Tolerant pattern recognition: evidence from phonotactic responses in the cricket Gryllus bimaculatus (de Geer)

When the amplitude modulation of species-specific acoustic signals is distorted in the transmission channel, signals become difficult to recognize by the receiver. Tolerant auditory pattern recognition systems, which after having perceived the correct species-specific signal transiently broaden their acceptance of signals, would be advantageous for animals as an adaptation to the constraints of the environment. Using a well-studied cricket species, Gryllus bimaculatus , we analysed tolerance in auditory steering responses to ‘ Odd ’ chirps, mimicking a signal distorted by the transmission channel, and control ‘ Silent ’ chirps by employing a fine-scale open-loop trackball system. Odd chirps on their own did not elicit a phonotactic response. However, when inserted into a calling song pattern with attractive Normal chirps, the females' phonotactic response toward these patterns was significantly larger than to patterns with Silent chirps. Moreover, females actively steered toward Odd chirps when these were presented within a sequence of attractive chirps. Our results suggest that crickets employ a tolerant pattern recognition system that, once activated, transiently allows responses to distorted sound patterns, as long as sufficient natural chirps are present. As pattern recognition modulates how crickets process non-attractive acoustic signals, the finding is also relevant for the interpretation of two-choice behavioural experiments.

Transcriptional expression changes during compensatory plasticity in the prothoracic ganglion of the adult cricket Gryllus bimaculatus

Most adult organisms are limited in their capacity to recover from neurological damage. The auditory system of the Mediterranean field cricket, Gryllus bimaculatus, presents a compelling model for investigating neuroplasticity due to its unusual capabilities for structural reorganization into adulthood. Specifically, the dendrites of the central auditory neurons of the prothoracic ganglion sprout in response to the loss of auditory afferents. Deafferented auditory dendrites grow across the midline, a boundary they normally respect, and form functional synapses with the contralateral auditory afferents, restoring tuning-curve specificity. The molecular pathways underlying these changes are entirely unknown. Here, we used a multiple k-mer approach to re-assemble a previously reported prothoracic ganglion transcriptome that included ganglia collected one, three, and seven days after unilateral deafferentation in adult, male animals. We used EdgeR and DESeq2 to perform differential expression analysis and we examined Gene Ontologies to further understand the potential molecular basis of this compensatory anatomical plasticity. Enriched GO terms included those related to protein translation and degradation, enzymatic activity, and Toll signaling. Extracellular space GO terms were also enriched and included the upregulation of several protein yellow family members one day after deafferentation. Investigation of these regulated GO terms help to provide a broader understanding of the types of pathways that might be involved in this compensatory growth and can be used to design hypotheses around identified molecular mechanisms that may be involved in this unique example of adult structural plasticity.

Different transcriptional levels of Corazonin, Elevenin and PDF according to the body-color of the two-spotted cricket, Gryllus bimaculatus

Body-color in insects changes according to the living environment and physiological stresses possibly involved in endocrine factors. To date, three predominant bioactive peptides, Corazonin, Elevenin, and pigment-dispersing factor (PDF) have been illuminated to be involved in the body-color in insects and crustaceans. Here, we examined the possibilities that these three factors would contribute to body-color changes via melanization in the two-spotted cricket, Gryllus bimaculatus, whose body color changes according to population density drastically. Quantitative analyses revealed that the higher transcriptional levels of Corazonin and Elevenin in the crowded-conditioned crickets, whereas the transcriptional level of PDF was higher in the isolated-conditioned crickets. However, the body color was not changed by knockdown of Corazonin, Elevenin, and PDF by RNA interference. The present data indicated that coloration mechanisms in G. bimaculatus is differently controlled from the previous observation in Locusta migratoria, a closely related orthopteran species.

Transcriptional expression changes during compensatory plasticity in the terminal ganglion of the adult cricket Gryllus bimaculatus

Background Damage to the adult central nervous system often leads to long-term disruptions in function due to the limited capacity for neurological recovery. The central nervous system of the Mediterranean field cricket, Gryllus bimaculatus, shows an unusual capacity for compensatory plasticity, most obviously in the auditory system and the cercal escape system. In both systems, unilateral sensory disruption leads the central circuitry to compensate by forming and/or strengthening connections with the contralateral sensory organ. While this compensatory plasticity in the auditory system relies on robust dendritic sprouting and novel synapse formation, the compensatory plasticity in the cercal escape circuitry shows little obvious dendritic sprouting and instead may rely on shifts in excitatory and inhibitory synaptic strength. Results In order to better understand what types of molecular pathways might underlie this compensatory shift in the cercal system, we used a multiple k-mer approach to assemble a terminal ganglion transcriptome that included ganglia collected one, three, and 7 days after unilateral cercal ablation in adult, male animals. We performed differential expression analysis using EdgeR and DESeq2 and examined Gene Ontologies to identify candidates potentially involved in this plasticity. Enriched GO terms included those related to the ubiquitin-proteosome protein degradation system, chromatin-mediated transcriptional pathways, and the GTPase-related signaling system. Conclusion Further exploration of these GO terms will provide a clearer picture of the processes involved in compensatory recovery of the cercal escape system in the cricket and can be compared and contrasted with the distinct pathways that have been identified upon deafferentation of the auditory system in this same animal.

Toll signalling promotes blastema cell proliferation during cricket leg regeneration via insect macrophages

Hemimetabolous insects, such as the two-spotted cricket Gryllus bimaculatus, can recover lost tissues in contrast to the limited regenerative abilities in human tissues. Following cricket leg amputation, the wound surface is covered by the wound epidermis, and plasmatocytes, which are insect macrophages, accumulate in the wound region. Here, we studied the function of Toll-related molecules identified by comparative RNA-seq during leg regeneration. Among 11 Toll genes in the Gryllus genome, expression of Gb'Toll2-1, Gb'Toll2-2, and Gb'Toll2-5 was upregulated during regeneration. RNA interference (RNAi) of Gb'Toll, Gb'Toll2-1, Gb'Toll2-2, Gb'Toll2-3, or Gb'Toll2-4 produced regeneration defects in more than 50% of crickets. RNAi of Gb'Toll2-2 decreased the ratios of S and M phase cells, expression of JAK/STAT signalling genes, and accumulation of plasmatocytes in the blastema. Depletion of plasmatocytes in crickets using clodronate also produced regeneration defects, along with reduced proliferating cells in the regenerating legs. Plasmatocyte depletion also downregulated the expression of Toll and JAK/STAT signalling genes in the regenerating legs. These results suggest that Spz-Toll-related signalling in plasmatocytes promotes leg regeneration through blastema cell proliferation by regulating the Upd-JAK/STAT signalling pathway.