Species with elaborate parental care often also show intense sibling competition over resources provided by parents, suggesting joint evolution of these two traits. Despite this, the evolution of elaborate parental care and the evolution of intense sibling competition are often studied separately. Here, we examine the interaction between parental food provisioning and sibling competition for resources through the joint manipulation of the presence or absence of parents and brood size in a species with facultative parental care: the burying beetle Nicrophorus vespilloides. The effect of the interaction between the presence or absence of parents and brood size was strong; brood size had a strong effect on growth when parents provided care, but no effect when parents were absent. As in previous studies, offspring grew faster when parents were present than when parents were absent, and offspring grew faster in smaller broods than in larger broods. Our behavioral observations showed that brood size had a negative effect on both the amount of time parents spent providing resources to individual offspring and the offspring's effectiveness of begging, confirming that the level of sibling competition increased with brood size. Furthermore, offspring in larger broods shifted more from begging toward self-feeding as they grew older compared to offspring in small broods. Our study provides novel insights into the joint evolution of parental care and sibling competition, and the evolution of offspring begging signals. We discuss the implications of our results in light of recent theoretical work on the evolution of parental care, sibling competition, and offspring begging signals.

SUMMARY The functional significance of the uncinate processes to the ventilatory mechanics of birds was examined by combining analytical modeling with morphological techniques. A geometric model was derived to determine the function of the uncinate processes and relate their action to morphological differences associated with locomotor specializations. The model demonstrates that uncinates act as levers, which improve the mechanical advantage for the forward rotation of the dorsal ribs and therefore lowering of the sternum during respiration. The length of these processes is functionally important;longer uncinate processes increasing the mechanical advantage of the Mm. appendicocostales muscle during inspiration. Morphological studies of four bird species showed that the uncinate process increased the mechanical advantage by factors of 2–4. Using canonical variate analysis and analysis of variance we then examined the variation in skeletal parameters in birds with different primary modes of locomotion (non-specialists, walking and diving). Birds clustered together in distinct groups, indicating that uncinate length is more similar in birds that have the same functional constraint, i.e. specialization to a locomotor mode. Uncinate processes are short in walking birds, long in diving species and of intermediate length in non-specialist birds. These results demonstrate that differences in the breathing mechanics of birds may be linked to the morphological adaptations of the ribs and rib cage associated with different modes of locomotion.

Endogenous near-24 h (circadian) rhythms in brain, behavior, and physiology are generated by cell autonomous circadian oscillators present in neural and non-neural tissues (Herzog 2007). The molecular basis for these daily cellular timekeepers are well established and include the period (Per1-3), cryptochrome 1-2, brain and muscle Arnt-like protein-1 genes, and their protein products (Panda et al. 2002;Piggins 2002;Reppert and Weaver 2002;Hastings and Herzog 2004;Ko and Takahashi 2006). In the mammalian brain, the dominant circadian clock is localized to the suprachiasmatic nuclei (SCN) of the hypothalamus (Rusak and Zucker 1979;Weaver 1998). Studies of long-term recordings from fetal and neonatal rodent SCN cells dispersed and cultured onto multielectrode plates reveal that these neurons maintain circadian rhythms in spontaneous discharge activity (Welsh et al. 1995) with the daily period of these rhythms determined by genotype (Liu et al. 1997