Morphometric analysis of sexual dimorphism of Asellus aquaticus (Crustacea) at the micropopulation level

We carried out a comparative analysis of the morphometric structure and degree of sexual dimorphism in freshwater crustaceans Asellus aquatics from a small spring lake in the nature reserve “Golubye ozera”. On the example of micropopulations with different average seasonal density from two biocenoses: the algae Chara contraria (4.63 thousand ind./ m2) and leaf moss Fontinalis antipyretica (2.27 thousand ind./ m2 ), we considered dimensional characteristics of the body and limbs of sexually mature and pre-reproductive individuals. Differences in morphometric parameters between the sexes were analyzed using discriminant analysis and ANOVA. It was revealed that females and males significantly differ from each other in the length of the body, false-pincer (propodite L1) and carpopodite L5, as well as pleotelson width. The body size is subject to the greatest variance of the listed features. When compared at the micropopulation level, in females, the greatest load falls on the body length. In males, the aspecting signs of discrimination are the length of false-pincer and carpopodite L5. Differences in the coefficient of sexual dimorphism are most pronounced in the length of the false-pincer and carpopodite L5. Among the studied phenotypic traits, the head length demonstrates the smallest differences between the sexes and between individuals of the compared micropopulations. It is assumed that the spatial heterogeneity of the morphometric structure of crustaceans is due to different density of micropopulations and the regulatory mechanisms of fertility and behavior associated with it. Changing the size of females is a possible manifestation of the fertility regulation mechanism; in males, density affects behavioral responses that contribute to success in finding and retaining a partner at the precopula stage.