Patterns of growth and heterochrony in moundbuilders (Megapodiidae) and fowl (Phasianidae)

Megapode batchlings are ''superprecocial" compared to hatchlings of other G alliformes. In this paper, we examine patterns of growth and inquire about evolutionary processes that led to different degrees of precocity at hatchi ng in Galliformes. The postnatal development of body mass and that of seven morphometric parameters of wing and leg of Brush Turkey Alectura lathami, Peacock Pavo cristatus, Pheasant Phasianus colchicus and Japanese Quail Cot urnix japonica was characterized by the ratio of exponential growth rate (E GR) to relative size (ln(W/A); W = size at a given age; A = asymptote) at a given age. From that relationship, we derived developmental trajectories a s the slopes of a least squares regression of EGR on relative size. The slo pes of the developmental trajectories are indicative of the degree of preco city of development. We found that Brush Turkey, Peacock, and Pheasant foll ow the same developmental trajectory. However, the Brush Turkey hatches het erochronically delayed on that trajectory and consequently, its hatchlings are superprecocial. The Quail follows a significantly steeper developmental trajectory and hatches with a high degree of embryonic function (EGR). Fro m a comparative phylogenetic analysis we reconstruct the ancestral gallifor m developmental trajectory and infer that hypermorphosis of Brush Turkey em bryos led to the superprecocial hatchlings. The steeper developmental traje ctory of Quail is evolutionary derived from ancestral patterns of growth by somatic paedomorphosis. Using a multivariate approach we show that develop ment of different parts of the body is coherent, i.e., that patterns of dev elopment of wing and leg do not vary independently of each other. Consequen tly, selection for changed development of any part of the wing or the leg w ill cause the other parts to change too.