title: The mayfly nymphAustrophlebioides pusillusHarker defies common osmoregulatory assumptions.
abstract: Osmoregulation is a key physiological function, critical for homeostasis. The basic physiological mechanisms of osmoregulation are thought to be well established. However, through a series of experiments exposing the freshwater mayfly nymphAustrophlebioides pusillus(Ephemeroptera) to increasing salinities, we present research that challenges the extent of current understanding of the relationship between osmoregulation and mortality.A. pusillushad modelled 96 h LC10, LC50and LC99of 2.4, 4.8 and 10 g l-1added synthetic marine salt (SMS), respectively. They were strong osmoregulators. At aquarium water osmolality of 256 ± 3.12 mmol kg-1(±s.e.; equivalent to 10 g l-1added SMS), the haemolymph osmolality ofA. pusilluswas a much higher 401 ± 4.18 mmol kg-1(±s.e.). The osmoregulatory capacity ofA. pusillusdid not break down, even at the salinity corresponding to their LC99, thus their mortality at this concentration is due to factors other than increased internal osmotic pressure. No freshwater invertebrate has been previously reported as suffering mortality from rises in salinity that are well below the iso-osmotic point. Recently, studies have reported reduced abundance/richness of Ephemeroptera with slightly elevated salinity. Given that salinization is an increasing global threat to freshwaters, there is an urgent need for studies into the osmophysiology of the Ephemeroptera to determine if their loss at locations with slightly elevated salinity is a direct result of external salinity or other, possibly physiological, causes.
authors.affiliation: School of Life Sciences, University of Technology, Sydney, Science Building 7, Harris Street, Ultimo, New South Wales 2007, Australia; Unilever Centre for Environmental Water Quality, Institute for Water Research, Rhodes University, Old Geology Building, Artillery Road, Grahamstown, Eastern Cape 6139, South Africa.
authors.forename: Renee
authors.identifier: 0000-0003-2074-9943
authors.initials: R
authors.lastname: Dowse
authors.affiliation: Unilever Centre for Environmental Water Quality , Institute for Water Research, Rhodes University , Old Geology Building, Artillery Road, Grahamstown, Eastern Cape 6139 , South Africa.
authors.forename: Carolyn G
authors.initials: CG
authors.lastname: Palmer
authors.affiliation: Institute for Applied Ecology , University of Canberra , Building 3 , Canberra , Australian Capital Territory 2601 , Australia.
authors.forename: Kasey
authors.identifier: 0000-0003-2179-4893
authors.initials: K
authors.lastname: Hills
authors.affiliation: School of Life Sciences , University of Technology, Sydney , Science Building 7, Harris Street, Ultimo, New South Wales 2007 , Australia.
authors.forename: Fraser
authors.identifier: 0000-0002-9137-6948
authors.initials: F
authors.lastname: Torpy
authors.affiliation: Institute for Applied Ecology , University of Canberra , Building 3 , Canberra , Australian Capital Territory 2601 , Australia.
authors.forename: Ben J
authors.identifier: 0000-0001-6789-4254
authors.initials: BJ
authors.lastname: Kefford
keywords: Ephemeroptera; mayfly; osmolality; osmoregulation; salinization