- Allopatric montane wren-babblers exhibit similar song notes but divergent vocal sequencesM Abhinava Jagan, Ananda Shikhara Bhat, and Anand Krishnan2022
The songs of passerine birds consist of notes temporally arranged into vocal sequences following syntactic structures, and function both in courtship and territorial defense. Geographic barriers are important drivers of avian speciation, and also influence the divergence of song. However, there is relatively little quantitative study of the relationship between geographic barriers and the syntactic structure of vocal sequences. Here, we investigate interspecific divergence in song notes and syntax within a genus of allopatric montane Asian wren-babblers (Spelaeornis). Employing a robust quantitative analytical framework and song recordings from publicly accessible databases, we find that Spelaeornis appear to have undergone diversification in song syntax without divergence in note parameters. Broadly, we find three different syntactic structures across the eight species in the genus, each occurring in a different geographic region in Asia, with two species apparently exhibiting intermediate syntax. Species within the genus appear to possess similar song notes, but subgroups confined to different geographic regions (eg: hills south of the Brahmaputra river) arrange these notes according to different syntactic rules to construct songs. Our computational framework to examine signal structure and diversification across multiple scales of signal organization has potential implications for our understanding of speciation, signal evolution and more broadly in fields such as linguistic diversification.
- Studying the age of onset and detection of Chronic Myeloid Leukemia using a three-stage stochastic modelSuryadeepto Nag, Ananda Shikhara Bhat, and Siddhartha P. Chakrabarty2022
Chronic Myeloid Leukemia (CML) is a biphasic malignant clonal disorder that progresses, first with a chronic phase, where the cells have enhanced proliferation only, and then to a blast phase, where the cells have the ability of self-renewal. It is well-recognized that the Philadelphia chromosome (which contains the BCR-ABL fusion gene) is the “hallmark of CML”. However, empirical studies have shown that the mere presence of BCR-ABL may not be a sufficient condition for the development of CML, and further modifications related to tumor suppressors may be necessary. Accordingly, we develop a three-mutation stochastic model of CML progression, with the three stages corresponding to the non-malignant cells with BCR-ABL presence, the malignant cells in the chronic phase and the malignant cells in the blast phase. We demonstrate that the model predictions agree with age incidence data from the United States. Finally, we develop a framework for the retrospective estimation of the time of onset of malignancy, from the time of detection of the cancer.
- Behavioural context shapes vocal sequences in two anuran species with different repertoire sizesAnanda Shikhara Bhat, Varun Aniruddha Sane, K.S. Seshadri, and Anand KrishnanAnimal Behaviour, 2022
Acoustic signals in animals serve to convey context-dependent information to receivers. Birds and mammals combine diverse sounds into complex sequences to communicate, but the role of temporal sequencing of signals remains understudied in other taxa. Anuran vocalizations are a prominent feature of their life history, and function in defence of territories and to attract mates. However, there are few data on whether anurans pattern their calls into sequences, and whether temporal sequences convey information about context. Here, we investigated the context-dependent vocal repertoire and the use of vocal sequences by two anuran species belonging to different lineages, comparing frogs vocalizing alone and in the presence of a territorial rival. Using a robust analytical framework, we present evidence that both species modify their vocal sequence structure according to context. Specifically, one species (with a smaller repertoire, from a more basal lineage) appends notes to generate more complex sequences, whereas the other (more recently diverged and with a larger repertoire) shifts to different note types, resulting in different sequences for different contexts. Thus, despite differences in repertoire size, both frog species are capable of adjusting the temporal sequence of vocalizations to communicate in different contexts. Vocal sequences and context-dependent ‘syntax’ may be more common in anurans than previously thought, and our methodology presents a paradigm to study the evolution and function of these complex vocal patterns.
- A colony-level optimization model provides a potential mechanism for the evolution of novel castes in eusocial ant coloniesSuryadeepto Nag, and Ananda Shikhara BhatHeliyon, 2022
Ant species often have multiple morphologically distinct ‘castes’ within a single colony. Given that most of these castes are involved in non-reproductive tasks, and since such individuals thus never reproduce, the question of how ant castes can evolve is a non-trivial one. Over the years, several models have been proposed in order to explain the evolution of castes in ant colonies. Here, we attempt to answer this question using an economics-based approach, developing an optimization model that implements adaptation and selection at the colony level. We argue that due to the nature of ant colonies, selection is shifted to the group level, and, due to this, individual ants are sheltered from negative selection. We show that our framework can explain the evolution of novel castes in ant colonies, and discuss the novelty of our model with regard to previous models that have been proposed. We also show that our model is consistent with several empirical observations of ant colonies.