S4.5 Monday, Jan. 5 Osmoregulation in Insects CONTRERAS, HL*; BRADLEY, TJ; Univ. of California, Irvine; Univ. of California, Irvine firstname.lastname@example.org
Insects occupy thousands of ecological niches in terrestrial and aquatic habitats. In highly desiccating terrestrial environments, a major challenge is the acquisition of water. While most insects obtain water from their food, some can take up water from subsaturated air. This capacity has arisen several times independently. A second critical need for terrestrial insects is the production of concentrated excreta. This is achieved in the insects rectum. Freshwater insects face an entirely different physiological challenge, i.e. dilution of the hemolymph by osmotically-driven influxes of water across the external cuticle. The rectum in these insects plays an entirely different role, producing very dilute urine and preserving precious ions within the body in the process. Many aquatic insects also have specialized cells in the integument that actively transport ions into the hemolymph from the external medium. Such mechanisms have evolved independently in many insect orders. Both terrestrial and aquatic insects face an acute need to obtain sodium. To reduce the need for sodium, herbivorous insects use organic and often compatible solutes as major osmolytes in the hemolymph. This strategy is particularly well developed in highly derived insects such the lepidoptera and coleoptera. Although insects are conspicuously absent from the open oceans, insects can be quite abundant in inland saline waters. A number of distinct osmoregulatory strategies are found in these insect groups. The osmotic strategies found in extant insects will be discussed in an evolutionary and phylogenetic context.