Yerushalmi S, Bodenhaimer S, Bloch G.
Developmentally determined attenuation in circadian rhythms links chronobiology to social organization in bees. JOURNAL OF EXPERIMENTAL BIOLOGY. 2006;209 :1044-1051.
AbstractWe investigated labor- related plasticity in the circadian clock of the bumblebee Bombus terrestris. Bumblebee workers vary enormously in body size, and we found that size, division of labor, and diurnal rhythms in activity are correlated in B. terrestris colonies. Large workers typically perform foraging activities with strong diurnal rhythms and low activity at night, whereas small bees typically care for ( nurse) brood around the clock with weak or no diurnal rhythms. Under constant laboratory conditions, circadian rhythms in locomotor activity were weaker, less stable, and developed at a later age in small ( nurse- size) bees compared to their larger ( forager- size) sisters. Under a light: dark illumination regime, many small bees, particularly at a young age, were active during the dark phase, fewer small bees developed rhythms, and they did so later compared to large bees. Taken together these findings reveal naturally occurring attenuation or suppression in the circadian clock of small bees that is determined during pre- adult development. This deficiency in clock function, however, does not result in pathology but rather appears to be functionally significant, because it is associated with around- the- clock brood care activity and therefore apparently improves divisions of labor and colony efficiency. This in turn suggests that variation in social biology influences traits of the circadian clock.
Weinstock GM, Robinson GE, Gibbs RA, Worley KC, Evans JD, Maleszka R, Robertson HM, Weaver DB, Beye M, Bork P, et al. Insights into social insects from the genome of the honeybee Apis mellifera. NATURE. 2006;443 :931-949.
AbstractHere we report the genome sequence of the honeybee Apis mellifera, a key model for social behaviour and essential to global ecology through pollination. Compared with other sequenced insect genomes, the A. mellifera genome has high A+T and CpG contents, lacks major transposon families, evolves more slowly, and is more similar to vertebrates for circadian rhythm, RNA interference and DNA methylation genes, among others. Furthermore, A. mellifera has fewer genes for innate immunity, detoxification enzymes, cuticle-forming proteins and gustatory receptors, more genes for odorant receptors, and novel genes for nectar and pollen utilization, consistent with its ecology and social organization. Compared to Drosophila, genes in early developmental pathways differ in Apis, whereas similarities exist for functions that differ markedly, such as sex determination, brain function and behaviour. Population genetics suggests a novel African origin for the species A. mellifera and insights into whether Africanized bees spread throughout the New World via hybridization or displacement.
Rubin EB, Shemesh Y, Cohen M, Elgavish S, Robertson HM, Bloch G.
Molecular and phylogenetic analyses reveal mammalian-like clockwork in the honey bee (Apis mellifera) and shed new light on the molecular evolution of the circadian clock. GENOME RESEARCH. 2006;16 :1352-1365.
AbstractThe circadian clock of the honey bee is implicated in ecologically relevant complex behaviors. These include time sensing, time-compensated sun-compass navigation, and social behaviors such as coordination of activity, dance language communication, and division of labor. The molecular underpinnings of the bee circadian clock are largely unknown. We show that clock gene structure and expression pattern in the honey bee are more similar to the mouse than to Drosophila. The honey bee genome does not encode an ortholog of Drosophila Timeless (Tim1), has only the mammalian type Cryptochrome (Cry-m), and has a single ortholog for each of the other canonical ``clock genes.'' In foragers that typically have strong circadian rhythms, brain mRNA levels of amCry, but not amTim as in Drosophila, consistently oscillate with strong amplitude and a phase similar to amPeriod (amPer) under both light-dark and constant darkness illumination regimes. In contrast to Drosophila, the honey bee amCYC protein contains a transactivation domain and its brain transcript levels oscillate at virtually an anti-phase to amPer, as it does in the mouse. Phylogenetic analyses indicate that the basal insect lineage had both the mammalian and Drosophila types of Cry and Tim. Our results suggest that during evolution, Drosophila diverged from the ancestral insect clock and specialized in using a set of clock gene orthologs that was lost by both mammals and bees, which in turn converged and specialized in the other set. These findings illustrate a previously unappreciated diversity of insect clockwork and raise critical questions concerning the evolution and functional significance of species-specific variation in molecular clockwork.
