Academic literature on the topic 'Cricket Oecanthus henryi'

Predation risk is a strong driver of prey distribution and movement. However, fitness-influencing behaviours, such as mating, can alter risk and influence predator–prey space-use dynamics. In tree crickets, Oecanthus henryi , mate searching involves acoustic signalling by immobile males and phonotactic movement by females. Space-use patterns in tree crickets relative to their primary predators, green lynx spiders ( Peucetia viridans ), should therefore depend on their current mate-searching state; whether males are calling or non-calling and whether females are phonotactic or non-phonotactic. We first measured the degree of spatial anchoring of crickets to specific bushes in the field and determined whether that influenced the probability of broad-scale spatial overlap with spiders. In the absence of spiders, all crickets, independent of sex or male calling status, were found to be spatially anchored to specific types of bushes and not uniformly distributed on the landscape. At the broad spatial scale, spiders were more likely to be found on bushes with female crickets and, to a lesser degree, calling male crickets. At a finer spatial scale within a bush, movement strategies of crickets not only varied depending on the presence or absence of a spider, but also on their current mate-searching state. Phonotactic females showed clear predator avoidance, whereas calling and non-calling males moved towards the spider instead of away, similar to predator inspection behaviour seen in many taxa. As the strongly selected sex, males are more likely to undertake risky mate-searching activities, which includes inspection of predator positions. Overall, we found that all crickets were predictably anchored at the landscape scale, but their sex and mate-seeking behaviour influenced the degree of overlap with predators and their antipredator movement strategies. Reproductive strategies within a prey species, therefore, can alter predator–prey space race at multiple spatial scales.

Among the different sensory modalities that play a role in sexual selection, acoustic communication plays an important one. Acoustic communication has been known to be used for male-male competition (territory maintenance, male aggression during mating),for advertisement to the opposite sex (mating status, body condition, genetic quality, nutritional status) and used by females to sample and choose conspecific preferred males. The use of acoustic communication for sexual display and information exchange has been extensively studied in multiple taxa, including insects, anurans, birds and mammals. Among insects, crickets have proven to be good model systems to study sexual selection based on acoustic communication as most species have an elaborate acoustic communication system, male advertisements, diverse types of mating incentives for females (such as glandular feeding) and a female dominated mating system. Generally, in crickets males produce species-specific calls which are used by females to localize conspecific males. Besides, calls show high levels of intraspecific variation and are energetically costly to produce. Moreover, as in crickets predominantly the females show phonotaxis towards male calls, calls also can play a role in mate sampling and choice by acting as indicators of preferred male quality. Despite being studied for many decades there are certain gaps in the studies examining mate choice in crickets. Some of them are, lack of understanding of the variation of male calling traits in nature and its role in signal evolution, lack of understanding regarding the ecological context of mate sampling and the evolution of alternative mating strategies. Hence, the tree cricket Oecanthus henryi was chosen as a study system to address these gaps in the understanding of female choice based on acoustic signals. In the tree cricket Oecanthus henryi, males call and females use calls to localize conspecific males and hence potentially females can choose males based on acoustic cues. To understand the evolution of female preference for male acoustic cues it is important to understand the variation in the calling songs in the field and identify repeatable call features that are reliable indicators of preferred male traits (morphological, developmental or genetic). I measured repeatability of male call traits in the field to understand their variation, reliability and consistency. Carrier frequency was the only call trait that was highly repeatable and hence was reliable and consistent. Following this I examined whether any of these call traits were indicators of male morphological traits (such as male size and fluctuating asymmetry) which are known to be preferred by females. It was found that carrier frequency was negatively correlated with body size; hence carrier frequency was both reliable and indicated male size. I also found that females preferred larger males during mating, as revealed by the longer mating durations and longer spermatophore retention time. Interestingly, though this study indicated that females could in principle use lower call carrier frequency to localize preferred larger males, simultaneous choice experiments done in the laboratory revealed that the females do not use this cue. These contrasting results may be because females are incapable of discriminating small differences in frequency or because they use non-acoustic cues for mate choice. However, whichever cues the females use to discriminate between males in the laboratory conditions, often these preferences are not realized in the field. The main reason behind this is that searching for preferred mates in the field can be costly and this might force females to choose sub-optimal males. Theoretical models predict that male movement and spacing in the field should influence female sampling tactics and in turn, females should drive the evolution of male movement and spacing to sample them optimally. Moreover, simultaneous sampling of males using the best-of-n or comparative Bayes strategy should yield maximum mating benefits to females. Many of the theoretical mate sampling strategies involves recall of the quality and location of individual males, which in turn requires male positions to be stable within a night. Calling males of O. henryi showed high site fidelity within a night, potentially enabling female sampling strategies that require recall. To examine the possibility of simultaneous acoustic sampling of males, I estimated male acoustic active spaces using information on male spacing, call transmission and female phonotactic threshold. Males were found to be spaced far apart and active space overlap was rare. I then examined female sampling scenarios by studying female spacing relative to male acoustic active spaces. Only 15% of sampled females could hear multiple males, suggesting that simultaneous mate sampling is rare in the field. Moreover, the relatively large distances between calling males suggest high search costs, which may favor threshold strategies that do not require memory. Using the insights gathered from these two studies I examined a unique calling behaviour from leaf holes, baffling, observed in this species. Baffling behaviour has been found in multiple species of the genus Oecanthus where the males call from selfmade holes in leaves rather than calling from leaf edges (their natural calling surface) thus increasing their loudness many fold. I started by examining the natural history of baffling and found that baffling is an extremely rare behaviour in the field. However field observations and laboratory experiments revealed that many males can baffle and hence it is not an obligatory behaviour shown only by a few males. It was hypothesized that one reason for the rarity of baffling could be resource limitation. It was found that baffling males prefer larger leaves possibly due to higher SPL gains achieved by baffling on the larger leaves, which is a limited resource in the field. However this alone was insufficient to explain extreme rarity of bafflers in the field. Hence I examined which males were using this behaviour in the field. Using field observations and laboratory experiments it was found that less preferred males (smaller and quieter) baffled more which provided them with higher calling SPL and greater sound-field volume and thus a higher number of potential mates. Moreover, baffling also increased the mating duration for the less preferred males thus providing more time to these males for sperm transfer. The females could not differentiate between an inherently loud caller and a caller whose SPL was increased artificially (as if it was baffling). Hence I concluded that baffling is probably a cheater strategy used by the less preferred males to fool the females into approaching them and mating for longer durations. To my knowledge, this is the first study that has estimated male call variation in the field to understand its role in female choice in tree crickets. Moreover this is also the first study to examine the ecological context of mate choice in tree crickets. This is also the first study to examine the advantages of baffling behaviour and its potential evolutionary implications. the different sensory modalities that play a role in sexual selection, acoustic communication plays an important one. Acoustic communication has been known to be used for male-male competition (territory maintenance, male aggression during mating),for advertisement to the opposite sex (mating status, body condition, genetic quality, nutritional status) and used by females to sample and choose conspecific preferred males. The use of acoustic communication for sexual display and information exchange has been extensively studied in multiple taxa, including insects, anurans, birds and mammals. Among insects, crickets have proven to be good model systems to study sexual selection based on acoustic communication as most species have an elaborate acoustic communication system, male advertisements, diverse types of mating incentives for females (such as glandular feeding) and a female dominated mating system. Generally, in crickets males produce species-specific calls which are used by females to localize conspecific males. Besides, calls show high levels of intraspecific variation and are energetically costly to produce. Moreover, as in crickets predominantly the females show phonotaxis towards male calls, calls also can play a role in mate sampling and choice by acting as indicators of preferred male quality. Despite being studied for many decades there are certain gaps in the studies examining mate choice in crickets. Some of them are, lack of understanding of the variation of male calling traits in nature and its role in signal evolution, lack of understanding regarding the ecological context of mate sampling and the evolution of alternative mating strategies. Hence, the tree cricket Oecanthus henryi was chosen as a study system to address these gaps in the understanding of female choice based on acoustic signals. In the tree cricket Oecanthus henryi, males call and females use calls to localize conspecific males and hence potentially females can choose males based on acoustic cues. To understand the evolution of female preference for male acoustic cues it is important to understand the variation in the calling songs in the field and identify repeatable call features that are reliable indicators of preferred male traits (morphological, developmental or genetic). I measured repeatability of male call traits in the field to understand their variation, reliability and consistency. Carrier frequency was the only call trait that was highly repeatable and hence was reliable and consistent. Following this I examined whether any of these call traits were indicators of male morphological traits (such as male size and fluctuating asymmetry) which are known to be preferred by females. It was found that carrier frequency was negatively correlated with body size; hence carrier frequency was both reliable and indicated male size. I also found that females preferred larger males during mating, as revealed by the longer mating durations and longer spermatophore retention time. Interestingly, though this study indicated that females could in principle use lower call carrier frequency to localize preferred larger males, simultaneous choice experiments done in the laboratory revealed that the females do not use this cue. These contrasting results may be because females are incapable of discriminating small differences in frequency or because they use non-acoustic cues for mate choice. However, whichever cues the females use to discriminate between males in the laboratory conditions, often these preferences are not realized in the field. The main reason behind this is that searching for preferred mates in the field can be costly and this might force females to choose sub-optimal males. Theoretical models predict that male movement and spacing in the field should influence female sampling tactics and in turn, females should drive the evolution of male movement and spacing to sample them optimally. Moreover, simultaneous sampling of males using the best-of-n or comparative Bayes strategy should yield maximum mating benefits to females. Many of the theoretical mate sampling strategies involves recall of the quality and location of individual males, which in turn requires male positions to be stable within a night. Calling males of O. henryi showed high site fidelity within a night, potentially enabling female sampling strategies that require recall. To examine the possibility of simultaneous acoustic sampling of males, I estimated male acoustic active spaces using information on male spacing, call transmission and female phonotactic threshold. Males were found to be spaced far apart and active space overlap was rare. I then examined female sampling scenarios by studying female spacing relative to male acoustic active spaces. Only 15% of sampled females could hear multiple males, suggesting that simultaneous mate sampling is rare in the field. Moreover, the relatively large distances between calling males suggest high search costs, which may favor threshold strategies that do not require memory. Using the insights gathered from these two studies I examined a unique calling behaviour from leaf holes, baffling, observed in this species. Baffling behaviour has been found in multiple species of the genus Oecanthus where the males call from self- made holes in leaves rather than calling from leaf edges (their natural calling surface) thus increasing their loudness many fold. I started by examining the natural history of baffling and found that baffling is an extremely rare behaviour in the field. However field observations and laboratory experiments revealed that many males can baffle and hence it is not an obligatory behaviour shown only by a few males. It was hypothesized that one reason for the rarity of baffling could be resource limitation. It was found that baffling males prefer larger leaves possibly due to higher SPL gains achieved by baffling on the larger leaves, which is a limited resource in the field. However this alone was insufficient to explain extreme rarity of bafflers in the field. Hence I examined which males were using this behaviour in the field. Using field observations and laboratory experiments it was found that less preferred males (smaller and quieter) baffled more which provided them with higher calling SPL and greater sound-field volume and thus a higher number of potential mates. Moreover, baffling also increased the mating duration for the less preferred males thus providing more time to these males for sperm transfer. The females could not differentiate between an inherently loud caller and a caller whose SPL was increased artificially (as if it was baffling). Hence I concluded that baffling is probably a cheater strategy used by the less preferred males to fool the females into approaching them and mating for longer durations. To my knowledge, this is the first study that has estimated male call variation in the field to understand its role in female choice in tree crickets. Moreover this is also the first study to examine the ecological context of mate choice in tree crickets. This is also the first study to examine the advantages of baffling behaviour and its potential evolutionary implications.

Acoustic communication, used by a wide variety of animals, consists of the signaler, the signal and the receiver. A change in the behaviour of the receiver after reception of the signal is a prerequisite for communication. A response to the signal by the receiver depends on signal recognition and localization of the signal source. These two aspects, namely recognition and localization by the receiver, form the main body of my work. In the mating system of crickets, the males produce advertisement calls to attract silent females to mate. Females need to recognize the conspecific call and localize the male. The tree cricket Oecanthus henryi, due to aspects of its physiology and the environment it inhabits, generates interesting problems concerning these seemingly simple tasks of recognition and localization. In crickets, usually a species-specific sender-receiver match for the call features exists, which aids in recognition. A change in the call carrier frequency with temperature, due to poikilothermy, as seen in O. henryi, may pose a problem for this sender-receiver match. To circumvent this, either the response should shift concomitantly with the change in the feature (narrow tuning) or the response should encompass the entire variation of the feature (broad tuning). I explored the response of O. henryi females to the changing nature of call carrier frequency with temperature. The results showed that O. henryi females are broadly tuned to call carrier frequency. Being broadly tuned I next wanted to explore if within the natural variation in carrier frequency, the females were able to discriminate between frequencies. Females were found not to discriminate between frequencies. Cricket ears being pressure difference receivers are inherently directional, however their directionality is dependent on frequency, which may be affected by the change in carrier frequency due to temperature. Thus I also tested the effect of frequency on the azimuthal localization accuracy. The azimuthal accuracy was not affected by call carrier frequency within the natural range of frequency variability of the species. In south India, O. henryi is found in sympatry with Oecanthus indicus. Reproductive isolation between the two is maintained through calls. Since O. henryi is broadly tuned to frequency, call carrier frequency is unlikely to enable differentiation between conspecific and heterospecific calls. I thus tested whether the temporal features can account for the same. I constructed a quantitative multivariate model of response space of O. henryi incorporating results from various playback experiments. The model predicted high responses for conspecific calls and low responses for heterospecific calls, indicating that temporal features could suffice to discriminate between the two species. The quantitative model could also be used more generally to check responses to other heterospecifics and to compare responses between conspecifics from different populations. O. henryi is found on a bush and thus the female has to navigate in a 3D environment to localize the singing male. Very few studies have explored 3D localization in insects and moreover an algorithm explaining the procedure is missing. I attempted to model the 3D localization capability in O. henryi. To understand the rules behind the localization animals were observed in the wild as well as on a 3D grid in the laboratory and simulations were created to capture the nature of the phonotaxis. Neither a random model nor a deterministic model (which estimated the shortest path) could predict the paths observed in the grid. A less complex Bayesian stochastic model performed better than a more complex one. From the assumptions of the model it was inferred that the animal, for 3D localization, basically performs localization in the azimuthal plane and combines certain simple rules to go up or down. This study has examined receiver tuning in response to change in carrier frequency with temperature, which to my knowledge had not been explored before for insects. In this study I also attempted to create a quantitative multivariate receiver response space through statistical modeling, a method that can be applied in similar studies across taxa in various acoustic communication systems. A detailed Bayesian algorithm to explain 3D localization for an insect was attempted which has also not been attempted before.