Abstract
BackgroundThe Caligidae is a family of parasitic copepods containing over 30 recognised genera. They are commercially important parasites as they cause disease in numerous finfish aquaculture facilities globally. Morphological features are used to distinguish between the genera and Pseudocaligus has traditionally been differentiated from Caligus solely by the presence of a much reduced form of the fourth thoracic leg. Currently there are numerous DNA sequences available for Caligus spp. but only the type species, Pseudocaligus brevipedis, has molecular data available, so systematic studies using molecular phylogenetic analyses have been limited.MethodsThree gene regions, SSU rDNA, 16S and CO1, for Pseudocaligus fugu from puffer fish from Japan and Pseudocaligus uniartus from rabbit fish from Indonesia are sequenced and molecular phylogenetic analyses performed in order to infer phylogenetic relationships between Pseudocaligus and other caligid copepods.ResultsThe analysis revealed that there was no discrete grouping of Pseudocaligus spp. and that they had a polyphyletic distribution within Caligus taxa. Pseudocaligus fugu grouped with Caligus elongatus and contained a unique synapomorphy in the SSU rDNA region only seen in members of that clade. Pseudocaligus uniartus formed a well-supported group, in the SSU rDNA analyses, with a Caligus sp. that also infects rabbit fish, but was unresolved in the other analyses. Pseudocaligus brevipedis consistently and robustly grouped with Caligus curtus and C. centrodonti in all analyses. The majority of Lepeophtheirus spp. form a monophyletic sister group to the Caligus clade; however, L. natalensis is unresolved in all analyses and does not form part of the main Lepeophtheirus clade.ConclusionsThese findings do not support the morphological-based distinction between Pseudocaligus and Caligus, suggesting that the reduced fourth leg is a feature that has evolved on multiple occasions throughout caligid evolution. Congruent molecular phylogenetic data support groupings based on the presence of morphological features, such as lunules, geography and host fish type rather than appendage morphology. Therefore, we support the synonymy of Pseudocaligus with Caligus.
Highlights
The Caligidae is a family of parasitic copepods containing over 30 recognised genera
Pseudocaligus uniartus were collected from naturally infected rabbit fish, Siganus guttatus, reared in the Marine Research Station located in Barru Regency, South Sulawesi and P. fugu were obtained from naturally infected tiger puffer, Takifugu rubripes in Nagasaki Public Corporation, Japan
Phylogenetic analysis of Pseudocaligus within the Caligidae The DNA sequences for Pseudocaligus did not group together to form a discrete monophyletic clade in any of our phylogenetic analyses
Summary
The Caligidae is a family of parasitic copepods containing over 30 recognised genera. Parasitic copepods belonging to the family Caligidae are dorso-ventrally flattened ectoparasites that feed on the epithelium and blood of marine and brackish water fishes [1,2] but are found on other marine animals such a whales [3] They have the same general body plan consisting of a rounded cephalothoracic shield which is comprised of the head fused with four thoracic segments, a free fourth pedigerous segment, a genital complex and abdomen [1]. It has been estimated that the global annual cost attributed to sea lice infections, in salmonid aquaculture alone, was greater than 300 million Euros in 2006, which constitutes an average of 6% of the value of production for the countries affected by such infestations [8] These estimates do not take into consideration the additional costs to the environment associated with the use of chemical parasiticides or welfare aspects concerning the fish, farm staff and the consumer
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