Chitin distribution in the Oithona digestive and reproductive systems revealed by fluorescence microscopy

Abstract

Among copepods, which are the most abundant animals on Earth, the genus Oithona is described as one of the most numerous and plays a major role in the marine food chain and biogeochemical cycles, particularly through the excretion of chitin-coated fecal pellets. Despite the morphology of several Oithona species is well known, knowledge of its internal anatomy and chitin distribution is still limited. To answer this problem, Oithona nana and O. similis individuals were stained by Wheat Germ Agglutinin-Fluorescein IsoThioCyanate (WGA-FITC) and DiAmidino-2-PhenylIndole (DAPI) for fluorescence microscopy observations. The image analyses allowed a new description of the organization and chitin content of the digestive and reproductive systems of Oithona male and female. Chitin microfibrils were found all along the digestive system from the stomach to the hindgut with a higher concentration at the peritrophic membrane of the anterior midgut. Several midgut shrinkages were observed and proposed to be involved in faecal pellet shaping and motion. Amorphous chitin structures were also found to be a major component of the ducts and seminal vesicles and receptacles. The rapid staining protocol we proposed allowed a new insight into the Oithona internal anatomy and highlighted the role of chitin in the digestion and reproduction. This method could be applied to a wide range of copepods in order to perform comparative anatomy analyses.

Chitin Synthases Are Critical for Reproduction, Molting, and Digestion in the Salmon Louse (Lepeophtheirus salmonis)

“…We detected chitin in the cuticle, eyes, ovaries, oviduct, oocytes, papilla, mouth tube, epithelial cells in the gut, and the fertilized egg string of L. salmonis. Chitin components have also been reported in these tissues and organs in pancrustaceans [ 48 , 49 , 50 , 51 ].…”

“…WGA staining is commonly used to analyze chitin levels. WGA staining has been documented in the integument and midgut of several arthropods [ 49 , 50 , 52 , 53 , 54 ], in the egg, eggshell, and ovaries of Aedes aegypti [ 48 ], and the reproductive organs in the copepods Oithona nana and Oithona similis [ 49 ]. Similar to our results in adult females, WGA staining has been detected in the cuticle, intestine, and reproductive organs of the copepods Oithona nana and Oithona similis .…”

“…Similar to our results in adult females, WGA staining has been detected in the cuticle, intestine, and reproductive organs of the copepods Oithona nana and Oithona similis . WGA staining was also detected in the reproductive system of Oithona males [ 49 ].…”

Male Differentiation in the Marine Copepod Oithona Nana Reveals the Development of a New Nervous Ganglion Linked to Lin12-Notch-Repeat Protein-Associated Proteolysis

“…Among them, the genus Oithona is described as having the highest numerical density [3], being the most cosmopolitan [4], and playing a key role as a secondary producer in the marine food web and in biogeochemical cycles [5]. Due to its importance and abundance, Oithona phylogeography, ecology, behavior, life cycle, anatomy, and genomics are well studied [6][7][8][9][10][11][12][13][14].…”

Male Differentiation in the Marine Copepod Oithona nana Reveals the Development of a New Nervous Ganglion and Lin12-Notch-Repeat Protein-Associated Proteolysis

“…Among them, the genus Oithona is described as having the highest numerical density [3], being the most cosmopolitan [4] and playing a key role as a secondary producer in the marine food web and in biogeochemical cycles [5]. Due to its importance and abundance, Oithona phylogeography, ecology, behavior, life cycle, anatomy, and genomics are well studied [6][7][8][9][10][11][12][13].…”