Multiple gene analyses of caligid copepods indicate that the reduction of a thoracic appendage in Pseudocaligus represents convergent evolution

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.

Sea lice (Copepoda: Caligidae) from South Africa, with descriptions of two new species of Caligus

“…The position of Lepeophtheirus natalensis in molecular phylogenetic analyses of the caligids has been anomalous as it is recovered separate from other Lepeophtheirus species (Freeman et al, 2013). This has led to questioning of the monophyletic status of Lepeophtheirus (Morales- Serna et al, 2013).…”

“…Lepeophtheirus natalensis tends to be recovered separate from other Lepephtheirus species in sequence-based analyses of relationships within the Caligidae (e.g. Freeman et al, 2013), and this has fueled doubts concerning the monophyletic status of Lepeophtheirus (e.g. Morales-Serna et al, 2014).…”

“…These nine genera are: Alebion Krøyer, 1863 (five species), Caligodes Heller, 1865 (one species), Caligus Müller, 1785 (38 species), Euryphorus Milne Edwards, 1840 (two species), Gloiopotes Steenstrup & Lütken, 1861 (one species), Hermilius Heller, 1865 (two species), Lepeophtheirus von Nordmann, 1832 (nine species), Paralebion Wilson, 1911 (one species), and Tuxophorus Wilson, 1908 (one species) (Dippenaar, 2005;. The genus Pseudocaligus Scott, 1901 was regarded as valid in 2004 (Boxshall & Halsey, 2004;Dippenaar, 2005) but has since been synonymised with Caligus (Dojiri & Ho, 2013;Freeman et al, 2013;Ö zak et al, 2013). The single species of Pseudocaligus reported from southern Africa, P. apodus Brian, 1924, is included in the above list as Caligus apodus.…”

Meningitis associated with dracunculid nematodes in a spotted eagle ray (Aetobatus narinari)

“…DNA extractions were completed on the preserved tissues, and PCR products performed using the nematode‐specific primers Nem‐18SF/R and cycling conditions described by Floyd, Rogers, Lambshead, and Smith (2005). Initial sequencing reads allowed the design of a new forward primer ERN‐fwd 5′ acc gta gcg aga cgc cct act g that was more specific for philonemid nematodes to use with the reverse primer 18gM (Freeman, Anshary, & Ogawa, 2013). A consensus sequence of 1,734 bp was generated of small subunit ribosomal DNA (SSU rDNA) and submitted to GenBank with the accession number .…”

“…Blast searches in DNA databases showed that the eagle ray nematode was most closely related to Philonema oncorhynchi with an identity of 94.5% across the SSU rDNA. Phylogenetic analyses were performed using maximum likelihood and Bayesian methodologies (Freeman et al, 2013). The overall topology of the phylogenetic trees did not vary between the methods used, and the maximum likelihood tree (Figure 2) shows that the eagle ray nematode is robustly supported in a clade with Philonema spp., confirming that this nematode belongs to the superfamily Dracunculoidea and most likely to the genus Philonema (family Philonemidae).…”