Phenotypic Variation of Growth Trajectories in Finches

Abstract

Abstract.-Evolution cannot proceed without phenotypic variation for selection to act on. This is particularly true of ontogenetic parameters because it is changes in these parameters that give rise to new phenotypes. I analyzed the amount and dimensionality of phenotypic variation on growth trajectories in early ontogeny in three species of finches (Fringillidae) using the recently developed infinite-dimensional model. For two species, eight traits were analyzed, and for a third, six traits. Growth data were analyzed only up to 6 d of age in two species and 8 d of age in the third. The results were very similar for all species and traits. A very large proportion of the phenotypic variation in growth trajectories was confined to a single dimension. This dimension corresponded to a simultaneous increase/decrease at all ages in early ontogeny. The eigenfunctions, each describing a family ofsimilar-shaped growth trajectories, were highly collinear among traits. A high covariance existed among traits at the same and different ages. If some part of the phenotypic variation has an additive genetic basis, then any selection for a change in size at one age in one trait will lead to a response in a size at subsequent ages and in the other traits. This in tum suggests that morphological evolution frequently will move along a multivariate size axis, as has indeed been found in several taxa.

Similarity of growth among Great tits (Parus major) and Blue tits (P. caeruleus)

“…Bill traits may be of great use when opening the egg shell, and skull length may simply be a correlated response for selection on a large bill, or minimum brain size acceptable. This means that early advantages in terms of large size will be accentuated over time, which indeed has been found in finches (Bjorklund, 1993) and tits (Bjorklund, unpublished). It is interesting that the same relative order of completion of growth was found among Geospiza finches, three fringdlid finch species and two tit species.…”

Analyzing Fluctuating Asymmetry with Geometric Morphometrics: Concepts, Methods, and Applications

“…There is also unexplored potential for future analyses of the regulation of shape variation, because some studies used longitudinal data [349,351]. Analyses that explicitly address the covariation among the changes between successive ontogenetic stages can shed light on regulatory phenomena, but so far have only been used with traditional morphometric data [352][353][354][355][356][357].…”

Effects of temperature and growth hormone on individual growth trajectories of wild‐type and transgenic coho salmon Oncorhynchus kisutch

“…Only individuals that survived until the end of the experiment and increased in mass (since commonly a few individuals never initiate feeding after transfer to new conditions) at each consecutive measurement (70% of the wild fish and 100% of transgenics) were included in the analyses. The infinite‐dimensional growth trajectories were calculated using the method by Kirkpatrick & Lofsvold (1992), which has been used in other studies of growth of fishes and birds (Björklund, 1993, 1997; Björklund et al , 2003). This method uses the covariance matrix of ln‐transformed values of mass at a number of periods in time and interpolates the growth trajectory across all ages.…”

“…Studies monitoring variation in individual growth trajectories in animals with determinate growth, such as birds and mammals, show little between‐individual variation in growth patterns (Kirkpatrick & Lofsvold, 1992; Björklund, 1993, 1997), suggesting that no substantial selection for a change in the shape of the growth curves exists. The situation could be different for organisms with indeterminate growth, such as teleosts, since such species have the ability to increase in size throughout their life span and will therefore have the potential to compensate at a late stage for reduced growth at an earlier stage (Björklund et al , 2003).…”