Priti, H., Gururaja, K. V., Aravind, N. A., & Ravikanth, G. (2021). Influence of microhabitat on the distribution of tadpoles of three endemic Nyctibatrachus species (Nyctibatrachidae) from the Western Ghats, India. Biotropica. https://onlinelibrary.wiley.com/doi/10.1111/btp.12988
Short title: Microhabitat factors influencing Nyctibatrachus tadpoles
Species interactions are known to shape biological communities. While antagonistic interactions like competition and predation are well known, cooperative interactions have received comparatively less attention. Mixed-species foraging behaviour is a common phenomenon seen across various taxa including fish, birds and mammals, where different species form groups and forage together. Unlike symbiotic associations, these interactions are more dynamic and include a much larger subset of species of the community. We sampled mixed-species groups (MSG) of reef fish in the Lakshadweep islands, off the west coast of India. The data was gathered over four years following a mass-bleaching event which led to massive loss of coral in Lakshadweep in 2010. Though not widely reported, we discovered that mixed-species grouping is a common occurrence in the reef ecosystem. Around 130 of the 305 commonly observed species of fish in the Lakshadweep were seen participating in groups to some extent. Using a cluster analysis on species composition, we categorised the groups that were observed in Lakshadweep into nine compositional categories, which also exhibited variation in behaviour, habitat affinity and group cohesion. We then examined variation in grouping propensity, species richness, species evenness as well as species composition across space, time and habitat for the most commonly observed compositional categories. We found that invertivores tended to form smaller attendant groups, with clear nuclear-follower relationships, and likely form for direct foraging benefits. Herbivorous fish on the other hand formed large shoaling associations indicating benefits gained from increasing group size. We found evidence of the effect of the mass-bleaching event and subsequent ecosystem recovery on the formation of some groups. Reef fish MSGs are thus important components of these ecosystems and can both affect and be impacted by reef structure and function.
Collective movement is a fundamental process affecting the survival and reproductive success of group-living animals. Many of the hypothesized benefits of grouping such as predation evasion and foraging efficiency require the individuals in a group to move in a coordinated way. While moving in groups, animals are not only responding to the environment but also interacting with each other. These interactions give rise to emergent collective movement and behavioural patterns. A novel aspect of emergent behaviour is that a group can exhibit properties that no individual displays on its own.
Most studies on emergent properties of collective behaviour are conducted in controlled conditions. However, in natural settings, habitat is heterogeneous in terms of resource distribution, availability of hiding places and substrate for movement. Empirical studies have rarely investigated such fine-scale interactions (e.g. alignment, attraction among individuals) in their natural habitat. One reason for the dearth of such studies is the difficulty of data collection. Recent advances in techniques of aerial imagery allow us to observe and record such fine-scale data. For my PhD project, I studied the collective behaviour of blackbuck herds in their natural habitat. More specifically, I investigated the collective response of blackbuck herds during predation-like events. By analyzing multiple interactions among group members simultaneously, I aimed to understand the role of social interactions in shaping the collective response of blackbuck herds when faced with predation-like threats.
First, we overcome the difficulty of observing fine-scale interactions in animal groups (in their natural habitat) by using UAVs. We recorded blackbuck herding behaviour at high spatio-temporal resolutions (30 frames per second). Using this technique we were able to record the blackbuck herd’s collective escape behaviour in the context of predation using controlled-simulated threats.
Tracking animals in the videos recorded in natural habitat is extremely difficult due to varying background and light conditions and clutter in the background. Relatively basic image processing methods and default tools don’t perform satisfactorily in such a scenario.
Hence, we developed a machine learning method and GUI tool to extract the spatial locations and movement trajectories of all the individuals in a group from the videos recorded in natural field conditions.
Once we were able to obtain the movement trajectories from the videos, I then analysed these trajectories and interactions between individuals to explore - how the information about predatory risk spreads through a group in natural conditions. Broadly, our results suggest that transient leader-follower relationships emerge in these groups while performing the high-speed coordinated movement. Also, males and females respond differently to the threat scenario: adult females are more likely to be the response initiators whereas adult breeding males are more likely to influence the group movement during the escape response. Our results indicate that in fission-fusion groups associations are likely to last for short time scales and spatial positions of the individuals only affect their response-time (vigilance behaviour) but not their influence on the group.
Many insects such as ants, bees, wasps and termites organise themselves into societies with division of labour, communication, conflict, cooperation and altruism. Insect societies resemble human societies in many ways and are arguably more efficient than ours in some ways. They sustainably harvest environmental resources, engineer their environments both inside and outside their nests, practice agriculture, fight disease with a combination of individual and social immunity, organise social hunting parties, navigate their environment using terrestrial and celestial cues and majorly influence the evolutionary trajectories of other organisms such as flowering plants. So, can we humans learn anything from insect societies? In this talk I will attempt to answer this question in the affirmative, but with caution. I will consider such relatively non- controversial topics as communication, agriculture and robotics but also some relatively controversial topics such as cooperation, conflict, collective decision making and democracy.
Predation is a strong selection force that can potentially change the mate-finding strategies of prey. However, what makes one prey more risk-prone to predation relative to another depends on various ecological and behavioural factors and their interactions. Predation risk can be different for different species, different sexes of the same species and even for different behaviours of the same sex. One of the questions we try to address is why we see sex-biased predation by bats on katydids (bushcrickets) and to understand that we investigated the risks associated with different sex-specific behaviours. From the wing remains of katydids collected from the roosts of a bat predator Megaderma spasma, we see interesting patterns of predation for two different katydid species. For the genus Mecopoda, more male wing remains are found in the breeding season, and more female wings are found in the non-breeding season, whereas for another katydid Onomarchus uninotatus, more female wings are found throughout the year. Interestingly, these two katydids have different strategies for mate-finding. In Mecopoda, only the males signal and the silent females move towards the singing males, whereas O. uninotatus performs a multimodal duet, where both males and females can signal and search. We conducted behavioural experiments and observed bat responses to free-moving males and females of these two katydids, while they engaged in signalling using acoustic or vibratory cues and searching by walk or flight. Flight emerged as the highest risk factor for males and females of both katydid species, whereas walking was not found to be risky.
Sleep or sleep-like behaviour has been observed in most animals examined, from invertebrates to mammals. Sleep is ecologically important as it renders the sleeping individual vulnerable to environmental stressors, yet the evolution of sleep and its ecological context remain poorly understood. Reptilian sleep in the wild is likely to be influenced by ecological processes of predation, competition, and thermoregulation. In this talk, I present an overview of what is known of sleep ecology in reptiles. I illustrate such ecological constraints and sleep strategies (e.g. for predator-avoidance) using agamid lizards. Finally, I outline the likely relevance of sleep ecology as an evolutionary driver, its application to conservation, and other interesting research directions.
Behavioural variation is ubiquitous in the animal kingdom and typically comprises of multiple components — across-individual variation (a.k.a personality), within-individual variation, stochastic noise, and unmeasured variation. Most behavioural research tends to focus on the population mean behaviour, ignoring the aspect of inter- and intra-individual variability. Such variability has been linked to ecological, evolutionary and conservation implications with fitness consequences. Despite the recent explosion in number of studies on animal personality, the focus has been short-term, laboratory-based studies and on a limited number of personality axes.
In this study, I will study variation at the individual level along multiple personality axes, with an in-depth focus on exploratory behaviour and test how this variation links to survival, a crucial component of fitness. I will use the South Indian Rock Agama (Psammophilus dorsalis) as a model system by monitoring and assaying wild individuals throughout their lifespan. I will quantify the different levels of variation by taking repeated measures of each behavioural trait of interest and using variance partitioning statistics.
In my first chapter, I will test whether there are differences in trait variation based on the selection pressure acting on the trait - sexual selection versus viability selection. I expect that the mechanism by which the two selection pressures act would give rise to differences in how variable these traits are. Preliminary results reveal that traits under viability selection tend to exhibit higher consistent differences across individuals.
Taking this result forward, I will focus on a trait under predominantly viability selection - exploratory behaviour. Exploratory behaviour - a measure of response to novelty can have implications for ecology of an organism from foraging performance, habitat selection to mate acquisition and escape from predators. Further, these responses are expected to be plastic across contexts to avoid phenotype-environment mismatch. These plastic responses are expected to have correlations with behavioural types across traits and contexts.
In my second chapter, I will test if there is behavioural differentiation along this axis and how it varies at the intra-individual level. I will use individual responses to novel prey and novel environment as proxy for exploration behaviour and test how this response relates with foraging performance.
In my third chapter, I will look at behavioural plasticity of exploratory behaviour by exposing individuals to different levels of perceived predation pressures and measuring exploratory tendencies. I will also look for evidence of behavioural type-plasticity associations.
Behavioural variation rarely evolves and persists independent of other traits; hence it is prudent to test for fitness consequences by looking at suites of traits. In my fourth chapter, I will test for the presence of correlations between behaviours - exploration, boldness, activity, and social responsiveness (competition and dominance) and check how such a correlation, if existent, affects survival.
Broadly, I will look at the form and nature of inter-individual variation under different selection pressures across time and contexts and test their link to fitness.
Organisms face the allocation problem of investing resources in different traits. Investment strategies are expected to maximise fitness by balancing the costs and benefits of investing in multiple traits used in diverse contexts, including acquiring territories, food, and mates. The trade-offs associated with trait investment are likely to be dynamic. For example, ecological factors, such as climate, temperature, and diet, and demographic factors, such as male and female densities and sex ratio, can affect trade-offs and, thereby trait investment.
Many animals show strikingly exaggerated traits like antlers in Cervids. Such traits represent costly trade-offs because they decrease the residual resources available for allocation to other traits. Moreover, individuals within a population often exhibit variation in exaggerated traits, with relative trait sizes increasing with body size. This pattern of positive allometry where individuals ‘invest disproportionately more resources to traits as body sizes are larger’ has been proposed to be due to sexual selection. However, studies have also suggested that sexually selected traits might not universally display positive allometry; these studies provide examples of sexually selected traits that show slight negative to isometric scaling. More recent studies have proposed that whether sexually selected traits show positive allometry depends on the trait's behavioural context and functional relevance.
A long history of examining resource investments using the approach of allometry has focused on quantifying how behaviours, morphology, and other traits scale with body size. Our understanding of the processes underlying the maintenance of positive allometry in a population is limited. Specifically, investigations of how dynamic changes in ecological and demographic factors affect positive allometry are few. Moreover, empirical studies investigating how trait allometries contribute to individual fitness are scarce. Such studies are necessary for deciphering the selective factors maintaining positive allometry in a population.
Using the rupicolous agamid species Psammophilus dorsalis, we aim to understand how positive allometry in morphological traits is affected by dynamic variation in the selection environment. By employing microsatellite markers for genotyping and parentage analysis, we also propose to examine the contribution of positive allometry in morphological trait to reproductive fitness. Finally, in polygynous systems like P. dorsalis, males commonly use multiple traits in the competition for mates. We also aim to understand how investment patterns and relative scaling of the focal morphological traits affect the payoffs to other traits used in the competition for mates, including the diverse set of signals. The questions in the thesis will be answered using long-term morphology and demography datasets, together with behavioural observations and field experiments.