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Downloaded from Brill.Com10/07/2021 11:30:31AM Via Free Access 10 S Contributions to Zoolog)>, 69 (1/2) 9-20 (2000) SPB Academic Publishing bv, Amsterdam The distribution of exocrine glands in Lepeophtheirus salmonis and Caligus elongatus (Copepoda: Caligidae) S. Bell,J.E. Bron & C. Sommerville Institute ofAquaculture, University of Stirling, Stirling, Scotland FK9 4LA Keywords: gland, sea lice, diaminobenzidine, peroxidase, Caligidae, Copepoda Abstract Adults 15 Caligus elongatus 16 Other species 17 The morphology, function and distribution of exocrine glands Discussion 17 of copepods have rarely been studied in detail and almost not- References 19 is known hing about them in the sea lice species L. salmonis andC. elongatus. This study utilised a novel application of a of light-microscopy staining technique to reveal a variety glands m nauplius, copepodid, chalimus, preadult and adult stages. Introduction The stain, 3’,3-diaminobenzidinetetrahydrochloride (DAB), applied to fresh exocrine material, differentiated a population of Descriptions of glandular structures of copepods glands and stain was enabled a study of their distribution. The have been a feature of the literature for successful with many in highlighting the ducts and pores associated the decades larger glands. The locations of gland sub-populations were (Richards, 1891; Yonge, 1932; Clarke, conserved in all life-stages, although glands in the swimming Conover, David, & Nicol, 1962; Fahrcnbach, 1962; legs were found better in mobile and free- to be represented Park, 1966; Mauchline, 1977; Briggs, 1978; swimming stages i.e. copepodids, preadults and adults. Glands Gharagozlou-van Ginnekcn, 1979; Arnaud, Bru- associated with the mouth-tube were also located. Other, non- net, & Mazza, 1988a; Arnaud, Brunet, & Mazza glandular, peroxidase-positive regions were also highlighted by Dumont & Silva-Briano, Unfortu- the stain. These and 1988b; 1997). regions were foundmainly in preadult adult the few detailed studies which stages where they formed characteristic bi-symmetrical nately have been patterns on the cuticle of the dorsal surface. A of some study undertaken serve only to highlight our lack of calanoid copepods suggested that peroxidase-positive glands understanding of these structures, their secretions are a feature peculiar to caligid copepods. This staining technique and their the and has significance to biology ecology proven useful for elucidating the ontogeny of gland of these animals. populations in caligids. the fact that different Despite many types of have glands been located in various parts of the Contents copepod body, few of them have had their secre- tions characterised and their biological significance Introduction • 9 determined conclusively. Those best studied in- Material and methods 10 clude the glands of the buccal cavity (Boxshall, DAB 10 1982; Arnaud et ah, 1988ab; Zeni & Zaffagnini, Light microscopy 11 Klein & the lumi- Results 1992; Vaupcl Koomen, 1994) 11 nous glands of the Calanoida (Clarke et ah, 1962; Lepeophtheirus salmonis II & Nauplii 11 Herring, 1988; Bannister Herring, 1989) and the Copcpodid II mucous glands of the capsule-dwelling copepods Chalimus 13 (Hicks & Grahame, 1979). Glandular complexes Preadults 14 have been in the urosome described previously by Downloaded from Brill.com10/07/2021 11:30:31AM via free access 10 S. Bell et al. - Exocrine glands in Lepeophtheirus and Caligus (Gharagozlou-van Ginneken, 1979) who suggested Peroxidase enzymes have been reported to be in- they produced chemicals involved in sexual activ- volved in many different functions within animal ity. Fahrenbach (1962) and Boxshall (1982) also tissues, including: free radical neutralisation (Salin & described glands in the urosomes of copepods but Brown-Peterson, 1993), prostaglandin produc- tion & did not suggest a function for them. Glands in the (Bowman, Dillwith, Sauer, 1996) and io- thoracic limbs have also been widely reported dine binding as part of protothyroid activity in (Fahrenbach, 1962; Park, 1966; Dumont & Silva- tunicates (Fredriksson, Ofverholm, & Ericson, Briano, 1997). 1988). As of a wider into the func- Other glands arc commonly found in close asso- part investigation tional ofexocrine in salmonis ciation with the integument (‘integumental glands’) significance glands L. we undertook a locate all the but their role is still the subject of debate. Dennell study to DAB-posi- tive regions in all life-stages of that species and (1947) and Stevenson (1961) suggested that they the related might be involved in cuticle tanning, while Rybakov parasitic copepod Caligus elongatus. determine whether & To are a Dolmatov (1991) suggest a role in cuticle for- DAB-positive regions widespread feature of the Copepoda, we stained mation. Other functions such as predator deter- several of and also some rence (Pochon-Masson, Renaud-Mornant, & Cals, species free-living copepod other aquatic arthropods. 1975) immunity to host nematocysts (Briggs, 1978), cuticle anti-fouling (Boxshall, 1982; Bannister, 1993), drag reduction (Bannister, 1993) ‘secretion- Materials and methods trap’ for water-borne chemical cues (Hipeau- Jacquotte, 1987) and production of pheromones DAB for mate attraction (Gharagozlou-van Ginneken, 1979) have all been suggested as functions of these One lOmg DAB tablet (Sigma D5905) was added glands. It is likely that there is variation in integu- to 15ml of Tris buffer to give a 0.66% w/v solu- mental gland products and functions between spe- tion which to 12 pi of H,0, was added (0.026% cies which probably represent evolutionary changes solution) to provide a substrate for the reaction. necessitated the environment in which by particular of The reaction was halted by the addition 70% the animal lives. ethanol. In contrast to the widely accepted idea that glands Fresh specimens were added to the prepared are actively involved in secretion, Chapman (1981) DAB solution and left to stain at room tempera- showed that the of Neocalanus ‘dermal’glands The ture for a range oftime periods. optimal staining involved in the of dissolved plumchrus were uptake found time was to be: =15min for nauplii and glucose from the sea water. surrounding =6h for chalimus and ~16h for copepodids, pre- Previous work (Bron, 1993; Andrade-Salas, 1997) adults and adults. After these periods had elapsed has shown that the immunohistochemical stain 3’,3- the reaction was halted by carefully pipetting off diaminobenzidine (DAB) high- tetrahydrochloride the stain solution and replacing it with 70% etha- in L. salmonis larvae and lighted glandular regions nol. adults. DAB is a chromogenic compound used Chalimus, preadult and adult stages were stained routinely in immunohistochemical analyses. It is soon after collection (i.e. not exceeding 48h post- often used coupled to antibodies, as a marker, to removal) to minimise any effects on gland activ- of highlight areas antibody Used on its binding. ity that being removed from the salmon host may it own however in the of reacts, presence hydro- incur. gen peroxide to produce a characteristic (H,0,) The same procedures were followed for naup- brown product which is insoluble in alco- the water, lius, copepodid and adult specimens of caligid hol and This reaction xylene. positive to the DAB copcpod Caligus elongatus Nordmann, 1832. Adults stain generally occurs with endogenous peroxidases of the free-living marine copepods Eurytemora but also with may occur catalase, cytochrome affinis (Poppe, 1880) and Acartia tonsa Dana, 1849, oxidase of and possibly a number other the cladoceran and compounds. Daphnia magna Straus, 1820, Downloaded from Brill.com10/07/2021 11:30:31AM via free access Contributions to Zoology, 69 (1/2) - 2000 11 larval stages of the anostracan Artemiasalina (L.), Nauplii and the palaemonid Macrobrachium rosenbergii (de also stained in the for Both the first and second lar- Man) were same way (NI) (Nil) nauplius comparison. vae displayed the same general pattern of DAB- positive staining, although some slight differences were evident. In addition to two large dorsal and Light microscopy ventral ‘median’ glands, both larval stages con- sistently displayed three pairs of distinct glandu- Small larval in stages (i.e. nauplius, copepodids and lar regions arranged a bilaterally symmetrical chalimus I and II) were examined in a cavity slide pattern (Fig. 1). These gland populations have been under a cover slip. Lactic acid (87.5%) was used named in accordance with their location within the to aid in the clearing of the body tissues of larval animal. stages, to enhance visualisation of In addition to these late Nil larvae gland structures glands, pos- without affecting the quality of staining, although sessed up to 10 small DAB-positive areas, arranged this method could not be used as a permanent in a symmetrical pattern, in the posterior half of mountant (Huys & Boxshall, 1991). the body between the lateral and posterior glands, made BH- in 1. Observations were using an Olympus position ‘TIT Fig. These areas corresponded 2 compound microscope and photographs were to the position of glands present in the thoracic taken limbs of the using an Olympus C-35AD-2 camera. following copepodid stage. The pos- terior exited via small glands two pores, one lying close to the ventral side of each balancer. Results During the staining process some individual, un- hatched of salmonis eggs L. were inadvertently stained Lepeophtheirus salmonis along with the hatched nauplius stages. Examination of these showed that eggs pre-hatch DAB was successful in highlighting gland struc- nauplii had the same
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