Morphological traits often covary within and among species according to simple power laws referred to as allometry. Such allometric relationships may result from common growth regulation, and this has given rise to the hypothesis that allometric exponents may have low evolvability and constrain trait evolution. We formalize hypotheses for how allometry may constrain morphological trait evolution across taxa, and test these using more than 300 empirical estimates of static (within-species) allometric relations of animal morphological traits. Although we find evidence for evolutionary changes in allometric parameters on million-year, cross-species time scales, there is limited evidence for microevolutionary changes in allometric slopes. Accordingly, we find that static allometries often predict evolutionary allometries on the subspecies level, but less so across species. Although there is a large body of work on allometry in a broad sense that includes all kinds of morphological trait-size relationships, we found relatively little information about the evolution of allometry in the narrow sense of a power relationship. Despite the many claims of microevolutionary changes of static allometries in the literature, hardly any of these apply to narrow-sense allometry, and we argue that the hypothesis of strongly constrained static allometric slopes remains viable. K E Y W O R D S :Adaptation, evolutionary constraint, microevolution, macroevolution, ontogenetic allometry, static allometry.

Online enhancement: appendix tables.abstract: Ontogenetic and static allometries describe how a character changes in size when the size of the organism changes during ontogeny and among individuals measured at the same developmental stage, respectively. Understanding the relationship between these two types of allometry is crucial to understanding the evolution of allometry and, more generally, the evolution of shape. However, the effects of ontogenetic allometry on static allometry remain largely unexplored. Here, we first show analytically how individual variation in ontogenetic allometry and body size affect static allometry. Using two longitudinal data sets on ontogenetic and static allometry, we then estimate variances and covariances for the different parameters of the ontogenetic allometry defined in our model and assess their relative contribution to the static allometric slope. The mean ontogenetic allometry is the main parameter that determines the static allometric slope, while the covariance between the ontogenetic allometric slope and body size generates most of the discrepancies between ontogenetic and static allometry. These results suggest that the apparent evolutionary stasis of the static allometric slope is not generated by internal (developmental) constraints but more likely results from external constraints imposed by selection.

To what extent within‐species (static) allometries constitute a constraint on evolution is the subject of a long‐standing debate in evolutionary biology. A prerequisite for the constraint hypothesis is that static allometries are hard to change. Several studies have attempted to test this hypothesis with artificial‐selection experiments, but their results remain inconclusive due to various methodological issues. Here, we present results from an experiment in which we selected independently on the slope and the elevation of the allometric relationship between caudal‐fin size and body size in male guppies (Poecilia reticulata). After three episodes of selection, the allometric elevation (i.e. intercept at constant slope) had diverged markedly between the lines selected to increase or decrease it, and showed a realized heritability of 50%. In contrast, the allometric slope remained unaffected by selection. These results suggest that the allometric elevation is more evolvable than the allometric slope, this latter representing a potential constraint on adaptive trait evolution. To our knowledge, this study is the first artificial‐selection experiment that directly tests the evolvability of static allometric slopes.

Variation in static allometry, the power relationship between character size and body size among individuals at similar developmental stages, remains poorly understood. We tested whether predation or other ecological factors could affect static allometry by comparing the allometry between the caudal fin length and the body length in adult male guppies (Poecilia reticulata) among populations from different geographical areas, exposed to different predation pressures. Neither the allometric slopes nor the allometric elevations (intercept at constant slope) changed with predation pressure. However, populations from the Northern Range in Trinidad showed allometry with similar slopes but lower intercepts than populations from the Caroni and the Oropouche drainages. Because most of these populations are exposed to predation by the prawn Macrobrachium crenulatum, we speculated that the specific selection pressures exerted by this predator generated this change in relative caudal fin size, although effects of other environmental factors could not be ruled out. This study further suggests that the allometric elevation is more variable than the allometric slope.

Children's play and exploration involves risk and a possibility for being injured. Early childhood and care institutions (ECECs) should provide children with physical challenges in a safe environment. Over the past years, the attention towards playground safety and injuries in ECECs has increased. Norwegian practitioners have a liberal approach to children's risk taking in play, raising questions on injury prevalence in Norwegian ECECs. The aim for this study was to gain knowledge about the injury prevalence and characteristics of the injuries in Norwegian ECECs. Managers from 2105 institutions completed an electronic questionnaire retrospectively asking the managers to report injuries and accidents the past year. The results indicate that injuries are rare in Norwegian ECECs, and that most of the injuries are minor and do not require a follow-up from professional medical personnel. The moderate and severe injuries are very rare, and often mishaps. There are some indications that boys experience injuries more often than girls do and that the most injuries happen outdoors. The main cause of moderate injuries is falling, both outdoors and indoors.