Search

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.

La massa corporea di un individuo, oltre alla sua morfologia e struttura, è una delle caratteristiche che influisce maggiormente sulla sua ecologia. La variazione della taglia (body size), sia che essa diminuisca o sia che essa aumenti, porta a cambiamenti importanti nell’ecologia della specie: influisce sulla sua “longevità stratigrafica” (per le specie fossili), sulla complessità delle strutture ornamentali, sulla capacità di occupare determinati habitat, sulla grandezza degli areali che possono occupare (range size), sull’abbondanza (densità di individui) che esse possono avere in un determinato areale, sulla capacità di sfruttare le risorse, sul ricambio generazionale, sulla loro capacità di dispersione e conseguentemente sulla capacità di sopravvivere ai mutamenti ambientali (in seguito ai mutamenti si estinguono o tendono a spostarsi per seguire condizioni ecologiche ottimali – habitat tracking). Una delle leggi evolutive meglio note in letteratura riguardo la variazione della taglia è la “regola di Cope” che afferma l’esistenza di un netto trend verso l’aumento della massa corporea delle specie all’interno di un clade nel corso del tempo (Cope 1887). L’aumento della taglia comporta dei vantaggi ecologici maggiori rispetto alle specie più piccole: per esempio hanno un migliore approvvigionamento di risorse, range size più grandi ed una maggiore longevità; affinché tali vantaggi si traducano in una maggiore idoneità evolutiva (Brown and Sibly 2006) essi non devono essere controbilanciati dagli svantaggi che una taglia grande comporta (maggiore fabbisogno energetico (Calder 1996), turnover generazionale più lungo e conseguente minore capacità di resistere ai cambiamenti ambientali a lungo termine). La regola di Cope è stata dimostrata per i mammiferi fossili (Stanley 1973; Alroy 1998; Finarelli 2007) e per i rettili mesozoici (Hone and Benton 2007). Oltre a questi studi che la supportano, evidenze discordanti o inconcludenti derivano da studi effettuati sui primi ruminanti (Gingerich 1974), sui primi amnioti (Laurin 2004), sugli uccelli mesozoici (Butler and Goswami 2008; Hone et al. 2008) e sui mammiferi viventi (Clauset and Erwin 2008, Monroe and Bokma 2010). La regola di Cope rappresenta un trend evoluzionistico a larga scala e possono essere avanzate due tipi di spiegazioni opposte: o è generata da un meccanismo passivo (passive drive) o è guidata dalla selezione (active drive; Mc Shea 1994; Wagner 1996). L’ipotesi della passive drive raffigura l’evoluzione della taglia come una via di diffusione dal limite inferiore di una taglia minima (Stanley 1973; Gould 1988; Clauset and Erwin 2008). Per esempio, la passive drive ipotizza, da osservazioni empiriche, l'esistenza di un limite inferiore di 2g per la taglia dei mammiferi (Clauset and Erwin 2008). A causa di tale limite, l'evoluzione favorirebbe specie di grandi dimensioni (Stanley 1973; Clause and Erwin 2008). All’opposto, l’ipotesi dell’active drive considera i vantaggi competitivi derivanti da una grande taglia come causa primaria della regola di Cope (Kingsolver and Pfennig 2004; Hone and Benton 2005). L’ipotesi dell’active drive assume che le specie durante il tempo siano sostituite da quelle più grandi, più comuni, geograficamente più diffuse e relativamente più longeve. Considerando che il range size e la commonnes (quanto è presente una specie in una data località fossilifera) sono segni evidenti del successo ecologico di una specie, la longevità filetica è qui assunta come il naturale risultato di questo successo nel tempo evolutivo (Wilson 1987; Jablonski and Hunt 2006). I mutamenti climatici modificano gli habitat e questo guida le specie verso condizioni sub-ottimali. Le risposte delle specie possono variare da un adattamento alle nuove condizioni, alla dispersione verso territori con condizioni più simili al loro habitat naturale (habitat tracking), oppure può prevedere l’estinzione. Evidenze paleontologiche suggeriscono che la maggior parte delle specie mantiene la tolleranza ai cambiamenti ambientali quasi costante durante la loro esistenza (Brett et al. 2007, Lister 2004). Ciò è particolarmente vero per gli organismi di taglia grande, che potrebbero non essere in grado di evolvere abbastanza velocemente per stare al passo con i cambiamenti ambientali a causa dei loro lunghi tempi generazionali (Blois and Hadly 2009). Habitat tracking ed estinzione sono, quindi, due reazioni molto importanti ai grandi mutamenti ambientali in particolare per le specie di taglia grande. L’habitat tracking è stato ampiamente documentato nei mammiferi cenozoici su larga scala e nei ripetuti eventi di raffreddamento globale (Blois and Hadly 2009, Hewitt 2000). E’ noto che nel tardo Pleistocene i mammiferi si spostano ripetutamente da nord a sud (e viceversa) a seguito delle glaciazioni (Cardillo et al. 2005). La vulnerabilità delle specie alle estinzioni dipende in larga misura, dalle loro caratteristiche biologiche ed ecologiche, in particolare dalla taglia (Payne and Finnegan 2007), dal range size geografico (Liow et al. 2009) e dalla loro specializzazione ecologica (Raia et al. 2011). Di fronte ad un cambiamento ambientale, le specie in grado di disperdersi su lunghe distanze per seguire i loro habitat preferiti possono avere maggiori possibilità rispetto a quelle che possono disperdersi su distanze minori (Eldredge et al. 2005, Eldredge 2003). Nel mio lavoro presento, oltre ad un attenta analisi del trend di aumento di taglia dei mammiferi durante il Cenozoico, un’analisi paleobiologica dell’effetto dell’habitat tracking sulla durata delle specie e sulla loro tendenza alla stasi morfologica. Ho usato porzioni di range dove le specie sono più comuni rispetto ai successivi intervalli di tempo per verificare se le specie che si spostano su lunghe distanze presentano una maggiore durata stratigrafica. Ho testato poi la correlazione tra distanza percorsa e variazione morfologica all’interno dei cladi. Inoltre ho analizzato l’andamento dei tassi di evoluzione fenotipica e tassonomica dei mammiferi lungo il Cenozoico e l’influenza della regola di Cope sulla complessità delle strutture ornamentali.

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 .

Animal clades tend to follow a predictable path of waxing and waning during their existence, regardless of their total species richness or geographic coverage. Clades begin small and undifferentiated, then expand to a peak in diversity and range, only to shift into a rarely broken decline towards extinction. While this trajectory is now well documented and broadly recognised, the reasons underlying it remain obscure. In particular, it is unknown why clade extinction is universal and occurs with such surprising regularity. Current explanations for paleontological extinctions call on the growing costs of biological interactions, geological accidents, evolutionary traps, and mass extinctions. While these are effective causes of extinction, they mainly apply to species, not clades. Although mass extinctions is the undeniable cause for the demise of a sizeable number of major taxa, we show here that clades escaping them go extinct because of the widespread tendency of evolution to produce increasingly specialised, sympatric, and geographically restricted species over time.

Understanding the effect of climate on the composition of communities and its change over time and space is one of the major aims in ecology and paleoecology. Herein, we tackled on this issue by studying late Quaternary large mammal paleocommunities of Eurasia. The late Quaternary was a period of strong environmental instability, especially characterized by the occurrence of the last glacial maximum (LGM). We used community phylogenetics and joint species distribution models in order to understand the factors determining paleocommunity composition in the late Quaternary. Our results support the existence of strong climatic selection operating on the LGM fauna, both through the disappearance of warm-adapted species such as Elephas antiquus, Hippopothamus amphibious, and Stephanorhinus hemitoechus, and by setting the stage for the existence of a community characterized by cold-adapted large mammals. Patterns of abundance in the fossil record, co-occurrence between species pairs, and the extent of climatic forcing on faunal composition, differ between paleocommunities, but not between extinct and extant species, which is consistent with the idea that climate change, rather than the presence of humans, exerted a major effect on the survival of the late Quaternary megafauna. © 2016 Elsevier Ltd

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.

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. © 2015 The Society for the Study of Evolution.

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.

Species response to environmental change may vary from adaptation to the new conditions, to dispersal towards territories with better ecological settings (known as habitat tracking), and to extinction. A phylogenetically explicit analysis of habitat tracking in Caenozoic large mammals shows that species moving over longer distances during their existence survived longer. By partitioning the fossil record into equal time intervals, we showed that the longest distance was preferentially covered just before extinction. This supports the idea that habitat tracking is a key reaction to environmental change, and confirms that tracking causally prolongs species survival. Species covering longer distances also have morphologically less variable cheek teeth. Given the tight relationship between cheek teeth form and habitat selection in large mammals, this supports the well-known, yet little tested, idea that habitat tracking bolsters morphological stasis.

A classic question in evolutionary biology concerns the tempo and mode of lineage evolution. Considered variously in relation to resource utilization, intrinsic constraints or hierarchic level, the question of how evolutionary change occurs in general has continued to draw the attention of the field for over a century and a half. Here we use the largest species-level phylogeny of Coenozoic fossil mammals (1031 species) ever assembled and their body size estimates, to show that body size and taxonomic diversification rates declined from the origin of placentals towards the present, and very probably correlate to each other. These findings suggest that morphological and taxic diversifications of mammals occurred hierarchically, with major shifts in body size coinciding with the birth of large clades, followed by taxonomic diversification within these newly formed clades. As the clades expanded, rates of taxonomic diversification proceeded independently of phenotypic evolution. Such a dynamic is consistent with the idea, central to the Modern Synthesis, that mammals radiated adaptively, with the filling of adaptive zones following the radiation.