Hydrobiologia 360: 153–159, 1997. 153A. Brancelj, L. De Meester & P. Spaak (eds), Cladocera: The Biology of Model Organisms.c 1997Kluwer Academic Publishers. Printed in Belgium.

Mating behaviour in Moina brachiata(Jurine, 1820)(Crustacea, Anomopoda)

Laszlo ForroDepartment of Zoology, Hungarian Natural History Museum, Baross u. 13, H-1088 Budapest, Hungary

Key words: Moina brachiata, Crustacea, Anomopoda, mating behaviour, mate choice, copulation

Abstract

Information on mating behaviour in Anomopoda is available for very few species only, though mate locationand recognition certainly play an important role in maintaining reproductive isolation between species. Ephippialfemales and males ofMoina brachiatawere observed in a drop of water under a microscope for 10–20 minutes.Different combinations of specimens were used, but copulation was only observed when two males and twoephippial females were placed together. Males were very active, and often tried to grasp a female, whereas femalesusually made attempts to escape during the entire period of mating. Three phases were recognized: capture,positioning and copulation. The male captured the female from the dorsal side, then moved to the ventral side andtook a position with its length axis being perpendicular to that of the female, forming a sort of cross. Thereafterthe pair started rotating around the length axis of the female, while the male pushed the postabdomen into thefemale’s brood pouch. Copulation lasted from 16 to 25 seconds. When different kinds of females were used, malesshowed preference for ephippial females with an empty ephippium and enlarged ovaries. Our results indicate thatnot only visual and tactile cues may be important in identifying species identity and receptivity of the female, butalso chemical signals.

Introduction

Studies on the behaviour of various species ofAnomopoda have mostly been carried out at the popu-lation level, and very few details of mating behaviourof these species are known (Dodson & Frey, 1991),though some early papers on ‘Cladocera’ already con-tain some information. O. F. Muller (1785) recog-nized the presence of males, described the develop-ment of the ephippium, and observed copulation (cit-ed after Scharfenberg, 1911). Jurine (1820) describedthe copulation ofDaphnia, and Weismann (1880) pro-vided descriptions of mating in several taxa, includ-ing Moina. Scharfenberg (1911) investigated the eggdevelopmentand life cycle ofDaphnia magnaand pro-vided data on mating in this species. Goulden (1966)observed sexual behaviour of co-occurringMoinaspecies. In his monograph on Moinidae, Goulden(1968) summarized the knowledge on secondary sexcharacters and gave a short summary of observations

on copulation. Shan (1969) and Smirnov (1971) dealtwith mating of some chydorid anomopods.

Moina brachiata is the commonest of the fiveMoina species occurring in Hungary. It inhabits vari-ous types of astatic waters, including sodic ones. Most-ly M. brachiatais the only species ofMoina in thesewater bodies, but in a number of small, temporary poolsM. macrocopawas found to co-occur with it. Ephippialfemales and males of both species can often be encoun-tered together in samples. These findings inspired meto start a study of these populations, and of the matingbehaviour in both species to find out whether matingbehaviour acts as a mechanism in maintaining repro-ductive isolation. The present paper provides informa-tion on the mating behaviour ofM. brachiata: matingand copulation are described and compared with exist-ing descriptions of Spinicaudata and Anomopoda.

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Materials and methods

The specimens used were collected from natural habi-tats or hatched in the laboratory from dried mud. Theanimals were placed in a drop of water (diameter about1 cm) and observed during 10–20 minutes under aWILD M420 stereomicroscope. Their behaviour wasfilmed with a Panasonic WV-BP-100/G camera fitted tothe microscope. A Panasonic VHS video recorder wasused in combination with a JVC monitor for recordingand for analysis of the videotape.

Different combinations of the specimens were usedto observe mating behaviour. It was experienced thatmating only occurred if two ephippial females andtwo males are placed together in the drop of water.Thus, this combination was mainly used to observemating behaviour, and a total of fifteen experimentswere run for ten minutes with different combinationsof animals to study mate choice of the male. The com-binations were: one male and one ephippial female;two males and two ephippial females; two males andtwo parthenogenetic females; one male, two ephip-pial females and one parthenogenetic female; twomales; four males; three males and one dead ephip-pial female; two males, one dead ephippial female andone parthenogenetic female. The animals were video-taped for ten minutes immediately after they had beenput together in a drop of water. The first, third, fifthand tenth minutes of the videotapes were used in theanalyses. In order to obtain more information on matepreferences, the first five minutes of seven videotapedobservations (not used in the experiments mentionedabove) were analyzed, in which the two ephippialfemales and two males combination was employed.The females and males involved in the experimentswere kept individually in culture for at least one daybefore the experiment.

Results

Mating behaviour

The animals placed in the drop of water often swamvigorouslyaround, the males being usually more activethan the females. Both males and females were fre-quently swimming along the edge of the drop. Thisbehaviour could also be seen in much larger drops andin small Petri dishes under the microscope.

Based on observations and analyses of the video-tape, four types of interactions between the ani-

mals could be established: contact, capture, pur-suit and fighting. Contact is a very brief interaction:while swimming around, the animals, both males andfemales, may touch each other briefly, mostly with thesecond antennae, and then they swim apart again. Dur-ing capture, a males approaches a females and tries tograsp her with his first antennae. If successful, captureis the initial phase of the mating process (see below).In a few cases it was observed that a male approachedanother male and tried to catch him.Pursuit also mainlytook place as an interaction between male and female,with the male swimming behind the female, in an effortto get close enough for capture. In many cases pursuitalso occurred after capture. Pursuit, as defined here, ischaracterized by the absence of direct contact betweenthe two specimens. Fighting, as it is defined here, wasa rare behaviour occurring between two males: facingeach other they were beating very quickly with theirsecond antennae. All these interactions (contact, cap-ture, pursuit and fighting) lasted very short in time.Contacts mostly lasted less than a second, the otherthree behaviours lasted for 1–3 seconds. When a maleencountereda female, the possible sequences of behav-iour were contact – capture - mating, capture - matingor capture – pursuit. When a male encountered a male,the possible sequences of behaviour were contact –fighting – pursuit or contact – capture – pursuit. Of thefour above mentioned behaviours, contacts occurredmost frequently, very often not followed by any of theother behaviours. Capture also occurred sometimes asa single unit, while pursuit and fighting were alwayspreceded by either contact or capture.

Three phases can be differentiated in the matingbehaviour: capture, positioning, and copulation. Dur-ing capture, the male tried to grasp the female. Suchan attempt was always made from above and behindthe female. Even if the animals were very close to eachother frontally or laterally, males did not try a capture.The male used its first antennae to grasp the femalearound the groove between the head and body cara-pace, behind her second antennae (Figure 1). Imme-diately after capture, the male started moving to theventral side of the female and clinged to the ventralmargin of her carapace with the hooks of his first legs.Once secured this way, the male loosened his grip withthe first antennae and asssumed in a position where hislength axis was perpendicular to that of the female, sothat they formed a sort of cross (Figure 2). Thereafter,the pair startd rotating: the male was swimming aroundand thus turned the female around her length axis. Dur-ing this circumvolution phase, the male was pushing

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Figure 1. Capture, the first phase of the mating process inMoinabrachiata: the male is grasping the female.

several times his postabdomen between the valves ofthe female and inserted it into the female’s brood pouchto ejaculate the sperm. After the circumvolution, themale and female immediately splitted apart again.

Several mating attempts by a male were observed,but we could observe only five copulations. During theentire mating process, the female was trying to escapeby swimming away and by moving vigorously withher postabdomen. Very often the female was able toescape while the male attempted to take his positionon the ventral side. In the few cases that the femalecould get rid of the male while they were rotating, themale continued the circumvolution alone and pushedout his postabdomen.

The duration of the mating process varied between16 and 25 seconds (mean 19.6). Capture and position-ing took only 3–8 seconds, while the circumvolutionphase lasted 12–18 seconds. A successful mating prob-ably requires a certain period for circumvolution, whilethe capture and positioning phases may be very short,

Figure 2. Circumvolution, the final phase of the mating process inMoina brachiata: copulation takes place.

their length very likely depending on the skill of themale.

Mate preferences

Males and different females (parthenogenetic andephippial ones) were observed for periods of tenminutes in eight different combinations as listed above.Generally the animals were active in the first minutesand they were much less active in the tenth minute.During the observation periods, almost exclusivelycontacts were seen, other behaviours being very rare.Therefore, the number of contacts in the different com-binations will be evaluated. When one male and oneephippial female were placed together in a drop ofwater, very low activity was observed, and the ani-mals mostly stayed at the edge of the drop and dis-played only contacts (1.5 contacts/minute). In the caseof two males and two ephippial females, the activ-ity was higher (3.25 contacts/minute between malesand 7.5 contacts/minute between males and ephippial

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Table 1. Number of contacts and captures in trials withtwo males and two ephippial females. Seven observa-tions were made, each during a period of five minutes.Numbers refer to mean values for a given period offive minutes; minimum and maximum values are giv-en between brackets.

Contacts Captures

Male & male 5.1 0

(1–12)

Male & ephippial female 12.1 1

(5–22) (0–3)

females). When two males were put together with twoparthenogenetic females, the mean number of contactsper minute between males was 2.5, whereas betweenmales and parthenogenetic females 4 contacts/minutewere observed. In the experiment with different kindsof females, the male showed greater interest in theephippial female (3.25 contacts/minute) than in theparthenogenetic one (0.5 contact/minute). When onlymales were put together the mean number of contactswas 2 (two males) and 0.75 per minute (four males). Inthe experiment with three males and one dead ephip-pial female, the males contacted each other less fre-quently (0.5 contacts/minute) then the dead ephippialfemale (3.75 contacts/minute). When two males wereput together with one parthenogenetic female and onedead ephippial female, the number of contacts betweenmales was 0.5 per minute, between males and the deadephippial female 1 per minute, and between males andthe parthenogenetic female 0.25 per minute.

The number of contacts and captures was countedthrough the first five minutes in seven trials with thecombination of two males and two ephippial females.The mean number of male-ephippial female contactswas 12.1 and the number of male-male contacts was5.1 (Table 1). Since the probability of a male-ephippialfemale encounter in this setup is twice as high as that ofa male-male encounter, such a difference was expect-ed. However, none of the male-male contacts initiat-ed capture, while seven captures were observed aftermale-ephippial female encounters.

Discussion

Moina brachiatais a cyclical parthenogen. The firstgeneration hatching from ephippia contains femalesonly, and this is the only generation which invari-ably and uniformly consists of parthenogenetic females

(Grosvenor & Smith, 1913). Any of the succeedinggenerations may be mixed, containing both partheno-genetic and ephippial females,as well as males. Matureephippial females have a well developed ephippiumand, depending on the species, one or two large eggsin the ovaries wich will be deposited in the ephippiumafter copulation (Weismann, 1880; Goulden, 1968).

The present observations of the mating behaviourprovided very similar results to those of Weismann(1880) and Goulden (1968). There are some differ-ences, however. Weismann (1880) and Goulden (1968)reported that the ventral sides of the male and femaleare apposed during capture, whereas I found that thecouple forms a sort of cross. Also, the circumvo-lution during copulation was not mentioned in theprevious studies. Most likely, the specimens previ-ously observed did not display these characteristics.This is particularly striking in the case of Weismann(1880) since he studiedM. rectirostris, a synonym ofM. brachiata. Goulden (1966, 1968) studied copula-tion in different, American species ofMoina. Duringmy study, I also made an observation of the copulationof M. micruraspecimens, and observed that the male ofthis species too tries to secure himself in a transversalposition and make circumvolution (Forro, unpubl.), sothis behaviour most likely cannot be considered speciesspecific forM. brachiata. A possible explanation forthe discrepancy between my observations and previousstudies may be that in the present study, the animalswere observed in such a small amount of water thatthey were not able to display their natural behaviour.This is unlikely, however, because I observed one mat-ing with the same characteristics under the microscopein a Petri dish, i.e. in a larger amount of water.

The cross-position and circumvolution do not seemto be restricted toMoina species, or not to theAnomopoda. The cross-position was seen by Brauer(1872) in Leptestheria dahalacensisand, the cross-position as well as the circumvolution were describedin Cyzicus tetracerusby Gravier & Mathias (1930) andMathias (1937). Although Martin et al. (1986) illustrat-ed a non-cross behaviour during mating in a species ofLynceus, this drawing was based on a photograph takenduring the early stages of mating. Laevicaudatans doin fact form a cross during mating (J. Martin, personalcommunication). In his description ofDaphniamating,Jurine (1820) wrote that ‘I noticed other animals thatwere embraced almost transversely, in such a way as toform a sort of cross’. According to Weismann (1880),succesful fertilization can occur inDaphniaonly if themale and female are face to face and parallel. However,

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Scharfenberg (1911), among the thousands of coupleshe observed, did not see a single one for a long period inparallel position. Instead, he observed the most malesstayed lateral to the female and with their body axis ori-ented parallel to that of the female. Sometimes therewere males on both sides of the female, an observationalso reported by Muller (1785). It should be noted thatthis position is different from that ofMoina: as can beseen on Figure 2. in Scharfenberg (1911), the lengthaxes of the large female and of the two, much small-er males are parallel, whereas it are the body planesthat are at right angles. Although the appearence of thecross-position inDaphniamay thus be questioned, itcertainly occurs and is followed by circumvolution inat least two species of Spinicaudata.

Table 2 provides a comparison of the duration ofmating in various crustacean groups and species. Thereare considerable differences between species of the dif-ferent groups. Of the anomopods studied so far,Moinabrachiata has the shortest mating process. Unfortu-nately, neither Weismann (1880) nor Goulden (1966,1968) provided data on the duration of mating. Impor-tantly, within the mating sequence, the precopulatoryphase (capture and positioning) is very short, varyingbetween 3–8 seconds. This indicates that the time forlocating and identifying a receptive female after anencounter is very short.

The observations of the present study indicate thatmales are the actors in mating: they initiate the processby grasping the female,while the females invariably tryto swim away and escape. Weismann (1880) reportedthat the female was first trying to escape and then ‘sub-mitted to her fate’. In other anomopod species, it wasreported that the female was agitated (Jurine, 1820) orstimulated by the activity of the male (Shan, 1969).Some studies observed precopulatory courtship (e.g.Glatzel & Schminke, 1996; Cohen & Morin, 1990) inother microcrustaceans, but this could not be observedduring the short mating process ofM. brachiata.

Our preliminary examinations on mate preferencesof the males yielded some indicative data. Our obser-vations revealed that the males positively selected forephippial females and recognized them as potentialmating partners. Both Weismann (1880) and Goulden(1966) noted thatMoina males almost invariablygrasped ephippial females. Goulden (1966, 1968)hypothesized that males might use visual cues in locat-ing ephippial females, and that they recognize ephip-pial females by the presence of an ephippium. Withthe medial seta of the antennule, the male might sub-sequently identify the female as conspecific since the

structure and surface sculpture of the ephippium isspecies specific inMoina. Goulden (1968) thus hypoth-esized that the elaborate ephippium does not merelyserve the protection of the egg but is also developedto maintain reproductive isolation among species. Theephippium and the large egg in the ovary of ephip-pial females have a dark colour and are clearly visi-ble. However,Moina species, particularlyM. brachi-ata, usually inhabit turbid waters, and visual cuesmay therefore be of limited value forM. brachiatain locating mates. Chemical signals involved in matingbehaviour of copepods and rotifers have been described(Snell & Morris, 1993; Snell & Carmona, 1994), andthe use of sexual pheromones in Anomopoda is verylikely. The possible role of the aesthetascs of the maleantennule in chemoreception and mate location wasalready hypothesized by Scourfield (1905). Howev-er, Crease & Hebert (1983) did not find evidence forthe presence of sex pheromones inDaphnia magna.In their review on chemical communication in zoo-plankon, Larsson & Dodson (1993) came to the con-clusion that there must be minimum one chemical sig-nal involved in the location and attraction of mates inDaphnia pulex. Carmona & Snell (1995) demonstratedthe presence of glycoproteins on the ovary ofDaph-nia obtusaandCeriodaphnia dubia, and hypothesizedthat these species specific molecules may be involvedin contact recognition of mates, as they are in rotifers.We still lack a coherent view of the role of chemicalcommunication in sexual behaviour of Anomopoda.From the available data onMoina mating, it seemslikely that chemical signals (diffusible pheromones)are involved in mate location. The identification of themate might be aided by the surface structure of theephippium (mechanoreception), and it is also possi-ble that the ovary produces glycoproteins for contactchemoreception inMoina. However, further behav-ioural studies are necessary to provide insight into howcontact chemoreception is performed. As a matter offact, such examinations are also desirable inDaphniaand other anomopod genera.

After a successful copulation, when sperm has beenejaculated into the brood pouch, the egg is releasedfrom the ovary into the brood chamber and fertil-ized. Weismann (1880) observed that the spermato-zoa ofM. brachiatadesintegrate quickly, while theyremain intact for a longer period inM. macrocopa.This difference may be related to the fact that the latterspecies has a two-egg ephippium. Because the ovariesare not functioning simultaneously, some time is nec-essary until both eggs are released. A given ephip-

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Table 2. Mating duration in various crustacean taxa.

Taxon Duration of mating Source

Anostraca

Branchipus schaefferi 6–15 sec Mathias, 1937

Eubranchipus grubei 1 min Mathias, 1937

Notostraca

Lepidurus apus 30 sec Mathias, 1937

Spinicaudata

Cyzicus tetracerus 15–20 min Gravier & Mathias, 1930,

Mathias, 1937

Laevicaudata

Lynceus gracilicornis 5 min Martin et al., 1986

Anomopoda

Daphnia spp max. 8–10 min Jurine, 1820

Daphnia magna up to 1 day Scharfenberg, 1911

Moina brachiata 16–25 sec this study

Pleuroxus denticulatus >20 min Shan, 1969

Copepoda, Harpacticoida

Parastenocaris phyllura > 14 minutes Glatzel & Schminke, 1996

Ostracoda <1 min to over 30 min Cohen & Morin, 1990

pial female can produce several ephippia and thenswitch to parthenogenesis. For instance, Gordo et al.(1994) observedM. salinaproducing a maximum oftwo ephippia. Hence, an ephippial female ofMoinamay copulate several times, most probably with dif-ferent males, resulting in the production of geneticallydiverse offspring. It is conceivable that the continuousattempt to escape by females during mating is a sort ofmate selection behaviour.

Acknowledgments

Several colleagues in the Department of Zoology pro-vided technical assistance, and A. Urban made manyof the observations. Dr Koen Martens (Brussels) anddr. Alain Thiery (Avignon) provided important infor-mation and copies of the relevant literature. Dr AntonBrancelj partially supported my stay in Postojna, andI benefitted from the inspiring discussion at the 4thCladocera Symposium. Comments from Dr Luc DeMeester and two anonymousreferees greatly improvedthe paper. I am very grateful for their kind help.This research was supported by the National Scien-tific Research Fund (OTKA 017464).

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