title: Taking their breath away: metabolic responses to low-oxygen levels in anchialine shrimps (Crustacea: Atyidae and Alpheidae).
abstract: Crustaceans generally act as oxy-regulators, maintaining constant oxygen uptake as oxygen partial pressures decrease, but when a critical low level is reached, ventilation and aerobic metabolism shut down. Cave-adapted animals, including crustaceans, often show a reduced metabolic rate possibly owing in part to the hypoxic nature of such environments. However, metabolic rates have not been thoroughly explored in crustaceans from anchialine habitats (coastal ponds and caves), which can experience variable oxygenic regimes. Here, an atypical oxy-conforming pattern of oxygen uptake is reported in the Hawaiian anchialine atyid Halocaridina rubra, along with other unusual metabolic characteristics. Ventilatory rates are near-maximal in normoxia and did not increase appreciably as PO₂ declined, resulting in a decline in VO₂ during progressive hypoxia. Halocaridina rubra maintained in anoxic waters survived for seven days (the duration of the experiment) with no measureable oxygen uptake, suggesting a reliance on anaerobic metabolism. Supporting this, lactate dehydrogenase activity was high, even in normoxia, and oxygen debts were quickly repaid by an unusually extreme increase in oxygen uptake upon exposure to normoxia. In contrast, four related anchialine shrimp species from the Ryukyu Islands, Japan, exhibited physiological properties consistent with previously studied crustaceans. The unusual respiratory patterns found in H. rubra are discussed in the context of a trade-off in gill morphology for osmoregulatory ion transport vs. diffusion of respiratory gasses. Future focus on anchialine species may offer novel insight into the diversity of metabolic responses to hypoxia and other physiological challenges experienced by crustaceans.
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA; Molette Biology Laboratory for Environmental and Climate Change Studies, Auburn University, Auburn, AL 36849, USA. Electronic address: jhavird@auburn.edu.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Havird
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA; Molette Biology Laboratory for Environmental and Climate Change Studies, Auburn University, Auburn, AL 36849, USA.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Vaught
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA; Molette Biology Laboratory for Environmental and Climate Change Studies, Auburn University, Auburn, AL 36849, USA.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Weeks
authors.affiliation: University Education Center, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan; Marine Learning Center, 2-95-101 Miyagi, Chatan-cho, Okinawa 904-0113, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishihara-cho, Okinawa 903-0213, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Hidaka
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA; Molette Biology Laboratory for Environmental and Climate Change Studies, Auburn University, Auburn, AL 36849, USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Santos
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA.
authors.forename: Raymond P
authors.initials: RP
authors.lastname: Henry
mesh_terms: D052636:Allostasis; D000818:Animals; D059552:Caves; D033364:Decapoda / Q000201:enzymology / Q000502:physiology*; D004734:Energy Metabolism; D006254:Hawaii; D000860:Hypoxia; D007564:Japan; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D064587:Osmoregulation; D010101:Oxygen Consumption; D010802:Phylogeny; D061005:Ponds; D020545:Respiratory Mucosa / Q000502:physiology; D056152:Respiratory Rate; D013045:Species Specificity; D013312:Stress, Physiological; D016019:Survival Analysis; D015854:Up-Regulation
chemical_list: D007770:L-Lactate Dehydrogenase
keywords: Anaerobic metabolism; Anoxia; Antecaridina lauensis; Caridina rubella; Halocaridina rubra; Hypoxia; Lactate dehydrogenase (LDH); Metabetaeus minutus; Oxygen consumption; Respiration