Seasonal changes in song nuclei and song behavior in Gambel's white-crowned sparrows

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspeices. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal change in stereotypy of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in song control nuclei may correlate with seasonal changes in song stereotypy. © 1995 John Wiley & Sons, Inc.     

Cellular Morphogenesis In Silico

We describe a model that simulates spherical cells of different types that can migrate and interact either attractively or repulsively. We find that both expected morphologies and previously unreported patterns spontaneously self-assemble. Among the newly discovered patterns are a segmented state of alternating discs, and a “shish-kebab” state, in which one cell type forms a ring around a second type. We show that these unique states result from cellular attraction that increases with distance (e.g., as membranes stretch viscoelastically), and would not be seen in traditional, e.g., molecular, potentials that diminish with distance. Most of the states found computationally have been observed in vitro, and it remains to be established what role these self-assembled states may play in in vivo morphogenesis.     

Habituation Is More Than Learning to Ignore: Multiple Mechanisms Serve to Facilitate Shifts in Behavioral Strategy

Recent work indicates that there are distinct response habituation mechanisms that can be recruited by different stimulation rates and that can underlie different components (e.g., the duration or speed) of a single behavioral response. These findings raise the question: why is “the simplest form of learning” so complicated mechanistically? Beyond evolutionary selection for robustness of plasticity in learning to ignore, it is proposed in this article that multiple mechanisms of habituation have evolved to streamline shifts in ongoing behavioral strategy. Then, speculations are offered regarding the implications of this reconceptualization of habituation for approaching the analysis of mechanisms of more complex forms of learning and memory.     

Auditory Corticothalamic Neurons Are Recruited by Motor Preparatory Inputs

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The absorption efficiency and respiration rate of the Florida Lancelet, Branchiostoma floridae

The present study investigates some aspects of the digestive biology and physiological energetics of the Florida lancelet, Branchiostoma floridae. Florida lancelets are able to remove 47.2–56.9% of the energy from a diet of mixed algae. The respiration rate is 0.100 mL O₂ (STPD) h^− 1 g^− 1 (wet), which estimates a metabolic rate of 0.248 J h^− 1, at an average body mass of 0.125 g (wet). Published values of the chlorophyll a concentration in its natural habitat indicate that a 125 mg lancelet would need to filter 0.018–0.031 L h^− 1 to remove sufficient food to support its resting metabolism. The filtration rate of lancelets has been reported as 0.138 L h^− 1, indicating that the actual filtration rate is 4–7 times greater than the filtration rate needed to meet resting metabolic demands. It appears that lancelets have the potential to be raised in aquaculture, because their absorption efficiency and respiration rate are comparable to suspension-feeding invertebrates that have been successfully aquacultured.