Growth pattern and sexual dimorphism in life history of the freshwater crab Potamon ruttneri (Decapoda: Brachyura: Potamidae)

Brachyuran crabs due have a rigid and inextensible exoskeleton, discontinuous growth and parental care are ideal models for morphometric studies. Size at the onset of sexual maturity and patterns of relative growth are most important parameters for determining the reproductive potential and species survival. During development stages of freshwater crabs, the certain dimension of the body grows at different rates in proportion size, resulting in a phenomenon known as relative growth or allometry. Allometric growth is applied to identify immature of adult crabs and to show the difference in the growth patterns of the body parts in males and females. The difference in relative growth patterns between male and female crabs, for the size of chela and abdominal dimensions, represent sexual dimorphism and used to predict the size at the onset of maturity. The main purpose of this study is to provide an estimate for the onset of morphological sexual maturity in freshwater crab, Potamon ruttneri Pretzmann, 1962 based on relative growth. The species’ populations are isolated from each other by the two Qara-e-Qaˈm and Kavir Markazi drainage basins in northeast Iran. In total Seventy-eight specimens belong to ten populations were collected from Khorasan Razavi and Khorasan Jonubi Provinces. Eighteen morphological traits were measured from carapace, abdomen, and cheliped by digital caliper (0.01mm). For comparison and relative growth the power linearized lny= lna+blnx were used where y is the dependent variable, x is the independent variable and b is the allometric growth index. To evaluate the size at the onset of puberty, we used the piecewise linear regression analysis provided in the R environment v.3.2.5 and Multivariate Analysis of Variance (MANOVA) were used for determining sexual dimorphism between sexes performed in the SPSS v22. Based on the breakpoint of the regression line, carapace length at the onset of maturity in males was CL≥24.83 mm and in females was CL≥30.68 mm. Therefore females reached maturity at a larger size than males. The positive allometry growth in female’s abdominal dimensions is probably associated with the process of incubation the eggs to increase reproductive efficiency. On the other hand, positive allometric growth was observed in length and height of cheliped in both sexes which males are greater in terms of body size and cheliped traits than females, according to MANOVA analysis; representing a sexual dimorphism. Almost such differences have a protective and major role in agonistic and aggressive interactions during inter- and intraspecific competition for limited resources and retention of shelter. However, the growth of crustacean is also affected by different environmental factors such as temperature, precipitation, quality and availability of food.

Keywords:

Allometry growth , Sexual maturity , Freshwater crab , Potamon ruttneri