Biology subjects

Rajaraman, B. K.

Publications and source records attributed to Rajaraman, B. K..

9 recordsLinked to original sources

bioRxiv2026

Passive acoustic monitoring of Ensiferan calling diversity in a sub-tropical forest of Northeast India.

Ensiferans are nocturnal insects (Order Orthoptera) that produce mating advertisement calls using stridulatory organs on modified forewings. These calls, typically made by males, are species-specific and serve as indicators of forest health. In biodiverse ecosystems like the subtropical forests, caller density is high, and ecological constraints such as intra- and interspecific acoustic competition, masking interference, and predation pressure can influence calling behavior. These pressures lead to variation in call structures and differences in spatiotemporal acoustic space use, leading to variations in community call type composition across the seasons. Passive Acoustic Monitoring (PAM), a non-invasive and cost-effective technique, is widely used for long-term monitoring in vertebrate taxa, but is less commonly applied to terrestrial invertebrates. In this study, we employed PAM to quantify acoustic diversity, acoustic space use, separation of different call types, seasonal calling patterns, and seasonal variation in call type composition among nocturnal Ensiferan callers. Year-round recordings were conducted using AudioMoth devices in the Khasi Hills of Meghalaya, part of the Indo-Burma Biodiversity Hotspot, at a 48 kHz sampling rate. Acoustic samples were processed using Raven Pro software. We identified 33 distinct call types, mutually distinctly differing in spectral, temporal, or both parameters. Principal Component Analysis revealed fine-scale separation of call types. While there were seasonal shifts in call types, with the dry season having the least number of callers, overall call type composition remained stable across pre-monsoon and monsoon seasons. Acoustic Space Use (ASU) analysis indicated greater use of lower frequency bands consistent with ground cricket presence, as well as seasonal variation in spectral occupancy. This foundational study is the first of its kind in Northeast India and demonstrates the potential of PAM in studying invertebrate soundscapes.

zoology↗

bioRxiv2026

Sex-specific weighting of shoal size and movement speed but no evidence of asymmetric dominance effect in zebrafish shoal-size preference

Social decisions often require animals to integrate information across multiple attributes of potential partners. Using biological motion stimuli, point-displays generated from tracked live shoals, we tested how adult zebrafish (Danio rerio) weigh shoal size and movement speed during social preference, and whether these preferences are susceptible to contextual manipulation by an asymmetrically placed alternative. In Experiment 1, we established a multi-attribute indifference point by presenting males and females with dichotomous contrasts in which shoal size and movement speed were traded off. Both sexes showed no preference when a larger, slower shoal (4 fish at 0.75x speed) was pitted against a smaller, faster shoal (2 fish at 1.25x speed), but preferred the smaller, faster shoal when the speed difference was greater (4 fish at 0.5x versus 2 fish at 1.25x), indicating that zebrafish are sensitive to graded differences in movement speed relative to numerical cues. In Experiment 2, unidimensional tests confirmed that both sexes preferred larger shoals when speed was held constant but revealed sex-based differences in speed sensitivity: males preferred faster-moving shoals at both shoal sizes tested, whereas females showed no significant speed preference. Male shoal size preferences were stronger at higher movement speeds, suggesting that speed modulates the strength of size preference. In Experiment 3, we tested the asymmetric dominance effect in males, the only sex sensitive to both dimensions, using the indifferent contrast from Experiment 1 as the primary options and four decoy shoals asymmetrically placed along either the size or speed dimension, under counterbalanced presentation orders. No decoy shifted male preference significantly from chance under any condition. These results indicate that zebrafish weigh social cues in a sex-specific manner, and that asymmetric decoy options do not induce preference biases in males when shoals vary along the dimensions of movement speed and size.

animal behavior and cognition↗

bioRxiv2026

Irrational groups: decoy placement, not group size, shapes collective shoal-size preference in adult zebrafish

Group living often improves decision accuracy in animals, yet whether increasing group size buffers against context-dependent biases remains unexplored. One such bias is the decoy effect, where the presence of a third option shifts preferences between two alternatives. Here, we tested whether introducing a decoy shoal influences collective preference for the larger female shoal in adult male zebrafish (Danio rerio), and whether the strength of this effect depends on group size. Groups of two, three, or four males were presented with female shoals under two choice contexts: a dichotomous contrast (four vs. two fish) and a trichotomous contrast including an additional alternative of one, three, or five fish. The order of presentation (dichotomous-first or trichotomous-first) was counterbalanced, and multi-animal tracking was used to quantify group-level shoal-size preference (time spent near shoals), inter-individual distance (IID), polarization, and swimming speed. In the dichotomous-first order, across all group sizes, subject shoals consistently showed a baseline preference for the larger shoal. Adding a third decoy option altered this preference only when the decoy was extreme (one or five fish relative to the 4 vs. 2 alternatives), reducing relative preference toward indifference. Group IIDs were associated with context-dependent shifts in relative preference in the dichotomous-first order, whereas polarization and swimming speed were not. In the trichotomous-first order, groups showed no preference for the larger shoal, with or without a decoy shoal. Our results demonstrate that context-dependent biases, shape collective shoal choice, with effects driven by choice structure and order of presentation of options than by group size.

animal behavior and cognition↗

bioRxiv2025

State or personality trait: Determinants of boldness and shoal size preference in adult zebrafish

Animals adjust their behavior in response to physiological states to optimize the trade-off between energy acquisition and survival. A key question in animal personality research is whether behavioral variation is driven by consistent physiological state differences or stable personality traits. This study evaluates boldness and shoal size discrimination in adult male zebrafish (Danio rerio) across three hunger states: same-day feeding (H0), 24-hour food deprivation (H1), and 48-hour food deprivation (H2). Behavioral assessments were conducted over two testing cycles, with each individual undergoing every test twice for each hunger state within each cycle. The assays comprised the Open Field Test (OFT), Emergence Test (ET), and Social Preference Test (SPT), with the SPT conducted under binary (4 vs. 2 fish) and ternary (4 vs. 2 vs. 1 fish) choice conditions. Hunger significantly reduced emergence latency, but did not affect exploratory behavior in the OFT. Hunger also enhanced preference for larger shoals above chance in the binary SPT during the second testing cycle, though this effect was absent in ternary choices. Testing cycle effects revealed habituation-driven increases in boldness in both the tests and a progressive shift toward larger shoal preferences in the binary SPT. Among all assays, only the OFT showed significant repeatability, making it a reliable measure of boldness. However, it did not show consistent individual differences in plasticity due to hunger. These results highlight the crucial role of labile physiological states, such as hunger and habituation, in driving behavioral variation and underscore the importance of designing studies that disentangle state-dependent behaviors from stable personality traits in animal personality research.

animal behavior and cognition↗

bioRxiv2024

Social isolation reduces metabolic rate and social preference in Wild-type Zebrafish (Danio rerio)

Group living is a common feature of many animals and serves a variety of functions, including predator avoidance, collective foraging, and reproduction. Individuals from group-living species may face isolation from their social group in their natural environment. Prior research has shown that social isolation in zebrafish (Danio rerio), a highly social fish, results in physiological and behavioural changes, including reduced locomotor activity and loss of interest in their environment. We investigated whether social isolation was associated with differences in dissolved oxygen consumption rate, movement speed, and social preference in adult zebrafish. We subjected fish to one month of visual and olfactory social isolation, and measured metabolic rate via dissolved oxygen consumption rate before and after social isolation. A control group was not subjected to any form of social isolation but held in comparable housing. We measured movement speed and social interaction before and after social isolation using a social preference assay. We found that socially isolated fish show a significant decrease in oxygen consumption rate compared to Day 0 isolation baseline levels, whereas control fish did not show this decrease. After a month of social isolation fish also showed lower social preference, and lower movement speed. These findings could suggest reduced energy expenditure in the context of social isolation in this species. This work enhances our understanding of the physiological and behavioural consequences of isolation in social animals.

ecology↗

bioRxiv2024

Syntopic call diversity among morphologically similar calling morphs ofthe paleotropical katydid of genus Mecopoda (Tettigoniidae) from an Indo-Burma biodiversity hotspot.

The acoustically diverse family of Tettigoniidae (Ensifera, Orthoptera) (commonly called bushcrickets or katydids), constitutes an excellent system to study the evolution of calling songs. Mecopoda is a genus that is particularly interesting because of the many morphologically cryptic calling morphs that have been described across South, East, and Southeast Asia, some of which are considered endemic to India. We describe five new syntopic and sympatric calling morphs of the genus Mecopoda that are morphologically similar but acoustically diverse from a sub-tropical forest in Meghalaya, in the Indo-Burma biodiversity hotspot. We report the morphological and acoustic characterization of these five call types, finding morphological overlap but well-separated acoustic clusters based on a PCA analysis of call temporal and spectral features. We also sequenced the COI gene mitochondrial gene of these five call types as well as other call types previously reported from India and performed a phylogenetic analysis of this gene relative to previously reported COI gene sequences from genus Mecopoda. Phylogenetic results suggest our five call types are not mutually monophyletic and relate from different subspecies of Mecopoda, of which three call types are genetically well separated from other calling morphs. This broadens our understanding of the evolution of acoustic diversity among paleotropical katydids.

zoology↗

bioRxiv2023

Description of three new species of predatory Genus Hexacentrus (Orthoptera: Tettigoniidae) from India, with bioacoustic and morphological characterization.

Hexacentrus is a genus of predatory katydids. In India, the genus Hexacentrus is represented by 7 species of which 6 are morphologically characterized while one is only acoustically characterized. In this study, we describe three new species under the genus from India based on detailed morphological, stridulatory, and acoustic features.

zoology↗

bioRxiv2022

Violation of rationality in shoaling decision making in zebrafish (Danio rerio)

The decoy effect, a bias in choice between two options when a third, inferior option is introduced, has been observed across various organisms, from slime molds to humans. In this study, we investigated whether zebrafish (Danio rerio), a widely used biological model organism, exhibit the decoy effect in their shoaling group choices, specifically examining this effect by varying only shoal size. Using spatial trajectory analysis of freely swimming zebrafish interacting with conspecifics in adjacent display tanks, we tested how shoaling decisions varied between dichotomous (two-option) and trichotomous (three-option) choice sets. Our experiments compared preferences for 4 versus 2 and 6 versus 3 shoal sizes, with a single fish serving as a decoy in the trichotomous sets. The results revealed sex-specific differences in the decoy effect: males exhibited a shift in preference only in the Trichotomous-first condition, where prior exposure to the decoy led to a significant preference for the larger shoal. In contrast, females displayed the decoy effect exclusively in the Dichotomous-first condition, shifting from a significant preference for the larger shoal to showing no clear preference in the presence of the decoy. Notably, our findings demonstrate that the decoy effect can occur even when studied unidimensionally, with both sex and the order of presentation influencing zebrafish shoaling preferences. These results offer new insights into decision-making processes and highlight the importance of considering order effects in studies of choice behavior, with potential methodological implications for research in other species.

animal behavior and cognition↗

bioRxiv2022

Symbolic quantitative cognition in wild zebrafish (Danio rerio)

Zebrafish (Danio rerio) constitute an excellent model system to investigate the neural and genetic basis of quantitative cognition We tested the ability of reward quantity discrimination of wild-type zebrafish in an associative learning task. We used an operant conditioning paradigm in which the number of horizontal lines zebrafish approached in a 2-alternative forced choice task predicted the number of food reward pellets they would receive. Zebrafish did not learn a preference for the 2-line stimulus predictive of receiving 2 food pellets. However, a subset of the fish performed significantly above chance in a discrimination task with the same apparatus, in which the 2-line stimulus was associated with the same reward but the choice of the 1-line stimulus was not rewarded. Zebrafish also showed a population level learning in a simpler spatial association task with the same apparatus. We also explored the explanatory value of alternative spatial learning hypotheses such as a Win-Stay, Lose-Shift (WSLS) strategy at the individual level for fish in navigating these spatially randomised tasks.

animal behavior and cognition↗