title: Without gills: localization of osmoregulatory function in the copepod Eurytemora affinis.
abstract: The Pancrustacea, which include crustaceans and hexapods, have successfully colonized marine, freshwater, and terrestrial habitats. While members of the class Malacostraca (e.g., crabs, shrimp) often display immense osmoregulatory capacities, more basally branching crustaceans (e.g., copepods, branchiopods) tend to possess less-specialized osmoregulatory structures that have been poorly characterized. Remarkably, some of these more basal taxa have also colonized diverse habitats. For instance, the copepod Eurytemora affinis has recently invaded freshwater habitats multiple times independently but lack obvious osmoregulatory structures. To explore localization of ion exchange, we performed silver staining, immunohistochemical staining, and transmission electron microscopy. Our results revealed localization of ion transport within the maxillary glands and on four pairs of swimming legs. Silver staining revealed ion exchange at the maxillary pores and on the endopods and exopods of swimming legs P1 through P4. Immunohistochemical assays localized ion transport enzymes V-type H(+)-ATPase and Na(+)/K(+)-ATPase in the maxillary glands and swimming legs as well. Finally, transmission electron microscopy identified specialized ionocytes within these anatomical regions. These investigations uncovered novel osmoregulatory structures at the swimming legs, which we designate the "Crusalis organs." Our findings identified specific tissues specialized for ion transport, potentially enabling this small crustacean to rapidly transition into freshwater habitats.
authors.affiliation: Center of Rapid Evolution (CORE), University of Wisconsin, 430 Lincoln Drive, Madison, Wisconsin 53706; 2Equipe AEO, Adaptation Ecophysiologique et Ontogenèse, Unité Mixte de Recherche 5119 Ecolag UM2-CNRS-IRD-IFREMER, Université Montpellier 2, cc 092, Place E. Bataillon, 34095 Montpellier cedex 05, France.
authors.forename: Kelsey Elizabeth
authors.initials: KE
authors.lastname: Johnson
authors.forename: Lucile
authors.initials: L
authors.lastname: Perreau
authors.forename: Guy
authors.initials: G
authors.lastname: Charmantier
authors.forename: Mireille
authors.initials: M
authors.lastname: Charmantier-Daures
authors.forename: Carol Eunmi
authors.initials: CE
authors.lastname: Lee
mesh_terms: D000818:Animals; D033342:Copepoda / Q000378:metabolism* / Q000648:ultrastructure*; D007150:Immunohistochemistry; D007474:Ion Exchange; D046529:Microscopy, Electron, Transmission; D064587:Osmoregulation; D013045:Species Specificity