Learned traits are thought to be subject to different evolutionary dynamics than other phenotypes, but their evolutionary tempo and mode has received little attention. Learned bird song has been thought to be subject to rapid and constant evolution. However, we know little about the evolutionary modes of learned song divergence over long timescales. Here, we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis of the order of hundreds of thousands of years or more, broken up by evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes over evolutionary timescales. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over long time periods.
Cells rely on molecular motors moving along an ever-shifting network of polymers (microtubules) for the targeted delivery of cell organelles to biologically-relevant locations. We present a stochastic model for a molecular motor stepping along a bidirectional bundle of microtubules, as well as a tractable analytical model. Using these models, we investigate how the preferred stepping direction of the motor (parallel or antiparallel to the microtubule growth, corresponding to kinesin and dynein motor families) quantitatively and qualitatively affects the cargo delivery. We predict which motor type is responsible for which cargo type, given the experimental distribution of cargo in the cell, and report experimental findings which support this guideline for motor classification.
36Signals used in animal communication, especially those that are learned, are thought to be 37 prone to rapid and/or regular evolution. It has been hypothesized that the evolution of song 38 learning in birds has resulted in elevated diversification rates, as learned song may be subject to 39 especially rapid evolution, and song is involved in mate choice. However, we know little about 40 the evolutionary modes of learned song divergence over timescales relevant to speciation. Here 41 we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island 42 sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis, on the order of 43 hundreds of thousands of years or more, broken up by strong evolutionary pulses. Stasis in 44 learned songs is inconsistent with learned traits being subject to constant or frequent change, 45 as would be expected if selection does not constrain song phenotypes, or if novel phenotypes 46 are frequently advantageous. Learned song may instead follow a process resembling peak 47 shifts on adaptive landscapes. While much research has focused on the potential for rapid 48 evolution in bird song, our results suggest that selection can tightly constrain the evolution of 49 learned songs over fairly long timescales. More broadly, these results demonstrate that some 50 aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over fairly 51 long time periods. 52 53 Introduction: 54
We study a stochastic particle system with a logarithmically-singular inter-particle interaction potential which allows for inelastic particle collisions. We relate the squared Bessel process to the evolution of localized clusters of particles, and develop a numerical method capable of detecting collisions of many point particles without the use of pairwise computations, or very refined adaptive timestepping. We show that when the system is in an appropriate parameter regime, the hydrodynamic limit of the empirical mass density of the system is a solution to a nonlinear Fokker-Planck equation, such as the Patlak-Keller-Segel (PKS) model, or its multispecies variant. We then show that the presented numerical method is well-suited for the simulation of the formation of finite-time singularities in the PKS, as well as PKS pre-and post-blow-up dynamics. Additionally, we present numerical evidence that blow-up with an increasing total second moment in the two species Keller-Segel system occurs with a linearly increasing second moment in one component, and a linearly decreasing second moment in the other component.
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