| Description |
Two major strategies exist among developing warm-blooded vertebrates to cope with the vulnerable nature of being diminutive and inexperienced as a juvenile. Precocial juveniles decrease their vulnerability by entering the world in a relatively mature state of development - newly born or hatched neonates are capable of independently foraging and avoiding predators with little influence from the parent. In contrast, altricial juveniles enter the world in a relatively immature state of development (relying heavily on parental care), but adopt extremely high rates of growth - thus decreasing the period of time spent being vulnerable. The contrasting strategies of premature form (precociality) and high growth rate (altriciality) could set potential limits on the degree to which animal form and function are capable of changing throughout development. Two discrete investigations attempt to measure the developmental differences in animal design and utility between precocial and altricial growth strategies. Mallards (Anas platyrhynchos), like most Anseriformes (waterfowl), undergo differential development of the forelimbs (wings) and hindlimbs (legs) - the ability to run and swim initiates upon hatching, while the ability to fly is delayed into adulthood. Musculo-skeletal dimensions were tracked throughout the mallard's 60-day ontogenetic (post-hatching developmental) period and coupled with whole-body locomotor performance during maximal running, swimming and flying efforts. The attainment of mallard locomotor performance parallels the independent morphological maturation of the forelimbs and the hindlimbs - running and swimming performance (hindlimb dominated) initiate at relatively high levels but only gradually improve throughout the first month of development, while flying performance (forelimb only) initiates at relatively low levels but dramatically improves within the last two weeks of development. In a complementary study, aerodynamic forces were measured across a developmental series of precocial chukar partridge (Alectoris chukar) and altricial mallard wing development. Lift and drag production improved dramatically over the course of each species' ontogeny, but chukar generate lift starting at day eight and improve only a minor extent, while mallard delay lift production until just prior to fledging and improve function dramatically. The prevailing theme in each study indicates precocial strategies offer early functional forms that change very little into adulthood, while altricial strategies offer rapid and dramatic change in morphology that can only be utilized in the adult. |
