Sex ratio and sexual selection in wormshrimps (Crustacea, Amphipoda,

Small populations of several species of the groundwater dwell-ing amphipod genus Ingolfi ella are found in caves, wells, seabot-toms, beaches and riverbed interstitial habitats. To gain insight in the socio-ecology of these elusive species, we used data from collected specimens to explore the relationships between sex-ratios, display of secondary sexual characters and other morpho-logical features, and habitat use. We extracted data on the sex ratios and the presence-absence of secondary sexual characters of 13 species from the literature and through examination of museum material. We found a clearly skewed sex ratio with a preponderance of females, both in the individual species as in the genus as a whole. However, sex ratio and the display of secondary sexual characters were not correlated, nor did these characters correlate with the amount of sexual dimorphism. I