Neurosecretory system of the ventral ganglia in the dragonfly,Orthetrum chrysis (selys) (Odonata: Libellulidae)

Summary The neurosecretory cells of the ventral ganglia in the adult dragonfly, Orthetrum chrysis, are classified into A, B, C1 and C2 cells. The neurosecretory material in the ventral ganglia is composed of PAS-positive material with 1-, 2-glycol groups and some proteins. The proteins rich in cystine or cysteine occur predominantly in the A cells, moderately in C cells and negligibly in B cells. Proteins containing arginine occur in A and B cells only, and those containing basic amino acids occur in C2 cells. The neurosecretory pathways and the neurohemal organs are also described.     

Reproductive behavior of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

The reproductive behavior of the dragonfly,Orthetrum japonicum, is described. Behavioral processes of turnover of territorial males, simultaneous guarding of 2 females by a male, and copulation by non-territorial males are described. The males with longer hind wings won the territorial conflicts more frequently. The total duration of territorial residence of a given male was correlated with the number of his matings, but not correlated with the length of his abdomen or hind wings. The territorial site with the lower degree of vegetation cover was occupied by males more consistently. Males in more consistently occupied territorial sites did not have longer abdomen and hind wings than males in less consistently occupied sites. The territorial site where the larger number of copulations was observed was not occupied more consistently. Selection episode analysis using the method of Arnold & Wade (1984a, b) showed that direct selection on the hind wing length favored the short wing and that direct selection on the abdomen length favored the long abdomen during mating.     

Sexual difference of lifetime movement in adults of the Japanese skimmer,Orthetrum japonicum (Odonata: Libellulidae), in a forest-paddy field complex

The mark-and-recapture method was used to study the lifetime movement of the Japanese skimmer,Orthetrum japonicum, in a forest-paddy field complex in the warmtemperate zone of Japan. The flight season was from mid April to late June. The age structure showed that the maiden flight occurred towards the forest from the emergence sites (paddy fields) for both sexes. The insects returned to the paddy fields after maturation. The total number of skimmers estimated in the whole survey area was about 1000–2000, of which about 200 males were found in the paddy fields. The average lengths of the immature and reproductive periods were about 10 and 20 days in both sexes, respectively. Most mature males tended to stay in the paddy fields and showed territorial behavior, while most mature females moved frequently between the forest and the paddy fields. The average extent of each territory was about 19 m², being established mainly in the shady paddy fields. Few males were sneakers. The available habitat throughout the life span for the skimmers was both the paddy fields and the forest.     

Foraging behavior ofPachydiplax longipennis (Odonata: Libellulidae)

Food intake, prey availability, and prey capture behavior at feeding areas were quantified in the dragonflyPachydiplax longipennis by observing focal individuals on artificial perches, where they exhibited marked short-term site fidelity. Prey capture success was high and relatively constant, but the frequency and duration of feeding flights depended on the time of day and season (at least in part because of associated variation in temperature and other physical factors), study site, sex, density of other dragonflies, and prey density. Individuals rapidly responded temporally and spatially to changes in prey availability, particularly to localized prey concentrations.     

Neuroendocrine control of vitellogenesis in the dragonfly, Orthetrum chrysis (Selys) (Odonata: Libellulidae).

1. Histological correlative studies on the cerebral neurosecretory cells, the corpora allata and the oocyte development strongly suggest the involvement of cerebral NSM mostly produced by the A cells of pars intercerebralis and the CA hormone in the vitellogenesis. 2. Biochemical studies reveal the incorporation of haemolymph proteins and lipids in the yolk during vitellogenesis. 3. Exogenous administration of the extract of the brain-CC and FME demonstrates, to some extent, the stimulation of protein synthesis during vitellogenesis in the haemolymph by the cerebral NSM and the CA hormone, while the lipid metabolism lies, mostly, under the control of juvenile hormone.     

Mechanisms of sperm removal and sperm transfer in Orthetrum coerulescens (Fabricius) (Odonata: Libellulidae)

ABSTRACT An account of the structure of the secondary genitalia of male Orthetrum coerulescens (Fabricius) is given together with an outline of the internal genitalia of the female. Observations on the experimental inflation of the penis are described. No sperm was released during fast inflations and deflations of the penis, but sustained inflation of the penis led to the release of a clear fluid followed by the slow discharge of sperm. Examination of natural copulations in the field has shown that rapid rhythmic movements at up to 5 Hz take place in the male's third abdominal segment throughout most of copulation, but towards the end they cease though inflation is maintained. It is suggested that the rapid movements coincide with the removal of rival sperm from the female and that sperm is transferred to the female only during the maintained inflation. Possible mechanisms of sperm translocation, sperm removal and sperm transfer are discussed with reference to male and female genital structures and the action of relevant muscles.     

Differences in adult and reproductive lifespan in the two male forms ofMnais pruinosa costalis selys (Odonata: Calopterygidae)

The damselflyMnais pruinosa costalis (Odonata: Calopterygidae) is unusual in that males are dimorphic, existing as clear-winged non-territorial ‘sneaks’ and orange-winged territorial ‘fighters’. Here we report the results of population census data and behavioural observations in the field and laboratory, and present estimates of emergence period, reproductive period, total lifespan, and reproductive success of each morph. Clear-winged males are smaller and have lower daily reproductive success than orange-winged males, but live for longer in the field and laboratory. We accounted for the difference in the ‘operational reproductive life’ of the two morphs and estimated lifetime reproductive success: there was no difference between clear-winged and orange-winged males. We discuss possible mechanisms for the maintenance of the two forms.     

The influence of body size on immediate reproductive success in Dugesia gonocephala (Tricladida,Paludicola)

The individual reproductive output of the stream-dwelling flatworm Dugesia gonocephala was investigated. Various measures of reproductive success were related to body size. (I) For the first 30 days in the laboratory small individuals produced no cocoons, individuals of intermediate size produced unfertilized cocoons and large individuals usually produced fertilized cocoons. (II) In individuals that produced a cocoon, no correlation was found between the number of cocoons produced in one month and body size. (III) Large individuals, however, produced larger cocoons. This was not due to the fact that unfertilized cocoons were smaller. (IV) Large cocoons tended to contain more young. (V) The average size of young hatching from large cocoons was larger. (VI) Large individuals produced their first cocoon soon after their arrival in the laboratory and seemed to have a higher chance of producing a fertilized first cocoon. (VII) A trade-off existed between producing many small versus few large young.     

Shade Alone Reduces Adult Dragonfly (Odonata: Libellulidae) Abundance

We demonstrate that physical habitat conditions influence adult dragonfly (Odonata: Anisoptera) riparian site selection. In naturally treeless riparian areas of South Africa, invasive trees create shade and reduce native vegetation. We hypothesized that most breeding odonates select riparian areas (1) without shade, and (2) with high density and variety of understory perch structures. In two experiments at reservoir shorelines, we varied shade and perch structures. Dragonfly abundances (predominantly Trithemis species) were lower at sites with high (75%) or moderate (55%) shade cover than at sites with no shade, and lower at bare sand sites than sites containing stick perches. Perch density and variety (variety of heights and diameters) did not affect dragonfly abundance. These results indicate that shade alone directly reduces dragonfly habitat selection, isolating one aspect of habitat change that can alter insect behaviors.     

Fecundity and oviposition in three skimmers,Orthetrum japonicum,O. albistylum andO. triangulare (Odonata: Libellulidae)

Females of three skimmers,Orthetrum japonicum, O. albistylum andO. triangulare, were captured in forests and paddy fields. They were dissected and examined for the number of submature and mature eggs.Orthetrum japonicum andO. albistylum continuously developed eggs throughout their reproductive period. The volume of mature eggs inO. albistylum was the smallest among the three species. The number of mature eggs in ovaries decreased from morning to afternoon, suggesting that all of them oviposited around noon. The number of mature eggs laid byO. japonicum, O. albistylum andO. triangulare was estimated at about 400, 800 and >2000 a day, respectively.     

Phylogeny of the dragonfly genus Sympetrum (Odonata: Libellulidae)

The libellulid dragonfly genus Sympetrum has been recognized since 1833, but lacks any morphological synapomorphies to unite the taxon. Previous researchers have disagreed over which species belong in Sympetrum, bringing the monophyly of the genus into question. We use DNA sequence data from 6 genetic loci (16S, tRNA-valine, 12S, elongation factor 1 alpha, cytochrome oxidase subunit I, and the second internal transcribed spacer region) and 25 morphological characters (mainly genitalic) to test the monophyly of Sympetrum with Bayesian inference and maximum likelihood analyses. Under Bayesian inference, all Sympetrum species included in this study form a clade, which also contains the Hawaiian monotypic genus Nesogonia, often considered a close relative of Sympetrum. Phylogenetic analyses also reveal at least six strongly supported clades (treated as species groups) within Sympetrum, but relationships between these species groups remain unresolved or unsupported. Although the relationships between Sympetrum species groups remain unresolved, several species groups include taxa from multiple biogeographic regions/continents, and the species group sister to the rest of Sympetrum contains migratory species from the New World and Africa. This pattern suggests a complex biogeographic history in Sympetrum shaped by vicariance and dispersal. Preliminary estimates of the divergence dates of Sympetrum species groups outline a rapid radiation of the groups approximately 32-38 million years ago, possibly influenced by cooling and drying climates of the late Eocene and early Oligocene.     

The mating system ofBrechmorhoga pertinax (Hagen): The evolution of brief patrolling bouts in a “territorial” dragonfly (Odonata: Libellulidae)

Males of Brechmorhoga pertinax(Hagen) patrolled and competed for narrow strips of stream edge, 2–8 m long, containing a few barely submerged patches of sandy or fine gravel substrate. These scarce patches were used as oviposition sites by females that usually, but not always, mated with a patrolling male just prior to egg-laying. Females visited the oviposition sites evenly throughout the day from 0830 to 1430 but male activity rose until midday and then declined sharply after 1330. Some gravid females refused to mate in the midafternoon despite male efforts to copulate with them. The average patrolling bout by a male lasted less than 15 min, with defenders usually leaving immediately after one or two aggressive interactions with intruders or leaving voluntarily without apparent cause. Many individuals returned for additional bouts of patrolling at the same site, but the total daily period of patrolling for any one individual almost never exceeded 1 h.     

Female rank and reproductive success among arashiyama B Japanese macaques (Macaca fuscata)

Five hypotheses that related female rank and reproductive success were tested in an intact troop of free-ranging, provisioned, Japanese macaques. The hypotheses stated that high-ranking females (1) begin parturition earlier in life than low-ranking females; (2) produce more offspring than low-ranking females; (3) give birth during some optimal time during the birth season to a greater extent than low-ranking females; (4) experience less infant mortality than low-ranking females;and (5) more frequently produce male offspring, while low-ranking females more frequently produce female offspring. A statistical analysis of the data which included three birth seasons and 55 adult females and 34 pubescent females, all of known age, rank, and matrifocal membership in the Arashiyama B troop, revealed few significant results. An association was found between the rank of the matrifocal unit and the age of first birth. However, the relationship was the reverse of hypothesis 1, i.e., females of the lower-ranking matrifocal units began parturition earlier than females of higher-ranking matrifocal units. Therefore, in this troop of Japanese monkeys— where alternative feeding strategies existed— there was little association between female rank and reproductive success.     

Choice of Lookout Posts by Territorial Amberwing Dragonflies, Perithemis tenera (Anisoptera: Libellulidae)

Many territorial insects use specific perches, or lookout posts, from which they perceive and react to conspecific males and females. We investigated the lookout post choice of territorial male amberwing dragonflies (Perithemis tenera). An observational study indicated that males rarely perched directly at their oviposition site; rather, they perched farther out from shore than, and within 2 m from, their oviposition site. In an experimental study, we provided an array of perches at different distances from the shore and oviposition site to eliminate perch limitation as a factor in perch choice. The results of the experimental study confirmed the patterns evident in the observational study; males perched farther from shore than their oviposition site was located. Interestingly, in both the observational and the experimental study, when neighbors were close, a male perched away from his closest neighbor, which usually resulted in his oviposition site being closer to his neighbor than he was. Thus, male amberwings apparently alter their perch choice within their territories in response to the location of other males. These lookout post locations may provide the best opportunity for the territorial male to perceive passing females and intruding males, while minimizing conflict with their neighbors.     

The histological and histochemical studies on the ovary in relation to vitellogenesis in the dragonfly, Orthetrum chrysis Selys (Libellulidae: Odonata).

The ovaries consist of large number of panoistic ovarioles in the last instar nymph and the adult dragonfly Orthetrum chrysis (Selys). In the nymph the vitellaria are compactly filled with the primary oocytes and the vitellogenesis takes place only in the adult stage. During vitellogenesis oocytes change widely in their shape, size and cytological organisation and their developmental stages can be divided into pre-vitellogenic, early-vitellogenic, vitellogenic, late-vitellogenic and maturation age. PAS-positive material appears first around the germinal vesicle in the early-vitellogenic stage and lateron it migrates towards the periphery. Glycogen appears in the late-vitellogenic stage. DNA is abundantly present in the nuclei of the oocytes during the pre-vitellogenic and completely absent in early-vitellogenic, vitellogenic, late-vitellogenic and maturation stages. It is observed in the nuclei of follicular epithelial cells of all the stages. RNA is abundantly present in cytoplasm of the pre-vitellogenic oocytes but lateron is gradually decreases. During the early-vitellogenic and vitellogenic stages high concentration of RNA in the follicular epithelial cells has been observed. The protein bodies appear first in the interfollicular spaces and towards the periphery of the oocytes just near the enveloping follicular epithelial cells, during the early-vitellogenic stage suggesting the formation of yolk proteins from the haemolymph. In Orthetrum chrysis the sudanophilic bodies appear first in the follicular cells and then lie in the peripheral region of the oocytes suggesting the incorporation of yolk lipid either from the follicular epithelium or from the haemolymph through the follicular epithelium. The phospholipids are synthesised in pre-vitellogenic to the late-vitellogenic stages. In the late-vitellogenic stages the phospholipid granules are present abundantly in the follicular epithelium while in the maturation stage they disappear suggesting their utilisation in the formation of membranes like vitelline and chorion. The neutral fats are present in the form of large number of droplets in the oocytes during the maturation stage.     

Microhabitat selection as an antipredator strategy in the aquatic insect Pachydiplax longipennis Burmeister (Odonata: Libellulidae)

Summary An investigation of the larval dragonfly fauna associated with the plant, Sagittaria platyphylla, was conducted in a small pond. Despite the presence of several larval anisopteran species in the pond, only Pachydiplax longipennis larvae were found on Sagittaria plants. A study of the microspatial distribution of P. longipennis larvae on S. platyphylla indicated that larvae use the various regions of a plant in a highly non-random fashion. Larvae show a strong preference for the leaf axil area. A generalized predator, the bluegill sunfish (Lepomis macrochirus), was allowed to selectively eat either of two larvae placed in various plant regions. This experiment indicated that larvae in a leaf axil area were significantly less susceptible to bluegill predation than larvae positioned in other plant regions. The microspatial distribution of starved larvae revealed that larvae with high hunger levels occupied the leaf axil area significantly less than well fed larvae, suggesting 1) larvae do not use these regions as feeding sites, and 2) high hunger levels may induce a behavioral shift in habitat use, with starved larvae forced into areas of high predation risk by the need to fulfill nutritional requirements.     

Plant size,breeding system,and limits to reproductive success in two sister species of Ferocactus (Cactaceae)

Plant reproductive output can be limited by a variety of factors, bothintrinsic and extrinsic. I investigated the reproductive biologies of twospecies of unbranched short-columnar cacti, Ferocactuscylindraceus and F. wislizeni. I recordedfemalereproductive output (flowers produced, fruit set, seeds per fruit and seedmass), plant size and growth, and used hand-pollination experiments todeterminebreeding systems and pollen limitation. In both species, the ability to selfvaried among individuals, but self-pollination resulted in very few seeds,suggesting strong inbreeding depression. Neither species was pollen-limited.Numbers of flowers produced increases with plant size for both species, andseeds per fruit may also be related to plant size, although the relationship isunclear. Seed mass is not correlated with plant size. Flower production wassimilar in both species, but F. cylindraceus producedfewerseeds per fruit than F. wislizeni, and its seeds weighedless. Fruit set by F. cylindraceus was heavily impacted bya florivorous lepidopteran. Fruit set was very high (94 to 96%) inF. wislizeni, suggesting that architectural constraints(e.g., meristem limitation) are more limiting than resource levels or the levelof pollinator services. In F. cylindraceus, numbers ofseeds per fruit was positively correlated with seed mass, whereas inF. wislizeni, the relationship was negative (tradeoff).Thegrowth rates of F. wislizeni are affected by rainfall theprevious season, and growth rates increase as the plant ages.Ferocactus cylindraceus and F.wislizeni are thought to be sister species, meaning that observeddifferences between them are more likely to be the result of recentevolutionaryprocesses in their lineages rather than differing phylogenetic histories.     

Influences on variation in territorial tenures of male white-faced dragonflies (Leucorrhinia intacta) (Odonata: Libellulidae)

Some individuals in species with extended periods of territorial occupancy may change territory locations within a single bout of territorial activity. Length of occupancy of mating territories among males in a local population of white-faced dragonflies (Leucorrhinia intacta) varied from more than 6 h to 15 min or less. Males with short tenures often established territories in several locations on the pond during a day. Several hypotheses have been proposed to explain shifting territorial sites rather than remaining in a single site during one bout of territoriality. We attempted to test the hypothesis that males shift to leave low-quality sites. Site quality may be affected by costs of defense in relation to intruder rate and the mating benefits of holding the territory. To test whether variation in these possible effects of benefits and costs of territoriality influenced tenure, we manipulated local quality of oviposition substrate and perch density. The quality of oviposition substrate, but not perch density, influenced both potential benefits and costs of territoriality. Female density was higher in areas with good substrate, but so were rates of males intruding into the territories, rates of chasing by territorial males, and local density of territorial males. More matings occurred in areas with good substrate, but among males with tenures of 15 min or more, mating success per male and tenure lengths did not differ statistically among treatments. Defense costs were low for all treatments and perhaps were not an important influence on tenure duration. Territorial males in this population probably adjusted local density to expected mating success by initial choice of site rather than by varying tenure length. Variation in tenure length at a site resulted, in part, from stochastic external factors, such as predation attempts.     

Dominance,age, and reproductive success in free-ranging female hanuman langurs (Presbytis entellus)

Correlations among female age, dominance, and reproduction were investigated for a 12-year period in free-ranging, provisioned Hanuman langurs (Presbytis entellus), living in one-male groups near Jodhpur in Rajasthan, India. Of 2940 displacement episodes, 27% occurred over natural food, 26% over provisioned food, 8% over grooming, 23% over position and shade, and 16% for other reasons. It was possible to reconstruct a displacement hierarchy that was linear and stable over short periods but fluctuated according to the age composition of the troop, resulting in an age inversed dominance structure. Females occupied top ranks as soon as they experienced menarche (around 2.4 years of age) and gradually declined thereafter, with postmenopausal females (≥30 years) being the lowest ranking individuals. Old females tended to be peripheral, while young females were highly social and active. Fertility peaked at about 7 years and gradually decreased thereafter, but infant mortality was much higher in young females than in old ones. During years when females gave birth, their ranks, especially those of old females, were higher than the average expectation for their age class, which suggests that females compete more vigorously if they have an infant. Reproductive success (i.e., infant survival to ≥2 years) declined significantly from high-over middle-to low-ranking females but did not differ for the three age classes investigated, because the higher fecundity of young females was balanced by better rearing success of older females. These results are discussed in light of the controversy over whether the langur social system is strongly influenced by kin selection (Hrdy and Hrdy, 1976; Dolhinow et al., 1979).