Odonatologica 16(2): 201-207 June I. 1987 Sperm competitionin Ischnura elegans (Vander Linden) (Zygoptera: Coenagrionidae) P.L. Miller Department of Zoology, University of Oxford, South Parks Road Oxford, OX1 3PS, United Kingdom Received March 19, 1986 / Accepted July 10, 1986 examination times The capture, preservation and subsequent at known during copulation has shown that most mature females copulate more than once. By marking copulating pairs it was found that some females accepted second males on the same day. Copulations ofdecapitatedmales with intact females were relatively short-lasting as also was the case when both sexes had been decapitated.However, copulations of of intact males with decapitated females were long-lasting and resembled those undisturbed pairs. Males therefore apparently control the duration of copulation. Measurements of volumes in females the that sperm copulating support hypothesis rivals from from the copulating males remove all the sperm of the bursa, but none 3 spermatheca. Sperm vesicles of males contain a mean of0.011 ± 0.0019 mm ( n=14) of of females after transfer contain during stage 1 copulation. Spermathecae sperm a 3 mean of 0.0064 ± 0.0023 mm (n=I I), whereas bursae contain a mean of 0.0023 ± 3 0.0009 mm (n=14). During stage II of copulation, males transfer the whole vesicle about the the contents, which is 5 times volume that can be accommodated in bursa. This apparent anomaly is discussed. INTRODUCTION Ischnura sometimes for than known inother spp. copulate periods longer are species of Odonata (KRIEGER & KR1EGER-LOIBL, 1958; PAULSON & CANNINGS, 1980; ROBERTSON, 1985). In a population of I. elegans (Vander L.) examined in southern France, copulation commonly lasted for of 6-7 h, and I suggested that such long copulations represent a form mate guarding by the male (MILLER, 1987). This may have benefited males since for females in females competition the high-density population was strong, and did not oviposit until late in the day. 1 described a method which allowed copulation to be observed closely in pairs whose heads had been crushed and 202 P.L. Miller this movements of the whose abdomens had been dissected. In way the penis of the female could be watched and within the transparent genital tract filmed, and removal of sperm from the bursa by the penis was witnessed (MILLER, in 1987). It is important to know more about the extent of sperm competition this species, and to this end copulating pairs were caught and preserved at from femalesand their volumes recorded times. Sperm masses were dissected out of WAAGE The were measured following the methods (1979, 1982, 1984). results, presented here, show that females commonly mate more than once, and removed from the bursa but not from the they suggest that sperm are sperma- in with what has been found in I. ramburi theca by a copulating male, agreement (WAAGE, 1986). MATERIAL AND METHODS abundant and flooded fields close a biological Ischnura elegans was very at some ponds recently to Tour du Valat in the France 04° research station at La Camargue, southern (43° 30'N, 30'E), during recorded July and August, 1984 and 1985, Single females and copulatingpairs were caught at times; in heads were immediatelypreserved 2% formaldehyde their were crushed ("decapitation”) and they while still in copula. Further copulatingpairs were caught, marked on the wings with a permanent- -ink writer, and then released. the total other The terms "sperm volume” and "sperm mass" areused tomean mass of sperm and seminal which and be the male or the materials (e.g. fluids) accompany sperm may produced by assessed in In the first (cf. WAAGE, 1979, 1984) female. Sperm volumes were one of two ways. and offemales and their and sperm masses were dissected out from the bursae spermathecae lengths breadths measured under with Their estimated were a binocular microscope a graticule. lengthx breadth then in units which could be used to make mean was calculated to give a figure arbitrary the volumes measured 3 comparisons between individuals. In the second method, were in mm by from females from the vesicles of males uniform thickness compressing sperm masses or sperm to a 100 under slide. The area of the mass was then accurately of n m a supported coverslip on a under microscope and from this the determined by drawing it on squared paper a high-power the showed reliability for volume was calculated. Repeated measurements on same masses good but bursae the cylindrical spermathecal masses and for the kite-shaped masses from sperm vesicles, because of the sometimes less than 100 mu' gave more variable values probably parts mass were thick. and estimated the Values are expressed in means ± standard deviations significance was using Mann Whitney U test. The state of maturity ofinsects was estimated from body coloration (PARR & PALMER, 1971; HAMMOND, 1983). RESULTS OCCURRENCE OF MORE THAN ONE COPULATION BY FEMALES in tandem between 08.00 Nine pairs of I. elegans were caught pre-copulatory sunrise at 06.29 h and 08.30 h (a time when many copulations were starting; was and the of the females wereexamined. Table I shows on 31st July) storage organs contain in both and all had therefore that all wire foundto sperm storage organs Sperm competition in Ischnura elegans 203 In further 20 females I of copulated on a previous day. a caught during stage well-filled copulation at a time when all the corresponding males had sperm their and contained vesicles, 19 had abundant sperm in spermathecae, one no Thus 28 out of29 copulating females examined contained and had sperm. sperm copulated previously. the Forty copulating pairs were then captured between 09:30 and 10:30 h; released still in males and females were both marked on the wings and then found in with unmarked males later copula. Of these, 2 females were copulation males the on the same day, 2 were found with unmarked on following morning, and one was found in copulation with an unmarked male48 h later. Thus some males the the after females accepted second on same or subsequent day a mating, if first male had transferred A further 33 but it was not known the sperm. pairs 09:15 and 10:15 h and the heads of the males were therefore captured between in where were crushed. They were then marked on the wings and released a region flew off the but they could be observed. In some pairs the female towing male, had after 78 most remained settled. Of 15 pairs which were watched, 5 separated min and the remainderhad doneso after 2 h. After separation, the femaleseither while males the The perched nearby or flew off the dropped to ground. copula- like that of in which the heads ofboth had tory performance was pairs partners been crushed (MILLER, 1987). Eighty minafterthefirst pair had been released, a male. the marked female was found in copulation with a new unmarked During in with unmarked ensuing 4 h, 7 marked females were found copulation males, and a further 2 were in tandem. The second copulations persisted for at least an normal. Thus females which had hour and activity appeared to be some copu- latedwith decapitated males accepted second males within a few hours ofleaving the first. Sperm transfer by decapitated males was not confirmed, but previous observations have shown that it does occur when both partners have been decapitated (MILLER, 1987). marked the Thirteen pairs, captured between 10:30and 10:50 h, were on wings and then released after crushing the heads of the females. Of these, 10 were observed to continue to copulate for at least 150 min, and of these 2 continuedfor after which females and the males flew off. Thus intact 280 min, the were dropped males copulated with decapitated females for 2-4.5 h, whereas decapitated males copulated with intact females for about 1-1.5h, as did pairs in which the heads of This that males control the both had been crushed (MILLER, 1987). suggests durationof copulation. In the same population undisturbed pairs were found to whereas copulate for a mean of 324 ± 90 min (S'.D., n=13) (MILLER, 1987), has found shorter in less dense in Banham (pers. com.) a mean populations England. 204 P.L. Miller SPERM REMOVAL FROM FEMALES DURING COPULATION Table I shows the volumes of sperm masses dissected from femaleswhich had been caught at the times given. A further 3 solitary females caught between 15:30 10:00 and 10:20 and 17:30 h, and one female caught copulating between h, of contained no sperm andare not includedin TableI. The volumes sperm masses from the spermathecae of females caught before, during and after copulation do from the bursae of females not differ significantly. In contrast, sperm masses smaller < than those caught in stage I of copulation were significantly (P 0.005) from those from females in II. As Table pre- or post-copulatory females, or stage in their 1 shows, 15 out of 20 (75%) of stage-I females had no detectable sperm well-filled did9 bursae, whereas 8 out of 10 (80%) stage-II females had bursae, as out of 10 (90%) post-copulatory females. in the horns of In 12 out of 19 females caught in stage I and preserved copula, in in the other 7 within the the penis were found the bursa, while cases they lay within duct. vagina. In none were they found the spermathecal 3 from females’ Table II shows the mean volumes in mm of sperm masses and from males’ vesicles. The males all and storage organs sperm were caught transferred whereas the preserved in stage I of copulation before they had sperm alone late in the females were either in stage II of copulation or they were caught for of0.01 3 is day.