Behavioural switching during oscillations of intracellular Ca2+ concentration in free-swimming human sperm

Lay summary A human sperm must swim to the egg to fertilise it. To do this the sperm uses different types of swimming (behaviours) as they are needed. When we watch sperm swimming we see that they regularly change behaviour, sometimes repeatedly switching between two different types. Calcium ions inside cells are crucial in controlling many cell functions and in sperm they play a key role in regulating their behaviour. Here we have measured the concentration of calcium ions inside swimming human sperm. We found that in 12/35 (34%) of the cells we assessed, the concentration of calcium changed repeatedly, averaging more than one cycle of rise and fall per minute. These changes in the concentration of calcium ions occurred as the sperm switched swimming stroke, suggesting that oscillation of calcium concentration is involved in controlling the switching of sperm behaviour. Impaired sperm motility is an important cause of subfertility in men. Understanding how sperm behaviour is controlled will allow the development of treatments that can rescue the fertility of sperm with impaired motility.

Evolved Transistor Array Robot Controllers

For the first time, a field programmable transistor array (FPTA) was used to evolve robot control circuits directly in analog hardware. Controllers were successfully incrementally evolved for a physical robot engaged in a series of visually guided behaviours, including finding a target in a complex environment where the goal was hidden from most locations. Circuits for recognising spoken commands were also evolved and these were used in conjunction with the controllers to enable voice control of the robot, triggering behavioural switching. Poor quality visual sensors were deliberately used to test the ability of evolved analog circuits to deal with noisy uncertain data in realtime. Visual features were coevolved with the controllers to automatically achieve dimensionality reduction and feature extraction and selection in an integrated way. An efficient new method was developed for simulating the robot in its visual environment. This allowed controllers to be evaluated in a simulation connected to the FPTA. The controllers then transferred seamlessly to the real world. The circuit replication issue was also addressed in experiments where circuits were evolved to be able to function correctly in multiple areas of the FPTA. A methodology was developed to analyse the evolved circuits which provided insights into their operation. Comparative experiments demonstrated the superior evolvability of the transistor array medium.

Active foraging for toxic prey during gestation in a snake with maternal provisioning of sequestered chemical defences

Many animals sequester dietary defensive compounds and incorporate them into the offspring, which protects the young against predation. One possible but poorly investigated question is whether females of such species actively prey upon toxic diets. The snake Rhabdophis tigrinus sequesters defensive steroids from toads consumed as prey; it also feeds on other amphibians. Females produce chemically armed offspring in direct proportion to their own level of toad-derived toxins by provisioning the toxins to their eggs. Our field observations of movements and stomach contents of radio-tracked R. tigrinus showed that gravid snakes preyed upon toads by actively foraging in the habitat of toads, even though toads were a scarce resource and toad-searching may incur potential costs. Our Y-maze experiments demonstrated that gravid females were more likely to trail the chemical cues of toads than were males or non-gravid females. These results showed behavioural switching in females and active foraging for scarce, toxic prey during gestation. Because exploitation of toads by gravid females results in their offspring being more richly endowed with prey-derived toxins, active foraging for toxic prey is expected to be an adaptive antipredator trait, which may enhance chemical defence in offspring.

Motivational Models of Courtship in Male Threespine Sticklebacks (Gasterosteus Aculeatus)

The objective of this study was to determine which of the Random, Competition, and Time-sharing models provides the best description of courtship in the male threespine stickleback (Gasterosteus aculeatus). A critical re-evaluation of experiments in this field revealed both theoretical and methodological difficulties. An attempt was made to correct these problems and provide a more quantitative and statistically valid approach to the motivational study of behavioural switching. Eighteen subjects were tested over four stimulus conditions in a modified double-interruption experiment, where they alternated between courtship and nest-related behaviour. The animals were visually presented with one or three females, with or without eggs in the nest. Assessments of motivational 'dominance' were made on the basis of incomplete visits and variation of visit durations. Data on time budgets, and temporal variability and associations were also analyzed. The results provided little support for the Competition model. In 33 of the 36 sessions, the Random model was accepted as a logical default when the various methods of assessment failed to support, or contradicted the Time-sharing model. The remaining assessments of Time-sharing (both female- and nest-dominant) may be considered as artefacts of the assessment procedure. Four possible explanations of these results were discussed with respect to experimental design and motivational theory.