Biology subjects

Isvaran, K.

Publications and source records attributed to Isvaran, K..

14 recordsLinked to original sources

bioRxiv2025

Females use multiple cues to assess competition for egg-laying decisions

Animals deploy a wide suite of behavioural responses to reduce fitness costs related to competition. One common strategy is spatial avoidance of resource patches associated with high competition and this involves a need to accurately assess the level of competition associated with patches. Although well-studied in the context of predation risk (alarm cues vs kairomones), we lack in our understanding of how inputs from multiple types of cues are used for assessing the level of conspecific competition. We tested how Aedes aegypti females select sites for oviposition when they encounter multiple types of cues from varying densities of conspecifics. We hypothesised that females perceive conspecific young within these sites as potential competition for their offspring, and tailor their response to the type and level of competition. Through binary choice trials, we assessed female oviposition behaviour in response to a gradient in two types of conspecific cues - egg and larvae. Our results indicate that female response was sensitive to the type of cue. Females showed attraction towards pools with low densities of both egg and larval conspecifics indicating conspecific cueing and the strength of response was stronger towards egg cues. However, this attraction response disappeared at high densities of conspecifics (both egg and larvae) suggesting that the resulting trade-off between benefits from conspecific cueing and costs of competition likely shapes oviposition site selection responses. The broad nature of the oviposition response was similar toward both egg and larval cues, but there were fine level differences in responses towards egg and larvae that depended on the conspecific density level. Our study shows that animals are under selection to use multiple cues to assess conspecific competition to minimise the costs of competition.

animal behavior and cognition↗

bioRxiv2025

Peers over the past: Prior predation-risk experience does not dictate antipredator responses of individuals in groups

Animals with predation-risk experiences can use the information to modulate their antipredator responses and survive future risk conditions (behavioural carryover). However, different contexts, such as sociality, may alter the risks and associated responses for an individual. A group can provide benefits to an individual, such as dilution of risk, confusion effect, and improved vigilance, potentially modifying carryover payoffs. Therefore, we tested the impact of sociality on the behavioural carryover of predation-risk experience. We used Aedes aegypti as a model system, where we had already established carryover, showing that predation-risk experience dictates future behaviour in a solitary setting. In contrast to solitary settings, we predicted that the behavioural carryover would not manifest in a group setting due to differences in trade-offs. We compared the behaviour of experienced and naive individuals in group settings in the presence and absence of an immediate threat. Our findings revealed that the past predation-risk experience did not influence the behaviour of individuals in a group setting. Instead, the immediate threat environment affected experienced and naive individuals similarly. These results suggest that the experience from predation past is more relevant when prey are solitary than when they are in a group due to the additional group advantages.

ecology↗

bioRxiv2024

Decoding the Dewlap: Multiple signals in females and males of a gliding lizard

Social interactions across taxa are often mediated through multiple signals. Studies examining the maintenance of multiple signals are mostly focused on males and often fail to capture female signalling diversity and strategies. In the recent decade, there has been a surge in the documentation of female signalling, however, our understanding of the functional relevance of multiple signals in females still lags behind. In this study, we examined multiple signals in females of an arboreal gliding lizard, Draco dussumieri, and compared them to those in males. We specifically tested the relative role of the backup signal and the multiple receiver hypotheses in the maintenance of multiple signals in both sexes. Female D.dussumieri used a variety of signals to socially interact with conspecifics, especially using their dewlap. The signalling repertoire of females was as diverse as that of males, although the relative use of the signals varied. In females, a few signals seem to be maintained by the backup signal hypothesis, with limited support for the multiple receiver hypothesis as well. For males too, both mechanisms appeared to maintain multiple signals. Interestingly, for some signals, the sexes differed in the context in which they used a given signal. Overall, these findings highlight the functional role of multiple signals in females, which can differ from that observed in males. Therefore, traits conventionally considered male-exclusive when also examined in females can provide finer insights into trait function and evolution.

animal behavior and cognition↗

bioRxiv2024

Social clues in risky pools: Perceived conspecific rivals strongly modify individual oviposition decisions in response to larval predation and competition

Reproductive choices are imperative in shaping organismal fitness across diverse taxa. Such choices are particularly critical in organisms with biphasic lifecycles, as females must maximize offspring survival pre-oviposition, with no parental care extended afterward. Consequently, females face strong site selection pressures to effectively respond to offspring competition and predation risks. Ovipositing females encounter yet another challenge during site selection: assessing future competition for their offspring from potential conspecific rivals. Our current knowledge, based on average social versus solitary behaviours, fails to clarify how social signals influence individual behavior within groups. To address these challenges, we leveraged the unique oviposition biology of the mosquito Aedes aegypti where only blood-fed females can lay eggs. By tracking individual behaviour in a social setting, we ask: how does social information from perceived conspecific rivals influence an individuals oviposition site selection? In our lab-based experiment, we examined oviposition strategies at two spatial scales under varying larval competition and predation risk. Our findings reveal that social information exerts a stronger influence on egg-laying behavior at larger spatial scales, i.e., at the scale of pool networks, than between neighboring pools. Social cues facilitated oviposition with increasing larval predation, as social females transitioned from rejecting to accepting pool networks. Conversely, under larval competition, social cues led to inhibition, with females withholding their eggs likely in anticipation of future competition. At finer spatial scales, social information only weakly modified oviposition behavior despite potential negative fitness consequences for the offspring. Thus, perceived conspecific risk strongly modifies oviposition--facilitation, inhibition, or no effect--and is scale-dependent.

ecology↗

bioRxiv2024

Gut feeling: host and habitat as drivers of the microbiome in blackbuck (Antilope cervicapra)

The gut microbiome can be shaped by both intrinsic host factors and extrinsic environmental factors. However, the relative importance of intrinsic and extrinsic factors in gut microbial composition has rarely been investigated, particularly for a single host across its natural range. Here, we characterise the gut microbiome of an endemic, endangered antelope, the blackbuck or Antilope cervicapra. We evaluated the influence of seven predictor variables, which were classified into intrinsic and extrinsic factors, on the gut microbiome. We determined which of these seven variables explains greater variation in the microbiome within (-diversity) and between ({beta}-diversity) the blackbuck host. We analysed the microbiome of 60 blackbuck hosts from ten different populations across India. We recorded 11800 unique OTUs across 30 known phyla and 2.9 million reads. We find an average of 2056 OTUs per individual, with firmicutes and bacteroidetes being the most dominant phyla. We find that nucleotide diversity (intrinsic), blackbuck population density (intrinsic), distance to human settlement (extrinsic), and anthropogenic land-use (extrinsic) explain within-host variation. In contrast, precipitation (extrinsic), nucleotide diversity, distance to human settlement, and anthropogenic land-use explain between-host variation. Overall, we also show that the genetic diversity of the host is more important than their environment for both within- and between-host variation in the microbiome, in blackbuck. Therefore, conservation efforts should be directed to not only preserve natural habitats but also increase the genetic pool of the blackbuck populations, which will positively impact their survival through diverse gut microbiomes.

ecology↗

bioRxiv2024

Don't Leave the Past Behind: How Larval Experience Shapes Pupal Antipredator Response in Aedes aegypti

Animals use predation encounters or risk experiences to influence their future antipredator responses. Such carryover effects of predation can benefit them by enhancing their antipredator behaviour and thereby decreasing their risk of mortality through predation. Despite these fitness benefits, behavioural carryovers of predation past may not be a common phenomenon in complex life cycles. Complex life cycles pose a unique evolutionary and physiological challenge to behavioural carryovers since every life stage is distinct in morphology, physiology, and function. Each life stage of a complex life cycle is expected to evolve its independent response based on the real-time threat level and manage the trade-offs accordingly. Along with the evolutionary challenge, physiological barriers can hamper behavioural carryovers, especially in holometabolous insects, where we observe extensive tissue remodelling and developmental compartmentalisation. We investigated behavioural carryover in the holometabolous mosquito model system, Aedes aegypti. We asked whether predation risk during a life stage carries over to the subsequent stage, influencing its behaviour, or if the next life stage responds according to its threat environment. Aedes aegypti has four major stages- egg, larva, pupa, and adult. We examined the effect of predation-risk experience across larval and pupal stages. Larval and pupal stages differ in morphology, physiology and function. They share the same habitat and, therefore, similar threats. We manipulated the threat of predation experienced by larvae and investigated its influence on pupal behaviour. We found behavioural carryover in the pupal stage for the first time and discovered exciting interactions between past experiences and the current threat environment. Our study underscores the crucial role of predation pressure in shaping the evolution of complex life cycles, emphasising the significance of early experiences with predators in influencing behavioural traits across distinct life stages.

ecology↗

bioRxiv2023

Dance or disappear: Strategic sexual signalling in Peninsular rock agama

Sexual signalling has largely been studied in the context of indirect competition among males through displays and mate choice by females. Historically, sexual signalling in females was expected to be of limited consequence. However, there is growing evidence of sexual signalling in females and its value in the context of sexual selection. Here, we test how females strategize the use of sexual signals in a socially polygynous lizard, Psammophilus dorsalis. We evaluated key hypotheses for how females should modulate their signalling, including male quality and mate availability. We simulate male quality using artificial male models to individually tagged, and intensely monitored wild female lizards, measuring their strategic investment in sexual signalling. We found that females invest more in signalling towards high quality males and increased their investment towards the later part of the only breeding season. Contrary to what is typically expected in a polygynous mating system, females not only invest in costly and elaborate sexual signals, they also modulate their usage to maximise their benefits and minimise their costs. Even in polygynous mating systems, dispersed distribution of individuals can result in females experiencing limitation in mate availability, resulting in costly sexual signalling.

ecology↗

bioRxiv2023

Leadership and information transfer in groups escaping a (simulated) threat in the wild

Collective motion in many species is believed to be driven by predation, which is considered a crucial evolutionary force. However, there are limited studies on how information about predators spreads through a group, particularly in natural settings. Here, using high-resolution drone-based recordings, we analyze the collective escape dynamics of a group living species - blackbuck (Antilope cervicara), an Indian antelope - under the conditions of a simulated threat in their natural grassland habitat. Our analysis reveals that, in response to the simulated threat, group cohesion first increases, followed by a simultaneous increase in median speed and polarization. We also observe the emergence of a temporary leader-follower relationship during the collective escape. Interestingly, we found that the distance of individuals from the "predator" affected only their response time, not their influence on the group movement. The individuals furthest from the threat were the least likely to initiate movement and were uncoordinated with the groups speed. Additionally, we discovered that the most influential individuals during the collective escape were the least likely to occupy front positions during group movement. Instead, our results indicate that individuals at the rear "push" individuals at the front during collective escape events. This contrasts with the typical notion of individuals at the front determining group movement and those at the back trying to catch up.

animal behavior and cognition↗

bioRxiv2022

Long-term bird abundance in a threatened grassland ecosystem: an assessment using daily bird lists

Open Natural Ecosystems (ONEs), such as tropical grasslands, are among the most threatened habitats on Earth today. The long-term monitoring of ONEs is an important research domain that is essential for understanding anthropogenic impacts and facilitating conservation action. Using a simple day-listing method over a 13-year period, we studied species trends in a central Indian grassland-agriculture mosaic experiencing several land-use changes. Our results indicate that some grassland species (such as the Great Indian Bustard Ardeotis nigriceps) show steep declines during the study period, while other generalist species (such as the Indian Peafowl Pavo cristatus) show an increasing trend. Daily listing also reveals distinct seasonal patterns, and we discuss the Great Indian Bustard and Western Marsh Harrier Circus aeruginosus as examples. Our study highlights the utility of consistent checklist surveys to monitor population trends of bird communities within a changing landscape.

ecology↗

bioRxiv2022

Competing females strategically combine signals and physical aggression differently from males in a polygynous tropical lizard

Intrasexual competition, the intense competition between individuals of the same sex, is a strong evolutionary force that is well known to select for elaborate and spectacular traits in males. In contrast, female-female competition is poorly understood. Although historically expected to be weak, evidence for female-female competition is fast accumulating. Yet, systematic studies of such competition are rare. Here, we frame and test for a strategy of competition in females in a wild population of a classically polygynous lizard, Psammophilus dorsalis. We used models of female P. dorsalis to simulate a gradient in perceived competitor threat to individually tagged, wild females on their territories, and comprehensively measured their signalling and aggression responses. Similar experiments were performed with males. Our results clearly demonstrate a complex, threat-sensitive strategy of direct competition among females in this species with conventional sex roles. Females systematically escalate their use of diverse signals along a gradient in threat and show surprisingly high levels of physical aggression. Comparisons with the responses of males to simulated threats reveal distinct sex differences in competition strategies that match theoretical expectations derived from life history. Using these findings, we argue that female-female competition may be complex but cryptic, requiring experimental manipulations to uncover.

animal behavior and cognition↗

bioRxiv2021

Antelope space-use and behavioural responses to varying anthropogenic influences may permit long-term persistence in a highly human-dominated landscape

The only means of conserving a species or a habitat in a human-dominated landscape is through promoting coexistence while minimizing conflict. To achieve this, it is vital to understand how wildlife are impacted by direct and indirect human activities. Such information is relatively rare from areas with high human densities. To investigate how animals respond to altered ecological conditions in human-dominated landscapes, we focussed on a wild herbivore of conservation concern in Krishnasaar Conservation Area (KrCA) in Nepal. Here, blackbuck Anticope cervicapra, a generalist grazer, lives in refugia located in a growing human population. We studied the impacts of humans on habitat-use and behaviour of blackbuck. We laid 250 x 250 m grid cells in the entire KrCA and carried out indirect sign surveys with three replications for habitat-use assessment. We observed herds of blackbuck for 89 hours in different possible habitat types, location and time of the day using scan sampling methods. Our habitat-use survey showed that habitats under intensive human use were hardly used by blackbuck, even when high-quality forage was available. In areas with low levels of human activity, natural risk factors, primarily habitat openness, was the major predictor of habitat-use. Interestingly, livestock presence positively influenced habitat-use by blackbuck. Blackbuck were substantially more vigilant when they were in forest than in grassland, again indicating an influence of risk. Overall, blackbuck appear to be sensitive to risk associated with both natural and anthropogenic factors. Our findings have direct implications for managing human-wildlife interactions in this landscape, specifically regarding strategies for livestock grazing in habitats highly used by blackbuck and concerning predictions of how changing land-use will impact long-term persistence of blackbuck. Our work suggests that wild herbivores may be able to persist in landscapes with high human densities so long as there are refuges where levels of human activity are relatively low.

ecology↗

bioRxiv2019

Trait evolution under multiple selection pressures: Prey responses to predictable and unpredictable variation

When a strong selection pressure, such as predation risk, varies widely in space and time, how should prey respond? When risk varies predictably, prey are hypothesized to respond in a risk-sensitive manner. It is less clear how prey should respond when risk varies unpredictably.\n\nAdditionally, prey response may also depend on how predation risk interacts with other selection pressures. Our understanding of the complex action of multiple and variable selection pressures on prey traits is still comparatively poor. Here, we examine how predictable and unpredictable aspects of predation risk act together with another important selection pressure to influence prey behaviour in the rock pool breeding mosquito, Aedes vexans. Through the selection of sites for oviposition, female mosquitoes can influence the predation risk faced by their offspring. We tested how females select oviposition sites, when encountering pools that vary in larval predation risk and desiccation risk. We comprehensively quantified spatial and temporal variation in predation risk by measuring densities of predatory dragonfly nymphs in rock pools of different sizes, along the mosquito breeding season. We also measured hydroperiod length. We next conducted manipulative experiments in rock pools and measured female oviposition responses to variation in predation and desiccation risks. Predation risk varied widely in space and time. Desiccation risk only appeared important for the small pools. Ovipositing females appeared to respond to these multiple aspects of variation in selection pressures. Females seemed to respond to predictable variation by avoiding large pools that permanently harboured predators in natural settings. Female responses were more variable to medium-sized pools with naturally stochastic predator densities, highlighting the role of unpredictability in predation risk in shaping behaviour. Females did not clearly prefer small pools that were naturally devoid of predators but carried high desiccation risk, suggesting that they balance multiple risks - predation versus desiccation - when choosing oviposition sites. Our study suggests that wild populations may commonly experience multiple and variable selection pressures that can favour seemingly puzzling trait variation. We highlight the need to quantify variation in selection pressures and investigate how such variation, especially the unpredictable aspects, shapes prey traits.

ecology↗

bioRxiv2018

Truncated power-law distribution of group sizes in antelope

Group size distributions are instrumental in understanding group behaviour in animal populations. We analysed group size data of the blackbuck, Antilope cervicapra, from six different field sites to estimate the group size distribution of this antelope. We show that an exponentially truncated power law (called the polylog distribution in this paper) is the best fitting distribution, against the simple power law and lognormal distributions as other contenders, and the exponential distribution as a control. To show this, we use two likelihood based methods (AICs and likelihood ratios). Finally, we show that polylog distribution parameters can be used to better understand group dynamics, by using them to explore how habitat openness affects group behaviour.

animal behavior and cognition↗

bioRxiv2018

Is the predation risk of mate-searching different between the sexes?

In animals that communicate for pair formation, generally one sex invests more effort in mate searching. Although searching by males is prevalent in most animals, in orthopteran insects and some other taxa females physically move to localise signalling males who are predominantly sedentary. Although the two sexes thus share mate searching effort in orthopterans, their behavioural strategies are different and sexual selection theory predicts that signalling males may be following the riskier strategy and incurring higher costs. However, relative levels of risk posed by the two mate searching strategies remain largely unexplored. Hence, we estimated the relative predation risk experienced in natural populations by signalling males and responding females. We did this by quantifying predation risk as a probability of mortality in the context of acoustic communication in a tree cricket, Oecanthus henryi from its ecologically relevant predator, a lynx spider, Peucetia viridans. Spiders may perceive calling in males and movement in females by their ability to detect both airborne acoustic cues and substrate-borne vibratory cues. Probability of mortality was quantified by partitioning it into three spatial components at which crickets and spiders interact, using a combination of extensive field observations and manipulative experiments in a semi-natural setup. We found no differences in predation risk faced by calling males and responding females, suggesting that direct benefits offered by males to females upon pair formation may better explain shared mate searching effort between the sexes in orthopterans.

ecology↗