Population structure of the rare damselfly,Ischnura gemina (Kennedy) (Odonata: Coenagrionidae)

Summary The population structure of the endemic San Francisco Bay Area damselfly, Ischnura gemina, is examined using mark-recapture methods. Average daily movements, sex ratios, population size, maturation times, survivorship, and dispersion patterns, were recorded and calculated from two small (each less than one hectare) sites 150 m apart in Glen Canyon, San Francisco. Of 563 adults marked over 36 days, 412 (73%) were recaptured at least once. Average daily movements for males and females were less than 6 m, suggesting local movements. However, directional movements of 150 m were observed from one site to the other, indicating dispersal potential. One of the populations was a satellite composed entirely, of emigrating individuals from the other site; no larvae or teneral adults were found at the satellite area. Males were more aggregated than females at both sites. Both sexes were highly clumped at one site but were nearly randomly dispersed at the other site. Total population size for both sexes tended to be constant throughout the sampling period, at about 250. Adult population estimates showed more males were present than, females, but larval counts at one site indicated only a slight excess of males. Average life span estimates ranged from 6.5 days (females) to 23.3 days (males). One male lived at least 36 days. Maturation time for males was about 5–7 days, 7–10 days for females. A long life span and long flight season (March to November) are probably adaptations to the foggy San Francisco climate. All populations of I. gemina located to date are small, possibly originating from founders from nearby demes, and may be subject to different selection pressures. The dispersal potential of I. gemina may increase its chance of survival should small urban demes be threatened with destruction.     

Ontogenetic Behaviour Changes in Larvae of the Damselfly Ischnura verticalis (Odonata: Coenagrionidae)

Larvae of most animals go through large changes in size. Because change in size can lead to changes in ability to gain food and in predation risk, changes in behaviour are predicted to reflect this. Models consider change in amounts of the same behaviour, but different selective pressures on different larval sizes may also lead to qualitative differences in behavioural repertoire. In the damselfly Ischnura verticalis we observed ontogenetic changes in behaviour under controlled laboratory conditions. We found that frequency and duration of feeding behaviour and behaviour related to activity were increased in larger instars. Larger larvae also had higher transition probabilities to the behaviour abdomen wave, straight abdomen raise, and rotate + head out. We also found that the behavioural repertoire of damselfly larvae changed with development: some behavioural patterns were performed almost exclusively by smaller larvae (F - 4 to F - 7) while others were performed almost exclusively by larger larvae (F - 3 to F - 0).     

福建狭翅蟌属一新种(蜻蜓目:蟌科)

记述采自福建省华安县的狭翅蟌属一新种华安狭翅蟌（Aciagrion huaanensis Xu, sp.nov.）,模式标本存放于福建省漳州教育学院.     

Larval Ischnura verticalis (Odonata: Coenagrionidae) Respond to Visual Cues of Predator Presence

Larvae of some species of damselflies respond to chemical cues of fish predators but, while larvae of many species are thought to detect prey through vision, there is little evidence that larvae respond to visual cues of predator presence. This laboratory study indicated larval Ischnura verticalis behaviours are affected by visual cues and, to a much lesser extent, chemical cues of fish; there was no significant interaction between the effects of visual and chemical cues. Responses to chemical cues of fish did not depend on whether fish were fed I. verticalis larvae versus commercial fish food. Larvae were more active in the spring than the fall when they were likely in diapause. Results suggest larvae can use vision to detect large, active predators but can also detect predators through olfaction when visual cues are unreliable.     

Depth selection by larval Ischnura verticalis (Odonata: Coenagrionidae): effects of temperature and food

SUMMARY. 1. Water temperatures in a shallow, weedy bay of a reservoir in southern Ontario were related to depth; mid-day temperatures in summer were approximately 30°C at the water surface and 20°C below 25 cm.
2. In the laboratory, larval Ischnura verticalis released in a thermal gradient (warmest water near the surface) did not remain near the surface any more than larvae in isothermal conditions. However, larvae in both isothermal and gradient conditions tended to spend more time close to the surface than expected by chance.
3. Larvae provided with food at all depths spent more time near the surface than did larvae with no food. Larvae provided with one feeding site in the coldest water remained near the food as much as did larvae provided with a single feeding site in the warmest water.
4. Results suggest that selection of microhabitats is based primarily on food availability and secondarily on proximity to the surface.     

Fluctuating asymmetry, size and mating success in males of Ischnura elegans (Vander Linden) (Odonata: Coenagrionidae)

Fluctuating asymmetry (FA) is thought to be an indicator of developmental stability and negatively related to male mating success in many animal taxa. We investigated the relationships between mating success of males, body size and FA for both wing length and number of setae on the legs in the damselfly Ischnura elegans. Males were classified as mated or unmated at the time of sampling. Fluctuating asymmetry, expressed as right-left differences, showed normal distributions without evidence of directional asymmetry or antisymmetry. Univariate analyses showed a significant negative correlation between size and mating success, and significant negative correlations between FA and mating success for both characters. On the other hand, with a multivariate analysis, new to studies on FA, the effect of body size was still significant but FA did not reach significance for either character. We conclude that the multivariate analysis should be used to assess the role of the different factors affecting mating success. Copyright 2000 The Association for the Study of Animal Behaviour.     

Isolation and characterization of microsatellite loci to study parthenogenesis in the citrine forktail,Ischnura hastata (Odonata: Coenagrionidae)

The citrine forktail, Ischnura hastata, is an American damselfly species, widely distributed, with only‐female populations also found at the Azores islands. Here we report the development of nine microsatellite loci for this species. The number of alleles per locus ranged from six to 11, with an observed heterozygosity ranging from 0.245 to 0.737. Eight of the nine loci successfully amplified in a sample of parthenogenetic females from the Azores. The developed microsatellite system will be a useful tool to investigate population structure, as well as the number of clones, the type of parthenogenesis and the origin of the parthenogenetic populations of this species.     

Diurnal changes and frequency dependence in male mating preference for female morphs in the damselfly Ischnura senegalensis (Rambur) (Odonata: Coenagrionidae)

Ischnura senegalensis females exhibit color dimorphism, consisting of an andromorph and a gynomorph, which might be maintained under a frequency-dependent process of mating harassment by mate-searching males. Males change their mating preference for female morph depending on prior copulation experience. Binary choice experiments between two female morphs were carried out in four local populations in the early morning (07.00–09.00 hours) and the afternoon (12.00–14.00 hours), times which mark the onset and the end of diurnal mating activity, respectively. According to the line census along the water's edge, the proportion of andromorphs in the female population varied from 21 to 67% throughout the survey period for four local populations. Males showed non-biased preference for female morphs in the early morning in each local population, while they chose the common morph in the afternoon. Male mating preference for female morphs was positively correlated to the proportion of female morphs in the population. If the selective mating attacks on the common female morphs inhibit their foraging and/or oviposition behavior, frequency-dependent male mating attacks might provide a selective force for maintaining the female color dimorphism in I. senegalensis .     

Molecular systematics and adaptive radiation of Hawaii's endemic Damselfly genus Megalagrion (Odonata: Coenagrionidae)

Damselflies of the endemic Hawaiian genus Megalagrion have radiated into a wide variety of habitats and are an excellent model group for the study of adaptive radiation. Past phylogenetic analysis based on morphological characters has been problematic. Here, we examine relationships among 56 individuals from 20 of the 23 described species using maximum likelihood (ML) and Bayesian phylogenetic analysis of mitochondrial (1287 bp) and nuclear (1039 bp) DNA sequence data. Models of evolution were chosen using the Akaike information criterion. Problems with distant outgroups were accommodated by constraining the best ML ingroup topology but allowing the outgroups to attach to any ingroup branch in a bootstrap analysis. No strong contradictions were obtained between either data partition and the combined data set. Areas of disagreement are mainly confined to clades that are strongly supported by the mitochondrial DNA and weakly supported by the elongation factor 1alpha data because of lack of changes. However, the combined analysis resulted in a unique tree. Correlation between Bayesian posterior probabilities and bootstrap percentages decreased in concert with decreasing information in the data partitions. In cases where nodes were supported by single characters bootstrap proportions were dramatically reduced compared with posterior probabilities. Two speciation patterns were evident from the phylogenetic analysis. First, most speciation is interisland and occurred as members of established ecological guilds colonized new volcanoes after they emerged from the sea. Second, there are several instances of rapid radiation into a variety of specialized habitats, in one case entirely within the island of Kauai. Application of a local clock procedure to the mitochondrial DNA topology suggests that two of these radiations correspond to the development of habitat on the islands of Kauai and Oahu. About 4.0 million years ago, species simultaneously moved into fast streams and plant leaf axils on Kauai, and about 1.5 million years later another group moved simultaneously to seeps and terrestrial habitats on Oahu. Results from the local clock analysis also strongly suggest that Megalagrion arrived in Hawaii about 10 million years ago, well before the emergence of Kauai. Date estimates were more sensitive to the particular node that was fixed in time than to the model of local branch evolution used. We propose a general model for the development of endemic damselfly species on Hawaiian Islands and document five potential cases of hybridization (M. xanthomelas x M. pacificum, M. eudytum x M. vagabundum, M. orobates x M. oresitrophum, M. nesiotes x M. oahuense, and M. mauka x M. paludicola).     

Effects of size on predation risk,behavioural response to fish,and cost of reduced feeding in larval Ischnura verticalis (Coenagrionidae: Odonata)

Summary We used laboratory studies to examine the role of predation risk and cost of anti-predator behaviour in determining the behavioural response of several larval instars of Ischnura verticalis to a fish predator (Lepomis gibbosus). Smaller larvae were less susceptible to fish predation than larger larvae. Smaller larvae depressed movement to a greater degree in the presence of fish than did larger larvae; large larvae were generally less active than small larvae regardless of fish presence. Reduced feeding resulted in smaller larvae suffering more in terms of reduced growth than did large larvae. In general, our results tend to support the hypothesis that individuals that suffer high costs of anti-predator behaviour but little risk of predation may only exhibit anti-predator behaviours in the presence of predators, whereas individuals with a higher risk of predation and a lower cost of anti-predator behaviour may evolve anti-predator mechanisms that are in effect even in the absence of predators.     

Isolation and validation of eight microsatellite loci in a damselfly Ischnura senegalensis (Odonata: Coenagrionidae) by pyrosequencing a bead-enriched library

Eight microsatellite markers for the population genetics and evolutionary ecology of Ischnura senegalensis (Rambur 1842), which shows body color polymorphism in females, were developed using a streptavidin-bead enrichment library and pyrosequence by a next generation sequencer. The number of alleles per locus and effective number of alleles ranged from 3 to 11 and from 1.24 to 5.51, respectively. Observed and expected heterozygosities were 0.18–0.75 and 0.19–0.77, respectively. No linkage disequilibrium between loci was detected. One locus, IsenAC75, deviated significantly from the Hardy–Weinberg equilibrium, and the locus and additional two loci, IsenAC40 and IsenAC8, were suspected for the presence of null alleles. Altogether, these eight microsatellite loci are considered to be useful for population genetic analyses because of the high polymorphic status and independency.     

Investigating damselfly populations at springs in Banff National Park, Canada, with special focus on Argia vivida, Amphiagrion abbreviatum, and Ischnura cervula (Odonata: Coenagrionidae)

The objective of this study was to estimate Argia vivida (Odonata: Coenagrionidae) populations, identify breeding habitat, and investigate movement of adults within Banff National Park, Alberta, Canada, during the summer of 2003. Mark-recapture techniques and standardized dip-net surveys were used to monitor Argia vivida at various life stages. A reproductive index identified which sites Argia vivida recognized as suitable breeding habitat, and exuvia surveys confirmed breeding sites. The basic structure of emergent and surrounding vegetation was measured to investigate the importance of available ovipositing or roosting sites and the condition of the matrix habitat. Data was recorded for Amphiagrion abbreviatum and Ischnura cervula (both Odonata: Coenagrionidae) to determine if these spring-associated damselflies were successfully breeding within Banff National Park. Comparisons were made between the highly protected Middle Springs and the heavily altered Cave & Basin Springs. Additional surveys at the Vermilion Lake cool spring and Middle Springs Bog investigated their use as breeding habitat for Amphiagrion abbreviatum and Argia vivida, respectively. Results suggest the ecological value of thermal springs extends beyond their origin to outflows and downstream pools. Conservation of Argia vivida must recognize the value of unobstructed thermal outflows, and consider the condition of the forested habitat surrounding springs with regard to its potential use as nocturnal roosts and dispersal corridors. Amphiagrion abbreviatum was confirmed breeding within Banff National Park, while no sign of breeding activity was recorded for Ischnura cervula.     

Alternative mate-finding tactics in a non-territorial damselfly (Odonata: Coenagrionidae)

Males of the non-territorial damselfly Enallagma hageni have two alternative tactics for finding mates: (1) they search the banks of the pond for unmated females (searching tactic), or (2) wait at oviposition sites for females that resurface prematurely from underwater oviposition (waiting tactic). Although the searching tactic yielded more fertilizations than the waiting tactic, for time invested, the waiting tactic became increasingly successful later in the reproductive season due to changes in female oviposition behaviour. The two tactics can be maintained in the population because males can mate by the waiting tactic during the afternoon when few females are available to searchers. Among males visiting the breeding site an equal number of times, males mating by a mixture of tactics were as successful as males mating only by the main tactic. Because marked males were found to use both tactics, these behaviours are interpreted as evidence of behavioural plasticity within individuals, representing one conditional evolutionary strategy.     

Asymmetric intraspecific competition among larvae of the damselfly Ischnura elegans (Zygoptera: Coenagrionidae)

Abstract. 1. A laboratory competition experiment is described in which the growth and development rates of larvae of the damselfly Ischnura elegans (Lind.) were measured over an entire instar.
2. Two larval instars which commonly occur together in the field were used in the experiment; they were maintained with a superabundance of prey and either larvae from the same or the larger/smaller instar.
3. Small larvae suffered increased development times and decreased size increases at the moult in the presence of large larvae but similar interference effects were not evident when these smaller larvae were in the presence of other small larvae.
4. Development time and size increases of large larvae were not significantly affected by the presence of small larvae.
5. Irrespective of the instar combinations investigated, interference effects were reduced when there were more perches available, although in only a few cases was this reduction significant.
6. The consequences of the asymmetric competition reported in the experiment for the study of lifetime reproductive success in damselflies are discussed. Late emerging adults may incur reduced reproductive success.     

Function of abdomen wave behavior in larvalischnura verticalis (Odonata: Coenagrionidae)

Odonate larvae are important predators in the littoral zone of freshwater systems, and in an effort understand their population dynamics, researchers have described and analyzed many of their behaviors. The behavior we call abdomen wave has been considered to be both an aid to respiration and an aggressive display to conspecifics. We found that, under laboratory conditions, abdomen wave was not increased when the oxygen concentration was low or when larvae were in the presence of conspecifics. These results suggest the behavior is not involved in oxygen uptake or in agonistic interactions. The behavior was increased when larvae had food in their guts and was most dramatically increased in the hours preceding a molt. Abdomen wave may function to loosen the exoskeleton prior to molting and/or release of metabolites.     

Reintroduction of the rare damselfly <Emphasis Type=Italic>Ischnura gemina</Emphasis> (Odonata: Coenagrionidae) into an urban California park

Habitat degradation led to local extinction of the San Francisco forktail damselfly (Ischnura gemina) in Glen Canyon Park, San Francisco, California. In this study, we reintroduced I. gemina into Glen Canyon after the damselfly’s habitat was restored. Upon release, we carried out a mark-release-recapture study to monitor the damselfly’s population dynamics. Our data were compared to two “baseline” studies on I. gemina, conducted in the park prior to the damselfly’s demise. Our recapture rates were significantly lower than the prior studies due to a large initial decline in marked individuals upon release. Despite a lower recapture rate, the reintroduction was initially successful since the damselflies reproduced throughout the summer and the following year. However, the population failed to persist during the second year when the habitat became degraded with excess vegetation. Future success is contingent on the continual management and upkeep of the habitat.     

Pre-oviposition mate-guarding and mating behaviour of Argia vivida (Odonata: Coenagrionidae)

Abstract. 1. At Halcyon Hotsprings, British Columbia, Canada, male and female Argia vivida Hagen encountered to mate in two different ways.
2. In the morning (before 12.30 hours solar time), males basked at sunspots in the forest and darted out at passing females, attempting to take them in tandem (the first method of encounter).
3. If a male was successful, the pair engaged in a 31.3±4.8 min copulation followed by an hour of tandem flight before beginning oviposition.
4. As the day progressed, unmated males moved slowly toward the water and arrived at the water at about the same time as the earliest ovipositing pairs (1131±27.5 min solar time).
5. Males retained their grasp on their mates during oviposition (contact-guarding) but since some tandems separated during oviposition, non-tandem males at the water could capture recently released, gravid females (the second method of encounter).
6. The new pairs performed a brief copulation (10.2±3.38 min) and began ovipositing immediately thereafter.
7. Some females that avoided recapture attempted to oviposit unguarded.
8. We believe the long duration of morning copulations and period of tandem constitute a male strategy, which we call 'pre-oviposition guarding', to guard females until it is warm enough at the oviposition site for the females to begin ovipositing.
9. Separation of tandems during oviposition may be initiated by either member of the pair and we suggest that one benefit to a female of leaving a guarding mate is increased efficiency of oviposition when the intensity of male harassment is low.
10. The mating system of A. vivida thus comprises a series of complementary male and female mating behaviours.     

The ecological role of caudal lamellae loss in the larval damselfly,Ischnura posita (Hagen) (Odonata: Zygoptera)

Summary Damselfly larvae may autotomize and regenerate any of their 3 caudal lamellae. At least one missing or regenerating lamella was evident in 50.1% of field collected Ischnura posita larvae. Lamellae loss during molting is very infrequent (1 out of 117 recorded molts). Laboratory trials indicate that conspecifics remove lamellae and that this process is density dependent. The percentage of larvae losing lamellae during 24 h trials ranged from 73.5 at the highest density tested to 17.3 at the lowest density. I. posita larvae are cannibalistic. The presence of lamellae reduces an individual's chance of being cannibalized. More than twice as many final instar lamellae-less larvae were cannibalized during 24 h trials than analogous individuals having 3 lamellae at experimental initiation. Costs are also associated with lamellae autotomy. 1) Although individuals without lamellae can swim they are more reluctant to release from a wooden stalk and swim when threatened (9% release) than are larvae with lamellae (29% release). Since swimming is part of their repertoire of anti-predator behaviors this behavioral shift should be detrimental. 2) Caudal lamellae function in O₂ uptake. Trials were conducted with larvae having and not having lamellae in an experimental horizontal oxygen gradient system. Relative to larvae without lamellae, those with lamellae preferred deeper depths at PO₂ values greater than 70 torr. Many lamellae-less larvae distributed themselves at the water surface throughout the range of PO₂ values tested. Differential depth distribution between larvae with and without lamellae is highly significant (P < 0.01).