Haematocrit, eggshell colouration and sexual signaling in the European starling (Sturnus vulgaris).

BACKGROUND: One hypothesis to explain the blue-green colour of the eggs of many bird species is that it is a sexually-selected signal of the laying female's quality, which males use to determine their investment. This hypothesis requires that eggshell pigmentation carries a cost or is otherwise linked to female quality. One potential cost is that biliverdin, a haem derivative and the pigment responsible for eggshell colouration, is limiting. To assess this potential cost, we attempted to manipulate haematocrit and haemoglobin in free-living European starlings (Sturnus vulgaris Linnaeus). Upon collecting unmanipulated first clutches, we treated females with phenylhydrazine (PHZ), a haemolytic agent, and measured the blue-green chroma and reproductive performance of replacement clutches. We also investigated whether eggshell colour was associated with haematocrit or haemoglobin levels in unmanipulated first clutches. To test whether eggshell colour might act as a sexual signal, we examined associations between eggshell colour and reproductive performance, as well as the provisioning rate of the male. RESULTS: PHZ-treatment did not affect eggshell colour in replacement clutches. In unmanipulated first clutches, eggshell colour was not correlated with haematocrit or haemoglobin levels. Eggshell colour was correlated with female mass in unmanipulated first clutches but not replacement clutches. Chicks from eggs with higher eggshell colour had higher haemoglobin levels and longer tarsi just prior to fledging, suggesting that eggshell colour could reflect brood quality. However, eggshell colour was not correlated with the provisioning rate of the male or any other measure of reproductive performance. CONCLUSIONS: We found no evidence to support the hypothesis that the availability of resources required for the synthesis of pigment limits eggshell colour in European starlings, or that eggshell colour is used by males to determine their level of reproductive investment. We found little evidence that eggshell colour is correlated with female or offspring quality in this species.

Mid-winter temperatures, not spring temperatures, predict breeding phenology in the European starling Sturnus vulgaris.

In many species, empirical data suggest that temperatures less than 1 month before breeding strongly influence laying date, consistent with predictions that short lag times between cue and response are more reliable, decreasing the chance of mismatch with prey. Here we show in European starlings (Sturnus vulgaris) that mid-winter temperature ca 50-90 days before laying (8 January-22 February) strongly (r (2) = 0.89) predicts annual variation in laying date. Mid-winter temperature also correlated highly with relative clutch size: birds laid later, but laid larger clutches, in years when mid-winter temperatures were lower. Despite a high degree of breeding synchrony (mean laying date 5-13 April = ±4 days; 80% of nests laid within 4.8 days within year), European starlings show strong date-dependent variation in clutch size and productivity, but this appears to be mediated by a different temporal mechanism for integration of supplemental cue (temperature) information. We suggest the relationship between mid-winter temperature and breeding phenology might be indirect with both components correlating with a third factor: temperature-dependent development of the starling's insect (tipulid) prey. Mid-winter temperatures might set the trajectory of growth and final biomass of tipulid larvae, with this temperature cue providing starlings with information on breeding season prey availability (though exactly how remains unknown).

Protein accumulation underlying lifespan extension via ovariectomy in grasshoppers is consistent with the disposable soma hypothesis but is not due to dietary restriction.

Reduced reproduction extends lifespan in many experimental animals, but the mechanism by which this occurs is unclear. The disposable soma hypothesis suggests that when reproduction is reduced, more nutrients are allocated to the soma and lifespan is extended. Alternatively, the reproductive tissues or the process of reproduction may have a direct (i.e., non-nutritional) negative effect on lifespan. We used ovariectomized grasshoppers to examine the effects of reduced reproduction throughout the lifespan at the physiological level. We focused on protein, the limiting nutrient for egg production. Ovariectomized females lived significantly longer than sham females. Because both groups ingested similar amounts, the effect was independent of dietary restriction. Despite this, ovariectomized females gained less body mass than sham females. Ovariectomized grasshoppers produced the egg yolk-precursor protein vitellogenin. At the time sham females laid their first clutch, cumulative reproductive protein was similar in ovariectomized and sham females. By advanced ages, however, ovariectomized females had produced about five-fold less cumulative reproductive protein than sham females. In contrast, old ovariectomized females had at least two-fold more hemolymph storage protein. These results are consistent with ovariectomy extending lifespan in part via enhanced protein allocation to storage at the expense of reproduction.