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Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 627 _____________________________ _____________________________ Reproduction in the Hermaphrodite Aeolidiella glauca A Tale of Two Sexes BY ANNA KARLSSON ACTA UNIVERSITATIS UPSALIENSIS UPPSALA 2001 Dissertation for the Degree of Doctor of Philosophy in Animal Ecology presented at Uppsala University in 2001 Abstract Karlsson, A. 2001. Reproduction in the Hermaphrodite Aeolidiella glauca. A Tale of Two Sexes. Acta Universitatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 627. 43 pp. Uppsala. ISBN 91-554-5020-2. This thesis focuses on reproduction in a simultaneous hermaphrodite with internal fertilization; the nudibranch Aeolidiella glauca. Unlike most other nudibranchs, where copulation is the rule, A. glauca was found to transfer sperm via external spermatophores that were attached to the partner’s back. Despite elaborate courtship the actual spermatophore transfer, which always involved two animals only, was of short duration. In most matings (88%) spermatophores were reciprocally exchanged. A. glauca was further found to be very promiscuous. During mating and sperm transfer the receiver exerts considerable control over sperm, and manipulative behaviours designed to increase the donor’s reproductive success are thus likely to have evolved. An example of such manipulative behaviour may be A. glauca’s unique spermatophore avoidance behaviour. I found that slugs carrying a sign of previous mating activity, i.e. a spermatophore, were discriminated against in a situation where mate choice was possible. Furthermore presence of a spermatophore was found to reduce the carrier`s ability to successfully interrupt matings between other slugs. Body size, however, had no direct effect on displacement in A. glauca as small slugs interrupted matings as successfully as large ones. Furthermore, pair formation and mating were found to be random with respect to size. This was true also for pairs formed in the field. In addition to mate choice hermaphrodites may increase their reproductive success by differential sex allocation. I tested whether differing mate encounter rates had any effects on allocation to male and female function in A. glauca. Slugs with more mating opportunities mated more, and had higher proportional spermatophore production that others. As predicted they also laid significantly fewer eggs than slugs presented with partners less often. Keywords: Aeolidiella glauca, simultaneous hermaphrodite, mating behaviour, mate choice, sex allocation. Anna Karlsson, Department of Animal Ecology, Evolutionary Biology Centre, Norbyvägen 18D, SE- 752 36 Uppsala, Sweden ([email protected])  Anna Karlsson 2001 ISSN 1104-232X ISBN 91-554-5020-2 Printed in Sweden by Uppsala University, Tryck & Medier, Uppsala 2001 “Result! Why, man, I have gotten a lot of result. I know several thousand things that won`t work” - Thomas A. Edison “It was the best of times, it was the worst of times…” - Charles Dickens, “A Tale of Two Cities” This thesis is based on the following papers, which will be referred to in the text by their Roman numerals I-V. I. Haase, M. & Karlsson, A. 2000. Mating and the inferred function of the genital system of the nudibranch Aeolidiella glauca (Gastropoda: Opisthobranchia: Aeolidioidea). Invertebrate Biology 119: 287–298. II. Karlsson, A. & Haase, M. The enigmatic mating behaviour of a simultaneous hermaphrodite, the nudibranch Aeolidiella glauca (Gastropoda, Opisthobranchia). Submitted manuscript. III. Karlsson, A. Mate choice in a hermaphroditic nudibranch – does size matter? Manuscript. IV. Karlsson, A. & Haase, M. Mate choice in a hermaphrodite - you won’t score with a spermatophore. Animal Behaviour, In press. V. Karlsson, A. Sex allocation in a naked hermaphrodite. Submitted manuscript. Papers I and IV are reproduced with permission from the publishers. The order of the authors reflects their involvement in the papers. I have personally written and performed all analyses of papers II, III, IV and V. My co-author in papers II and III collected data, discussed ideas, analyses and commented on the text. In paper I I collected part of the field data, discussed ideas and commented on the text. CONTENTS INTRODUCTION ………………………………………………………….……...…… 7 What is an Hermaphrodite? …………………………………………...…………. 7 Nudibranchs ……………………………………………………………………… 8 Reproductive anatomy of nudibranchs ……………………………….…………... 9 Hermaphrodite reproduction …………………….…………………………..…… 11 Sexual selection in hermaphrodites ………………….……………..………......… 12 Sex allocation ………………………………………….………………………… 14 NATURAL HISTORY OF AEOLIDIELLA GLAUCA ………………...…….………… 15 GENERAL METHODS ……………………………………….…………………..…... 17 Anatomical investigations ………………………………...…………….………… 18 RESULTS AND DISCUSSION ……………………………………………………….. 18 Aeolidiella glauca’s peculiar mating behaviour ……………………………….…. 18 Mate choice in Aeolidiella glauca ………………...……………….……….……. 24 Sex allocation in Aeolidiella glauca ………………………………...…….……… 27 GENERAL CONCLUSIONS …………………………………………………….…… 29 ACKNOWLEDGEMENTS …………………………………………………………… 30 REFERENCES ……………………………………………………………………...… 33 SWEDISH SUMMARY – SVENSK SAMMANFATTNING ……………………..… 39 INTRODUCTION This thesis deals with different aspects of reproduction in a simultaneous hermaphrodite, the nudibranch Aeolidiella glauca. At present, comparatively little is known of mating systems of hermaphroditic animals. However, their reproductive structures often show amazing compexity, and mating behaviours can be very elaborate (Hyman 1951; Lind 1976; Vreys & Michiels 1997; Michiels 1998 and refs. therein). Thus, simultaneous hermaphrodites represent an almost untapped potential for behavioural studies that can increase our understanding of the evolution and maintenance of mating systems. The aim of this introductory part is threefold; I want to provide the reader with some background information on hermaphroditism and nudibranchs. In addition I wish to give a brief outline of the theory underlying my studies. Finally, I hope to be able to convey some of the excitement and joy that the work on this peculiar and fascinating animal has given me. There’s a whole world of hermaphrodites out there, just waiting to be explored… What is an hermaphrodite? An hermaphrodite is defined as an organism possessing both male and female reproductive organs. Hermaphroditism has been known since antiquity, but its functional significance is, as yet, only partly understood. The word hermaphrodite is derived from Greek, referring to the androgynous diety Hermaphroditos. This beautiful bisexual being was the result of an extra- marital affair between Hermes and the love Godess Aphrodite. In biology hermaphrodites are specifically defined as organisms that possess a functional male and female reproductive system during at least part of their lives. This type of gender expression is widespread throughout the animal kingdom, including entire taxa such as flatworms, pulmonate gastropods and ascidians (Ghiselin 1969). Two-thirds of all phyla containhermaphroditic representatives, and approximately 40% of the molluscan genera are hermaphroditic (Heller 1993). 7 Usually two major types of hermaphroditism are distinguished. Sex-changers, or sequential hermaphrodites, start out as one sex and change into the other later in life. Sequential hermaphroditism is relatively well studied, and much research has been devoted to the question of when to change sex (Warner 1975, 1988; Berglund 1986, 1991; Charnov 1982). The second type, and the focus of this thesis, are simultaneous hermaphrodites. These have functional male and female genitalia simultaneously present for most of their lives, and reproductive acts usually involve both the male and female function in each individual. Nudibranchs The order Nudibranchia – the name meaning "with naked gills – is the major representative of the molluscan subclass Opisthobranchia. All nudibranchs are marine, and in the adult stage both shell and operculum have been lost. The loss of shell has allowed for a diverse array of body forms, and not suprisingly nudibranchs are often referred to as “sea-slugs”. Following the classification outlined by Thompson (1976), nudibranchs are divided into four suborders; Dendronotacea, Doridacea, Arminacea and Aeolidacea (Fig. 1). Fig. 1. The external appearance of some nudibranch species. A. Dendronotus frondosus (Dendronotacea). B. Polycera quadrilineata (Doridacea). C. Archidoris pseudoargus (Doridacea). D. Coryphella verrucosa (Aeolidacea). E. Armina lovenii (Arminacea). 8 Since nudibranchs lack a shell they may appear more vulnerable to predators than other gastropods. However, to compensate for the loss of a hard shell nudibranchs have developed a wide range of defensive mechanisms, mainly through prey exploitation. Most nudibranchs are browsing predators, and they often have very limited and specific food preferences. Dorid nudibranchs (for examples see Fig. 1) mainly feed on sponges and bryozoans, and many have the ablity to synthesize unpleasant or poisonous chemicals, usually as secondary metabolites from the prey. Aeolids prey on cnidarians, and have evolved an immunity to the damaging effects of nematocysts. Interestingly, they can also use the nematocysts for their own defence. The nematocysts are transported undigested to the apices of the digestive gland in the cerata, and if disturbed the nudibranch can release a whole cloud of discharging nematocysts in the direction of the potential danger. To date, the mechanisms behind this intriguing use of nematocysts are, however, completely unknown. Their frequently exotic colouration and appearance have made nudibranchs highly popular among SCUBA-divers and naturalists, while other properties such as their ability to synthesise chemical compounds for anti-predatory defence, have made them interesting for bio-medical research and other branches in the scientific community. But despite their wide popularity, comparatively little is actually known about nudibranchs. Reproductive anatomy of nudibranchs All nudibranchs are simultaneous hermaphrodites with internal fertilization. To date there is no evidence suggesting that self-fertilization takes place among nudibranchs. Their reproductive systems are often complex (Ghiselin 1966; Hyman 1967; Schmekel 1971, Hadfield & Switzer-Dunlap 1984, Gosliner 1994), but most species copulate and exchange sperm reciprocally. A few species, however, transfer sperm via hypodermic impregnation (Rivest 1984), or in a spermatophore (von Ihering 1886). Sperm, even when transferred in a spermatophore, is usually confined within the reproductive system. Nudibranchs have a single unpaired gonad, the ovotestis, which is composed of 9 individual acini or follicles. It may be difficult to distinguish between male and female parts, but frequently a single male acinus is surrounded by several female. However, eggs and sperm are occasionally produced by the same acinus. The gametes are transported through the hermaphroditic duct to the ampulla, where autosperm, i.e. own sperm, is stored until copulation takes place. The ampulla opens into the spermoviduct, which connects to the vas deferens and, via an oviduct, to the fertilization chamber. Eggs are transported directly to the fertilization chamber. In contrast autosperm is channeled through the vas deferens, to the ductus ejaculatoris and the evertible penis. The vas deferens usually contains a glandular part, the prostrate. The function of the prostatic fluid is not completely clear, but it may help to agglutinate the sperm into a ball (Schmekel 1971). A great diversity is found in the penes of nudibranchs, often including various appendages and spines. Many of these specializations are of taxonomic value. The distal female genitalia can be organized according to a diaulic or triaulic scheme. Schmekel (1970) distinguished two diaulic types and a single triaulic type among nudibranchs (Fig. 2). All Doridacea are triaulic, whereas most Aeolidacea and Dendronotacea belong to one of the diaulic types. Nudibranchs with a triaulic reproductive system have separate orifices and ducts for receiving allosperm and for laying the fertilized eggs. A vagina leads to the receptaculum seminis, where allosperm, i.e received sperm, is stored. Close to the receptaculum is a copulatory bursa, where allosperm is digested. A duct then leads sperm to the fertilization chamber. Fertilized eggs pass through another duct with a series of glandular parts. Here eggs are provided with the protective layers that form the spawn mass. The morphology of the glands is extremely complex, and the terminology thus confused. In general three glands are recognized, which are named according to function. The albumen gland adds nourishment to the eggs whereas the membrane gland secretes a thin egg membrane. The mucus gland finally, secretes the gelatinous layers that hold the eggs together, and give the completed spawn its specific shape. 10 Diaulic nudibranchs lack the copulatory bursa, and have a common orifice and duct for sperm reception and egg laying. The principal difference between the diaulic types is where the spermoviduct branches into oviduct and vas deferens. Fig. 2. Schematic diagrams of the three major patterns of reproductive anatomy found in the Nudibranchia. A. Diauly I. B. Diauly II. C. Triauly. Abbreviations: Am, ampulla; Cb, copulatory bursa; Ed, ejaculatory duct; Me, membrande gland; Mu, mucus gland; Ot, ovotestis; Ov, oviduct; Pe, penis; Poa, postampullar duct; Pr, prostate; Pra, preampullar duct; Sr, seminal receptacle; Va, vagina; Vc, vaginal duct; Vd, Vas deferens; Ve, vestibule. (After Schmekel, 1971) Hermaphrodite reproduction Genital morphology plays a central role in the systematics of many animal groups. It has been proposed that a principal factor contributing to the vast diversity of genitalia is sexual selection (Eberhard 1996). In order to understand how sexual selection processes operate in a certain organism it is essential to know the function of its genital system. Among molluscs opisthobranchs are known for their particularly complex and diverse genitalia. Literature 11

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marital affair between Hermes and the love Godess Aphrodite. In biology functional male and female reproductive system during at least part of their lives.
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