Morphological differences between females of different Jaera species (Crustacea: Asellota: Isopoda) in the White Sea: a possible solution to an old problem

It is well known that females of "Jaera albifrons" species complex cannot be determined on the basis of morphological analysis. In this work, an attempt to separate females of three Jaera species on the basis of morphometric characters, the length of so-called "coupling zones" (CZ), was made. Coupling zones are those parts of the partners' bodies that contact during copulation. Female CZ is a region between the posterior edge of the pleotelson and the border between the fourth and the fifth thoracic segments, where openings of dorsal vaginas are situated. Male CZ extends from the anterior edge of the cephalon to the first abdominal segment carrying the copulative organ. Absolute and relative lengths of CZ were used. The latter was calculated as ratio of absolute length of CZ to body length. Two settlements of Jaera in the White Sea were studied for 3 years. Species composition of these populations was quite different (the first one was dominated by J. ischiosetosa and the second by J. albifrons and, 1 year by J. praehirsuta). Males of different species were shown to be distinct in terms of absolute and relative length of CZ. Frequency distributions of absolute and relative CZ length of females differed significantly in the two settlements. The experiments based on male choice in mixed samples were organized. They revealed that females chosen by males of different species differ significantly by CZ parameters. [PUBLICATION ABSTRACT]