological maturity size was estimated at 9.9 mm for males and 10.9 mm for females. Relative growth analysis confirmed positive allometry for cheliped growth in males (b = 1.29 for juveniles and b = 1.88 for adults; F = 32.87; p < 0.001) and for abdomen in females (b = 1.52 for juveniles and b = 1.18 for adults; F = 39.99; p < 0.001). The population structure showed moderate negative skewness, with adults prevailing over juveniles. No significant handedness preference was observed among males, with a 1:1 ratio between right- and left-clawed individuals. A review of morphological maturity sizes in Brazilian fiddler crab species was provided to identify possible patterns for each sex. These findings highlight the importance of population studies for a better understanding of species life history traits and conservation strategies.