Pheasant sexual ornaments reflect nutritional conditions during early growth

Abstract

Differences in growth conditions during early life have been suggested to cause long-lasting effects on morphology and quality of adult birds. We experimentally investigated the effect of early growth conditions on the expression of sexual ornaments later in life in male ring-necked pheasants (Phasianus colchicus). We also investigated the effects on immune function, as it could be a functional link between early nutrition and ornament expression. We manipulated the dietary protein intake during the first eight weeks post hatching. Males receiving fodder with 27% protein during the first three weeks of life grew larger and more colourful wattles when sexually mature than males receiving a low-protein diet (20.5% protein). Spur length was unaffected by diet treatment. Manipulation of food protein levels during weeks 4-8 after hatching had no effect on the development of ornaments. The different protein treatments had no longterm effect on either humoral or cell-mediated immune responses. There was, however, a positive relationship between spur length and cell-mediated immune responsiveness. Our study shows that expression of a sexual ornament in adult pheasants reflects nutritional conditions early in life. Because the expression of secondary sexual ornaments is affected by conditions during early growth, by selecting more ornamented males, females would choose mates that are superior at handling early nutritional stress. If the susceptibility to early nutritional stress also has a hereditary basis, females may benefit by obtaining 'good genes'.

Temporal patterns of nutrition dependence in secondary sexual traits and their varying impacts on male mating success

“…Many characters become fixed after production (e.g. avian plumage) or after maturation, but nutrition intake prior to maturation can affect the resources available to produce pigmentation or ornamentation (Ohlsson, Smith, Raberg, & Hasselquist, 2002;Taylor, Clark, & McGraw, 2011;Uetz, Papke, & Kilinc, 2002). On the other hand, energetically demanding behaviors such as elaborate courtship displays may be more strongly affected by adult (or current) diet, which has an impact on available energetic resources (Brown, 2011;Droney, 1996Droney, , 1998Dussourd, Harvis, Meiwald, & Eisner, 1991;Kolluru & Grether, 2004;Wedell, 1994).…”

A window on the past: male ornamental plumage reveals the quality of their early-life environment

“…In summary, we have shown that colourful plumage grown after leaving the nest is a window on the developmental history of the male [5], in common with other avian integuments that are known to be affected by neonatal environmental conditions [8,10]. Although the mechanisms that link developmental history with colourful plumage have yet to be identified, our study adds to the diversity of secondary sexual traits whose expression is strongly linked to the environment in which they developed.…”

“…In addition, some studies have tracked the downstream effects of developmental environment on colourful adult traits. However, these have tended to focus on non-plumage-based ornaments, such as the fleshy red wattles of ring-necked pheasants (Phasianus colchicus) [8,17], and the carotenoid-based bills of zebra finches (Taeniopygia guttata) [7,10,18,19] and mallard ducks (Anas platyrhynchos) [20]. Despite this important work, the relevance of developmental conditions for colourful adult plumage is largely unknown.…”

“…Previously, the importance of developmental conditions has been demonstrated for some colourful adult integuments [8,10,20], and for nestling plumage [12,14], but never for adult plumage. The effect was most pronounced for yellow carotenoid-based plumage, which reflected multiple attributes of the nestling environment, such as brood size, hatch date and nutritional conditions.…”

“…Colourful avian ornaments are also susceptible to perturbations in developmental environment [6][7][8] but their potential role as developmental indicators, particularly in natural populations, has received limited attention. It is reasonable to expect a link between developmental environment and colourful traits.…”