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.

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The evolutionary importance of genetic constraints has always been recognized by biologists, but very little data is available to quantitatively assess the role of constraints in shaping the biology of organisms. The field of quantitative genetics provides the tools necessary to study evolutionary constraints, mainly through the estimation of the matrix of additive genetic variance and covariance (the G matrix). The main goals of this Ph.D. dissertation were to study the persistence of constraints across environments and across species, to explore the consequences of constraints on species divergence, and to try to understand some morphological and life history characteristics of field crickets in light of genetic variation. Populations of seven wing-dimorphic cricket species from the genera Gryllus and Teleogryllus were sampled from the wild and reared in the laboratory. Using multiple statistical approaches to the comparison of G matrices, results revealed little variation in G matrices across species. Moreover, the relatively small effect of rearing environment and of the two wing morphologies on G were shown to be of the same magnitude as variation between species, therefore confirming the general constancy of genetic constraints through evolutionary time scales. Mean trait values, selection regimes and phylogenetic distances were all shown not to be predictors of G matrix variation. In agreement with the constraint hypothesis of quantitative genetic theory, morphological divergence between species was shown to be predictable from a reconstructed ancestral G matrix. In addition, information on genetic variation was used to explain various patterns relating to size, ovipositor length, wing morphology and diapause occurrence in field crickets. Overall, we suggest that genetic constraints, as described by quantitative genetics, have played a major role in shaping the observed biological diversity of field cricket species, a conclusion tha

2 pp. / Indian house crickets and field crickets are the two most common crickets in Arizona. Although these crickets do not bite or carry diseases, they are considered a nuisance because of their "chirping". This publication focuses on common crickets found in Arizona, including the Indian house crickets, field crickets, and Jerusalem crickets. It also discusses the problems they cause and the strategies to control them.

Acoustic communication in orthopterans and anurans provides a suitable model system for studying the evolutionary mechanisms of sexual selection mainly because males use acoustic signals to attract females over long distances for pair formation. Females use these signals not only to localize conspecific males but also to discriminate between potential mates. Investigations on the effect of sexual selection on acoustic signals requires an understanding of how female preferences for different features of the acoustic signal affect male mating success under ecological constraints in wild populations. The effect of female preferences on male mating success depends on the mate sampling strategy that females employ to search for potential mates. Despite its relevance, female mate sampling strategies based on male acoustic signals have rarely investigated in orthopterans and anurans, especially in the field. Considering the elaborate knowledge of the role of sensory physiology in female phonotaxis behaviour and characterization of the male acoustic signal, I used the field cricket species Plebeiogryllus guttiventris as a model system in this study. In this thesis, I first investigated the ecology of callers in wild populations. I then investigated female mate sampling strategies by incorporating relevant information on the ecology of signalers and the sensory physiology of receivers. Amount of calling activity is a strong determinant of male mating success in acoustically communicating species such as orthopterans and anurans. While many studies in crickets have investigated the determinants of calling effort, patterns of variability in male calling effort in natural choruses remain largely unexplored. I therefore investigated the spatio-temporal dynamics of acoustic chorusing behaviour in a wild population. I first studied the consistency of calling activity by quantifying variation in male calling effort across multiple nights of calling using repeatability analysis. Callers were inconsistent in their calling effort across nights and did not optimize nightly calling effort to increase their total number of nights spent calling. Next, I investigated calling site fidelity of males across multiple nights by quantifying movement of callers. Callers frequently changed their calling site across calling nights with substantial displacement but without any significant directionality. Finally, I investigated trade-offs between within-night calling effort and energetically expensive calling song features such as call intensity and chirp rate. Calling effort was not correlated with any of the calling song features, suggesting that energetically expensive song features do not constrain male calling effort. The two key features of signaling behaviour, calling effort and call intensity, which determine the duration and spatial coverage of the sexual signal, are uncorrelated and function independently Acoustic signal variation and female preference for different signal components constitute the prerequisite framework to study the mechanisms of sexual selection that shape acoustic communication. Despite several studies of acoustic communication in crickets, information on both male calling song variation in the field and female preference in the same system is lacking for most species. First, I quantified variation in the spectral, temporal and amplitudinal characteristics of the male calling song in a wild population, at two temporal scales, within and across nights, using repeatability analysis. Carrier frequency (CF) was the most repeatable call trait across nights, whereas chirp period (CP) had low repeatability. I further investigated female preferences based on song features with high and low repeatability (CF and CP respectively). Females showed no consistent preferences for CF but were more attracted towards calls with higher rates (shorter CP). I also examined the effect of signal intensity, which is known to play a critical role in female phonotaxis behaviour, on female preferences for faster calls. Females preferred louder calls over faster ones, implying a dominant role for signal intensity in female evaluation of potential mates based on acoustic signals. Call intensity was also the only signal feature that was positively correlated with male size. In the final chapter, I investigated female mate sampling strategies based on acoustic signals using both theoretical and empirical approaches. Analytical models of mate sampling have demonstrated significant differences in individual fitness returns for different sampling strategies. However these models have rarely incorporated relevant information on the ecology of signalers and the sensory physiology of receivers. I used simulation models to compare the costs and benefits of different mate sampling strategies by incorporating information on relative spacing of callers in natural choruses and the effect of signal intensity on female phonotaxis behaviour. The strategy of mating with males that were louder at the female position emerged as the optimal sampling rule in the simulations. When tested empirically in the field using callers in natural choruses, females seemed to follow the optimal strategy of mating with males that were perceived as louder at their position.