Abstract
Allometric relationships describe the proportional covariation between morphological, physiological, or life‐history traits and the size of the organisms. Evolutionary allometries estimated among species are expected to result from species differences in ontogenetic allometry, but it remains uncertain whether ontogenetic allometric parameters and particularly the ontogenetic slope can evolve. In bovids, the nonlinear evolutionary allometry between horn length and body mass in males suggests systematic changes in ontogenetic allometry with increasing species body mass. To test this hypothesis, we estimated ontogenetic allometry between horn length and body mass in males and females of 19 bovid species ranging from ca. 5 to 700 kg. Ontogenetic allometry changed systematically with species body mass from steep ontogenetic allometries over a short period of horn growth in small species to shallow allometry with the growth period of horns matching the period of body mass increase in the largest species. Intermediate species displayed steep allometry over long period of horn growth. Females tended to display shallower ontogenetic allometry with longer horn growth compared to males, but these differences were weak and highly variable. These findings show that ontogenetic allometric slope evolved across species possibly as a response to size‐related changes in the selection pressures acting on horn length and body mass.
Highlights
Allometric relationships describe patterns of proportional covariation between morphological, physiological, or life-history traits and the size of the organisms among populations or species, or within population, among individuals measured at similar, or different age or developmental stages
Despite the plethora of studies on ontogenetic, static, and evolutionary allometry, variation in ontogenetic allometric parameters and the consequence of this variation on static and evolutionary allometry is poorly known. It remains uncertain whether evolutionary allometry mostly results from ontogenetic scaling, that is, the extension of the ancestral allometric trajectory among species with no variation in slope or intercept (Figure 1a; Corner & Shea, 1995; Shea, 1983; Weston, 2003), heterochrony, that is, the acceleration or retardation of the development that generates changes in the ontogenetic intercept (Figure 1b, Gould, 1971, 1977) or changes in both ontogenetic slope and intercept (Figure 1c, Gould, 1966)
For each species and population, we estimated sex-specific ontogenetic allometries and tested whether these allometries changed in response to variation in body mass, and whether such a change differed between sexes
Summary
It remains uncertain whether evolutionary allometry mostly results from ontogenetic scaling, that is, the extension of the ancestral allometric trajectory among species with no variation in slope or intercept (Figure 1a; Corner & Shea, 1995; Shea, 1983; Weston, 2003), heterochrony, that is, the acceleration or retardation of the development that generates changes in the ontogenetic intercept (Figure 1b, Gould, 1971, 1977) or changes in both ontogenetic slope and intercept (Figure 1c, Gould, 1966) Distinguishing between these different scenarios that represent different levels of evolutionary constraints is difficult, because the invariance of allometric parameters may result from the consistency of the selection pressures among populations or species. For each species and population, we estimated sex-specific ontogenetic allometries and tested whether these allometries changed in response to variation in body mass, and whether such a change differed between sexes
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