Evaluating the capability of organisms to adapt and persist in face of environmental change is critical for assessing risk of biodiversity loss. Freshwater salinization has severe consequences for lake environments, aquatic organisms, and the services they provide. Although the number of studies investigating the ecological impacts of freshwater salinization is steadily rising, our understanding of the capacity of the adaptive potential of aquatic organisms to increasing freshwater salinity remains limited.  We used Daphnia pulicaria/pulex, a ubiquitous herbivorous zooplankter found across North America and Europe, to assess intraspecific variation in tolerance to acute exposures of NaCl. We isolated 95 iso-female lines from 59 lakes and assessed survival after 48-hr exposure to chloride concentrations ranging from 18 to 2700 mg/L.  We detected high variation in survival among iso-female lines; LC₅₀ (the chloride concentration where 50% of organisms die) ranged from 675 to 2763 mgCl^-/L, and had a coefficient of variation equal to 30%. Survival was influenced by test media chloride concentration and lake chloride concentration. For lakes with multiple iso-female lines, we found that variation within lakes was much less than variation among lakes. High genetic variation in salt tolerance among D. pulicaria across regions suggests that local adaptation to increasing salinity may be possible if dispersal is high enough to allow the movement of salt-tolerant genotypes.

Authors:

Shelley Arnott, Queen's University  (arnotts@queensu.ca)

Alison Derry, UQAM  (derry.alison@uqam.ca)

Pedro Manoel, Queen's University  (pedrosartori.bio@gmail.com)

Carlos Barata, Institute of Environmental Assessment and Water Institute  (carlos.barata@idaea.csic.es)

Julien Beaulieu, UQAM  (julien-beaulieu@hotmail.ca)

Lisa Cicchetti, Queen's  (21lec5@queensu.ca)

Sarah Cook, Trent University  (scook@trentu.ca)

Amy Downing, Ohio Wesleyan University  (aldownin@owu.edu)

Kameron Finch, State University of New York - Fredonia  (finc4977@fredonia.edu)

Justin Gross, Queen's University  (justin.gross@queensu.ca)

Jana Isanta-Navarro, University of Copenhagen  (jana.isanta-navarro@bio.ku.dk)

Brieanna Limkilde, Toronto Metropolitan University  (brie.limkilde@torontomu.ca)

Stephanie Melles, Toronto Metropolitan University  (stephanie.melles@torontomu.ca)

Michael Pfrender, University of Notre Dame  (Michael.Pfrender.1@nd.edu)

Paula Redondo, IMDEA  (paula.redondo@imdea.org)

Catherine Searle, Purdue  (searlec@purdue.edu)

Ben Berman, Queen's University  (ben.berman@queensu.ca)

Christopher Steiner, Wayne State University  (csteiner@wayne.edu)

Pablo Urrutia Cordero, IMDEA  (pablo.urrutia@imdea.org)

Paul Frost, Trent University  (paulfrost@trentu.ca)

Courtney Wigdahl-Perry, The State University of New York at Fredonia  (Courtney.Wigdahl@fredonia.edu)