The role of chemoreception in sex recognition by male crickets: Acheta domesticus and Teleogryllus oceanicus

ABSTRACT. Contact chemoreception is important in female recognition by Teleogryllus oceanicus (Le Guillou) males. Antennal contact of female conspecifics, body regions, detached antennae and conditioned substrate elicited mostly courtship responses including courtship songs. Aggressive acts were produced only in response to male conspecifics. Male body regions, detached antennae and conditioned substrate elicited very few courtship or aggressive acts and no songs. This suggests that one or several communication modes, in addition to chemical communication, are necessary to elicit aggressive responses. Acheta domesticus (L.) males cannot rely upon chemical cues for recognition of either sex. Responses to conspecifics suggest that A. domesticus males produce aggressive acts immediately after antennal contact with either sex. Aggressive response to males usually persists, but response to females often switches to courtship. Responses to body regions, detached antennae, and conditioned substrate were few, with courtship and aggressive responses elicited by both male- and female-generated stimuli. The importance of contact chemoreception in cricket communication is suggested by (1) failure of hexane-washed antennae to elicit aggressive or courtship acts, and (2) males spending more time in contact with body regions and conditioned substrates than with corresponding controls. Lack of response to male or female odour-laden air suggests that chemical signals are used by males only if directly contacted. Chemical and other signals supplement the obvious use of acoustic signals for intra- and intersexual communication in these crickets. The importance of multimodal communication in sex recognition is discussed.     

Susceptibility of North-American and European crickets to Acheta domesticus densovirus (AdDNV) and associated epizootics

The European house cricket, Acheta domesticus L., is highly susceptible to A. domesticus densovirus (AdDNV). Commercial rearings of crickets in Europe are frequently decimated by this pathogen. Mortality was predominant in the last larval stage and young adults. Infected A. domesticus were smaller, less active, did not jump as high, and the adult females seldom lived more than 10-14 days. The most obvious pathological change was the completely empty digestive caecae. Infected tissues included adipose tissue, midgut, epidermis, and Malpighian tubules. Sudden AdDNV epizootics have decimated commercial mass rearings in widely separated parts of North America since the autumn of 2009. Facilities that are producing disease-free crickets have avoided the importation of crickets and other non-cricket species (or nonliving material). Five isolates from different areas in North America contained identical sequences as did AdDNV present in non-cricket species collected from these facilities. The North American AdDNVs differed slightly from sequences of European AdDNV isolates obtained in 1977, 2004, 2006, 2007 and 2009 and an American isolate from 1988. The substitution rate of the 1977 AdDNV 5 kb genome was about two nucleotides per year, about half of the substitutions being synonymous. The American and European AdDNV strains are estimated to have diverged in 2006. The lepidopterans Spodoptera littoralis and Galleria mellonella could not be infected with AdDNV. The Jamaican cricket, Gryllus assimilis, and the European field cricket, Gryllus bimaculatus, were also found to be resistant to AdDNV.     

Ultraviolet nuptial colour determines fight success in male European green lizards (Lacerta viridis)

Animal communication through colour signals is a central theme in sexual selection. Structural colours can be just as costly and honest signals as pigment-based colours. Ultraviolet (UV) is a structural colour that can be important both in intrasexual competition and mate choice. However, it is still unknown if a UV signal alone can determine the outcome of male-male fights. European green lizard (Lacerta viridis) males develop a nuptial throat coloration with a strong UV component. Among males differing only in their manipulated UV colour, females prefer males with higher UV. Here, we experimentally decreased the UV coloration of randomly chosen males from otherwise similar male pairs to test the hypothesis that a difference in UV colour alone can affect fight success during male-male competition. Our results fully supported the hypotheses: in almost 90 per cent of the contests the male with reduced UV lost the fight. Our results show that UV can be an important signal, affecting both female mate choice and determining male fight success.     

Genetic composition of social groups influences male aggressive behaviour and fitness in natural genotypes of Drosophila melanogaster

Indirect genetic effects (IGEs) describe how an individual''s behaviour—which is influenced by his or her genotype—can affect the behaviours of interacting individuals. IGE research has focused on dyads. However, insights from social networks research, and other studies of group behaviour, suggest that dyadic interactions are affected by the behaviour of other individuals in the group. To extend IGE inferences to groups of three or more, IGEs must be considered from a group perspective. Here, I introduce the ‘focal interaction’ approach to study IGEs in groups. I illustrate the utility of this approach by studying aggression among natural genotypes of Drosophila melanogaster. I chose two natural genotypes as ‘focal interactants’: the behavioural interaction between them was the ‘focal interaction’. One male from each focal interactant genotype was present in every group, and I varied the genotype of the third male—the ‘treatment male’. Genetic variation in the treatment male''s aggressive behaviour influenced the focal interaction, demonstrating that IGEs in groups are not a straightforward extension of IGEs measured in dyads. Further, the focal interaction influenced male mating success, illustrating the role of IGEs in behavioural evolution. These results represent the first manipulative evidence for IGEs at the group level.     

Danger detection and escape behaviour in wood crickets

The wind-sensitive cercal system of Orthopteroid insects that mediates the detection of the approach of a predator is a very sensitive sensory system. It has been intensively analysed from a behavioural and neurobiological point of view, and constitutes a classical model system in neuroethology. The escape behaviour is triggered in orthopteroids by the detection of air-currents produced by approaching objects, allowing these insects to keep away from potential dangers. Nevertheless, escape behaviour has not been studied in terms of success. Moreover, an attacking predator is more than “air movement”, it is also a visible moving entity. The sensory basis of predator detection is thus probably more complex than the perception of air movement by the cerci. We have used a piston mimicking an attacking running predator for a quantitative evaluation of the escape behaviour of wood crickets Nemobius sylvestris. The movement of the piston not only generates air movement, but it can be seen by the insect and can touch it as a natural predator. This procedure allowed us to study the escape behaviour in terms of detection and also in terms of success. Our results showed that 5-52% of crickets that detected the piston thrust were indeed touched. Crickets escaped to stimulation from behind better than to a stimulation from the front, even though they detected the approaching object similarly in both cases. After cerci ablation, 48% crickets were still able to detect a piston approaching from behind (compared with 79% of detection in intact insects) and 24% crickets escaped successfully (compared with 62% in the case of intact insects). So, cerci play a major role in the detection of an approaching object but other mechanoreceptors or sensory modalities are implicated in this detection. It is not possible to assure that other sensory modalities participate (in the case of intact animals) in the behaviour; rather, than in the absence of cerci other sensory modalities can partially mediate the behaviour. Nevertheless, neither antennae nor eyes seem to be used for detecting approaching objects, as their inactivation did not reduce their detection and escape abilities in the presence of cerci.