Olfaction in dragonflies: Electrophysiological evidence
Graphical abstract
Highlights
► Olfaction in Paleoptera (Odonata/Ephemeroptera) is still an open question. ► Libellula depressa bears presumed olfactory sensilla on its antennae. ► We performed an electrophysiological investigation (EAG, SCR) on these antennae. ► Depolarizing EAG and SCR responses to chemicals were recorded in males and females. ► This is the first clear identification of olfactory receptor neurons in Odonata.
Introduction
In insects, the sense of smell is a complex and highly sensitive modality, governing essential decisions such as choice of mates, food, and oviposition sites. A pair of antennae bearing olfactory sensilla represents the main olfactory organ of hexapods and the olfactory sensory system is organized in a very similar fashion in most insects.
The problem of olfaction in Paleoptera (Odonata, Ephemeroptera) is still an open question. These insects have been traditionally considered anosmic, because their brain lacks glomerular antennal lobes and mushroom body calyces, which in Neoptera are involved in odor perception (Strausfeld et al., 1998, Farris, 2005).
Slifer and Sekhon (1972), in an ultrastructural overview on adult antennal flagellum of some Odonata species, identified coeloconic sensilla located in simple and compound cavities. On the basis of their apparent porous cuticle, the authors hypothesized a chemosensory function for these sensilla.
A recent ultrastructural investigation (SEM, TEM) on the adult of the dragonfly Libellula depressa (Odonata: Libellulidae) revealed sensilla located in pits on the lateral–ventral side of the antennal flagellum (Rebora et al., 2008). These sensilla are represented by sensilla coeloconica and by deeply sunken sensilla styloconica. The sensilla coeloconica (Fig. 1) are innervated by three unbranched dendrites entering the peg and they show a dendritic sheath ending at the base of the peg. The peg shows no socket and its cuticle is irregular with wide pore-like structures at the base of which actual pores with pore tubules are evident. The structure of these sensilla is in agreement with that reported for single-walled insect olfactory receptors. The deeply sunken sensilla are represented by two kinds of sensilla styloconica located at the bottom of deep cavities evident on the antennal surface as simple openings (Fig. 1). These sensilla are no-pore sensilla with inflexible socket and unbranched dendrites and, notwithstanding their structural differences, they share common features typical of thermo-hygroreceptors. The presence of putative olfactory and thermo-hygroreceptors has been confirmed in ultrastructural investigations on several Odonata families belonging to the suborders Anisoptera and Zygoptera (Rebora et al., 2009a, Piersanti et al., 2010).
Single cell electrophysiological recordings from adult males and females of L. depressa, stimulating the antenna by rapid changes in temperature and humidity, showed the occurrence of a dry, a moist and a cold receptor neurons on the antennal flagellum, probably located in the deeply sunken sensilla styloconica (Piersanti et al., 2011).
Odonata are believed to have secondarily invaded freshwater environments. Therefore, the putative olfactory coeloconic sensilla identified on their antennae could be “silent receptors”, in which olfactory receptor genes are pseudogenes, as it occurs in secondarily aquatic mammals (Freitag et al., 1998).
On the basis of these data, in order to understand if the coeloconic olfactory receptors located on Odonata antennae represent vestigial organs or are really functioning, we performed an electrophysiological investigation with electroantennogram (EAG) and single cell recordings (SCR), using L. depressa as a model species. EAG measures the total amount of electrophysiological responses in the insect antennae, thus providing a general measure of odorant reception at the peripheral level (Schneider, 1957, Roelofs, 1984, Park et al., 2002). When recording the frequency of action potentials in single olfactory receptor neurons using the SCR technique, the specificity in each neuron is revealed (Masson and Mustaparta, 1990). SCR is particularly useful when the number of stimulated neurons is small and gives only a minute EAG (Schiestl and Marion-Poll, 2002).
Section snippets
Insects
Larvae of L. depressa, attributed to the ultimate (F-0) stage were collected in ponds in Central Italy (Perugia, Umbria) in the periods March–April 2010 and 2011. The specimens were kept outdoor in plastic containers (60 × 40 × 40 cm) with water, detritus, flora and fauna from the collecting site, in natural conditions of temperature, humidity and light. The larvae were fed ad libitum with plankton (Daphnia spp. and Cyclops spp.) up to the emergence of the adults. In the experiments male and female
Electroantennography
Depolarizing EAG responses were recorded in both males and females (Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6).
The magnitude of the response to the standard stimulus (octanal at 10% v/v) was similar in the two sexes (males, −0.014 mV ± 0.002 SE; females, −0.011 mV ± 0.001 SE (t = 0.90; d.f. = 29; P = 0.374).
Discussion
Our results show that some chemicals, belonging to different classes, elicit EAG activity in the antennae of L. depressa. In particular, in females all the tested chemicals elicited response except (Z)-3-hexen-1-ol, while in males the tested chemicals elicited response except (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol and butyric acid. Differences between male and female antennae have been highlighted also in the EAG dose–response curves to octanal. In both sexes EAG responses generally increased
Acknowledgments
We are grateful to Bill Hansson for his suggestions about chemicals and to Tor Jorgen Almaas for his support in the collection of some preliminary data. Many thanks to Jonas M. Bengtsson for his helpful support in single cell recordings. Thank you very much to the anonymous referees for their suggestions.
References (46)
- et al.
Variant ionotropic glutamate receptors as chemosensory receptors in Drosophila
Cell
(2009) - et al.
Odor coding in the Drosophyla antenna
Neuron
(2001) Evolution of insect mushroom bodies: old clues, new insights
Arthropod Structure and Development
(2005)- et al.
Sparse sensillar array on Trioza apicalis (Homoptera, Triozidae) antennae-an adaptation to high stimulus levels?
Arthropod Structure and Development
(2006) - et al.
Incomplete electrical isolation of sex-pheromone responsive olfactory receptor neurons from neighboring sensilla
Journal of Insect Physiology
(2008) - et al.
New insight into an ancient insect nose: the olfactory pathway of Lepismachilis y-signata (Archaeognata: Machilidae)
Arthropod Structure and Development
(2011) - et al.
Electroantennogram (EAG) responses of Microplitis croceipes and Cotesia marginiventris and their lepidopteran hosts to a wide array of odor stimuli: correlation between EAG response and degree of host specificity?
Journal of Insect Physiology
(2010) - et al.
An improved aphid electroantennogram
Journal of Insect Physiology
(1998) - et al.
Electrophysiological identification of thermo- and hygro-sensitive receptor neurons on the antennae of the dragonfly Libellula depressa
Journal of Insect Physiology
(2011) - et al.
The antennal sensilla of the adult of Libellula depressa (Odonata: Libellulidae)
Arthropod Structure and Development
(2008)
The antennal sensilla of adult mayflies: Rhithrogena semicolorata as a case study
Micron
Organization and evolutionary trends of primary olfactory brain centers in Tetraconata (Crustacea + Hexapoda)
Arthropod Structure and Development
Sense organs on the antennal flagella of damselflies and dragonflies (Odonata)
International Journal of Insect Morphology and Embryology
Pore structures in insect olfactory sensilla: a review of data and concepts
International Journal of Insect Morphology and Embryology
A spatial map of olfactory receptor expression in the Drosophila antenna
Cell
How the choice of method influence on the results in electrophysiological studies of insect olfaction
Journal of Insect Physiology
A technique of transplantation for Drosophila
American Naturalist
Dragonflies Behaviour and Ecology of Odonata
Ancient Protostome origin of chemosensory ionotropic glutamate receptors and the evolution of insect taste and olfaction
Plos Genetics
Odor detection in insects: volatile codes
Journal of Chemical Ecology
Olfactory receptors in aquatic and terrestrial vertebrates
Journal of Comparative Physiology A
Antennal electrophysiological responses of three parasitic wasps to caterpillar-induced volatiles from maize (Zea mays mays), cotton (Gossypium herbaceum), and cowpea (Vigna unguiculata)
Journal of Chemical Ecology
Insect olfactory receptors: contributions of molecular biology to chemical ecology
Journal of Chemical Ecology
Cited by (28)
Sensory pathway in aquatic basal polyneoptera: Antennal sensilla and brain morphology in stoneflies
2024, Arthropod Structure and DevelopmentRole of chemical cues in cabbage stink bug host plant selection
2020, Journal of Insect PhysiologyCitation Excerpt :Stimulations. Stimulations were carried out according to the procedure described in Rebora et al. (2012). In particular, 20 µl of each VOCs extract, as hexane solution, were absorbed on a filter paper strip (15 × 15 mm, Whatman No.1) placed into a glass Pasteur pipette (150 mm in length, Volac®) to constitute an odour cartridge.
The antennae of damselfly larvae
2018, Arthropod Structure and DevelopmentAntennal responses to volatile organic compounds in a stonefly
2017, Journal of Insect PhysiologyCitation Excerpt :Plecoptera, whose larvae live in water and show a gradual metamorphosis, could show a reduction of the olfactory ability also at the adult stage. As far as other aquatic insects such as Ephemeroptera and Odonata are concerned, olfactory sensilla have been described in both orders (Rebora et al., 2008; Rebora et al. 2009a; Rebora et al. 2009b; Piersanti et al., 2010) and, in particular in adult Odonata, electrophysiological and behavioural investigations on the antennae (Rebora et al., 2012; Piersanti et al., 2014a; Piersanti et al., 2014b; Piersanti et al., 2016; Frati et al., 2015, 2016) revealed the presence of the sense of smell, although poor in comparison with that of many other insects, also in consideration of the simple organization of the antennal lobe (Rebora et al., 2013). Behavioural and neuroanatomical investigations in adult Plecoptera, could be particularly interesting not only to increase the knowledge of the adult stonefly behaviour but also to better understand the adaptation of the olfactory sensory system in aquatic insects moving from land to water.
Antennal sensilla of the stonefly Dinocras cephalotes (Plecoptera: Perlidae)
2016, Arthropod Structure and Development