Mate choice for male and female size in aquatic isopod Idotea balthica

: Jormalainen V, Tuomi J, Merilaita S

Publisher: FINNISH ZOOLOGICAL BOTANICAL PUBLISHING BOARD

: 1992

: Annales Zoologici Fennici

: ANNALES ZOOLOGICI FENNICI

: ANN ZOOL FENN

: 29

: 3

: 161

: 167

: 7

: 0003-455X

: 1797-2450

In laboratory tests the pair formation of the sexually size dimorphic and colour polymorphic isopod Idotea balthica was non-random with respect to size, whereas colouration had hardly any effect on mate choice. When given a choice of two females, 70% of the males selected the larger female for precopula. In experimental populations, however, female size had no evident effect on mate choice, so that further confounding effects may complicate the pair formation in natural heterogenous habitats. Precopulatory males were larger than solitary males in the experimental populations, both in female- and male-biased populations. The larger size of precopulatory males may at least partly result from male-male competition, but the females may also affect the precopulatory success of the males in a size-dependent manner. Consequently, presumably both intrasexual and intersexual interactions favour larger males in I. balthica. Female size, on the other hand, may be only a second choice after female maturity. The male-biased sex ratio in early summer may in particular discourage males from being too size selective.