Morphological and molecular characterization of adults and larvae of Crassicauda spp. (Nematoda: Spirurida) from Mediterranean fin whales Balaenoptera physalus (Linnaeus, 1758)

Abstract

Crassicauda boopis is known to infect the kidneys and vascular system of mysticetes included Balaenoptera physalus and has been recently reported in Mediterranean waters. Identification at the species level relies on the observation of morphological features of the adult parasites, but field conditions during necropsy and the massive reaction of the host's immune system often prevent optimal conservation of the extremities. Moreover, larval stages of Crassicauda have never been described and no sequences are available in public databases to help such identification. Adult and larvae of Crassicauda were isolated from four specimens of B . physalus and studied with morphological and molecular techniques. Specimens of C . anthonyi , C . grampicola and Crassicauda sp. isolated from Ziphius cavirostris , Grampus griseus , Stenella coeruleoalba and Tursiops truncatus respectively were studied as well. Sequences of nuclear markers 18S and ITS-2 and of mitochondrial gene cox1 were obtained and phylogenetic relationships within the genus Crassicauda were analysed. Analysis of the ITS2 grouped the different species in accordance with morphological identification, as already evidenced in literature for other Spirurida. A higher intra-specific variability was observed for the cox1 gene, for which two species ( C. grampicola and C. anthonyi ) did not appear as monophyletic in the tree. Well-developed non-attached larval specimens in the intestinal lumen of a whale calf were molecularly identified as C . boopis , allowing new insights on the life cycle of this species. This work broadens the genetic database on cetaceans parasites, allowing species identification even in challenging field conditions or in poor conservation of the samples; moreover, the first morphological description of C . boopis larvae is provided.

Crassicaudiasis in three geographically and chronologically distant Cuvier's beaked whales (Ziphius cavirostris) stranded off Brazil

“…Pterygoid osteolytic lesions presumptively associated with crassicaudiasis were described in Guiana dolphin ( Sotalia guianensis ) ( Van Bressem et al, 2007 ) and common bottlenose dolphin ( Tursiops truncatus ) ( Basiolio, 2017 ; Nepote, 2020 ). Crassicauda anthonyi was originally described based on specimens collected from the kidneys of the True's beaked whale ( Mesoplodon mirus ) off the Atlantic coast of France ( Chabaud, 1962 ), and later reported in CBW from the Canary Islands ( Manfredi et al, 2005 ), Costa Rica ( Oliveira et al, 2011 ), Australia ( Robson, 1984 ) and Puerto Rico ( Mignucci-Giannoni et al, 1998 ), and fin whales off the Mediterranean Sea ( Marcer et al, 2019 ); some of these records documented renal lesions including necrosis, fibrosis and partial destruction of the organ ( Manfredi et al, 2005 ; Oliveira et al, 2011 ; Robson, 1984 ; Mignucci-Giannoni et al, 1998 ). There is lack of knowledge of C. anthonyi specific life history traits, transmission pathways and epidemiology.…”

Diseases and parasites

“…Presence of adult nematodes in the kidneys of weaning fin whale calves has provided support for the whale to calf transmission. Recent isolation of larval C. boopis from the intestinal lumen of a fin whale calf ( Marcer et al, 2019 ) provides support for the direct life cycle. Gross and histopathological renal examination of a mature pregnant female bowhead whale (NSB-DWM 2019B9) with severe Crassicauda infection and her full-term fetus (NSB-DWM 2019B9F) did not provide evidence for in utero transmission (Stimmelmayr and Rotstein, unpublished data).…”

“…Vestigial spicules are present in C. costata . Given the limitation of the 18S sequence for definitive molecular species identification (see Marcer et al, 2019 ), additional nematode molecular markers have been added to improve species discrimination, and morphological features are being analyzed. The life cycle of Crassicauda is not well understood.…”

ARGENTINEAN ORCA (ORCINUS ORCA) AS AN UMBRELLA SPECIES: CONSERVATION & MANAGEMENT BENEFITS

“…It is thought that pseudaliids have a terrestrial origin and made it to the sea with ancestors of marine mammals (LEHNERT et al 2010 and references therein). Finally, the family Tetrameridae is represented by Placentonema gigantisima, which is restricted to the placenta of sperm whales (Physeter macrocephalus), (DHERMAIN, SOULIER and BOMPAR, 2002) and species of Crassicauda, which are typically found in the circulatory and urogenital system of both mysticetes and odontocetes, and in the cranial pterygoid sinuses of odontocetes (KEEMAN-BATEMAN et al 2018;MARCER et al 2019;VAN BRESSEM et al 2020). The life cycles of tetramerids are also poorly known, but some species of Crassicauda are thought to reach cetaceans by trophic transmission (LEMPEREUR et al 2017).…”