Abstract

1. Testosterone and carotenoids in the avian egg: are there complementary but opposing effects?Marco Cucco, Giorgio Malacarne & Aurélie TanvezUniversity of Piemonte Orientale, via Bellini 25, 15100 Alessandria, Italy Results Abstract In bird species, maternal effects can be observed all along the breeding period and even at the earliest stages. Indeed, yolk contains various maternal nutritious elements which are dependent on the mother and/or maternal environment. By experiments on Grey Partridges and on Canaries, we aimed to study the consequences on chicks development of two essential but antagonistic components: Testosterone and β-carotene. To do so, we manipulated yolk and/or diet with T and/or β-carotene and witnessed chicks development. Our results show a positive effect of β-carotene diet enrichment on chicks growth and cellular immunity whereas an increase of yolk T tend to reduce chicks cellular immunity when they are fed with a rich β-carotene diet. Introduction There is increasing evidence that oviparous species induce within variation in their offspring through differential allocation of resources like hormones, nutrients, antioxidants or immune factors to eggs (Schwabl et al. 1997). Recently, Royle et al. (2003) found increasing T levels and decreasing carotene contents in clutches of gulls, and they suggested complementary but opposing effects of maternally derived androgens and carotenoids. Indeed, T can have several effects on chicks’ development such as increasing their growth or their social status, but it also has a double-edged function since its oxidant activity can also be deleterious to the chicks. Besides, eggs contain also powerful antioxidants such as carotenoids. CAROTENE - In the Canary, chicks’ beta-carotene diet enrichment improved their immunocompetence whereas yolk composition does not seems to matter. Considering their growth, the chicks hatched from yolk with high levels of carotenoids and fed with enriched diet after hatching are the ones showing the fastest growth. Objectives We utilized the Canary Serinus canaria and the Grey partridge Perdix perdix to study the consequences of yolk carotenoid and testosterone variations on chicks’ growth and immunocompetence. CAROTENE - In the grey partridge a high quantity of beta-carotene in the diet improved the growth and the immunocompetence Discussion In both the canary and the grey partridge a high quantity of β-carotene to chicks had a clear-cut positive effect on immunity and growth. The positive effect of β-carotene on the immune system is in line with findings on other bird species. On the contrary, the positive effect of carotenoid supplementation we found on mass increase was not reported in the majority of bird studies. Preliminary data on testosterone confirm that T has a negative effect on immunocompetence. This effect is present only in chicks fed with a rich b+ diet. Methods Experiements on Grey partridge (University of Piemonte Orientale, Italy) 64 pairs of were reared in a game farm in NW Italy. Carotenoids – Two diets were supplied to the breeding females: diets differed in the concentration of Beta-carotene: ß+: high concentrationß-: low concentration Testosterone – Two groups were created through egg injection in Grey partridge:T+: 20 ng T in 20 µL sesame oil injected in each Grey partridge egg Tc. Control eggs, 20 µL sesame oil only Immunocompetence and growth - PHA reaction and growth were measured at days 10 and 21. Experiment on Canaries (University of Paris X-Nanterre, France): 73 pairs were housed in individual cages. Carotenoids – All bird were fed with the same diet with the exeption of eggfood which was supplemented or not with Beta-carotene. The experimental groups differed on the period when the supplementation was administrated: CN.Before laying (ß carotene in the yolk and not given to the chicks) NC.After laying (ß carotene not in the yolk but given to the chicks) CC.Before and after laying (ß carotene in the yolk and given to the chicks) NN.Never Immunocompetence and growth - Chicks growth was daily mesured until fledging (day 20), PHAP response was measured on the day the chicks fledged. Conclusions Perspective – Mothers are supposed to influence fitness through maternal effects. It seems that the negative effect of T on immunity could be partially counteracted by carotene. We are currently performing experimental manipulation of T and b to increase the sample size and to better analyze the interplay of T and B. TESTOSTERONE - Chicks born from T+ eggs showed a reduction of immunocompetence. In the ß- groups, the immune reaction was very low; this probably prevented a further reduction of immunocompetence due to T+ injection. Acknowledgements Researches on Canaries were supported by grants from University of Paris X and from CEBC-CNRS and were conducted in the Laboratoire d'Ethologie et Cognition Comparées (France) ; Moreover, we wish to thank Gérard Leboucher and Olivier Chastel for supervising this study and for their helpful comments. References Royle NJ, Surai PF, Hartley IR (2001) Behav. Ecol. 12: 381-385. Schwabl H, Mock DW, Gieg JA (1997) Nature 386: 231. Tanvez A (2004) Ph.D. thesis, Université Paris X, Nanterre.