Since several decades, field crickets of the subfamily Gryllinae under order Orthoptera have been used as a model group by researchers working in the field of neuroethology, behavioural ecology and bioacoustics. Subfamily Gryllinae is a much diversified group and members are diverse in their biological traits however the most commonly used model systems in the research fields belong to only three genera: Gryllus, Teleogryllus and Acheta. All the three genera are related to each other therefore, they fail to represent the wide diversity of ecological and behavioral traits that are encompassed by other members of Gryllinae. To understand the diversity in an evolutionary framework in field crickets, it is thus necessary to take into account the evolutionary background of the model systems. A phylogenetic analysis is a prerequisite for all evolutionary studies. A phylogeny hypothesizes the relationship among the studied taxa on the basis of homology drawn from all the characters that were used for the analysis. The phylogenetic tree is a branching diagram where related taxa are grouped together at nodes and the terminal ends of the branches are the studied taxa. The characters are mapped on to this tree thus indicating the hypothetical ancestral state of each character at the nodes and explaining the transformational stages of each character that gave rise to the current character state. This procedure helps in understanding the evolutionary history and understanding the patterns of relationships among taxa that in turn also help in identification of species. This process of identification and classification by phylogenetic reconstruction is formally known as “phylogenetic systematics”. The main goal of this thesis work was to understand the phylogenetic relationships among field crickets of the subfamily Gryllinae. This study is of importance in the field of orthopteran classification because since the 19th century, taxonomists proposed several taxonomic rankings and various classificatory schemes either by describing new classificatory levels or by upgrading existing taxonomic levels to higher levels. In addition, different sets of morphological characters have been used in proposing the classification hypotheses which in turn leads to the existence of several mutually exclusive hypotheses. Although there have been several changes in the taxonomic positioning of these crickets under Gryllinae, none so far have been based on a phylogenetic hypothesis. Therefore, I described 100 characters based on external and internal morphological structures of crickets belonging to 17 genera to test all the previously proposed classificatory hypotheses, provide a scheme for classifying these crickets under different hierarchical levels under Gryllinae and a strong base for conducting further evolutionary studies. The results lend full support to one of the previously proposed hypotheses for classification. Subfamily Gryllinae is a monophyletic clade where all the field crickets should be grouped under two tribes. The results also invalidate several tribes that have been erected in recent years. The second aim was to test species concepts by examining concordance in species boundaries generated from different data sets and to study the pattern of song evolution in field crickets. Therefore, for this study a field cricket belonging to genus Itaropsis was selected. Only one species of Itaropsis is known from the Indian subcontinent which was described from Sri Lanka. Interestingly, five call types of Itaropsis were encountered when a field survey was performed at four different localities in the Western Ghats of India. Males of the all five call types (varying from long trills to short chirps) looked morphologically very similar to each other. However, they differed in their calling song structure, I described four call features (carrier frqeuncy, syllable period, syllable duration and call duration) and classified the individuals into clusters by calculating distances using these call features. The clusters thus obtained were considered to reflect different species under the genus Itaropsis. To assure that the clusters thus obtained reflect different species, concordance between the results was tested by comparing these results with the clades of an available phylogeny for the collected individuals of this genus using both morphological and molecular data. The acoustic clusters showed concordance with the phylogenetic lineages largely however an absolute match was not found suggesting that these lineages cannot be called as distinct species. The pattern of evolution of songs in Itaropsis was examined by optimizing the call features on the phylogenetic tree derived from molecular data. This showed short chirps with a dominant frequency of 7 kHz to be the ancestral call type within this genus, from which long trills with long syllable durations have evolved. There were no significant patterns in the evolution of carrier frequency. In most crickets, the calling songs that are produced by males to attract their conspecific females are considered species specific therefore, the calling songs serve as an additional tool in identification of crickets. The third aim of my work was to use only call features of crickets in delineation of species but for higher number of species. Therefore, for this I used recorded calling songs of 14 species of field crickets and described their call features. I then used either five or seven call features to construct clusters based on Euclidean distances between the songs of all pairs of individuals. I also carried out a discriminant function analysis of these data to test the efficiency of species identification when taxa were specified a priori. I varied the number of species used for the analysis systematically from 5 to 14 to examine the effect of varying the number of taxa on correct species identification. The results showed that taxa number can be increased upto ten to obtain almost correct classification however, using six to seven taxa is optimal since they provide 90% accuracy in classification. To the best of my knowledge, this study on understanding the phylogenetic relationships among field crickets is the first to be carried out at subfamily level. Description of new call types reflecting multiple or incipient species under the genus Itaropsis and use of acoustic features in species identification of Indian field crickets is also a new contribution to the area of orthopteran systematics and phylogenetics.

Animals detect, recognize and localize relevant objects in noisy, multi-source environments. Female crickets locate potential mates in choruses of simultaneously calling males using acoustic signals, a behaviour termed phonotaxis. The mechanisms underlying cricket phonotaxis are now understood across multiple levels: biophysical, neurobiological and behavioural. Phonotaxis has, however, rarely been tested in the complex real-world acoustic environments and no attempts have been made to predict acoustic orientation behaviour in these conditions despite our extensive understanding of its underlying mechanisms. In this thesis, I first characterized the acoustic environments faced by female crickets of the species Plebeiogryllus guttiventris in the field. Phonotaxis behaviour of females was then characterized under laboratory conditions using two sound sources. The data obtained were used to develop a simulation that predicted this behaviour. The predictions of the simulation were then tested against the phonotaxis behaviour of females in realistic, multi-source conditions in the field. My field studies of male behaviour showed that males of this species produced complex and variable songs in choruses where multiple males called simultaneously. The acoustic ranges of males in these choruses overlapped extensively and females performing phonotaxis in such choruses would hear multiple males simultaneously. The acoustic interactions of simultaneously calling males were also characterized for their timing relationships with each other and the changes they made to the temporal patterns of their songs. Males did not either synchronise or alternate their chirps, however they made changes to the temporal patterns of song in a way that is likely to make them more attractive to females. I then characterized the closed-loop walking phonotaxis behaviour of P. guttiventris females in the presence of two active sound sources playing conspecific song. Both the baseline and relative SPLs of the two speakers were systematically varied and female phonotactic paths were obtained. Females were found to preferentially approach louder songs. Several aspects of this behaviour were characterized, in particular orientation ability and motor behaviour under varied conditions of stimulus intensity. A stochastic simulation of closed-loop walking phonotaxis behaviour was developed using both current understanding of field cricket physiology and my data on closed-loop walking phonotaxis. The simulation was demonstrated to both qualitatively and quantitatively recapture female behaviour. It was also able to qualitatively recapture female behaviour in two previously published classical experiments in which the hearing of female crickets was disrupted. Female phonotaxis was then tested under real-world multi-source conditions. The behaviour of real females was compared to the predictions of the simulation. The simulation was found to recapture both female preference and phonotactic path forms at the population level. To my knowledge, this is the first study to both examine and successfully predict phonotaxis behaviour in complex real-world acoustic conditions.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

No description available.

The species-specific calling songs of male crickets are used by females for species recognition and mate choice. Heritabilities of variation of morphological structures involved in song production, components of the calling song, and body size were estimated for G.firmus. All morphological structures were shown to possess significant additive genetic variation (h$ sp2 sb{ rm S+D} > 0.42)$. One of the five song components examined, pulse rate, was shown to have a significant heritability (h$ sp2 sb{ rm S+D}$ = 0.35). Due to the low correlation between body size and song components, it is unlikely that female G.firmus could use the calling song to assess male body size or wing morph (micropterous or macropterous).

The responses and morphology of nine sound-sensitive interneurons are described in the cricket Teleogryllus oceanicus. Each of the neurons receives direction-specific input in the prothoracic ganglion, and each projects at least one interganglionic axon. Five of the neurons respond best to high frequencies ($>$10 kHz); four are most sensitive to low frequencies (3-10 kHz). Responsiveness to model calling songs was examined in addition to testing sensitivity to wind and light. Anatomical observations reveal that seven of the neurons receive auditory input via polysynaptic pathways, and that at least five of the neurons have morphology consistent with them providing input to mesothoracic motor neurons which are involved in behavioral responses to sound. Correlations between structure, topographic organization, and spectral sensitivity were found. The structure of one previously identified, auditory neuron was examined and found to change during late post-embryonic life. This represents a novel developmental pattern.

"January 1951." / Includes bibliographical references. / 1 v. (various pagings) : ill., maps ; 33 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, Waite Agricultural Research Institute, 1951

Thesis (doctoral)--University of Stockholm, 1993. / Includes bibliographical references.

Taking control of the protein production machinery of the host cell is a required step in the life cycle of viruses. Towards this end, viruses have evolved diverse strategies of cellular mimicry and deception to hijack and steal host cell ribosomes for viral protein production. In higher eukaryotes, where translation is sophisticated and access to ribosomes intricately regulated, numerous positive strand RNA viruses have evolved structured RNA sequences to evade translation regulation mechanisms. These RNA sequences, called Internal Ribosomal Entry Sites (IRESs), use their RNA structure to hijack the eukaryotic host cell ribosomes during the highly regulated initiation phase of translation. While a select few of such IRESs have been both biochemically and structurally characterized, the diversity of IRESs isn’t fully explored. Structural basis for the working mechanism of intergenic IRESs such as the Israeli Acute Paralysis Virus IRES (IAPV-IRES) with unique RNA features and expanded coding capacity is unavailable. Similarly, structural and biochemical understanding of newly described IRESs such as the complex IRES located at the 5′ untranslated region of the Cricket Paralysis Virus (CrPV 5′-UTR-IRES) is also unavailable. This body of work uses cryo-electron microscopy (cryo-EM) and biochemistry to characterize these two IRESs.Here, we show how the IAPV-IRES uses its unique features to exploit novel binding sites and commits the IRES-ribosome complexes towards a global pre-translocation mimicry. We trace a complete path of the IRES from its initial binding with the small subunit to its formation of an elongation-ready ribosome. We show that its mechanism of ribosome hijacking is different from currently accepted mechanistic paradigm for other IRESs from viruses similar to IAPV-IRES. We also identify another divergent mechanism of ribosome hijacking used by a different type of IRES. We show that the CrPV 5′-UTR-IRES features a novel, extended, and multi-domain architecture unlike any of the previously characterized IRESs from the group it belongs to. We also show that this IRES uses its novel structure and a minimal set of initiation factors to assemble a canonical-like pre-initiation complex on the small subunit of the ribosome at an upstream start-stop open reading frame. This body of work underscores the unexplored diversity in IRESs found in single stranded positive sense viral RNA genomes, invites re-visiting of the currently standing mechanisms of cap-independent initiation carried out by IRESs, and sheds light on a possible evolutionary past where IRESs could have given rise to the current eukaryotic translation initiation system.

No description available.