Understanding the Effects of Osmoregulatory Stress on Ion and Water Transport in Select Terrestrial and Aquatic Arthropods

Abstract

Arthropods including insects and crustaceans inhabit a wide range of environmental habitats and thus require fine-tuned mechanisms for ion and water balance (osmoregulation). Terrestrial insects face dehydration while freshwater insects face dilution of body fluids; both scenarios present challenges to osmoregulatory homeostasis. Adult female mosquitoes must deal with a salt and water load when blood feeding, while aquatic larval midges face a salt load from salinization of freshwater habitats. This research examined how transmembrane water channels known as aquaporins (AQPs) are involved in osmoregulation when arthropods face these challenges. The thesis focused on (1) AQP protein localization and abundance in adult mosquitoes (Aedes aegypti); (2) the effect of neurohormones on a specific AQP (AaAQP1) in mosquitoes; (3) cloning and characterization of a novel AQP from midge (Chironomus riparius) larvae; and (4) effects of road de-icers on osmoregulation in two freshwater arthropods, a crustacean (Hyalella azteca) and C. riparius larvae. In mosquitoes, AaAQP1 was localized to the apical membrane of the Malpighian tubules (MTs) while blood feeding had no effect on AaAQP1 localization or abundance. However, AaAQP1 proved to be vital for diuretic action of MTs. Starvation reduced AaAQP1 and AaAQP4 (another Ae. aegypti AQP) protein abundance in the male MTs, relative to sugar-fed males. In midge larvae, CrAQP2 expression was abundant in the MTs relative to other osmoregulatory organs and was salinity responsive in anal papillae and midgut. Knockdown of CrAQP2 expression resulted in dehydration of larval midges and survival decreased following 72-96hr de-icer exposure. Commercial de-icer containing beet juice caused profound changes in osmoregulatory parameters of H. azteca, including decreased activity of major enzymatic ion-transporters proving to be as harmful to freshwater amphipods as traditional de-icers. Overall, this thesis presents two significant advances in the field. Firstly, the characterization of AaAQP1 in the disease vector Ae. aegypti revealing a previously unknown role for an AQP in the diuretic and anti-diuretic hormone control of primary urine production. Secondly, this research uncovered the deleterious impact of a beet-juice based de-icer on the osmoregulatory physiology of representatives from two important aquatic arthropods, the larval insect C. riparius and the amphipod H. azteca.