Sexually dimorphic characteristics and their functions in a native crab <i>Leptochryseus kuwaitense</i> (Jones &amp; Clayton, 1983) (Decapoda: Brachyura: Camptandriidae) from the Persian Gulf

Abstract Understanding population dynamics requires knowledge of reproductive aspects such as sexual maturity, fertility, and growth changes of body components. We analyzed the relative growth and morphometry in a native brachyuran crab, Leptochryseus kuwaitense (Jones &amp; Clayton, 1983), that dominates mud flats along the Iranian coast of the Persian Gulf and Gulf of Oman. The carapace (length, width, height, front), pleon (abdomen) (length and width of the first, third, fifth, and sixth segments), second, third, and fourth walking legs (total length, length, and width of the merus), cheliped propodus (length and width), and eye dimentions (distance between the two eyes and eye-stalk length), and total weight were recorded for 83 specimens. A regression model with a segmented relationship was employed to examine the relative growth patterns of the characteristics in question. The breakpoints identified in the analysis provided insights into the body size at which crabs attain sexual maturity. The carapace length of sexual morphometric maturity in males and females was 20.43 mm and 19.20 mm, respectively. Males exhibited a positive allometric growth for most traits, with adults having a greater slope than juveniles with the exception of body height, weight, and in some traits (e.g., cheliped length and width) this slope is more than double. By contrast, the growth equation for females is positive allometric for the majority of traits in juveniles, whereas were negative allometric in mature individuals. Juvenile individuals of both sexes exhibited morphological similarities, but females tended to have a smaller body size compared to males. The carapace length of the largest male was 24.2 mm (with mean of 21.71 mm, N = 43), 21.7 and (with mean of 20.14 mm, N = 40) for females, a characteristic that is likely associated with their reproductive biology. Because males are larger in body size, energy investment in the growth of walking legs and chelipeds may be crucial for mating and intreasexual cambating. The rate of growth thus exhibited a more rapid increase in males. Our results indicate that the chelipeds do not play a role in combat, but the coloration of the male cheliped plays a role in its selection by females.