Pigmentation polymorphism of <i>Dikerogammarus villosus</i> (Amphipoda, Crustacea) from the Kuban River, Caucasus

Abstract

The purpose of this work was to determine the number of morphs and their ratio in the population of Dikerogammarus villosus from the Kuban River, as well as to establish color indicators and the total number of hemocytes in each morph. Amphipods were caught for study in the vicinity of the city of Krasnodar at the confluence of Lake Staraya Kuban with the Kuban River in 2023 and 2024. The analysis of color indicators was carried out using Adobe Photoshop (CIELab) and GIMP software. The total number of hemocytes was determined after the acclimation of individuals to laboratory conditions, which was performed for three days. In the Kuban River, D. villosus was found to be characterized by 4 types of pigment distribution: spotted or patterned (S), homogeneous pigmentation – melanin (M), with dorsal stripes (B) and amber (A). Based on this, we identified four morphs. At the same time, in the morphs with dorsal stripes, we identified two sub–morphs: B1 with wide pigment stripes along the entire pereon, and B2 with thin pigment stripes. The ratio (%) of morphs was as follows: B – 72.1, S – 16.0, M – 7.7, A – 3.3, and T – 0.9. There were no differences in color indices between the morphs, but statistically significant differences were found between morph M and the other morphs in color brightness, the melanin morph was 1.5 times darker as compared to morphs B and S (p 0.005). The total number of D. villosus hemocytes widely ranged from 2480 to 9020 pcs/ml, averaging 4858 ± 1684 pcs/ml. No correlations between the size of individuals and the number of hemocytes were established (p 0.05). There were also no differences in the number of hemocytes between males and females (p 0.05). Hematological variations between the five morphs were not statistically significant either (p = 0.36). Thus, for the first time, the ratio of amphipod morphs of the species D. villosus from the plain part of the lower reaches of Kuban River was determined. Data on the color indices of morphs and the total number of hemocytes of this species are presented.