Gyrinid Beetles Research Articles

Conditioned reinforcement in the crayfish Orconectes rusticus

AbstractThe crayfish Orconectes rusticus can form a learned association between alarm odour (an unlearned signal of elevated predation risk) and a formerly neutral odour. In this study the odours of gyrinid beetles and of the snail Campeloma decisum were each paired with alarm odour and subsequently those odours significantly reduced feeding behaviours in the presence of food odour. To test for second-order (=conditioned) reinforcement, crayfish were first exposed simultaneously to one of the neutral odours and alarm odour and later exposed simultaneously to the two formerly neutral odours. When tested with the second neutral odour (which was not paired with alarm odour) the crayfish showed significant reductions in food-related behaviours, thus demonstrating second-order conditioning.

Species-specific predation on gyrinid beetles by the backswimmer, Notonecta glauca

Species-specific predation on gyrinid beetles by the backswimmer, <i>Notonecta glauca</i>

Seasonal fat content fluctuations in a gyrinid beetle: comparison between an arctic and a temperate zone population (Coleoptera: Gyrinidae)

Seasonal fluctuations in fat content (percentage of dry body weight) of adult Gyrinus opacus were compared between a lake population at the northern range limit of the species in Greenland (G) and a rock pool population in south-central Sweden (S) near its southern range limit. From equally low values at emergence in summer, beetles of both populations accumulated substantial fat reserves, especially during their first weeks as adults. Hardened S-beetles were fatter than G-beetles at time of onset of hibernation. For late emerging (soft) G-beetles, however, the situation was severe because of an immediate freeze-up of the lake. There was a similar winter fat decline in both populations. During the first month after hibernation there was a significant decrease in fat content of the S-beetles, because they were still utilizing their fat deposits from the previous autumn. This trend was broken at the first emergence peak of chironomids in spring. Hibernating G-beetles used their lesser fat storage to the same extent, and led to some reproductive females reaching extremely low levels of fat. Still lower fat content and smaller body size of beetles in a closely situated small lake to G in early spring shows a between locality variation related to differences in habitat quality at the northern range limit.

To have and have not: volatile secretions make a difference in gyrinid beetle predator defence

I investigated the effect of low molecular weight substances (volatiles) such as 3-methyl-1-butanal and 3-methyl-l-butanol together with the norsesquiterpenes on gyrinid beetle defence. Rainbow trout, Onchorhynchus mykiss , ate significantly more G. minutus (lacking volatiles) than G. aeratus (with volatiles). Rainbow trout often exposed gyrinid beetles to oral flushing after capture, but spent more time (energy) flushing if the beetle was to be consumed. They did not flush palatable prey; therefore, oral flushing seems to be a strategy to remove noxious chemicals from potential prey. However, when experienced fish tasted a new gyrinid they were quicker to reject gyrinids with volatiles than those lacking volatiles. Hence, volatiles appeared to make the gyrinids more distasteful and experienced fish did not waste time flushing gyrinids with volatiles. Instead they expelled the gyrinid quickly after taking the beetle into their mouth. It seems that the taste of a gyrinid, rather than its odour, is the more effective predator defence, since there was no difference in fish behaviour towards gyrinids with or without volatiles prior to tasting them.

Chemical defense: aquatic beetle (Dineutes hornii) vs. fish (Micropterus salmoides).

Captive largemouth bass (Micropterus salmoides) reject the gyrinid beetle, Dineutes hornii. They also reject edible items (mealworms) treated by topical addition of the norsesquiterpene gyrinidal, the principal component of the defensive secretion of the beetle. The bass' oral tolerance of gyrinidal varies broadly as a function of the gyrinidal dosage and the state of satiation of the fish. When taking a D. hornii or a gyrinidal-treated mealworm in the mouth, the fish subjects the item to an intensive oral flushing behavior, seemingly intended to rid the item of gyrinidal. The duration of oral flushing is itself a function of the gyrinidal dosage and the state of satiation of the bass. To counter oral flushing, D. hornii emits its secretion as a slow trickle. Duration of emission is slightly longer (1.5 min) than the time (1.3 min) invested by the bass in flushing a D. hornii before rejecting the beetle. We postulate that flush resistance may be a general feature of defensive chemical delivery systems in aquatic prey, given that oral flushing may be a common strategy of fish.

The Possible Role of Volatile Secretions as Intra- and Interspecific Alarm Signals in Gyrinus Species

Gyrinid beetles have paired pygidial glands producing a secretion consisting of both a high molecular weight fraction, rendering them toxic for predatory fish, and usually also volatile fractions (8 of 10 north European Gyrinus species), which act as alarm signals. The presence of multi-species aggregations on the water surface raises the question whether the pygidial secretion of one species can elicit an escape response in other species. There were no differences in escape reaction to signals between two strongly scented species (G. aeratus and G. substriatus) and one species without obvious scent (G. opacus ). Furthermore, signals were received across the species borders, although only the two species emitting volatile components were able to alarm other individuals. The two scented species (G. aeratus and G, substriatus) often aggregate in large groups on open water, whereas the unscented species (G. opacus and G. minutus) rarely do so, but preferably occur singly or in loose groups among the emergent marginal vegetation of various standing waters. This suggests that the presence of alarm signals is correlated with behaviour and habitat choice. Furthermore, the putatively weak competitor G. opacus spends significantly more time below the water surface than G. substriatus, perhaps as a result of it lacking an alarm function. The occasional presence of individuals of the two unscented species in large aggregates of G. aeratus on open surface, may indicate that they may take advantage of the alarm signals produced by individuals of another species and as result escape approaching danger. It is not known whether G. opacus and G. minutus have lost the ability to produce volatile alarm substances or whether they never have had it. Comparisons with the ca 11000-year-old subfossil localities of G. opacus, however, indicate that at least from that date this species has inhabited localities similar to the present with respect to predation risks and other properties, i.e. mainly small, predatory fish-free waters.

Environmental Heterogeneity in Space and Time: Patch Use, Recruitment and Dynamics of a Rock Pool Population of a Gyrinid Beetle

A population of the whirligig beetle Gyrinus opacus inhabiting a cluster of 108 rock pools on a small peninsula in south-central Sweden was studied over a 3-year period. In terms of recruitment of new adults and population size, the study period included two good years, one dry (1990) and one wet (1991), and one bad, dry year (1992). Mean occupancy of pools was around 40% during the two good years and 18% during the bad year, i.e. most pools were vacant. As expected from theory, turnover rates were highest for pools with the lowest average population size. While new adults emerged from about half the pools, only 7.4% were successful in all three years. Beetles attempted to hibernate in about half the pools and succeeded in 41%. Most activities, such as local movements, recruitment of new adults and hibernation, involved the 19 major pools, but no pool was outstanding. Dispersal between pools was frequent and, as expected, breeding pools were in contact with a higher number of pools than those where no successful breeding took place. Surprisingly, during the dry good year, both recruitment number and reproductive success were positively related to the length of the dry period of pools, which may possibly reflect an escape from predators on eggs and larvae. During the two first years when the population was stable, pools that dried out in 1990 but not in 1991 produced significantly more new adults in the dry 1990. The size of the total population showed a seasonal bimodal pattern with a minimum in summer. The number of beetles in different pools tended to vary synchronously within and among years, but there were many exceptions. Beetles survived drought periods by transferring to neighbouring, permanent refuge pools, or by seeking refuge for up to a week under a boulder in the desiccating pool. This illustrates the great importance of environmental heterogeneity for local population survival, i.e. normally unimportant elements in the habitat may assume critical importance under stressful periods.

Local Dispersal and Its Life-History Consequences in a Rock Pool Population of a Gyrinid Beetle

Dispersal and reproduction were studied in a patchy rock pool population of the long-lived partially bivoltine Gyrinus opacus in south-central Sweden. In most years many pools dry out during spring ...

Volatile substances in the pygidial secretion of gyrinid beetles (Coleoptera: Gyrinidae)

Gyrinid beetles are common in freshwater habitats. They have paired pygidial glands with a secretion that contains high molecular weight substances rendering them toxic for predatory fish. In this paper we report on a laboratory study on volatile components released by three different gyrinid species when irritated. The volatile pattern had a clear difference between the different species.Gyrinus substriatus andG. aeratus, both produced 3-methyl-1-butanal and 3-methyl-1-butanol when irritated, but in quite different amounts. The third tested species,G. minutus, did not produce any substances above the detection level. It is suggested that the volatile compounds may be part of the beetles' communication and/or defence system.

Alarm substance in Gyrinus aeratus (Coleoptera, Gyrinidae).

Gyrinid beetles are common in ponds and lakes in Sweden, where they aggregate in open areas of the surface. Gyrinid beetles have pygidial glands which produce compounds rendering them unpalatable to fish. This study examines whether the pygidial secretion can be used for alarm purposes in addition to other functions. Experiments showed that gyrinid beetles responded to water prepared with the pygidial compounds by evasive behaviour. The beetles did not respond when the compound was mediated by air. One component of the defense system of gyrinids is how they advertise their presence. The aggregation of dark beetles with their typical motion pattern when alerted is very conspicuous and easily identified by an experienced predator. We suggest that this aspect of gyrinid defence can be characterized as aposematic.

The distributional patterns of surface-dwelling insects in a Tenerife stream (Canary Islands)

Eight surface-living insect species, two gyrinid beetles and six heteropteran bugs, were studied in 27 pools in a Tenerife stream. Gyrinus urinator was on average the most abundant species whereas Velia lindbergi was the most widely distributed one. Gyrinid abundance (numbers per pool), but not density (numbers per square metre), was positively associated with pool size and depth. In contrast, the densities of the bugs Velia lindbergi and Hydrometra stagnorum decreased with pool size. Both the number of species and individuals increased with pool area. Widely distributed species were represented with higher average densities than species with a more restricted distribution. Contrary to theory, there was a positive relationship between mean adult body size and density within the guild.

Population dynamics of gyrinid beetles : II. Reproduction.

Between 1974 and 1983 data concerning egg production and recruitment were obtained by sampling populations of the whirligig water beetle Gyrinus marinus Gyll. All females reproduce, but they differ in the number of eggs laid per oviposition and in the frequency of oviposition. There are two reproducing generations a year, one in spring (April-June) and one in summer (July-August). Females emerging in July and August reproduce immediately after emergence, but at a lower level than the females of the spring generation. In June the egg production of spring females also decreases. No significant differences in egg production occur between populations in different sites or in different years. Individual properties and circumstances of the females probably have a distinct influence on variation in egg production. A female probably oviposites and is fertilized at least once a week. Without, fertilization egg production and the viability of the eggs decrease after two weeks. On the average, 60 per cent of the eggs hatch.Development from egg to teneral takes about 10 weeks in spring and autumn and about six weeks in summer. The hatching and development of eggs laid in April is probably retarded until the half of May. Variation in the length of the developmental period will cause variation in recruitment and in the number of hibernating beetles. Variation in eggviability and in larval and/or pupal development are probably of equal importance to the variation in the numbers of tenerals emerging. The variation in egg production is of no importance.Recruitment (number of tenerals/female) of the generations reproducing, in spring and in summer are independent of each other. Between years the rate of recruitment differs significantly, and probably depends more on environmental conditions such as weather than egg production seems to do.

Population dynamics of gyrinid beetles : III. Survival of adults.

Survival chances have been estimated for populations of the waterbeetle Gyrinus marinus Gyll. from capture-recapture sequences in 1974-1978. The average weekly survival chance is estimated as 0.9247 in spring, decreasing to 0.7701 in autumn; males survive longer than females. Survival shows little variation in time or space (variation coefficient V<0.1). Survival chance did not significantly decrease with age. Freshly emerged tenerals apparently have a lower survival chance than older beetles. The survival chance during hibernation (October-April) is about 0.33, with a greater variation between years (V=0.7) than between populations (V=0.4).

Population dynamics of gyrinid beetles

As part of a comprehensive study of the population dynamics of the whirligig beetle Gyrinus marinus Gyll. experiments were performed concerning flight activity. From capture-recapture experiments it appears that only a small percentage of the beetles move from one pond to another by flight. Flight activity only occurs if the weather is favourable, i.e. if the air temperature is more than about 17° C and the wind is feeble, and probably only if the sun is shining. In the Netherlands the opportunity to fly is therefore very limited by weather conditions. Flight activity of males and females occurs from April till the middle of October, thus including the period of reproduction. During reproduction females fly, but to a lesser extent than males. The different degree of dispersal during and after reproduction corresponds with the different degree of dispersal of mothers (and their eggs) and offspring. The hypothesis that flight occurred simply because the weather was favourable for flight cannot be rejected. The possibility of randomly occuring flight dispersal and the significance of a small dispersal activity for population dynamics is analysed in a separate paper with the help of simulations (van der Eijk in press).

Observations on Dineutes aereus Klug (Coleoptera: Gyrinidae), a freshwater beetle from Al-Kharj, Saudi Arabia

Food analysis of 40 crops of Dineutes aereus showed that the diet in August consisted mainly of aerial and terrestrial insects; vegetable debris was also occasionally present. There appears to be intra-specific competition among these gyrinid beetles, and between them and fish for the same food items. It was observed that the length of the adults increased in direct proportion to the body-weight. The eggs and larvae were recovered from submerged grass and bottom fauna collected in July and August.

Chemical defense mechanisms of arthropods XXXVI. Stereospecific synthesis of gyrinidal, a nor-sesquiterpenoid aldehyde from gyrinid beetles

Chemical defense mechanisms of arthropods XXXVI. Stereospecific synthesis of gyrinidal, a nor-sesquiterpenoid aldehyde from gyrinid beetles

Gyrinidal: a sesquiterpenoid aldehyde from the defensive glands of gyrinid beetles.

Three species of gyrinid beetles (Gyrinus ventralis, Dineutes hornii, and D. serrulatus) have been found to produce the nor-sesquiterpenoid aldehyde gyrinidal in the secretion of their pygidial defensive glands. This highly functionalized terpene is shown to be (E,E,E)-3,7-dimethyl-8,11-dioxo-2,6,9-dodecatrienal on the basis of spectral evidence and chemical degradation. While a very wide range of sesquiterpenoid structures occur in nature, gyrinidal appears to be the most highly oxidized acyclic sesquiterpene known.

Diffraction gratings in gyrinid beetles

The primitive surface pattern of the cuticle of insects and the way in which diffraction gratings are formed is discussed. The appearance of plane and convex gratings when illuminated by parallel light at an arbitrary angle is described. It does not appear to have been previously noted that the direction of the streak of spectra and the apparent direction of the grating rulings form an orthogonal system. The form and distribution of grating lines in the family Gyrinidae are described. Species of Gyretes are the only insects that have diffraction gratings at right angles to each other on the dorsal surface. It is suggested that their unique system of grating lines is related to their habit of swimming in circles.

Periodic reversal of heart beat in the prolarva of a gyrinid

In prolarvae of the gyrinid beetle, Dineutus assimilis Aubé, the heart was observed through the transparent egg membranes after removal of an opaque outer case. At or near the time of hatching, there were regular periodic reversals of the direction of the peristaltic waves of contraction. Beats forward averaged 41·4 per min at 27°C, whereas beats backward averaged only 15·8 per min. The change from forward to reversed was preceded by a pause of 4–5 sec, but the opposite change occurred without a pause. There were fewer reversed beats than forward beats in any consecutive series, but because the rate forward was greater, the forward beat occurred on the average only 58·8 per cent of the time, and the reversed beat occurred 41·2 per cent of the time.