Changes in female colour across the ovulatory cycle in the brook stickleback, Culaea inconstans (Kirtland)

Abstract

The colour signal of the female brook stickleback (Culaea inconstans) is a mosaic of five components: intensity (1) and distribution (2) of black colouration on the body, presence or absence of gold colouration on the body (3), degree of development of the black eye bar (4), and colour intensity of the black dorsal spines (5). These components interact to produce three mosaics corresponding to the stage reached by a female in her ovulatory cycle. Nonbreeding individuals display a silver ventral surface, grey–green dorsal and lateral surfaces bearing dark grey, reticulate variegations, no eye bars, and noncoloured fins and spines. Interspawning-interval females develop a silvery gold ventral surface, light grey, spotted dorsal and lateral surfaces, narrow eye bars, noncoloured fins, and dark spines. The intensity of a female's body and spine colour is positively correlated with her aggressive response to an intruding male. Spine colour intensity is also positively correlated with her aggressive response to an intruding female. Courting females project a distinct signal comprising a pink–gold body, medium grey dorsal and lateral swirls, no eye bars, and noncoloured fins and spines. The golden courting female contrasts with the velvety black courting male, enhancing the exchange of information about species, sex, and sexual motivation via the two nuptial signals.