Abstract
Ascaridoid nematodes comprise a wide range of heteroxenous parasites infecting top fish predators and marine mammals as definitive hosts, with crustaceans, squids, and fishes acting as intermediate/paratenic hosts. Limited data exist on the species and role of several intermediate and paratenic hosts in the life cycle of these parasites. In the aim of adding knowledge on the role of squid species in their life cycle, we have here investigated the larval ascaridoid nematodes collected from the deep-sea umbrella squid Histioteuthis bonnelli and the reverse jewel squid Histioteuthis reversa captured in the Central Mediterranean Sea (Tyrrhenian Sea). Morphological study and sequence analysis of the internal transcribed spacer (ITS) regions of the ribosomal DNA (rDNA) and the mitochondrial cytochrome c oxidase subunit 2 (mtDNA cox2) gene locus revealed the occurrence of Anisakis physeteris and of an unidentified species of the genus Lappetascaris. Sequence analysis revealed that specimens of Lappetascaris from both squid species matched at 100% sequences previously deposited in GenBank from larval ascaridoids collected in octopuses of the genus Eledone of the Mediterranean Sea. The Bayesian inference tree topology obtained from the analysis of the fragments amplified showed that Lappetascaris specimens were included in a major clade comprising Hysterothylacium species collected in fishes of the families Xiphiidae and Istiophoridae. As regards the site of infection in the squid host species, A. physeteris larvae predominated (60.7%) in the gonads, while those of Lappetascaris (76.3%) were found infecting the mantle musculature. The overall high values of parasitic load suggest both squid species as transmitting hosts of third stage larvae of Lappetascaris to top predator fishes, as well as the umbrella squid as an intermediate/paratenic host in the life cycle of A. physeteris in the Mediterranean Sea.
Highlights
Histioteuthidae Verrill, 1881 is a family of pelagic cephalopods distributed circumglobally in the midwaters of the oceans, from the subarctic to the subantarctic r egions[1]
Chance of predation by the host and, the probability of parasite transmission. This is especially relevant for ascaridoid nematodes, which use squids as intermediate and/or paratenic hosts[14,18,19] and marine mammals or teleostean fishes as definitive o nes[20]. Due to their elusiveness, most of the records so far available in the literature about the umbrella and reverse jewel squids from the Mediterranean Sea have been limited to occasional captures with the description of morphometric features or data derived from the gastric contents of teuthophagous predators[21,22,23], or because they were included within studies on the cephalopod faunas of certain geographic a reas[6,24,25]
A genetic/molecular approach was applied to identify, at the lower possible taxonomic level, larval ascaridoid nematodes collected from poorly known squids species from the Tyrrhenian Sea in order to: i) add knowledge on the role of these squids species in nematode parasites having in top predators of a marine food webs their definitive hosts; ii) provide data on their infection level and site of infection in the hosts
Summary
Histioteuthidae Verrill, 1881 is a family of pelagic cephalopods distributed circumglobally in the midwaters of the oceans, from the subarctic to the subantarctic r egions[1]. The umbrella squid Histioteuthis bonnellii (Férussac, 1835) and the reverse jewel squid Histioteuthis reversa (Verrill, 1880) are the only species inhabiting the Mediterranean Sea[2], where they are usually found between 500 and 1500 m d epth[1,3,4,5,6] Both species are important prey-resources for higher trophic levels, such as those constituted by marine mammals and top fish predators; they are voracious consumers of crustaceans, other cephalopods, and fishes[1,6,7,8,9,10,11,12]. Chance of predation by the host and, the probability of parasite transmission This is especially relevant for ascaridoid nematodes, which use squids as intermediate and/or paratenic hosts[14,18,19] and marine mammals or teleostean fishes as definitive o nes[20]. Identification of the examined squid hosts was included by means of genetic/molecular analysis
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