EFFECTS OF MATING ON FEMALE BEHAVIOUR AND ALLOMETRIC GROWTH IN THE TWO PARASITIC BRANCHIALIS (L., 1767) () AND LEPEOPHTHEIRUS PECTORALIS (MÜLLER, 1776) (CALIGIDAE)

BY

the late MORTEN ANSTENSRUD Section of Marine Zoology and Marine Chemistry, Biological Institute, University of Oslo, P.O. Box 1064, Blindern, N-0316 Oslo 3, Norway')

RÉSUMÉ L'accouplement a un effect prononcé sur le développement post-larvaire des femelles de Ler- naeocerabranchialis (L., 1767) et de Lepeophtheiruspectoralis (Müller, 1776). Alors que les femelles vierges de la première espèce n'achèvent pas leur métamorphose, celles de la seconde se dévelop- pent et produisent des oeufs, mais ceux-ci ne se développent pas en laboratoire. Le développe- ment du complexe génital et la production d'oeufs sont l'un et l'autre plus élevés, et de façon significative, chez les femelles non vierges de Lepeophtheiruspectoralis. Les changements morphologiques relativement minimes, comme le renflement du complexe génital chez la femelle de Lepeophtheirus pectoralis,et les changements dans le micro-habitat préfé- rentiel semblent prédéterminés. Les changements morphologiques plus importants, tels que la métamorphose chez la femelle de Lernaeocerabranchialis, sont induits par la présence de fluides séminaux dans le receptaculum seminis. A la fois chez Lernaeocerabranchialis et chez Lepeophtheirus pectoralisles changements dans la préférence d'habitat semblent moins affectés par l'accouple- ment. Cependant, le temps que la femelle de Lernaeocerabranchialis passe sur l'hôte intermédiaire après la maturation dépend du nombre de copulations. Les implications écologiques de ces changements morphologiques et comportementaux sont discutés en relation avec la biologie et les stratégies d'accouplement.

INTRODUCTION

Like their free-living relatives, parasitic copepods develop through several instars separated by moults. and Lepeophtheirus pectoralis in- clude two nauplius stages, one copepodite stage, and four parasitic chalimus stages sessile on a (usually , Platichthys flesus (L., 1758)) (Sproston, 1942; Boxshall, 1974a). After developing from a chalimus IV larvae into an adult individual, Lernaeocera branchialis ceases to moult. Mating takes place on the intermediate host, and both sexes are polygamous (Anstensrud, in prep.). After mating, the post-chalimus female leaves its initial host, and after a brief

1) Mr. Morten Anstensrud died on 27 March 1990, in a tragic diving accident, only 32 years old. An obituary will be published in the Journal of Biology. 246 free-swimming period infects a final host (usually a gadid), where the main post-larval growth takes place. Lepeophtheirus pectoralis includes two preadult stages in the life cycle before moulting into an adult individual. The pre-adults and the adult males are more or less randomly distributed over the body surface of the host, usually flounder, whereas most adult females are found at the base of the pectoral or pelvic fins (Boxshall, 1974b). Like Lernaeocera branchialis, Lepeophtheirus pectoralis is also a polygamous species (Anstensrud, 1990). In contrast to free-living copepods, the most dramatic changes in the mor- phology of female parasitic copepods often occur after the final moult. These changes are accomplished by allometric growth, and usually include a marked swelling of the female's genital complex. The post-larval development may consist of simple diphasic growth (Kabata, 1979), as in Lepeophtheirus pectoralis, where the main development after the final moult is seen as an increase in the size of the genital complex. At the other extreme, post-larval development may take the form of dramatic morphological changes, as seen in female copepods belonging to the family Pennellidae, e.g. Lernaeocera branchialis. In this family the fully developed female ceases to bear any gross morphological resemblance to the juvenile stages. The most conspicuous changes include comparative gigantism of the genital complex and the development of cephalothoracic holdfasts. These post-larval changes in morphology of female parasitic copepods and their change in habitat preferences may be attributed to mating and transfer of spermatophores, and Bird (1968) concluded that post-larval development ceased in virgin females of the parasitic cyclopoid copepod Lernaea cyprinacea L., 1758. This paper demonstrates how transfer of spermatophores influences post- larval morphology of female Lernaeocera branchialis and Lepeophtheirus pectoralis, and the selection of habitat in laboratory experiments. The ecological implica- tions of these results are discussed in relation to life history and mating strategy.

MATERIAL AND METHODS

The cultivation of parasites and all experiments were performed at 10 to 12°C and 30-32%o salinity. Egg sacs of Lernaeocera branchialis were hatched in the laboratory and the lar- vae were raised in aquaria using the technique described by Schram & Anstensrud (1985). Adults of Lernaeocera branchialis were provoked to leave their host by removing gill lamellae carrying mature males or females from the flounder. The gill tips were placed in 200 ml glass beakers containing seawater, and the parasites left the lamellae within 1 to 2 h and attained a free-swimming life.