Biology subjects

Thaker, M.

Publications and source records attributed to Thaker, M..

9 recordsLinked to original sources

bioRxiv2026

How variable and stress-sensitive is sleep expression in lizards?

Sleep expression in wild animals is regulated by their ecological context. Yet, how populations of a species differ in their sleep in response to environmental challenges such as urbanization, remains to be fully understood. Robust quantification of sleep in small animals, such as lizards, has so far been methodologically difficult, limiting population-level assessments. Using recently developed miniature loggers, we recorded sleep in 19 wild-caught individuals of the Peninsular rock agama lizard (Psammophilus dorsalis). We compared individuals from urban and rural environments and measured electro-oculogram (EOG)-derived sleep parameters: sleep duration, bout frequency, bout duration, and interval between bouts. We then subjected all individuals to an acute stressor (handling-restraint) and examined changes in sleep expression. We found that this species slept mostly at night, with an average total sleep time of 11h 10min. EOG-derived sleep characteristics did not differ substantially between populations, although daytime sleep bouts were more consolidated (shorter interval between bouts) in urban lizards. Contrary to evidence from mammals, acute restraint stress did not impact sleep, overall or for either population. To complement these measures, we also measured the latency to arousal after exposure to vibration stimuli in a separate set of urban and rural lizards (n = 12 each), and found that urban individuals responded marginally quicker at night compared rural individuals, demonstrating greater vigilance and/or more fragmented sleep. Overall, we show that sleep characteristics of wild animals in a common garden condition can be conserved within a species, with limited context-dependent variation between populations.

animal behavior and cognition↗

bioRxiv2026

Plumage colour structures global patterns of mixed-species bird flocks

Mixed-species groups (MSGs) pose a particular challenge for our understanding of sociality in animals. Though MSGs are widespread social assemblages that form to enhance foraging success and reduce predation risk of participants, the role of traits in mediating grouping has received less attention. In particular, the role of body colour has not been tested quantitatively, despite the fact that visual similarity can reduce individual predation risk. Here, we examine whether plumage colour structures mixed-species bird flocks (MSFs) at a global scale. Using data spanning four continents, we developed a new metric that quantifies colour similarity among flock participants and compared observed flocks to null assemblages constructed from all flocking species at each site. We further examined whether MSF participants represented a colour subset of the available colours in the regional species pool. We found striking evidence that birds in MSFs were more similar in colour than expected by chance across all sites, indicating that plumage colour is a non-random structuring trait that shapes assembly of flocks globally. The strength and prevalence of colour structuring varied across geographies, but not flock size. Within communities, MSF participants differed systematically in colour composition from the regional species pool, occupying a restricted region of colour space dominated by yellow and brown plumage. Thus, plumage colour affects MSFs influencing both overall flock participation as well as species co-occurrence within flocks. Our findings illustrate the importance of visual traits in structuring interspecific social systems, by highlighting that birds of a feather do indeed flock together.

ecology↗

bioRxiv2026

Does diet influence physiological and behavioural responses to predation risk?

As one of the strongest selective forces, predation risk induces antipredator responses in prey that not only maximise survival probability but are energetically expensive. While these responses are known to affect foraging patterns and diet composition, the functional role of changes in dietary macronutrients remains unclear. We investigated the effect of dietary NPE (non-protein energy) concentration on the antipredator responses of the Indian rock agama Psammophilus dorsalis. In a manipulative experiment, wild-caught lizards were fed either a low or high NPE diet and exposed to repeated simulated predator attacks. We measured the space-use and hiding duration of lizards after each attack, as well as their circulating corticosterone concentrations at the end of the experiment. Predator exposure induced refuge use for all lizards. Diet had a context-dependent effect: lizards on the high NPE diet used riskier perch locations more frequently than those on low NPE diets, but only during safe periods and not during active threat. Physiologically, lizards on the low NPE diet had significantly higher baseline corticosterone levels, indicating a greater allostatic load. Overall, while dietary NPE did not alter reactive escape behaviour, it influenced the underlying physiological state and proactive behavioural decisions.

evolutionary biology↗

bioRxiv2026

Can tropical agamid lizards physiologically tolerate the altered thermal mosaic of urban microhabitats?

Urbanization and human-induced environmental changes create unique and unprecedented thermal landscapes, yet the extent to which species respond to these changes remains poorly understood. One major challenge in studying these responses is the spatial mismatch between the small scale at which organisms experience their environment and the broader scale at which climate data are typically collected. We use Infrared Thermography (IRT) to quantify the fine scale microclimate in urban and rural habitats used by two tropical agamid lizards, Calotes versicolor and Psammophilus dorsalis. By combining field-based body temperatures and lab-based measures of thermal limits (CTmax, CTmin)and preferences (Tpref), we assess how the thermal heterogeneity of these fine mosaics of microhabitats influence the degree of thermoregulation (k) of these species. We find that thermal responses to urbanization are shaped by species-specific thermal traits and patterns of microhabitat use. Between the species, urban individuals did not differ markedly in habitat thermal heterogeneity, substrate temperature used or degree of thermoconformity. However, within species, P. dorsalis experiences warmer and more heterogeneous conditions in rural habitats, whereas C. versicolor experiences similar thermal conditions across habitats. Calotes versicolor also exhibits broader thermal tolerance and preferred temperature ranges than P. dorsalis. Collectively, our results suggest that P. dorsalis may be more susceptible to the thermal constraints imposed by human-modified landscapes. Overall, we demonstrate the critical need to account for microclimatic conditions and species-specific thermal traits when determining how animals respond to changes in the thermal environment expected from climate change.

ecology↗

bioRxiv2025

Out of sight, out of mind: Removal of predators by fisheries alters reef fish behaviour.

Pervasive human activities have led to the extirpation of predator species in many ecosystems. Understanding the extent and mechanisms by which such predator loss influences prey behaviour is critical for predicting the ecological consequences of trophic downgrading. We investigated reef fish behaviour in response to predator presence within and outside a protected area in the South Andaman Islands, India. We used 3D printed models to simulate the presence of two different types of predators; a sit-and-wait predator, a grouper (Mycteroperca rosacea) and a wide-ranging pursuit predator, a barracuda (Sphyraena barracuda). We recorded foraging, vigilance, and movement behaviours of herbivorous and invertivorous fish encountered in each plot. Overall, we found that fish were significantly more vigilant in response to both predator models compared to a non-predator control within protected areas but not outside protected areas. Foraging behaviour was suppressed by the predator treatments; however, herbivorous and invertivorous fish responded differently within protected areas. Fish movement behaviours also differed across predator treatments, prey foraging guilds, and areas. Anti-predator responses are thus highly contingent on habitat and both predator and prey traits. We highlight how the selective removal of predators by humans alters predation risk for prey and hence their risk-sensitive behaviours.

ecology↗

bioRxiv2024

Are super-predators also super-scary? A systematic review and meta-analysis of animal responses to human interactions

Humans interact with wild animals through lethal and non-lethal activities. While theory predicts that these interactions should alter animal behaviour, the relative magnitude of impact is not well understood. We conducted a systematic review and meta-analysis of the past 30 years of research, focusing on changes in foraging, vigilance, and movement behaviours in wild animals. We found that lethal human activities (e.g., hunting) cause significant behavioural changes, with targeted species increasing vigilance and reducing foraging in affected areas. Active non-lethal activities (e.g., tourism) elicited similar but weaker patterns, with many species showing little to no change in their behavioural responses. In contrast, passive non-lethal interactions (e.g., roads) produced highly variable responses. Overall, human-induced fear elicits responses in wild animals that broadly align with predictions from the risk allocation hypothesis. However, the magnitude and direction of animal responses depend on the type of human activity and the ecological context. The most pronounced behavioural changes occurred where humans posed a direct lethal threat. Gaps in the literature, uneven data within and across species, and limited information on the history or context of interactions currently limit our ability to better predict when and why animals change their behaviour in response to humans.

animal behavior and cognition↗

bioRxiv2024

Dialogues in colour and behaviour - Integration of complex signalling traits and physiology

Animal communication can be complex, often involving multiple static and dynamic traits. The extent to which these traits are correlated can elucidate their function as either redundant or multiple messages. Using the agamid lizard, Psammophilus dorsalis, as a model system we examined patterns of trait expression and the role of steroid hormones in mediating these traits during social interactions. We staged male-male interactions in the lab and measured the repertoire of display behaviour and colours, which change dynamically in the visible and ultraviolet ranges in different body regions. Additionally, we measured testosterone and corticosterone levels before and after the social trials. Our results show that within behaviour and colour trait categories, components were strongly correlated within individuals, suggesting either a shared physiological pathway or redundant information content. However, across trait categories, correlation patterns varied. The chromatic contrast of the (yellow) dorsal region of lizards was correlated with both body size and level of aggression, whereas the size of UV patches was correlated with body size only. We also found a negative association between baseline corticosterone levels, body size and dorsal yellow chromatic contrast, suggesting a mechanistic link between these traits. However, social interaction induced testosterone and corticosterone levels were uncorrelated with the expression of the dynamic behavioural and colour displays during the social interactions itself. Notably, the intensity of colour and behavioural displays of males were matched by their opponents. Overall, our results suggest that multiple signalling traits can ensure both redundancy as well as provide multiple messages to receivers, thus improving the robustness of information transfer, particularly during competitions which have high fitness consequences.

animal behavior and cognition↗

bioRxiv2021

Correlated evolution of parental care with dichromatism, colour, and patterns in anurans

Parental care is widespread among vertebrates, with clear fitness benefits. Caring parents however incur costs that include higher predation risk. Anurans have among the most diverse forms of parental care, and we test whether the occurrence of care is associated with morphology that minimizes predation risk. We first examine whether parental care co-occurs with sexual dichromatism, testing the hypothesis that when one sex is conspicuous, the other is cryptically patterned and cares for the young. From our phylogenetic comparative analyses of 988 anurans distributed globally, we find that parental care is less likely to co-occur with dichromatism, irrespective of the caring sex. We then examine whether colour gradients and patterns that enhance crypticity are associated with the occurrence of parental care. We found that species with male-only care were more likely to have Bars-Bands, but contrary to our expectation, other colours (Green-Brown, Red-Blue-Black, Yellow) and patterns (Plain, Spots, Mottled-Patches) were not associated with caregiving behaviours. The lack of strong correlations between dorsal morphology and parental care suggests that crypticity is not the dominant strategy to minimise predation risk for care-giving anurans, and that the evolution of body colour and parental care are driven by independent selection pressures.

evolutionary biology↗

bioRxiv2019

A longitudinal study of perceived stress and cortisol responses in an undergraduate student population from India

Young adults entering into college experience immense shifts in both personal and professional environments and this may result in some of them experiencing a lot of stress and difficulty in coping with their new surroundings. Such potentially stressful events may trigger multiple psychological as well as physiological effects. The current study investigated multiple psychological parameters such as PSS14 (Perceived Stress Scale), K10 (distress scale) and positive mood measures, along with salivary cortisol levels, in a repeated measures longitudinal study of first year students (~ 19 years of age) enrolled at a residential college in India. Six salivary cortisol samples were collected over a one-year period from 20 students. On each sampling day, a questionnaire designed to evaluate (K10, PSS14 and Mood) psychological parameters was also administered. Overall, men showed a significantly lower level of salivary cortisol compared to women. Men also showed a decrease in perceived stress (PSS14) and distress (K10) with time. However, women reported similar perceived stress and distress levels all year round. Academic stress was reported by the students to be the most important stressor, whereas financial stress was reported the least number of times by all participants. Our results suggest that men seem to have a better capability to adjust to the new environment of a residential program with time. In contrast, women show an elevation in salivary cortisol at the end of the semester (the final assessment stage) in spite of a continuous assessment curricular design. This study not only provides an important glimpse into the sex differences in stress response in the first one year of joining an undergraduate program, but it also provides a valuable longitudinal dataset from the Indian undergraduate student cohort which is lacking in literature.

physiology↗