Search

Our aim is to identify ecomorphological adaptations in the skull shape of the South American howler monkeys (species of the genus Alouatta , Lacepede, 1799 , Primates, Atelidae). Since Alouatta is relatively homogenous in feeding ecology, we expect skull shape variation to be relatively conservative across species. We used geometric morphometrics to quantify craniodental morphology in six species of Alouatta . Multivariate regression, two-block Partial Least Squares, and variation partitioning were used to test for the impact of taxonomy, sexual dimorphism, allometry, geography and climate on skull shape. We found morphological overlap among species and sexes, although some discrimination occurs between species living in seasonal environments as opposed to rain forest species. There was a negative latitudinal gradient in skull size across species, with size explaining 34% of total shape variance. Latitude and climate, though important, were secondary in explaining shape variance. Amazonian Alouatta are larger, have thinner molars, wide incisors, and proportionally larger neurocranium. Overall, the shape of southern species seem well adapted to cope with proportionally tougher food items, whereas Amazonian species seem better equipped to deal with a diet richer in fruits, as confirmed by independent field observations. The small size of Alouatta in the South is possibly linked to the effect of competition with the larger folivorous atelid Brachyteles .

Fil: Raia, Pasquale. Università degli Studi di Napoli Federico II; Italia Fil: Passaro, Federico. Università degli Studi di Napoli Federico II; Italia Fil: Carotenuto, Francesco. Università degli Studi di Napoli Federico II; Italia Fil: Maiorino, Leonardo. Università degli Studi Roma Tre; Italia Fil: Piras, Paolo. Università degli Studi Roma Tre; Italia Fil: Teresi, Luciano. Università degli Studi Roma Tre; Italia Fil: Meiri, Shai. Tel Aviv University; Israel Fil: Itescu, Yuval. Tel Aviv University; Israel Fil: Novosolov, Maria. Tel Aviv University; Israel Fil: Baiano, Mattia A. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Baiano, Mattia A. Instituto Catalán de Paleontología Miquel Crusafont; España Fil: Baiano, Mattia A. Universidad Nacional de Río Negro; Argentina Fil: Martínez, Ricard. Universitat Autònoma de Barcelona; España Fil: Fortelius, Mikael. University Of Helsinski; Finlandia 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.

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.

The impact of environmental variation on phenotypic diversification is one major issue in evolutionary studies. Environmental variation is thought to be a primary factor in evolution, especially at high latitudes. In contrast, tropical areas are traditionally viewed as the cradle where the long-term effects of biological interactions on phenotypic change reside. We analyse patterns of skull shape variation in two New World monkey groups: capuchins and howlers. These two monophyletic clades are exceptionally similar in terms of the geographic distribution of their species. Yet, their body size and diet are different: howler monkeys are large and almost exclusively folivorous, whereas capuchins are small omnivorous. We found that the size, and direction of vectors of phenotypic changes across South American biomes in those clades are not statistically different. This similarity persists after removing the strong impact of allometry in our data. Additionally, partial least squares and comparative analyses confirm that "allometry free" skull shape is influenced to the same set of environmental variables in both clades. This study remarks the paramount importance of both body size and environmental variation on phenotypic evolution. �� 2013 Springer Science+Business Media New York.