Centre for Ecological Sciences (CES)https://etd.iisc.ac.in/handle/2005/42024-03-29T04:50:15Z2024-03-29T04:50:15ZAcoustic Signals, Mate Choice And Mate Sampling Strategies in a Field CricketNandi, Diptaruphttps://etd.iisc.ac.in/handle/2005/26972019-09-13T11:11:26Z2017-10-05T00:00:00ZAcoustic Signals, Mate Choice And Mate Sampling Strategies in a Field Cricket
Nandi, Diptarup
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.
2017-10-05T00:00:00ZAnts, Figs, Fig Wasps : The Chemical Ecology Of A Multitrophic SystemRanganathan, Yuvarajhttps://etd.iisc.ac.in/handle/2005/19592020-05-22T05:23:34Z2013-04-01T00:00:00ZAnts, Figs, Fig Wasps : The Chemical Ecology Of A Multitrophic System
Ranganathan, Yuvaraj
Plant–animal interaction systems are complex food webs where the members—plants, pollinators, herbivores, parasites and predators of the pollinators/herbivores—interact with each other in ways which maximize their own fitness. Based on the net outcome, such interactions could be mutually beneficial to the interacting members (mutualism) or beneficial to only one of the interacting members at the cost of the other interacting members (herbivory, predation, parasitism). It is possible that such outcomes are actually a continuum and could swing in either direction from beneficial to detrimental and vice versa. Such transitions happen not only over long time scales, but could also happen within shorter time scales based on conditionalities. Conditional outcomes are those in which the outcome of an interaction between two partners is conditional on the involvement of a third partner. Thus, studying such outcomes necessitates taking into account systems beyond the classical two-partner interactions.
In such complex multitrophic plant–animal interaction systems in which there are direct and indirect interactions between species, comprehending the dynamics of these multiple partners is very important for an understanding of how the system is structured. In Chapter 2 we investigate Ficus racemosa and its community of obligatory mutualistic and parasitic fig wasps that develop within the fig inflorescence or syconium, as well as their interaction with opportunistic ants. We focus on temporal resource partitioning among members of the fig wasp community over the development cycle of the fig syconia during which wasp oviposition and development occur and we study the activity rhythm of the ants associated with this community. We found that the members of the wasp community partitioned their oviposition across fig syconium development phenology and showed interspecific variation in activity across the diel cycle. The wasps presented a distinct sequence in their arrival at fig syconia for oviposition. We documented night oviposition in several fig wasp species for the first time. Ant activity on the fig syconia was correlated with wasp activity and was dependent on whether the ants were predatory or trophobiont-tending species; only numbers of predatory ants increased during peak arrivals of the wasps.
In Chapter 3, we found that predatory ants (Oecophylla smaragdina) patrolling F. racemosa trees were attracted to the odour from fig syconia at different developmental phases, as well as to the odours of fig wasps, whereas other predatory ants (Technomyrmex albipes) responded only to odours of syconia from which fig wasps were dispersing and to fig wasp odour. However, trophobiont-tending ants (Myrmicaria brunnea) patrolling the same trees and exposed to the same volatiles were unresponsive to fig or fig wasp odours. The predatory ants demonstrated a concentration-dependent response towards volatiles from figs receptive to pollinators and those from which wasps were dispersing while the trophobiont-tending ants were unresponsive to such odours at all concentrations. Naıve predatory ants failed to respond to the volatiles to which the experienced predatory ants responded, indicating that the response to fig-related odours is learned.
In Chapter 4 we characterise the dynamics of the volatile bouquet of the fig syconium from the initiation through pre-receptive, receptive, and late inter-floral stages which act as signals/ cues for different fig wasp species. We were also interested in diel patterns of volatile emission as some fig wasp species were strictly diurnal (the pollinator, Ceratosolen fusciceps) whereas other fig wasps such as Apocryptophagus fusca were observed ovipositing even during the nocturnal hours. We identified volatiles that were specific to syconium development phase as well as to the time of day in this bouquet. α-muurolene was identified as the sesquiterpene specific to receptive-phase as well as being present only during the day thus coinciding with the diurnal pollinator arrival pattern. Volatiles such as (E)-β-ocimene were present in increasing levels across the developmental stages of the fig and thus could act as background volatiles providing suitable information to fig wasps about host plants and their phases.
Chapter 5 examines the responses of predatory and trophobiont-tending ant species to the cuticular hydrocarbon (CHC) extracts of four galler and two parasitoid fig wasp species associated with F. racemosa. Interestingly, the antennation response of both experienced and na¨ıve ants to these wasp extracts was identical indicating that prior exposure to such compounds is not necessary for eliciting such response. We also characterised these cuticular hydrocarbon extracts to find potential compounds which could as short-range cues for predatory ants. Ants were more responsive to the cuticular extracts of parasitoids rather than to those of galler wasps, implying that the CHC profile of carnivorous prey may contain more elicitors of aggressive behaviour in ants compared to herbivorous prey whose profiles may be more similar to those of their plant resources. We also find congruency between the cuticular profiles of parasitoids and their hosts suggesting that parasitoids could sequester compounds from their diet.
Important findings and conclusions of the thesis are presented in Chapter 6.
The first two parts of the appendices section discuss work carried out on alternative ways of analysing multivariate data sets such as plant volatiles and insect cuticular hydrocarbons. Appendix A details the use of Random Forests, an algorithm-based method of analysing complex data sets where there are more variables than samples, a situation akin to microarray data sets. This work illustrates the use of such techniques in chemical ecology, highlighting the potential pitfalls of classical multivariate tests and the advantages of newer more robust methods. Appendix B, an invited article following the publication of the earlier work, compares different data transformation procedures currently employed in such multivariate analysis.
Appendix C details sex-specific differences in cuticular hydrocarbons of fig wasps, using the pollinator C. fusciceps as a case study.
2013-04-01T00:00:00ZAttributes Of Royalty In The Primitively Eusocial Wasp Ropalidia marginata : Pheromone, Ovaries And BehaviorMitra, Aniruddhahttps://etd.iisc.ac.in/handle/2005/18502020-06-09T06:13:29Z2012-12-07T00:00:00ZAttributes Of Royalty In The Primitively Eusocial Wasp Ropalidia marginata : Pheromone, Ovaries And Behavior
Mitra, Aniruddha
This thesis has looked at the proximate mechanisms by which eusociality is maintained in colonies of the primitively eusocial wasp Ropalidia marginata. Unlike other typical primitively eusocial species, the R, marginata queen is remarkably docile and non-interactive and hence cannot possibly use aggression to maintain her status. Recent evidence hints at pheromonal queen signalling through the Dufour’s gland. Hence, queen-worker difference in Dufour’s gland composition has been studied in details. Queens and workers differ with respect to overall composition of Dufour’s glands, categories of compounds, and individual compounds as well. The Dufour’s gland compounds may be having a bouquet effect in queen signalling, with individual compounds being less important than the overall composition. The queen pheromone also appears to be an honest signal of fertility, as compounds that differ consistently between queens and workers are correlated with ovarian development of queens, and solitary foundresses and potential queens, who are intermediate between queens and workers in ovarian development, are intermediate in their Dufour’s gland profile as well. When the queen is removed from a colony, one of the workers (potential queen, PQ) shows high aggression, and if the queen is not returned, goes on to become the next queen of the colony. The aggression of PQ comes down as a function of time since queen removal, and correlated with this, the ovaries of PQ increase. Dufour’s gland profile of PQ is similar to workers immediately after queen removal, but comes closer to queens with passage of time. This hints at an interesting transition in maintenance of eusociality from “queen control” by aggression to “queen signal” by pheromone during the queen establishment phase. It has generally been assumed that one set of chemicals can carry multiple information, namely queen signal and colony signal. Initial statistical analysis of chemical composition data showed that perhaps both caste and colony signals can be conveyed by the Dufour’s gland compounds, but detailed analysis cast some doubt on this, as the Dufour’s gland compounds could not be separated into non-overlapping subsets with respect to importance in caste and colony discrimination. A bioassay showed that the wasps do not make colony discrimination from Dufour’s gland compounds. This suggests that the ability to statistically differentiate groups of organisms from their chemical profiles does not guarantee similar discrimination by the organisms themselves, emphasising the need for bioassays to resolve such issues.
2012-12-07T00:00:00ZBiogeography and comparative phylogeography of freshwater snails of IndiaSil, Maitreyahttps://etd.iisc.ac.in/handle/2005/50672021-04-27T04:46:17ZBiogeography and comparative phylogeography of freshwater snails of India
Sil, Maitreya
Distribution of flora and fauna is shaped by both current and historical processes. In my thesis
I concentrated on how the historical component of the governing processes have dictated the
current distribution of biota. The history of a lineage is intricately linked to and is moulded by
the history of the place it occurs in. Hence, I made an attempt to investigate the course of two
families of freshwater snails distributed in the Indian subcontinent with respect to the
paleogeology and paleoclimate of the subcontinent. In the first chapter, I gave a brief overview
of the discipline of historical biogeography and the plate tectonic and climatic histories of the
Indian subcontinent. I also introduced my model systems: Ampullariidae and Viviparidae.
Indian biota has affinities to many different biogeographic regions- a legacy of its current
position and its plate tectonic history. Hence, the first step in order to trace the history of a
group is to understand its biogeographic origin. In the second chapter, I aimed to uncover the
historical biogeography of the pan-tropical freshwater snail family Ampullariidae with respect
to the plate tectonic history of the Indian subcontinent. I tested three hypotheses regarding the
time and route of colonization - colonization when India was a part of Gondwanaland,
colonization after Indian plate’s separation from Madagascar and northwards drift, and
colonization after the Indian plate collided with Asia. I employed phylogenetics, molecular
dating and ancestral range estimation analysis to address this question. I came to the conclusion
that Pila colonized India from Africa after India collided with Asia following a ‘Eurasian
route’.