Biology subjects

Rajakumar, A.

Publications and source records attributed to Rajakumar, A..

4 recordsLinked to original sources

bioRxiv2026

Decoupling Transcription from Cell Fate Preserves Germ Cell Totipotency

Only germ cells can give rise to a totipotent embryo, yet a conserved transcriptional program for germ cell identity remains elusive. Profiling Drosophila primordial germ cells (PGCs) across embryogenesis, we find that nascent PGCs are not silent, as previously thought, but instead transcribe the same totipotency program as the early embryo, reflecting an open chromatin state. This chromatin state, established by the pioneer factor Zelda, persists in PGCs throughout development. The associated transcriptional program normally drives somatic differentiation, but in PGCs the conserved RNA-regulator Nanos represses its translation, leaving germline chromatin uncommitted. Cells that fail to establish the totipotent state die before reaching the gonad. Thus, germ cells preserve developmental potential not by restricting transcription, but by preventing transcripts from determining cell fate.

developmental biology↗

bioRxiv2026

Data requirements for accurate extinction-risk prediction in bistable populations

Understanding and predicting extinction risk is a central challenge in population biology. Mathematical models incorporating Allee thresholds are commonly used to understand population dynamics and to assess extinction risks. Inaccurate predictions can have serious consequences for conservation management. In this simulation study, we develop a likelihood-based inference and prediction workflow to estimate parameters, including the Allee threshold and population diffusivity parameters, using noisy count data generated using a well-defined discrete model. Although parameters are identifiable according to commonly used criteria, the accuracy of resulting predictions depends strongly on the quantity, quality, collection time and spatial resolution of the data. Our workflow demonstrates that seemingly reliable parameter estimates can lead to inaccurate predictions, highlighting the need for careful consideration of data quality and quantity to guide extinction-risk modelling and prediction. Open source software is provided on GitHub to replicate and extend all results considered.

ecology↗

bioRxiv2023

Embryogenesis in myrmicine ants combines features of short and long germ-band modes of development

Ants exhibit complex social organization, morphologically distinct castes with division of labor, and the exploitation of diverse ecological niches. The extent to which these features have influenced embryonic development relative to other insects remains unclear. Insect embryogenesis has been classified into one of three modes: long, short, and intermediate germ-band. In long germ-band development, exemplified by the fruit fly Drosophila melanogaster, segments along the entire anterior-posterior axis of the embryonic primordium are established almost simultaneously, prior to gastrulation, with the initial embryonic primordium surrounding almost the entire volume of the egg. In short and intermediate germ-band modes, the embryonic primordium occupies a smaller proportion of the egg surface, with anterior segments initially specified, and remaining segments being added sequentially from a posterior growth zone. Here, we show a novel pattern of development in three myrmicine ants, the fungus-gardening ants Atta texana and Mycocepurus smithii, and the red imported fire ant Solenopsis invicta. Early in embryogenesis, they exhibit features of short germ-band development, while later in development they exhibit a newly-characterized progressive pattern of segmentation that has been associated with some long germ-band-developing insects. Moreover, despite similarities in the size of ant and Drosophila eggs, the duration of embryogenesis in the three ant species is 10 to 20-fold longer than in Drosophila and is also significantly longer than in the honeybee Apis mellifera and the jewel wasp Nasonia vitripennis. In addition, the embryos produced by A. texana foundress queens develop to first instar larvae 25% faster than embryos produced by mature queens. We discuss these results in the context of the eusocial lifestyle of ants.

developmental biology↗

bioRxiv2020

From egg to adult: a developmental table of the ant Monomorium pharaonis

Ants are one of the most ecologically and evolutionarily successful groups of animals and exhibit a remarkable degree of phenotypic diversity. This success is largely attributed to the fact that all ants are eusocial and live in colonies with a reproductive division of labor between morphologically distinct queen and worker castes. Yet, despite over a century of studies on caste determination and evolution in ants, we lack a complete ontogenetic series from egg to adult for any ant species. We therefore present a developmental table for the Pharaoh ant Monomorium pharaonis, a species whose colonies simultaneously produce both reproductive queens and completely sterile workers. In total, M. pharaonis embryonic, larval, and pupal development lasts 45 days. During embryogenesis, the majority of developmental events are conserved between M. pharaonis and the fruit fly Drosophila melanogaster. However, we discovered two types of same-stage embryos prior to gastrulation: (1) embryos with internalized germ cells; and (2) embryos with germ cells outside of the blastoderm at the posterior pole. Moreover, we found two-types of embryos following germ band extension: (1) fertile embryos with primordial germ cells; and (2) sterile embryos with no germ cells. Together, our data shows that the queen (fertile) and worker (sterile) phenotypes are already determined and differentiated by early embryogenesis. During larval development, previous studies and our data find 3 larval instars reproductives and workers. However, there is considerable variation within each caste-specific instar, making it difficult to lineate instar boundaries. Here, we propose that developmental and anatomical markers can segregate larvae into gyne (unmatted queen), male and worker castes, including during the 1st larval instar. Overall, we hope that the ontogenetic series we present here will serve as a blueprint for the generation of future ant developmental tables.

developmental biology↗