Egg components and offspring survival vary with group size and laying order in a cooperative breeder.

Prenatal resource allocation to offspring can be influenced by maternal environment and offspring value, and affect offspring survival. An important pathway for flexible maternal allocation is via egg components such as nutrients and hormones. In cooperative breeders, females with helpers may increase resource allocation to eggs-'differential allocation'-or reduce it-'load-lightening'. Yet, helper effects on egg composition have been poorly studied. Moreover, it is unknown how helpers' presence modulates laying order effects on egg content and survival. Here, we investigated how maternal allocation varied with group size and laying order in the cooperatively breeding sociable weaver (Philetairus socius). We estimated interactive effects of helpers and laying order on allocation to egg mass, yolk nutrients-yolk mass, proteins, lipids, carotenoids, vitamin A and vitamin E-and hormones-testosterone, androstenedione, and corticosterone. Results concurred with the 'differential allocation' predictions. Females with more helpers produced later-laid eggs with heavier yolks and more lipids, and laid eggs overall richer in lipids. Proteins, antioxidants, and hormones were not found to vary with helper number. We then analyzed how helper number modulated laying order effects on survival. Females with more helpers did not specifically produce later-laid eggs with higher survival, but eggs laid by females with more helpers were overall more likely to fledge. These findings show that some egg components (yolk mass, lipids) can positively vary according to females' breeding group size, which may improve offspring fitness.

Overexpression of grappa encoding a histone methyltransferase enhances stress resistance in Drosophila.

Histone deacetylases, such as silent information regulator 2 (Sir2) and Rpd3 are involved in chromatin silencing and implicated in lifespan determination in several organisms. The yeast Dot1 gene encoding a histone methyltransferase affects localization of silencing proteins including Sir2, and plays an essential role in the repair of damaged DNA. However, it is not known whether an alteration of a histone methyltransferase activity influences lifespan or stress resistance, which is often associated with extended lifespan. Here we investigated whether the Drosophilagrappa (gpp) gene, a Dot1 homolog influences lifespan and stress resistance using transgenic flies overexpressing gpp and those bearing a partial loss-of-function mutation. Overexpression of gpp throughout the adult stage did not extend the lifespan, but significantly enhanced resistances when they were kept on medium containing 1% H(2)O(2), or those with poor nutrients. As well, gpp-overexpressing flies were behaviourally more active than control flies. We investigated whether gpp overexpression induced anti-oxidant genes, Catalase, Sod, Sod2, GstD2, dhd, TrxT and Trx-2. However, none of these genes was induced. A partial loss-of-function mutations in gpp dramatically reduced the lifespan under oxidative and caloric stresses. Taken together, these results demonstrated that gpp is required for normal lifespan and stress resistance, and that its overexpression increases stress resistance in Drosophila, without obvious induction of representative anti-oxidant genes.