Without Gills: Localization of Osmoregulatory Function in the CopepodEurytemora 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.

Evolutionary mechanisms of habitat invasions, using the copepodEurytemora affinisas a model system

“…Concordant with cases of physiological innovation deriving from arthropod appendages, the sites of ion uptake in the copepod Eurytemora affinis were found to occur in their swimming legs (Figs and ) (Johnson et al. ; Gerber et al. ).…”

Label-free microscopy and stress responses reveal the functional organization of Pseudodiaptomus marinus copepod myofibrils

“…In addition, we suggest that the flavin autofluorescence signal overlapping the SHG periodic signal reflects in calanoid P. marinus copepods the existence of intersarcomeric mitochondria which have not been observed in cyclopoid copepods M. albidus and in other crustaceans investigated. This discrepancy could be explained by the different behavior of canaloid and cyclopoid copepods species (Hwang and Turner, 2008), by the specific osmoregulatory capacities of euryhaline (such as P. marinus) versus fresh water (such as M. albidus) copepods (Johnson et al, 2014) or by the fact that fixation when above mentioned electron microscopy studies were performed left a lot to be desired. Thus some features, like subsequently described lattices at the Z-line level (Rowe, 1971), were simply not clearly visible in (Fahrenbach, 1963).…”

“…Euryhaline copepods such as Pseudodiaptomus marinus are able to survive a wide range of salinities. They have developed specific tissues and structures responsible for osmoregulation (Johnson et al, 2014). They exhibit different types of swimming behaviors, with rapid movements of short duration (Michalec et al, 2012).…”

Myofibril Changes in the Copepod Pseudodiaptomus marinus Exposed to Haline and Thermal Stresses

“…This region contains specific tissues that are specialized in ion transport and are responsible of osmoregulation in the calanoid copepod E . affinis [29]. This could explain that only this area was repeatedly affected (see Fig 2b and 2c).…”