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The dynamics of a fully three-dimensional lid-driven cubical cavity (3D-LDC) flow at several post-critical conditions, i.e., beyond the first bifurcation, are elucidated using both linear and nonlinear analyses. When the Reynolds number is increased beyond the critical value, symmetry breaks down intermittently with subsequent gradual growth in spanwise inhomogeneity. This results in crossflow as well as pronounced secondary flow due to enhanced imbalance between centrifugal and pressure forces. Thus, while a stable solution is obtained at Re = 1900 (Reynolds number based on lid velocity and cavity side length), nonlinear analysis identifies intermittent and nearly saturated regimes at Re = 2100 and Re = 3000 , respectively. These changes in the regime are examined by considering five basic states at different Reynolds numbers starting from Re = 1900 . At the lowest Reynolds number, linear analysis yields only symmetric modes, characterized by Taylor–Görtler-like (TGL) vortices. However, at Re = 2100 , the intermittent breakdown of symmetry results in the emergence of an antisymmetric low-frequency mode apart from primary high-frequency mode. The frequencies of both these modes are numerically close to those obtained from corresponding nonlinear simulations. When the Reynolds number is increased even further, the TGL structures drift under the influence of the crossflow to occupy the previously structureless region near the wall. The frequency of each mode decreases with increase in Re ; between 1900 and 3000, the frequency of the primary mode changes by more than 20%. Furthermore, the spatial support of each mode becomes larger within the cavity. Both primary and secondary modes are increasingly destabilized with Re ; however, the secondary antisymmetric mode is destabilized at a higher rate. The current study thus provides a comprehensive picture of the overall dynamics of 3D-LDC flows in pre- and post-bifurcation regimes in an extended Re range not considered hitherto. [ABSTRACT FROM AUTHOR]

Primitively eusocial insects exhibit reproductive division of labour such that one or a small number of individuals monopolize reproduction while the remaining function as non-reproductive workers. They also exhibit non-reproductive division of labour such that some workers primarily perform the extra-nidal tasks of foraging, while others primarily perform the intra-nidal tasks of feeding larvae, building the nest and other nest maintenance activities. In some species, queens regulate both reproductive as well as non-reproductive division of labour by means of their dominance behavior toward the workers. Here we show that in the primitively eusocial species R. cyathiformis, (1) the queen shows significantly more aggression towards the potential queen (PQ) than to the rest of the workers; (2) the PQ shows significantly more aggression towards the workers than they show to each other; (3) the activities of the workers such as bringing food and feeding the larvae continue unabated in the absence of the queen; (4) the amount of dominance received by a worker does not predict her rate of foraging; (5) there is a positive correlation between workers' rates of bringing food and the rates at which they themselves feed the larvae. We suggest that while queen (along with PQ) regulates reproductive division of labour, dominance behavior is not used to regulate the non-reproductive activities of the workers such as bringing food and feeding the larvae; these are self-regulated by individual workers by themselves. [ABSTRACT FROM AUTHOR]

Ropalidia cyathiformis is a primitively eusocial tropical paper wasp usually with a single dominant queen per colony. When the queen is removed, one and only one individual increases her aggression and becomes the new queen of the colony, unchallenged by any other worker. We refer to such a successor as a potential queen (PQ) until she lays her first egg. By removing the queen and successive PQs, we show that there is not just one successor but a strict reproductive hierarchy of up to 3 PQs, who succeed the queen one after the other. Of many variables tested, we found that only the frequency of dominance behaviour is a significant predictor of whether or not an individual is part of the reproductive hierarchy and also of her position in the hierarchy. Dominance behaviour, however, does not perfectly predict the position of an individual in the reproductive hierarchy because we show that an average of three more dominant individuals, are bypassed when an individual becomes the next queen or PQ. This is in contrast to the reproductive hierarchy in the conspecific Ropalidia marginata, where age rather than dominance behaviour is a predictor (though imperfect once again) of an individual's position in the queue. Taken together, our results suggest that (a) these two sister species have evolved two rather different mechanisms of reproductive caste differentiation, (b) that neither of them strictly conform either to the so-called 'temperate' or 'tropical' patterns of queen succession seen in most other species studied so far. [ABSTRACT FROM AUTHOR]