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Investigates the differences in sexual dimorphism and gender differences in life histories of male and female damselfly Lestes forcipatus Rambur. Patterns of mass gain in congeners; Challenges of parasitism; Attribution of sex difference in parasitism to sex difference in trade-offs between reproductive and immune traits.

Summary 1. Variation in immune responsiveness within and among species is the subject of the emerging field of ecological immunology. The work reported here showed that individuals of Lestes forcipatus Rambur differ in their likelihood of mounting immune responses, and in the magnitude of those responses, against a generalist ectoparasite, the water mite Arrenurus planus Marshall. 2. Immune responses took the form of melanotic encapsulation of mite feeding tubes, occurred in the few days after host emergence, and resulted in mites dying without engorging. Such immune responses were more probable and stronger for hosts sampled later rather than earlier in the season. Such responses may act as selection affecting seasonal patterns of egg hatching and larval abundance of mites. 3. Contrary to expectation, metrics of host size (wing length) and wing cell fluctuating asymmetry were not related to the likelihood of immune responses. 4. The importance of season on immune expression of insects has not been explored in detail. These results suggest possible trade-offs in allocation of melanin (or its precursors) to maturation versus immunity, and indicate the need for studies on the synergistic effects of weather and parasitism on host species that use melanotic encapsulation to combat parasites and pathogens. [ABSTRACT FROM AUTHOR]

1. This study investigated inter-specific variation in parasitism by gregarines (Eugregarinorida: Actinocephalidae), among sibling species of damselflies (Odonata: Zygoptera), in relation to relative size of geographical ranges of host species. 2. Gregarines are considered generalist parasites, particularly for taxonomically related host species collected at the same sites or area. Prevalence and median intensity of gregarine parasitism was obtained for 1338 adult damselflies, representing 14 species (7 sibling species pairs) across 3 families within the suborder Zygoptera. Damselflies were collected at three local sites in Southeastern Ontario, during the same periods over the season. 3. Five out of seven species pairs had significant differences in parasitism between sibling species. The less widespread host species was the more parasitised for three species pairs with significant differences in gregarine prevalence, and for two species pairs with differences in median intensity. The more widespread host had a higher intensity of infection as expected, in two species pairs. 4. Future studies on ecological determinants of parasitism among related species should examine robust measures of abundance of species and representation of species regionally. [ABSTRACT FROM AUTHOR]

1. Insects commonly resist parasites using melanotic encapsulation. Many studies measuring immune response use the amount of melanin deposited on an artificial object that has been inserted into the animal as a proxy of the amount of resistance that the host is capable of mounting to natural parasites. 2. The relevance of this methodology to immune response in natural insect populations needs further study. Here, we examined two temperate damselfly species to elucidate the relationships among damselfly size, natural resistance to mites, and the immune response mounted by the same damselflies against nylon filaments. 3. The damselfly species that had high rates of melanotic encapsulation of mites in nature deposited more melanin on the nylon inserts than the species with low rates of natural resistance. 4. In females of this species, those that had resisted mites naturally melanised the nylon filament more aggressively than those that did not resist mites. 5. Our results show some support for the use of nylon filaments to assess natural patterns of immune response in these damselflies, but also suggest that caution should be used in interpreting the responses. [ABSTRACT FROM AUTHOR]

The effect of artificial habitat in altered landscapes on species interactions and their suite of enemies is largely unknown. Water mites have been associated with reduced fitness of model damselflies. Mite parasitism was variable, but higher for Ischnura verticalis damselflies from natural, than from artificial, wetlands in the same region. There were no differences in timing of sampling, temperature during sampling, or host age or sex composition of samples between wetland types. Landscape structure might constrain mite presence or abundance at wetland sites or wetland type might be a better predictor of mites, based on factors such as prey abundance. Fewer mites on damselflies from numerous artificial wetlands means that the strength of parasite-mediated selection is likely less than would be inferred if only natural wetlands were surveyed. Such effects of human changes in habitats on host species probably occur often. [ABSTRACT FROM AUTHOR]

The importance of multiple enemies from different trophic levels on investment in defence by prey has, with some exceptions, received little attention. Some defences may make the victim more susceptible to other enemies; this latter situation applies to predators and parasites of larval damselflies. Baker and Smith [ Oecologia 109 (1997) 622) showed that larval damselflies were as active in the presence of both mites and fish as they were when only mites were present, an apparently maladaptive behaviour that results in higher fish predation. In this paper, we further examine this maladaptive behavioural response to multiple enemies (fish predators and mite parasites) and test whether their defence responses are a result of the order in which they experience the parasite or predator, and/or if behavioural ‘personalities’ exist, such that some individuals show anti-predator behaviours and other show anti-parasite behaviours. Order of experience did not affect the four main behaviours (groom, crawl, turn and swim) exhibited when larval damselflies were simultaneously exposed to fish and mites. Grooming levels increased in response to mites, decreased in response to fish and when exposed to both mites and fish were similar to when they were exposed to mites alone. Duration of the other three behaviours was lower in the presence of both mites and fish. The crawling ‘personalities’ were evident. The apparently maladaptive response of high grooming levels in the presence of mites and fish is not a result of order of experience or ‘personalities’. It may be a result of relatively high encounter rates with mite parasites, compared with the encounter rates with fish. Lower encounter rates can result in diminishing investment in defence against an enemy. [ABSTRACT FROM AUTHOR]

Female-limited colour polymorphism occurs in many damselfly species, where one morph resembles the male (andromorph) and the other is dissimilar (gynomorph). Explanations for this phenomenon vary, but most assume that andromorphism has arisen in odonates, as a response to excessive male harassment. Here, we quantify the extent of continental and seasonal variation in female morph frequencies in a widely-distributed damselfly and ask whether the spatiotemporal patterns in andromorph frequency can be understood on the basis of sexual harassment theory. We sampled the damselfly, Nehalennia irene (Hagen) among regions across Canada, and at several sites, over the reproductive season, within Central Canada. Andromorph frequencies ranged from 0 to > 90% across Canada. In particular, sites in Western Canada had consistently high andromorph frequencies, whereas andromorph frequencies among Central sites were lower and variable and, among Eastern sites, were lower still (except one site) and relatively invariant. For populations in Central Canada, both andromorph frequencies and population densities varied significantly over time, reaching a peak mid-season. As expected, morph frequency covaried significantly with estimates of male harassment in some cases, but estimates of male harassment did not consistently account for variation in morph frequencies within all regions. Additional factors such as genetic drift may influence morph frequency at the edge of a species’ range. Future work also should test, and attempt to explain causation, for seasonal variation in morph frequency. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 501–508. [ABSTRACT FROM AUTHOR]

The damselfly, Nehalennia irene (Hagen), has two distinct female colour morphs. Individuals of one morph have male-like colouration and pattern (androchromes), whereas gynochromes are different from males and androchromes in these respects. In several damselflies, such female-limited polychromatism is attributable to a single genetic locus. We developed six polymorphic genetic markers, which were codominant, to test for genetic differentiation in N. irene, collected from two sites located 8 km from one another in eastern Ontario, Canada. Based on three censuses spanning a 10 year period (1992–2001), morph ratios differed consistently and significantly between these two sites. However, subpopulations at these sites were not genetically differentiated with respect to the putatively neutral markers. Our results suggest that site differences in morph ratios of female N. irene cannot be explained by genetic drift, but are consistent with spatially variable selection operating on different morphs, perhaps mediated by male density. Alternatively, morph type may be a plastic trait and cues for induction may differ between sites. [ABSTRACT FROM AUTHOR]

Female-limited polymorphism occurs in different animal taxa but is particularly abundant among species of damselflies (Insecta: Odonata), most likely as a consequence of selection to avoid excessive male harassment. Recent work on the damselfly Nehalennia irene indicated that within year spatial variation in female morph frequencies was limited in nearby populations (i.e. intra-regional scale), but large at a continental scale. As anticipated, some of the observed variation in morph frequency was correlated with variation in the estimated degree of male harassment towards female morphs, measured by male density and operational sex ratio. Here, we extended earlier work by quantifying variation in morph frequency over two to three years, allowing us to elucidate how morph frequencies vary temporally at both intra-regional and continental scales (data for 8 populations over three years and for 33 populations over two years, respectively). Annual variation in morph frequencies was relatively high at the intra-regional scale, but was never large enough to obscure the underlying spatial pattern at the continental scale. At both geographic scales, male density and operational sex ratio were highly variable between years. The estimated degree of male harassment correlated with variation in morph frequency within some regions, but not all. Together, the observed natural variation in female morph frequencies may be partly explained by variation in male harassment, but it appears that a complete understanding will require considering the role of other environmental factors. [ABSTRACT FROM AUTHOR]

Sex-biased dispersal is well known for birds and mammals, typically by females and males, respectively. Little is known about general patterns of sex-biased dispersal in other animal taxa. We reviewed return rates for a model group of invertebrates (damselflies) and explored putative costs and benefits of dispersal by males and females. We used published capture–mark–recapture data and examined whether a sex bias existed in likelihood of recapture at least once, at both emergence and/or breeding sites. We assessed whether this metric of likelihood of recapture was indicative of dispersal or philopatry, and whether any emerging pattern(s) were consistent across damselfly families. Using a meta-analysis, we found a higher likelihood of recapture at least once for males than for females at both natal sites and breeding sites, which seemed attributable to higher female-biased dispersal, although female-biased mortality cannot be discounted particularly for some species. Sex biases in dispersal among damselflies may be understood based on sex differences in maturation rate and foraging behaviour, both of which should affect the costs and benefits of dispersing. This hypothesis may be useful for explaining patterns of dispersal in other animal taxa. [ABSTRACT FROM AUTHOR]