Anax Junius Research Articles

Identified target-selective visual interneurons descending from the dragonfly brain

1. Eight large interneurons descending in the dragonfly (Aeshna umbrosa, Anax junius) ventral nerve cord from the brain to the thoracic ganglia were identified anatomically with intracellular dye injection (Fig. 3). All eight were strictly visual and responded only to movements of small patterns, such as black squares, ‘targets’, moving on a white background. 2. The target interneurons all projected from the protocerebrum at least as far as the metathoracic ganglion. Within the protocerebrum they arborized in the posterodorsal neuropil region, near the base of the circumesophageal connectives (Fig. 3). 3. The receptive fields of six of the cells were large, including most of the forward hemisphere of vision. For five of these, spiking responses were often restricted to a much smaller region within the receptive field, with stimulation of other areas yielding only subthreshold responses (Figs. 4 and 5, Table 1). 4. The pattern of selectivity for target size varied, with some neurons responding only to small targets, some showing consistent responses over a wide range of target sizes, and one preferring larger targets (Fig. 6, Table 1). 5. Five of the interneurons were directionally selective. Movement in the antipreferred direction elicited hyperpolarizing responses in two of them. Movements of large patterns, such as a checkerboard pattern covering the forward hemisphere, elicited opposite directional responses, i.e., hyperpolarizations in the preferred target direction and subthreshold depolarizations in the antipreferred direction (Fig. 7). A large pattern moving in any direction inhibited the response to target movement (Fig. 8). 6. These neurons mediate, in part, the visual control of flight orientation. I propose that they convey turning signals to the wing motor in response to objects moving relative to the animal.

A Mechanistic Interpretation of Prey Selection by Anax junius Larvae (Odonata: Aeschnidae)

Preferential orientation, pursuit, and capture by a predator have been proposed for the establishment of prey preference and prey switching; however, very little is known about which of these behaviors is actually involved in active prey selection. Based on laboratory arena experiments in which the proportions of two prey types were manipulated, I distinguished the specific foraging process underlying prey preference and prey switching in nymphs of the dragonfly Anax junius. Dragonfly nymphs showed a higher probability of pursuing the more abundant of two prey types than predicted from relative prey frequencies. An increase pursuit probability was correlated with an increased capture success on the abundant prey type. I hypothesize that prey selection in Anax junius nymphs results from a simple behavioral rule of thumb; Continue to pursue only those prey types you have successfully captured in the immediate past."

Prey Selection by Freshwater Predators with Different Foraging Strategies

We observed several freshwater predators, including the odonate larvae Pachydiplax longipennis and Anax junius, the hemipterans Notonecta unifasciata and Buenoa scimitra, the dytiscid larva Acilius semisulcatus, and juvenile Gambusia affinis, feeding on a variety of microcrustacean prey and determined the frequency of the component parts of predator–prey interactions (encounter, attack, capture, ingestion). Encounter rates were the most important determinant of predator selectivity when predators were presented with a variety of microcrustacean prey. When only copepod species were used as prey, however, both encounter rates and capture success were important in determining predator diets. We used our data to test hypotheses concerning relationships between predator foraging mode and patterns of prey selection: mobile predators exhibited stronger selection for sedentary prey than did sit-and-wait predators; our own and literature data also indicated that macroinvertebrate sit-and-wait predators are better able to capture, and have higher selectivity for evasive prey than do mobile predators. A predator's attack acceleration, however, may be a better predictor of its selectivity for evasive versus nonevasive prey than its mean swimming speed.

The Diet and Foraging Behavior of the Larval Dragonfly Anax Junius (Aeshnidae), with an Assessment of the Role of Refuges and Prey Activity

Larval Anax junius Drury living in a small pond consumed largely amphipods and Chaoborus larvae. Minor components of the diet were Coleoptera, Chironomidae, and Zygoptera. These prey types were consumed disproportionately to their relative abundance in the pond on the four dates studied. The effects of habitat complexity (refuges) and prey activity on the capture rate of prey by Anax larvae were investigated in the laboratory to obtain insight into how capture rates are limited in the field. The presence of sand, gravel, and Elodea stems significantly reduced the capture rate of amphipods. Relatively inactive prey types (Ephemeroptera, Chaoborus) were captured at a much lower rate than the more active Zygoptera, Amphipoda, and brine shrimp. Because amphipods were more active than Chaoborus in lab experiments, and because they were the more abundant of the two prey in the field, we expected amphipods to be more important than Chaoborus in the field diet. However, the opposite pattern actually occurred. To resolve this contradiction, the foraging behavior of Anax was observed in a pond-mimicking aquarium. Significantly more Chaoborus than amphipods were attacked in this aquarium, matching the observed pattern in the natural diet of Anax. The apparent reasons for the relatively low number of attacks on amphipods were 1) the amphipods found effective refuge in the gravel-debris substrate where they were not often visible to the Anax larvae, 2) the amphipods were less active in the presence of a natural substrate, than when placed in a bare arena during the prey activity-prey capture experiments, 3) the planktonic Chaoborus were more visible and accessible to the Anax larvae, and 4) the twitching that Chaoborus larvae make to move through the water apparently attracted more attention from Anax than the slow walking of the infrequently exposed amphipods.

Factors Controlling Tadpole Populations of the Chorus Frog (Pseudacris Triseriata) on Isle Royale, Michigan

At the northeast end of Isle Royale, the chorus frog, P. triseriata, breeds nearly exclusively in pools on the exposed rocky shores of Lake Superior. The persistence of these breeding pools increases with size and distance from the lake. Small pools and those next to the lake last less than the 55-83 d required for metamorphosis, and survivorship to metamorphosis in these pools is low. Large pools near the forest edge are permanent, but contain the predators Anax junius and AmnbYstoina laterale. Anaxjunius eliminates P. triseriata if they occur together in the same pool. P. triseriata sustains high densities only in pools at intermediate levels on the shore, where intraspecific competition is suggested by effects of density on initial growth rate and on the length of the larval period. A field experiment using randomized blocks in a factorial design showed significant effects of both food and density on survivorship and growth; in the experiment, tadpoles removed all supple- mental food. The results demonstrate density dependence and indicate that food is limiting and in short supply in the natural breeding pools. Two features of P. triseriata population control may be common to other anurans of ephemeral habitats. First, partitioning of the larval habitat may allow predators to eliminate tadpoles from many pools. yet create refuges from predation in others. Second, in pools free of predation, competition may be intense and exert control on recruitment.

An Index of Food Limitation in the Field for the Larval Dragonfly Anax junius (Odonata: Aeshnidae)

The fecal pellet mass of larval Anax junius of a given size is closely correlated with food intake. The fecal pellet mass under ad libitum feeding can be predicted from a knowledge of larval size, and the accuracy of the predictions is not sensitive to wide variation in the diurnal schedule of feeding, water temperature between 15 and 25°, and dietary composition. Comparisons of masses of fecal pellets produced by field collected larvae with predicted masses for ad libitum feeding should, therefore, be a measure of the degree of food limitation in the field.

Food Availability in Nature for the Larval Dragonfly Anax junius (Odonata: Aeshnidae)

A previously-developed Food Limitation Index (FLI) for larvae of the dragonfly Anax junius (Drury) was used to measure the food consumption of these animals in four water bodies in southern Ontario. Most mean FLI values from the dragonfly samples did not indicate strong food limitation, but at all sites the degree of limitation tended to increase late in the summer. The FLI could discriminate differences in food limitation among water bodies and seasons through analysis of variance. Food consumption of individual larvae was positively correlated with prey density in their immediate vicinity over the lower part of the natural range of prey densities. Five of 12 measurements of average prey densities in ponds were above the level at which larval food intake stopped responding to increasing prey density. The degree of food limitation tended to increase at unusually high Anax densities. An auxiliary measure of food limitation, percent of larvae with empty guts, did not correlate well with the FLI. The FLI app...

Object- and self-movement detectors in the ventral nerve cord of the dragonfly

1. Descending, movement-sensitive visual interneurons in the ventral nerve cord of the dragonfly,Anax junius, fall into two categories, based upon their responses to a variety of stimulus patterns. One group (object-movement detectors) is sensitive only to movement of small patterns; the other (self-movement detectors) responds maximally to movement of very large patterns or to rotation of the animal in the lighted laboratory. 2. Object-movement-detector responses to repeated identical stimuli habituate very rapidly. The habituation is region specific; pattern movement elsewhere in the receptive field elicits a renewed response (Fig. 3). The habituation is very long lasting and is not subject to dishabituation by mechanical or visual stimulation. Self-movement detectors, in contrast, show little or no habituation (Fig. 3). 3. Increasing the extent of the stimulus pattern in the direction of motion decreases responses of object-movement detectors slightly and greatly increases self-movement-detector responses (Fig. 4). 4. Increasing the length of the advancing edges perpendicular to the line of motion dramatically reduces object-movement-detector responses (Fig. 5). Such increases enhance self-movement-detector responses only slightly, unless they result in the pattern occupying especially sensitive regions of the receptive field (Fig. 7). 5. Over a wide velocity range, self-movement-detector responses are not dependent on pattern wavelength (Fig. 8). 6. These results indicate that the parameter upon which the object/world discrimination is based is different for the two groups of interneurons. The critical parameter for the self-movement detectors is the extent of the pattern in the direction of motion, whereas for the object-movement detectors, the critical parameter is the extent of the pattern perpendicular to the direction of motion.

Predator-prey relationships among larval dragonflies, salamanders, and frogs.

Tadpoles of the barking tree frog, Hyla gratiosa, are abundant in spring and summer in some ponds and Carolina bays on the Savannah River Plant near Aiken, South Carolina. To determine how these tadpoles survive in the presence of predaceous salamander larvae, Ambystoma talpoideum, and larvae of an aeshnid dragonfly, Anax junius, we determined fields densities and sizes of the predators and the prey and conducted predation experiments in the laboratory. Tadpoles rapidly grow to a size not captured by Ambystoma, although Anax larvae can capture slightly larger tadpoles. Differing habitat preferences among the tadpoles and the two predator species probably aid in reducing predation pressure. Preliminary work indicates that the tadpoles may have an immobility response to an attack by a predator. In addition, the smallest, most vulnerable tadpoles have a distinctive color pattern which may function to disrupt the body outline and make them indiscernable to predators.

Heat Transfer in Dragonflies: ‘Fliers’ and ‘Perchers’

ABSTRACT Both ‘perchers’ (Libellula saturata) and ‘fliers’ (Anax junius and Aeshna multicolor) remained active in the field in sunshine at air temperatures from at least 24 °C to 36 °C. The percher basked at low air temperatures and regulated exogenous heat input by postural adjustments. It markedly reduced flight activity at high air temperatures but flew nearly continuously at intermediate temperatures. In direct sunlight, the abdomen of L. saturata heated faster than the thorax, but this percher exhibited little or no capacity to transfer heat between abdomen and thorax. In contrast, the fliers gave no evidence of behavioural thermoregulation, but both showed impressive capacities for heat transfer from thorax to abdomen. When heated exogenously on the thorax the temperature of the entire abdomen of both fliers increased uniformly, but with endogenous heat production during pre-flight warm-up there was only a slight temperature increase near the anterior portion of the abdomen. Removal of abdominal air sacs or immobilizing the abdomen with wax to prevent all abdominal pumping did not significantly alter the capacity to transfer heat from thorax to abdomen. Ligation of the heart anywhere along the length of the abdomen abolished heat transfer. Given sufficient exogenous heat input, fliers that can regulate their thoracic temperature by transferring the excess heat to the abdomen died in about 2 min due to overheating when the heart was occluded. Under our experimental conditions the fliers appeared to thermoregulate exclusively via a control of blood circulation.

THE LARGE INVERTEBRATE‐SMALL VERTEBRATE FAUNA OF SEVERAL SOUTH LOUISIANA CRAWFISH PONDS WITH EMPHASIS ON PREDACIOUS ARTHROPODS

AbstractThe large invertebrate‐small vertebrate fauna (organisms caught or retained with a 3.2 mm mesh) were sampled in several south Louisiana crawfish ponds. Arthropods were the principal predators and included, in order of abundance (lowest to highest), the insect general Lethocerus, Cybister, Pelocoris, Ranatra, Belostoma, Notonecta, Buenoa, Anax, and Pachydiplax. The arachnids, Dolomedes spp., were more abundant than Cybister. On the basis of physical size and abundance, Anax junius (Odonata: Aesnidae) appeared to be the most significant crawfish predator. Diversity of all species was greater in ponds with extensive coverage of semi‐aquatic vegetation than in those ponds dominated by annual grasses (including rice) and sedges that died and decompsed following pond flooding. The mosquitofish (Gambusia affinis), when present, appears to reduce the numbers of predacious odonate nymphs.

Development of the compound eyes of dragonflies (Odonata). III. Adult compound eyes.

The distribution of ommatidial diameters and interommatidial angles, as determined by measuring the angles between the optic axes of adjacent ommatidia, are mapped across the surface of the compound eyes of a variety of species selected for different adult behaviors, developmental histories, and taxonomic positions. The size of the visual fields, prey capture foveas, foveas composed of large dorsal ommatidia, and other specializations in the numbers of ommatidia that view various directions in the visual field are discussed in relation to adult behavior. Advanced species have less resemblance between their larval and adult eyes than primitive species. In contrast to their larvae, adults increase the monocular resolution of each eye at the expense of binocular vision. Most species have foveas which view in approximately the anterior direction, instead of in a region of binocular overlap, and many species have foveal bands which view along the horizon. Some advanced perching species, which approach their prey and other odonates from below, have an additional vertical foveal band that views along a vertical plane from the anterior direction to a more dorsal direction. The most unusual foveal band is seen in active flying species. The large dorsal ommatidia of the migratory Anax junius, which cover approximately one third of the eye surface, view a narrow region of the visual field that extends along a plane from the most lateral direction of one eye to a dorsal direction, and continues without interruption to the most lateral direction of the other eye.

Susceptibility of nontarget organisms to Nosema algerae (Microsporida: Nosematidae), a parasite of mosquitoes

Laboratory studies were conducted to determine the susceptibility of nine mosquito predators to the microsoporidian pathogen of anopheline mosquitoes, Nosema algerae. The predators tested were: Anax junius (Odonata); Hydrophilus sp., Coptotomus interrogatus (Coleoptera); Notonecta undulata, Belostoma fluminea, Ranatra australis (Hemiptera); Chauliodes rastricornis (Megaloptera); Procambarus sp. (Decapoda); and Gambusia affinis (Pisces). Of these species, only Notonecta undulata was found to be susceptible to Nosema algerae after having fed upon diseased larvae. Infection rates in four tests averaged 47.9%. The following tissues were found to be infected in the adult notonectids: gut, muscle, fat body, Malpighian tubules, tracheal epithelium, testes, brain, hypodermis, and ommatidia.

Action spectra and chromatic mechanisms of cells in the median ocelli of dragonflies.

Spectral sensitivities were recorded intracellulary in median ocelli of Anax junius, Aeschnatuberculifera, and Libellulapulcella. All cells had peak sensitivities at 360 and 500 nm while UV-blue+green cells found only in Anax had a third peak sensitivity at 440 nm. Ratios of UV-to-green sensitivities varied from cell to cell in each ocellus, but no UV-only or green-only cells were recorded. Half of the cells tested had a reverse Purkinje shift: They were more sensitive in the green at low illuminations but more sensitive in the UV at high illuminations; their intensity-response curves at 370 and 520 nm crossed but became parallel for large responses. Wave-lengths 420 nm and shorter elicited a family of low intensity-response curves with one slope; wavelengths 440 nm and longer elicities a family of curves with another slope. Orange-adapting lights selectively adapted sensitivity in the green, but UV-adapting lights had little selective effect. Amounts of log-selective adaptation were proportional to log orange-adapting intensity. It is concluded that two spectral mechanisms can be recorded from each cell, possibly by coupling of UV and green cells or possibly because each cell contains two visual pigments. Selective chromatic adaptations may provide the ocellus with a kind of "authomatic color control," while the reverse Purkinje shift could extend the ocellus' sensitivity to prevailing skylight.

Predators of Solenopsis invicta1 Queens Prior to Successful Colony Establishment 23

An investigation was made in north Florida of the biotic factors affecting female Solenopsis invicta Buren (Hymenoptera: Formicidae) from the beginning of the nuptial flight until the emergence of minum workers in newly established colonies. Many predators attacked while the queen was airborne. In order of the increasing height at which the attacks are usually made, the following dragonflies preyed on the queens: Pachydiplax longipennis Burmeister, Tramea carolina L., Anax junius Drury, and Somatochlora provocans Calvert. Of the birds feeding on alates, the chimney swift, Cahaeura pelagica L., and the Eastern Kingbird, Tyrannus tyrannus (L.), were positively identified. Other entomophagous predators attacked during the time spent on the ground immediately following the mating flight and prior to excavation. In heavily infested areas, cannabalism by S. invicta workers was particularly important. In less infested areas, Conomyrma insana (Buckley) assumed significance. Eleven other species of ants were repeatedly observed to attack queens. A wolf spider, Lycosa timuga Wallace, an earwig, Labidura riparia Pallas, and a tiger beetle, Cicindella punctulata (Oliver), also preyed on queens. Another group of natural enemies were active during excavation and emergence of minum workers from the new colony. Information on these predators has been hard to obtain. S. invicta workers are again important. Lasius neoniger Emery and Labidura riparia destroy the young queens in their cells. The Eastern Bobwhite, Colinus virginianus virginianus (L.), dig out the young queens. Considering the large number of colonies started and the small number successfully established, other predators must also be significant.

Oxygen consumption of the dragonfly, Anax junius

Oxygen consumption by Anax junius was found to vary with body weight, life stage, and temperature. Regression analysis of log of oxygen consumption against log of dry body weight at 13, 20, 27, and 34°C resulted in respective coefficients of regression of −0·3153, −0·2410, −0·0298, and −0·0169. Larvae approaching the final instar consumed oxygen less slowly than early instar larvae at 13 and 20°C but had similar rates at 27 and 34°C. Neither season (spring vs. summer) nor mode of expressing body weight (dry weight vs. ash-free dry weight) influenced the calculated value of larval oxygen consumption.

The microstructure of the compound eyes of insects.

The apposition eyes of two diurnal insects, Sarcophaga bullata (Diptera) and Anax junius (Odonata), have been examined with the electron microscope. In the latter case only the rhabdom is described. The rhabdom of the fly consists of a central matrix and seven rhabdomeres, one for each retinula cell. The rhabdomeres show an ordered internal structure built up of transverse tubes, hexagonal in cross-section. These slender compartments running the width of the rhabdomere are 370 A in diameter. After fixation with osmium tetroxide the walls of the compartments are more electron dense than the interiors. The retinula cells contain mitochondria, and pigment granules smaller than those found in the pigment cells. These granules tend to cluster close behind the membranes which separate the retinula cells from their rhabdomeres. The rhabdom of the dragonfly is a single structure which appears to be composed of three fused "rhabdomeres," each similar to a rhabdomere of Sarcophaga. Reasons are given for believing that the rhabdom may be the site of photoreception, as well as the organ for analyzing plane-polarized light, as suggested by other workers.

Notes on Dragonflies in the Vicinity of New Smyrna Beach, Florida

The purpose of this paper is to report on the unusual dragonfly population near New Smyrna Beach, Fla., during the summer of 1943, and especially on the tremendous swarms of one species during July and August of that year. Observations on abundance and distribution of odonates made in this area during June and early July of 1942 are included in an attempt to picture the population present during normal years. New Smyrna Beach is located in about the middle of the Florida Atlantic Coast some 16 miles south of Daytona Beach. These observations covered the area from the Tomoka River marshes just a few miles north of Daytona Beach to the Oak Hill marshes about 15 miles south of New Smyrna Beach. This region contains large areas of salt marsh, both on the mainland and on the numerous islands formed by Mosquito Lagoon and Indian River (land-locked salt-water lagoons), that are excellent breeding grounds for the salt-marsh mosquitoes (Aedes sollicitans (Walk.) and A. taeniorhynchus (Wied.). The mainland, just west of the coastal marshes, contains numerous permanent and' semipermanent fresh-water habitats capable of breeding dragonflies. DRAGONFLY POPULATION DURING 1942.-The following is a list of dragonfly species and their relative abundance noted in the coastal areas during June and July, 1942. No species was observed in sufficient numbers to be listed as abundant. VERY COMMON: Erythrodiplax berenice (Drury) and Tramea carolina (Linnaeus). COMMON: Anax junius (Drury), Coryphaeschna ingens (Rambur), Libellula auripennis Burmeister, Erythemis simplicicollis (Say), and Erythrodiplax connada minuscula (Rambur). OCCASIONAL: Celithemis eponina (Drury), Libellula vibrans Fabricius, Pachydiplax longipennis (Burmeister), Cannacria gravida (Calvert), Enxallagma civile (Hagen), and Ischnura ramburii Selys. RARE: Celithemis ornata (Rambur), Nehalennia integricollis

The aortic diverticula of the Odonata

AbstractAlthough thoracic diverticula of the aorta ending dorsally in pulsatile organs were discovered by Brocher as early as 1917 no detailed account of their structure was published. The condition of these structures in the adult was not investigated and their development through larval instars was not followed. Brocher's later papers announced the discovery of similar organs in the orders Orthoptera, Coleoptera and Lepidoptera. In 1931 E. Meyer described in some detail pulsatile organs in the Ephemerida. In general these accounts are either superficial or of doubtful interpretation.The present paper deals with the Odonata and stresses the Anisoptera. Anax junius has been studied as the type both anatomically and histologically in all stages of larva and imago except the first four instars. Other types have been compared with Anax, and some of the other orders mentioned have been checked for presence and nature of these organs.Aortic diverticula and pulsatile organs occur in all Odonata both larval and adult. These are derived from the same origins and their histology is that of the membranes involved in aortic and body walls. Through inference from morphology and from physiological examination it appears that pulsatile organs (1) supplement heart action, perhaps substituting for it during emergence. (2) assist in the functioning of the ostia and ostial glands, and (3) may even be important in production and distribution of hormones.

CRITICAL INTENSITY AND FLASH DURATION FOR RESPONSE TO FLICKER: WITH ANAX LARVAE

Determinations of the flicker response curve (F - log I(m)) with larvae of Anax junius (dragonfly) for various ratios t(L)/t(D) of light time to dark time in a flash cycle provide relations between t(L)/t(D) and the parameters of the probability integral fundamentally describing the F - log I function, including the variability of I. These relations are quantitatively of the same form as those found for this function in the sunfish, and are therefore non-specific. Their meaning for the theory of reaction to visual flicker is discussed. The asymmetry of the Anax curve, resulting from mechanical conditions affecting the reception of light by the arthropod eye, is (as predicted) reduced by relative lengthening of the fractional light time in a cycle.