Examinando por Autor "Gil, Diego"

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Adaptive developmental plasticity in growing nestlings: sibling competition induces differential gape growth.
(The Royal Society, 2008) Gil, Diego; Bulmer, Elena; Celis, Patricia; López-Rull, Isabel
Sibling competition has been shown to affect overall growth rates in birds. However, growth consists on thecoordinated development of a multitude of structures, and there is ample scope for developmentalplasticity and trade-offs among these structures. We would expect that the growth of structures that areused in sibling competition, such as the gape of altricial nestlings, should be prioritized under intensecompetition. We conducted an experiment in the spotless starling (Sturnus unicolor), cross-fosteringnestlings to nests with different levels of sibling competition. We predicted that nestlings subjected tohigher levels of sibling competition should develop larger gapes than control birds. We found that, halfwaythrough the nestling period, overall size (a composite index of mass, wing, tarsus and bill) was reduced innests with intense sibling competition, whereas gape width remained unaffected. At the end of the nestlingperiod, experimental nestlings had wider gapes than controls. Additionally, a correlative study showed thatnestling gape width increased when feeding conditions worsened and overall size decreased. Thesepatterns could either be due to increased growth of gape flanges or to delayed reabsorption of thisstructure. Our results show that birds can invest differentially in the development of organs during growth,and that the growth of organs used in sibling competition is prioritized over structural growth
Do female spotless starlings (Sturnus unicolor) adjust maternal investment according to male attractiveness?
(Wiley, 2009) López-Rull, Isabel; Gil, Diego
In birds, female egg allocation patterns have a strong influence in offspring development and differential investment in egg size and composition has been shown to respond to male attractiveness. In this study we experimentally manipulated the perceived attractiveness of male starlings Sturnus unicolor by increasing the amount of green material in some nests (a male courtship display in this species). We predicted that, if female investment before laying is related to male attractiveness, experimental females would increase their reproductive investment in response to the addition of plants in their nests when compared to control females. We found that our manipulation caused variations in female reproductive investment in a way that seems to influence offspring quantity but not offspring quality: Females laid larger clutch sizes but not larger eggs when green plant material was added. However, yolk androgens contents were not related to the experimental manipulation. Contrary to expectations, females breeding in experimental nests laid eggs with smaller amounts of eggshell pigments. Interestingly, we found that eggs laid later in the sequence had higher testosterone levels and showed more intense egg colouration than eggs laid earlier in the sequence. These differences at the within-clutch level suggest that selection has favoured compensatory strategies for hatching asynchrony. Alternatively, since nest sabotages by other females are most common at the beginning of laying, this could be seen as female strategy to minimise losses due to nest sabotages. As far as we know, this is the first study to show that an external egg characteristic such as blue-green colouration reflects yolk androgen concentration.
Effects of temperature and nest heat exposure on nestling growth, dehydration and survival in a Mediterranean hole-nesting passerine
(Wiley Online Library, 2014) Salaberría, Concepción; López-Rull, Isabel; Celis, Patricia; Gil, Diego
Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double-brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra-seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest-site choice. Ambient temperature changed greatly during the chick-rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus-length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing-length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun-exposed to sun-protected nest-sites as the season progresses. However, nest-site availability and competition for sites are likely to impose constraints on this choice.
Egg pigmentation reflects female and egg quality in the Spotless starling Sturnus unicolor.
(Springer, 2008) López-Rull, Isabel; Miksik, Ivan; Gil, Diego
It has been proposed that blue colouration in eggs has evolved as a signal of female quality that males can use to modulate their parental investment. This hypothesis is based in the antioxidant properties of biliverdin whose costly deposition in the eggshell is expected to signal female antioxidant capacity and egg quality. Since maternally derived androgens are costly to produce and may adaptively affect offspring phenotype, high-quality females may benefit by signalling their androgen investment through egg colouration. Our aim was to investigate whether egg colour variation in the spotless starling reflected the amount of pigments on the eggshell and whether egg pigmentation was related to female and egg quality. Chromatography analyses revealed that spotless starling eggshells contained two different pigments: biliverdin and protoporphyrin IX with no correlation between them. Biliverdin contents correlated positively with egg colouration indicating that darker eggs with a higher peak in the blue–green segment of the spectrum contained higher amounts of biliverdin. Eggs containing more biliverdin were laid by high-quality females and contained higher yolk testosterone levels. However, despite the strong correlation between biliverdin and colorimetric variables, egg colouration did not reflect accurately female and egg quality. Our results provide evidence that eggshell pigmentation in the spotless starling is related to female and egg quality as shown by the yolk testosterone levels. However, the lack of relation between egg colour and female condition and egg quality do not provide evidence to support the signalling function of egg colouration.
Post-fledging recruitment in relation to nestling plasma testosterone and immunocompetence in the spotless starling.
(Wiley, 2011) López-Rull, Isabel; Salaberría, Concepción; Celis, Patricia; Puerta, Marisa; Gil, Diego
1.Social and ecological conditions experienced by individuals during early life can stronglyinfluence their development and survival. Nestlings of many species present important varia-tions in plasma androgens that can be associated with begging and sibling competition andmay translate into fitness effects, since broods with higher testosterone (T) production mayhave better body condition and higher fledging success. However, the positive effects of andro-gens may be counterbalanced by a reduction of immune defences and a greater susceptibilityto diseases.2.In this study we examined the potential relationships between natural variation in plasma T,immunity and post-fledging survival rate in nestlings of the spotless starling (Sturnus unicolor).3.We found that nestlings with higher cellular-mediated immune responses (CMI; measured asa swelling response to phytohaemagglutinin injection) were more likely to be recruited in thepopulation than nestlings with lower CMI responses. Males presented higher CMI response thanfemales, possibly due to differences in competitive advantage over food. We also found thatCMI response was negatively related to T levels, as predicted by the immunocompetence handi-cap hypothesis. However, despite this reduction in CMI response, we failed to find an associa-tion between nestling T levels and survival prospects. Our results add to the evidence of the roleplayed by immune defences in determining survival prospects in natural populations.4.In conclusion, our study reveals that CMI response can be considered as a good predictor ofpost-fledging recruitment. As far as we know, this is the first study attempting to evaluate therelationship between nestling T and post-fledging survival. Our results suggest that the potentialbenefits accrued by high levels of T in sibling competition during the nestling stage do not trans-late into increased survival