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Luxuriant, bushy antlers, bizarre crests, and huge, twisting horns and tusks are conventionally understood as products of sexual selection. This view stems from both direct observation and from the empirical finding that the size of these structures grows faster than body size (i.e., ornament size shows positive allometry).We contend that the familiar evolutionary increase in the complexity of ornaments over time in many animal clades is decoupled from ornament size evolution. Increased body size comes with extended growth. Since growth scales to the quarter power of body size, we predicted that ornament complexity should scale according to the quarter power law as well, irrespective of the role of sexual selection in the evolution and function of the ornament. To test this hypothesis, we selected three clades (ammonites, deer, and ceratopsian dinosaurs) whose species bore ornaments that differ in terms of the importance of sexual selection to their evolution.We found that the exponent of the regression of ornament complexity to body size is the same for the three groups and is statistically indistinguishable from0.25.We suggest that the evolution of ornament complexity is a by-product of Cope's rule. We argue that although sexual selection may control size in most ornaments, it does not influence their shape. [ABSTRACT FROM AUTHOR]

Conventional wisdom holds that the complex shapes of deer antlers are produced under the sole influence of sexual selection. We questioned this view by demonstrating that trends for increased body size evolution passively yield more-complex ornaments, even in organisms where no effect of sexual selection is possible, with similar allometric slopes. Recent investigations suggest that sexual selection on antlers of larger deer species is stronger than that in smaller species; hence, the use of conspicuous antlers for display in large male deer is a secondary function driven by especially intense sexual selection on these large-bodied species. Since ancestral deer were small and had very simple antlers, such an intense selection on antlers shape was probably absent in early deer. Therefore, the evolution of complex ornaments is coupled with body size evolution, even in deer. [ABSTRACT FROM AUTHOR]

Rates of biological evolution on islands are often presumed to exceed rates on the mainland. We tested this postulation by computing the evolutionary rate of head shape in Italian wall lizard Podarcis siculus, occurring on four islands off the coast of Southern Italy. We calculated the evolutionary rate using a phylogenetic tree whose node ages were derived from Lambeck et al. predicted ages of geographic isolation of the islands. Such ages are based on a relative sea-level change model for the late Pleistocene–Holocene. Through a likelihood optimization procedure, our method allows computing, besides the evolutionary rate, biological estimates of the ages of insular populations, with this indirectly testing Lambeck et al.’s model estimates. We found that the rate of evolution in Podarcis head shapes on islands is not statistically different from the mainland rate, although insular lizards have distinctive head shapes. Overall, the insular phenotype took 1–4000 years to arise (differing among islands). The estimated ages of insular populations are lower than Lambeck et al.’s estimates and fall in the 5- to 6-ka interval. [ABSTRACT FROM AUTHOR]

In South America, the crab-eating fox Cerdocyon thous occurs in sympatry to the ecologically similar, and phylogenetically close Lycalopex vetulus to the North, and Lycalopex gymnocercus to the South of its range. We studied character displacement in Cerdocyon under the effect of Bergmann's rule and the presence (or absence either) of Lycalopex within the crab-eating fox range. We performed skull shape analysis on 191 C. thous specimens and divided them in three distinct groups, depending on whether Cerdocyon occurs in sympatry or in allopatry to Lycalopex species. We tested for differences in size and shape between Cerdocyon groups and regressed both skull size and sexual size dimorphism against latitude and temperature, while controlling for spatial autocorrelation in the phenotypes. Southern Cerdocyon specimens present enlarged temporalis muscle and slender carnassial, both suggestive of a shift towards increased carnivory. Such a niche shift is interpreted as a mean to reduce competition to the larger Lycalopex species, which is still smaller than Cerdocyon. Consistently with the above, the degree of sexual shape and size dimorphism in Cerdocyon increases southward. We found a complex but coherent pattern of size and shape differentiation in Cerdocyon groups, which is consistent with the effects of both competition and Bergmann's rule. Cerdocyon reduces competition to Lycalopex by growing larger in the North. To the South, Cerdocyon is still larger, in keeping with Bergmann's rule, but strongly differs in skull shape from both its Lycalopex competitor and from any other Cerdocyon. Since the Southern Lycalopex species is much more similar in size to Cerdocyon than its Northern congeneric, this suggests that shape differences serve the goal of reducing competition between Cerdocyon and Lycalopex to the South, as size differences do to the North. The absence of the hypercarnivorous canid Speothos venaticus from the southern range of Cerdocyon may have allowed such a pattern to take place. [ABSTRACT FROM AUTHOR]

Chewing on different food types is a demanding biological function. The classic assumption in studying the shape of feeding apparatuses is that animals are what they eat, meaning that adaptation to different food items accounts for most of their interspecific variation. Yet, a growing body of evidence points against this concept. We use the primate mandible as a model structure to investigate the complex interplay among shape, size, diet, and phylogeny. We find a weak but significant impact of diet on mandible shape variation in primates as a whole but not in anthropoids and catarrhines as tested in isolation. These clades mainly exhibit allometric shape changes, which are unrelated to diet. Diet is an important factor in the diversification of strepsirrhines and platyrrhines and a phylogenetic signal is detected in all primate clades. Peaks in morphological disparity occur during the Oligocene (between 37 and 25 Ma) supporting the notion that an adaptive radiation characterized the evolution of South American monkeys. In all primate clades, the evolution of mandible size is faster than its shape pointing to a strong effect of allometry on ecomorphological diversification in this group. [ABSTRACT FROM AUTHOR]

Aim Because of their recent evolutionary radiation, capuchin monkeys represent an ideal group with which to investigate ecomorphological adaptations in relation to geography and climate. Our aim was to identify patterns of both skull size and shape variation in capuchins in relation to environmental variables and latitude. Location Tropical and subtropical South America. Methods We performed geometric morphometric analyses of skull shape in 228 capuchin monkey individuals belonging to either the genera Sapajus (seven species) or Cebus (two species), representing 94 localities in South America. Twenty-three homologous landmarks were digitized to describe skull shape. We regressed skull shape against latitude, longitude, skull size and environmental variables, using ordinary and partial least squares regressions. Variation partitioning was used to test for the relative contribution to shape variance by taxonomy, allometry and environment, and their interaction terms. Results We found a significant impact of latitude, climate and size on skull shape. The allometric component of shape variation, although large, is not congruent with shape differences between species, and probably reflects ontogenetic effects. Partial least squares between bioclimatic variables and skull shape explain some 98% of the covariation between environment and shape. Species distributed in drier, more seasonal southern localities exhibit a narrow skull with elongated muzzle and relatively larger teeth. Variation partitioning suggests that the difference in skull shape between species is highly correlated with climatic variation but not with skull size. Main conclusions Skull shape in capuchins is significantly related to both environment and skull size. The former, but not the latter, is significantly associated with shape differences between species. The Sapajus clade originated in the south, and experienced an evolutionary radiation during the Pleistocene. As new Sapajus species moved to the north, they adapted to the local environmental conditions, eventually resembling Cebus in skull shape as they reached the Amazon rain forest, in response to their shared environmental conditions. [ABSTRACT FROM AUTHOR]