Predictability and randomness of paw choices are critical elements in the behavioural plasticity of mouse paw preference

Half a century of handedness research: Myths, truths; fictions, facts; backwards, but mostly forwards

Although most people are right-handed and have language in their left cerebral hemisphere, why that is so, and in particular why about ten per cent of people are left-handed, is far from clear. Multiple theories have been proposed, often with little in the way of empirical support, and sometimes indeed with strong evidence against them, and yet despite that have become modern urban myths, probably due to the symbolic power of right and left. One thinks in particular of ideas of being right-brained or left-brained, of suggestions that left-handedness is due to perinatal brain damage, of claims that left-handers die seven years earlier than right-handers, and of the unfalsifiable ramifications of the byzantine Geschwind-Behan-Galaburda theory. This article looks back over the past fifty years of research on brain asymmetries, exploring the different themes and approaches, sometimes in relation to the author's own work. Taking all of the work together it is probable that cerebral asymmetries are under genetic control, probably with multiple genetic loci, only a few of which are now beginning to be found thanks to very large databases that are becoming available. Other progress is also seen in proper meta-analyses, the use of fMRI for studying multiple functional lateralisations in large number of individuals, fetal ultra-sound for assessing handedness before birth, and fascinating studies of lateralisation in an ever widening range of animal species. With luck the next fifty years will make more progress and show fewer false directions than had much of the work in the previous fifty years.

Morphological asymmetry and habitat quality: using fleas and their rodent hosts as a novel experimental system

Morphological asymmetry is widely used to measure developmental instability and higher levels of asymmetry often correlate with decreased mating success, increased inbreeding, increased stress and decreased habitat quality. We studied asymmetry and relationships between asymmetry and host identity in two flea species, host generalist Xenopsylla ramesis and host specialist Parapulex chephrenis, and asked: (1) what the level of asymmetry was in their femurs and tibiae; (2) which type of asymmetry predominates; and (3) whether fleas that fed on host species distantly related to their principal host species produced offspring that exhibited greater asymmetry compared with offspring of fleas that fed on their principal host species. We found fluctuating asymmetry in femurs and tibiae of X. ramesis and in the tibiae of P. chephrenis as well as significantly left-handed directional asymmetry in the femurs of P. chephrenis Host species identity significantly impacted asymmetry in leg segments of P. chephrenis but not in those of X. ramesis Offspring asymmetry increased when mother fleas fed on a host that was distantly related to the principal host. Fleas parasitizing multiple host species might compensate for developmental instability when utilizing a novel host species; therefore, host-switching events in host-specific parasites could be constrained by the relatedness between a novel and a principal host species.