Mnais costalis male male exist in 2 forms specialised for the demands of 2 distinct strategies, territorial fighters and non-territorial sneaks, which give approximately equal fitness payoffs. Territorial male male have orange wings, whereas typical non-territorial male male are clear-winged. By simulating agonistic encounters between male male it is shown that the 2 morphs showed distinct responses to the signal from orange wings: territorial orange-winged male male always tried to enter contests, while clear-winged male male always avoided them. On the other hand, the 2 morphs showed similar responses to the signal from clear wings: both morphs tried to attack models. Also presented are 'painted clear models' which were clear-winged male male whose wings had been painted orange, and both morphs responded as if they were orange-winged models. These observations indicate that male male discriminate between fighter and sneaker morphs using the colour of wings, and shows different styles of agonistic responses toward fighter and sneaker morphs. It is likely that non-territorial sneaks may gain an advantage from non-signalling because clear wings increase crypsis on another male territory, increasing their success in stealing copulations. No indication was found that clear-winged male male are female mimics, or that having clear wings reduced the level of aggression directed towards them by territorial orange-winged male male.

1. The relationship between the abundance of midgut parasites (eugregarine trophozooites) and the survival of hosts (field-collected damselflies, Mnais costalis) was investigated under laboratory conditions.2. Males of M. costalis are morphologically and behaviourally polymorphic, typically existing as clear-winged non-territorial sneaks and orange-winged territorial fighters (the latter are larger in size). The survival cost of eugregarine infection for the two morphs was compared.3. Orange-winged males showed shorter longevity compared to clear-winged males when they were fed at levels lower than the natural feeding rate, or when they were deprived of food. In contrast, morph longevity did not differ when they were fed until satiation every day.4. Within each morph, the survival of damselflies was negatively correlated with the parasite abundance except when damselflies were fed until satiation.5. The results suggest that the abundance of eugregarine parasites exerts a substantial cost, which is associated with the maintenance of alternative mating strategies, together with the higher developmental cost and energy expenditure of the fighter morph.

SummaryIn this paper we investigate the relationship between the chronic burden of mid‐gut parasites (eugregarine trophozooites) and the effect of an acute haemolymph challenge (a nylon insert) on two important insect immune effector systems (phenol oxidase (PO) and the encapsulation response) in a field‐population of damselflies. PO levels in the haemolymph, and the magnitude of the encapsulation response were maintained, regardless of chronic and subsequent acute experimental immune challenges. The maintenance of these effector systems is therefore probably an important life‐history requirement in these damselflies. Investment in mid‐gut PO levels was significantly negatively related to the animal's chronic parasite burden after an acute experimental challenge in the haemolymph, suggesting that maintaining PO levels across two physiological compartments (haemolymph and mid‐gut) is costly. The results suggest that the immune effector system activity in different physiological compartments in an insect's body is affected by chronic parasite burdens in the face of the demands imposed by an acute immune insult.

Males of the damselfly Mnais costalis Selys (Odonata: Calopterygidae) are morphologically and behaviourally polymorphic, typically existing as clear-winged non-territorial 'sneaks' and orange-winged territorial 'fighters'. The amount of orange pigment in the wing, as measured with a chromameter, varied between individuals, and decreased as the reproductive season progressed. Young individuals maintained in the laboratory on high or low nutrient diets differed in the amount of pigment that developed in the wing. Males in the high nutrient group developed darker wings faster than those in the low nutrient group. Young adults of both sexes and morphs were fed C-14-radiolabelled tryptophan or tyrosine (precursors of the pigments ommochrome and melanin, respectively). Ommochrome was restricted to the pseudopterostigma of the males of both morphs and was not present in females. The presence of tyrosine in the wing cells of orange males, but not of clear males, indicated that the orange pigment is at least partly constituted from melanin. These data show that at least some pigment levels must be maintained continuously in the wings of orange males, and that maintenance is costly as it is compromised at low nutrient levels.

Males and females of the Japanese calopterygid damselfly, Matrona basilaris japonica Fester, showed a rapid (within 24 h), and significant reduction in immune system function (encapsulation response) after reproductive activity (copulation or oviposition).A similar, but non-significant, change occurred in males that conducted energetically costly behaviour (fighting).These data suggest that there may be physiological costs other than energy-based trade-offs associated with copulation and oviposition that may have life-history consequences via their effects on immune system function.

Before reproductive events, female Calopteryx splendens xanthostoma show a distinctive Fight behavior over patches of oviposition substrate guarded by territorial males. We term such flights ''flybys.'' Since females fly most frequently (and nonrandomly) over the sire which they eventually utilize, the flight type appears to be related to the female's selection of a reproduction site. When males were experimentally excluded females made flybys over more sites than when males were present. We manipulated the levels of agonistic interactions between males to determine the effect of fighting on flybys. The frequency of flybys by females over each patch did not change with different levels of male agonistic activity, but females landed and copulated on patches where fighting between males was lowest. Moreover, when females secured access to an oviposition site without copulating with the resource holding male, they made flybys over more sites than when they secured access to a site by copulating with the territorial male. The results suggest that one function of flybys is to allow females to assess remotely potential male interference at oviposition sites.

We used the random amplified polymorphic DNA technique to determine last male sperm precedence (P2) in the damselfly Calopteryx splendens xanthostoma (Charpentier). We amplified DNA from mothers, putative fathers and from the embryos of individual offspring, and subsequently calculated band-matching coefficients between known first-order relatives (offspring within a clutch) and non-relatives (mothers and fathers) to estimate last-male paternity. The data indicate that, as in other Calopterygidae, P2 is high (0.98) in the bout of oviposition immediately following copulation, despite the fact that the males of this species do not completely remove the sperm of previous males (Siva-Jothy & Hooper 1995).

Female Calopteryx splendens xanthostoma have discrete sperm storage organs and secure oviposition in one of two ways: a female either mates with a male who subsequently guards her whilst she oviposits (MAG), or females can secure access to an oviposition site without copulating with the resident male (site). Random amplified polymorphic DNA (RAPD) analysis of the genetic diversity of sperm from individual sperm storage organs revealed that the spermathecae contained sperm of a greater genetic diversity than sperm in the bursa copulatrix. Males cannot remove sperm from the spermathecae during copulation, and we propose that the spermathecae might function as a sperm cache for the sperm of previous mates. Females that conduct SAG ovipositions have a higher genetic diversity of stored sperm than MAG females. We suggest that females which gain access to oviposition sites without remating have the potential to exercise postcopulatory choice during oviposition, on the basis of: (i) the observed patterns of sperm precedence in other calopterygids; (ii) the variation in genetic diversity of stored sperm; and (iii) the avoidance of recopulation in SAG females.