Heritable variation in traits that enhance dispersal rates can accumulate at population margins by spatial sorting. This mechanism of selection differs from natural selection as evolutionary change can ensue even in the absence of differential lifetime reproductive success. Although evidence suggests that populations are rapidly evolving at the margins due to global change pressures, such as invasions and range shifts, we lack a mathematical theory of spatial sorting to understand these evolutionary patterns. To this end, I present an algebraic theorem of evolution, which we call the sorting theorem, to elucidate the general mechanism of selection at margins. The sorting theorem suggests that at population margins, evolution can ensue by any biological mechanism that yields a statistical association between the number of offspring that individual leaves at the margin and the mean phenotype of those offspring. Thus, the sorting theorem can facilitate axiomatic development and criticism of spatial sorting theory. Its role in guiding research in this context is analogous to that of Price’s theorem in natural selection theory.

The evolution of morphological traits is often strongly influenced by functional and biomechanical demands. Perhaps the best example of this is the avian bill, a multifunctional appendage consisting of an inner bony core and an outer keratinous rhamphotheca, which presents a unique opportunity to study form-function relationships. Among the varied functions of the bill, certain groups of birds use their bills to excavate tree hollows for nesting, roosting, and feeding. The physical stresses experienced during this mechanically demanding task may be linked to bill shape and material properties, and also to broader factors like environmental conditions which influence the availability and mechanical properties of the substrate. Here, we examine these relationships in the frugivorous Asian and African barbets, which occupy diverse climatic regimes and excavate nest hollows in trees. Using micro-CT scans of museum specimens coupled with landmark-based geometric morphometrics, we find that bill shape diversity has accumulated gradually over time in both clades under allometric constraints, and exhibits a significant relationship with climatic variables. Secondly, using finite element analysis and beam theoretic approaches, we find that maxillary geometry trades off with excavation performance under different loading regimes. Our study thus aims for an integrative, interdisciplinary understanding of the evolution of morphological traits in birds.

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.

Honeybees are a well known example of self-organized collective systems. Individuals perform tasks and coordinate their behavior in a way that translates to the colony-level organization. Stressful situations such as high temperatures are common in the environment. Specifically, during heat stress periods individuals show enhanced behaviors such as fanning and spreading water. During such conditions, it is not understood how individuals in the colony vary in their behavior, what factors determine changes in behavior, and how these translate to the colonylevel response. We examine the honey bee heat stress response by introducing multiple agematched cohorts (i.e. several thousand tagged bees) into an observation hive, and analyzing their movement behavior. We use the behavior over time for each individual to extract the dominant modes of response, and furthermore ask how previous behavior predicts how an individual responds during heat stress. Broadly, such large scale colony-level analysis can reveal if there are general principles of reorganization that honeybees adhere to when encountered with sudden changes or stress.

Collective behavior is observed at different scales, from cells to animal groups to societies. Recent technological advancements have enabled an unprecedented increase in our ability to collect data for how individuals behave in a group. I will show results from a long-term tracking study of honeybees, where 5000+ bees were individually tracked using barcodes over their entire lives. This data provides a detailed picture of daily behavioral differences, and reveals lifetime differences in motion and task-switching behavior among bees. Using the same framework we introduced reproductive male drones into the hive, and analysis of their in-nest motion reveals synchronized periods of high-speed “hyperactive” motion that coincide with trips outside. By comparing with other collective systems we have analyzed – including fish, rats, and cellular collectives – I will highlight basic ways how “big data” can be used to describe biological variation, and discuss ongoing work which seeks to connect observed differences to group function and environmental characteristics.

Sexual selection in polygynous mating systems has largely been studied in the context of female mate choice and competition in males. There is empirical evidence on how males strategize their investment in costly displays. More recently, studies have observed sexual signalling in females, however, our understanding of how females invest in such costly signals is limited. Male Peninsular rock agama Psammophilus dorsalis show diverse displays in the context of competitions and courtship. Recent studies indicate that females also use complex displays during the breeding season. Here we test the hypothesis that females invest more in sexual signalling when there is reduced availability of mating opportunities with high-quality males. We also test whether females increase their sexual signalling through the breeding season to maximize terminal-mating opportunities. We caught and tagged wild female lizards and released them back into their territories. On these lizards, we carried out model presentation trials, where 3D printed models of a male lizard in breeding and non-breeding colours were presented following which, the initial response of the focal lizard was recorded. We have conducted and recorded 129 trials across three breeding seasons between 2019 and 2021. Preliminary analysis shows that females display using dynamic colour change and body postures in response to male models in breeding colour. This paper investigates how female Peninsular rock agama strategizes their investment in sexual signals based on various intrinsic factors, social conditions and life-history trade-offs.

India is the world’s largest consumer and importer of palm oil. In an aggressive push towards self-sufficiency in vegetable oils, the Indian government is prioritising the rapid expansion of domestic oil palm plantations to meet an expected doubling in palm oil consumption in the next fifteen years. Yet the current expansion of oil palm in India is occurring at the expense of biodiversity-rich landscapes. Using a spatially explicit model, we show that at the national scale, India appears to have viable options to satisfy its projected national demand for palm oil without compromising either its biodiversity or its food security. At finer spatial scales, India’s oil palm expansion needs to incorporate region-specific contingencies and account for trade-offs between biodiversity conservation, climate change, agricultural inputs and economic and social security. The policy decisions that India takes with respect to oil palm can significantly reduce future pressures to convert forests to oil palm plantations in the tropics globally.

Due to the absence of physical barriers, the open-nesting giant honeybee Apis dorsata has evolved a spectacular collective defence behaviour – known as “shimmering” – against predators, which is characterised by travelling waves generated by individual bees flipping their abdomens in a coordinated and sequential manner across the bee curtain. We examined if shimmering is visually-mediated by presenting moving stimuli of varying sizes and contrasts to the background (dark or light) in bright and dim ambient light conditions. Shimmering was strongest under bright ambient light, and its strength declined in dim-light. A. dorsata shimmered only when presented with the darkest stimulus against a light background, but not when this condition was reversed (light stimulus against dark background). We suggest that this is an effective anti-predatory strategy in open-nesting A. dorsata colonies, exposed to high ambient light, as flying predators are more easily detected when they appear as dark moving objects against a bright sky. Moreover, the stimulus detection threshold (smallest visual angular size) is much smaller in this anti-predatory context (1.6° - 3.4°) than in the context of foraging (5.7°), indicating that ecological context affects visual detection threshold.

Many biological systems, from flocks of birds, swarms of locusts, shoals of fish, to crowds of humans show collective behaviours which are emergent properties that manifest only at the level of a group. In each of these cases, local, individual-level interactions give rise to highly coordinated and synchronized emergent patterns that are observable at the group level. Theoretical, computational, and empirical research in this field have been used to address questions about various aspects of collective behaviour, from characterizing its structural and dynamical properties to deciphering how the individual behaviour produces emergent group patterns. However, most of these studies examine the group-level properties in terms of their mean values and do not attempt to characterize the variability present in the collective properties which arise due to the stochastic fluctuations. In real groups, stochastic fluctuations in the group-level properties arise due to the probabilistic interactions between finite number of individuals. As a result, this intrinsic noise present in collective systems can produce non-intuitive and non-trivial behaviours. Real groups in finite space will likely have some interaction with the boundary, and the observed collective dynamics may also include effects of interaction with the boundary. To gain comprehensive understanding of collective dynamics in real groups, examining the effect of interaction with the boundary is necessary. However, whether boundary interactions confound analyses of inferred interaction rules have not been investigated rigorously. In the current study, we examine how the parameters of the boundary conditions affect the simulated collective dynamics. We performed stochastic simulations of two data-inspired spatial models developed by Jhawar et al. that have contrasting collective properties: (i) where individuals show pairwise interactions and collective order is driven stochastically (ii) where individuals show ternary interactions and collective order is driven deterministically. We characterize intrinsic noise in the data generated from the simulations and examine the susceptibility of the results to the presence of boundary. In these data-inspired spatial models, we show that the essential features of the group-level dynamics obtained from the simulated time-series do not change because of boundary interactions. Furthermore, our inference of local interactions also remains unaffected by the boundary conditions – at least within the model framework and the context we investigated, which were parameterized to the experimental conditions of our laboratory.

When a blackbird swallows an earthworm, there is little doubt about the nature of the interaction. Sadly, few microbial interactions are this clear. This is particularly true when bacteria reside inside eukaryotes. Who gains, who loses, and the role of evolution are large questions in the biology of microbial interactions. Many look at the mechanisms of interaction, but here we take a different approach. First we explore the landscape of interactions across the eastern US, determining how commonly specific bacteria interact with amoebae, beginning with the obligate endosymbionts Amoebophilis and Neoclamydia and the eukaryote host Dictyostelium discoideum. We image the interactions and measure health effects on the host. Then we turn to a novel facultative endosymbiont, Paraburkholderia spp. where geographic distribution and health effects can be measured for both host and endosymbiont. We name three new species, two of which are highly dependent on the host and then use experimental evolution techniques to reveal how tightly they have co-evolved. Combining the tools of landscape surveys, microscopy, fitness assays, genomics, and experimental evolution allow a much deeper understanding of host-pathogen or host-mutualist interactions.