An organism is built through a series of contingent factors, yet it is determined by historical, physical, and developmental constraints. A constraint should not be understood as an absolute obstacle to evolution, as it may also generate new possibilities for evolutionary change. Modularity is, in this context, an important way of organizing biological information and has been recognized as a central concept in evolutionary biology bridging on developmental, genetics, morphological, biochemical, and physiological studies. In this article, we explore how modularity affects the evolution of a complex system in two mammalian lineages by analyzing correlation, variance/covariance, and residual matrices (without size variation). We use the multivariate response to selection equation to simulate the behavior of Eutheria and Metharia skulls in terms of their evolutionary flexibility and constraints. We relate these results to classical approaches based on morphological integration tests based on functional/developmental hypotheses. Eutherians (Neotropical primates) showed smaller magnitudes of integration compared with Metatheria (didelphids) and also skull modules more clearly delimited. Didelphids showed higher magnitudes of integration and their modularity is strongly influenced by within-groups size variation to a degree that evolutionary responses are basically aligned with size variation. Primates still have a good portion of the total variation based on size; however...

Despite the fact that heterochronic processes seem to be an important process determining morphological evolution of the delphinid skull, previous workers have not found allometric scaling as relevant factor in the differentiation within the genus Sotalia. Here we analyzed the skull ontogeny of the estuarine dolphin S. guianensis and investigate differential growth and shape changes of two cranial regions the neurocranium and the face in order to evaluate the relevance of cranial compartmentalization on the ontogeny of this structure. Our results show that, even though both cranial regions stop growing at adulthood, the face has higher initial growth rates than the neurocranium. The rate of shape changes is also different for both regions, with the face showing a initially higher, but rapidly decreasing rate of change, while the neurocranium shows a slow decreasing rate, leading to persistent and localized shape changes throughout adult life, a pattern that could be related to epigenetic regional factors. The pattern of ontogenetic shape change described here is similar to those described for other groups of Delphinidae and also match intra and interspecific variation found within the family, suggesting that mosaic heterochrony could be an important factor in the morphological evolution of this group. (C) 2012 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.; CAPES; CAPES; FAPESP; FAPESP [07/52144-5...

As bases moleculares da diversidade fenotipica dentro de espécies são de grande interesse aos biólogos evolutivos porque a evolução morfológica adaptival depende da seleção de variantes genéticas. Entretanto, há poucos exemplos da variação fenotípica cuja a base molecular é compreendida, especialmente entre animais vertebrados. Biólogos em geral concordam que o processo da seleção natural é a fonte predominante de diversificação morfológica. Tem sido documentado previamente que existe diversificação adaptativa da morfologia craniana entre os taxa mais elevados de Platyrrhini e também em espécies e em muitos géneros, que aparentemente diversificaram na morfologia do crânio por seleção natural. O hormônio de crescimento (GH) é um hormônio multifunctional, produzido principalmente pela glândula pituitária de todos os animais vertebrados para regular o metabolismo e para promover o crescimento pos-natal linear. A evolução molecular do GH foi estudada extensivamente em um grande número espécies de vertebrados, incluindo primatas. A evolução rápida do gene do GH em primatas, especiamente em regiões funcionalmente importantes, sugere a seleção darwiniana positiva. Entretanto, o relaxamento da seleção purificadora depois de múltiplas duplicações do locus GH não podem ser descartadas. O objetivo deste estudo era investigar a evolução molecular do gene do GH em primatas neotropicais...

Este trabalho busca entender a diversificação craniana dos macacos do Velho Mundo (Catarrhini) integrando duas abordagens para o estudo da evolução de caracteres complexos: a genética quantitativa e a integração morfológica. A investigação tem três objetivos principais: 1) comparar a magnitude e o padrão das relações entre os caracteres cranianos entre todos os Catarrhini; 2) testar a hipótese de que deriva genética é o único agente responsável pela diversificação craniana; 3) explorar as conseqüências evolutivas da associação entre caracteres. De posse de um banco de dados bastante representativo da diversidade dos macacos do Velho Mundo (39 medidas cranianas de cerca de 6.000 crânios de mais de 130 espécies), gerei as matrizes de correlação e de variância/covariância, que resumem as relações entre os caracteres, e comparei-as entre vários grupos. Comparei-as também a expectativas derivadas de modelos teóricos de evolução por deriva genética, além de simular a ação de seleção natural sobre essas matrizes para observar o comportamento evolutivo dos diversos padrões de associação entre caracteres. De maneira geral, o padrão das relações é o mesmo entre todos os Catarrhini, mas a magnitude com que os caracteres estão associados varia bastante. Isso tem conseqüências evolutivas importantíssimas...

Dentro da biologia evolutiva, uma das questões centrais é a compreensão de como os processos evolutivos, em particular a seleção e o acaso (deriva genética) moldaram a diversidade obervada nos organismos. Dentro deste contexto, a utilização de abordagens como a integração morfológica e a genética quantitativa nos fornecem poderosas ferramentas. Enquanto a primeira descreve os padrões de relação entre caracteres e testa hipóteses sobre as relações de desenvolvimento e/ou funções subjacentes, a segunda possui ferramentas para investigar as forças que podem ter gerado os fenótipos atuais. Utilizando como modelo de estudo os gêneros de marsupiais da Ordem Didelphimorphia, analisei a evolução morfológica craniana unindo estas duas linhas de pesquisa. Central a genética quantitativa está a matriz de covariância genética (G) que descreve a porção da variância que é efetivamente herdada (no sentido de transmissão de valor entre gerações) e conseqüentemente serve como substrato à seleção. Apesar de ter sido desenvolvida inicialmente para estudos em escala microevolutiva, o arsenal matemático da genética quantitativa pode ser estendida a escalas macroevolutivas caso a matriz G permaneça relativamente estável. Entretanto...

As últimas décadas têm apresentado um crescente número de contribuições para o entendimento sobre quando e onde ocorreu o surgimento do Homo sapiens. Modelos baseados nessas evidências, geralmente, sugerem que a gênese dos humanos modernos ocorreu na África, há cerca de 200.000 anos antes do presente, de onde migraram para as outras partes do mundo. Análises da diversidade genética de populações atuais corroboram esse cenário, ao sugerir que, a partir de uma origem única, a espécie foi, gradativamente, perdendo variabilidade à medida que as populações divergiram, espacial e temporalmente, umas das outras e de suas ancestrais africanas. No que se refere especificamente à morfologia craniana, diversos autores sugerem a existência deste mesmo padrão de decréscimo da variabilidade em função do distanciamento em relação a África, embora seja, também, reconhecida entre os especialistas a partição da diversidade craniana humana entre dois padrões fundamentais: um representado pela morfologia similar àquela que caracterizou os primeiros Homo sapiens, antes que o processo de raciação, no sentido de diversificação, tivesse ocorrido, representado pela denominada "morfologia generalizada"; e outro representado pelas demais variações morfológicas...

Dissertação de Mestrado Integrado em Medicina Veterinária, Ciências Veterinárias; A rotura do ligamento cruzado cranial (RLCCr) é uma das principais causas ortopédicas de visita ao veterinário. A rotura tanto pode ser traumática como degenerativa, representando esta última a maioria do casos. Pode ocorrer em animais de qualquer porte, idade ou raça, embora seja mais comum em jovens adultos de raças grandes. Investigações relativas à patogenia RLCCr referem variados mecanismos que conduzem à sua consumação. No entanto, ainda nenhum destes mecanismos mostrou ser transversal aos mais diversos casos de RLCCr, mantendo-se a patogenia indefinida e polémica, acreditando-se que a degenerescência do ligamento cruzado cranial (LCCr) é uma doença multifatorial. Deste modo, o estabelecimento de estratégias preventivas da RLCCr torna-se bastante difícil. Para o diagnóstico de RLCCr recorre-se a métodos simples como o exame físico e exame radiográfico. Os testes de gaveta e de compressão tibial são bastante fiáveis para evidenciar a típica subluxação cranial da tíbia aquando da RLCCr. Em caso de dúvida a artrotomia exploratória é um procedimento muito comum, embora a artroscopia tenha vindo a ganhar muitos apologistas. A decisão terapêutica baseia-se em fatores dependentes do animal...

Dissertação de Mestrado Integrado em Medicina Veterinária; A Ruptura do Ligamento Cruzado Cranial (RLCCr) é uma das entidades clínicas mais comuns do membro posterior do cão, a mais comum do joelho, e a principal responsável pela doença degenerativa articular. A sua origem pode ser traumática ou degenerativa e as duas estão frequentemente interligadas. Os doentes podem apresentar claudicação sem apoio ou com apoio parcial do pé, apresentando vários graus de dor à manipulação da articulação, exibindo todos eles o movimento cranial da tíbia (sinal de báscula) patognomónico da doença. Os testes de gaveta e de compressão tibial são ambos recomendados como primeira escolha no diagnóstico de RLCCr, devendo ser realizados em flexão, no ângulo normal de apoio e em extensão. A terapêutica pode ser conservativa ou cirúrgica, e o sucesso depende essencialmente do restabelecimento da estabilidade articular. A escolha da terapêutica deve depender da claudicação, peso e função do paciente, experiência do clínico, equipamento disponível, existência de patologia concomitante e da resposta de tratamento anterior. Uma recuperação de sucesso deve incluir a capacidade do paciente em conseguir sentar-se com flexão completa do joelho...

Contemporary studies of vertebrate cranial development document the essential role played by the embryonic neural crest as both a source of adult tissues and a locus of cranial form and patterning. Yet corresponding and basic features of cranial evolution, such as the extent of conservation vs. variation among species in the contribution of the neural crest to specific structures, remain to be adequately resolved. Investigation of these features requires comparable data from species that are both phylogenetically appropriate and taxonomically diverse. One key group are amphibians, which are uniquely able to inform our understanding of the ancestral patterns of ontogeny in fishes and tetrapods as well as the evolution of presumably derived patterns reported for amniotes. Recent data support the hypothesis that a prominent contribution of the neural crest to cranial skeletal and muscular connective tissues is a fundamental property that evolved early in vertebrate history and is retained in living forms. The contribution of the neural crest to skull bones appears to be more evolutionarily labile than that of cartilages, although significance of the limited comparative data is difficult to establish at present. Results underline the importance of accurate and reliable homology assessments for evaluating the contrasting patterns of derivation reported for the three principal tetrapod models: mouse...

The means by which various microevolutionary processes have acted in the past to produce patterns of cranial variation that characterize modern humans is not thoroughly understood. Applying a microevolutionary framework, within- and among-population variance/covariance (V/CV) structure was compared for several functional and developmental modules of the skull across a worldwide sample of modern humans. V/CV patterns in the basicranium, temporal bone, and face are proportional within and among groups, which is consistent with a hypothesis of neutral evolution; however, mandibular morphology deviated from this pattern. Degree of intergroup similarity in facial, temporal bone, and mandibular morphology is significantly correlated with geographic distance; however, much of the variance remains unexplained. These findings provide insight into the evolutionary history of modern human cranial variation by identifying signatures of genetic drift, gene flow, and migration and set the stage for inferences regarding selective pressures that early humans encountered since their initial migrations around the world.

Cranial neurogenic placodes and the neural crest make essential contributions to key adult characteristics of all vertebrates, including the paired peripheral sense organs and craniofacial skeleton. Neurogenic placode development has been extensively characterized in representative jawed vertebrates (gnathostomes) but not in jawless fishes (agnathans). Here, we use in vivo lineage tracing with DiI, together with neuronal differentiation markers, to establish the first detailed fate-map for placode-derived sensory neurons in a jawless fish, the sea lamprey Petromyzon marinus, and to confirm that neural crest cells in the lamprey contribute to the cranial sensory ganglia. We also show that a pan-Pax3/7 antibody labels ophthalmic trigeminal (opV, profundal) placode-derived but not maxillomandibular trigeminal (mmV) placode-derived neurons, mirroring the expression of gnathostome Pax3 and suggesting that Pax3 (and its single Pax3/7 lamprey ortholog) is a pan-vertebrate marker for opV placode-derived neurons. Unexpectedly, however, our data reveal that mmV neuron precursors are located in two separate domains at neurula stages, with opV neuron precursors sandwiched between them. The different branches of the mmV nerve are not comparable between lampreys and gnatho-stomes...

Abstract: Archosauria, the "ruling reptiles," characterized along their stem by relatively large, macrocarnivorous animals, are today represented by two enormously successful but divergent extant clades: Aves, the birds, and Crocodylia, the crocodiles and alligators. This thesis seeks to characterize major transformations in the cranial region of archosaurs, a prominent theme in their evolution.

Background: Which factors influence the distribution patterns of morphological diversity among clades? The adaptive radiation model predicts that a clade entering new ecological niche will experience high rates of evolution early in its history, followed by a gradual slowing. Here we measure disparity and rates of evolution in Carnivora, specifically focusing on the terrestrial-aquatic transition in Pinnipedia. We analyze fissiped (mostly terrestrial, arboreal, and semi-arboreal, but also including the semi-aquatic otter) and pinniped (secondarily aquatic) carnivorans as a case study of an extreme ecological transition. We used 3D geometric morphometrics to quantify cranial shape in 151 carnivoran specimens (64 fissiped, 87 pinniped) and five exceptionally-preserved fossil pinnipeds, including the stem-pinniped Enaliarctos emlongi. Range-based and variance-based disparity measures were compared between pinnipeds and fissipeds. To distinguish between evolutionary modes, a Brownian motion model was compared to selective regime shifts associated with the terrestrial-aquatic transition and at the base of Pinnipedia. Further, evolutionary patterns were estimated on individual branches using both Ornstein-Uhlenbeck and Independent Evolution models...

The relative importance of the two main cranial complexes, the neurocranium and the splanchnocranium, has been examined in the five species of extant hominoids and in a huge sample of extinct hominins using six standard craniometric variables that measure the length, width and height of each cranial module. Factor analysis and two-block partial least squares were used for establishing the major patterns of developmental and evolutionary integration between both cranial modules. The results obtained show that all extant hominoids (including the anatomically modern humans) share a conserved pattern of developmental integration, a result that agrees with previous studies. The pattern of evolutionary integration between both cranial modules in australopiths runs in parallel to developmental integration. In contrast, the pattern of evolutionary and developmental integration of the species of the genus Homo is the opposite, which is probably the consequence of distinctive selective regimes for both hominin groups.

1. The hominid brain has increased approximately three times in size since the Pliocene, but so has the brain of equids. The tripling of hominid brain size has been considered as an indicator of increased mental abilities, as it coincided with the production of tools, weapons and other artefacts of increasing sophistication. No indicators of the increase in equid intelligence are known. Intraspecific correlation between brain size and variously measured 'intelligence' is, in modern humans, very weak if not completely absent. With the exception of size, there are no major differences between the anatomy of ape and human brains. 2. A study of 297 estimates of body height, 626 estimates of bodyweight and 276 estimates of the cranial capacity of hominids dated at various periods over the past 5 million years shows that the increase in hominid brain size was paralleled by an increase in body size. 3. In a sample of 45 variously dated fossil hominids, brain size correlates isometrically with body size. 4. Since the Late Pleistocene (approximately 30,000 years ago), human brain size decreased by approximately 10%; yet again, this decrease was paralleled by a decrease in body size. 5. Therefore, it may be concluded that the gross anatomy of the hominid brain is not related to its functional capabilities. The large human brain:body size ratio may be a result of the structural reduction of the size of the gastrointestinal tract and...

Anatomically, modern humans differ from archaic forms in possessing a globular neurocranium and a retracted face and in cognitive functions, many of which are associated with the temporal lobes. The middle cranial fossa (MCF) interacts during growth and development with the temporal lobes, the midface, and the mandible. It has been proposed that evolutionary transformations of the MCF (perhaps from modification of the temporal lobes) can have substantial influences on craniofacial morphology. Here, we use three-dimensional (3D) geometric morphometrics and computer reconstructions of computed tomography-scanned fossil hominids, fossil and recent modern humans and chimpanzees to address this issue further. Mean comparisons and permutation analyses of scaled 3D basicranial landmarks confirm that the MCF of Homo sapiens is highly significantly different (P < 0.001) from H. neanderthalensis, H. heidelbergensis, and Pan troglodytes. Modern humans have a unique configuration with relatively more anterolateral projection of the MCF pole relative to the optic chiasm and the foramen rotundum. These findings are discussed in the context of evolutionary changes in craniofacial morphology and the origins of modern human autapomorphies. In particular...

This comparison of morphological and neutral genetic variation in 10 human populations was designed to test a neutral hypothesis of cranial evolution in living and recent humans and to explain deviations from neutrality where detected. Overall, among-population differences in extant Homo sapiens cranial morphology are proportional to among-population differences in neutral molecular characteristics. For most of the populations studied, cranial morphology varies among regions in a manner consistent with neutral expectations. Removal of the effects of shared population history and structure by using the partial Mantel's test, however, does not remove the correlation between some aspects of cranial morphology and a measure of coldness of climate. The excess differentiation is most apparent in those population comparisons that involve a Siberian population living in an extremely cold environment. This finding suggests the action of natural selection, associated with regional variation in temperature, leading to among-population differentiation in excess of neutral expectations for some cranial dimensions. Those dimensions reflect the breadth of the skull, cranial vault size and shape, and aspects of nasal morphology. Although morphology for most of the world appears to vary among populations in accordance with neutral expectations in the context of population structure and history...

The vertebrate head and face, one of the defining features of vertebrates, is an evolutionary novelty that enabled the major radiation of Vertebrata. The emergence of the multipotent neural crest cells, often mentioned as the “fourth germ layer”, which produces most of the bone, cartilage and dentine of the vertebrate head, was the key to this innovation. Unlike the appendicular and axial skeletons in the rest of the body, which have relatively uncomplicated anatomy and are generated from cells of mesodermal origin, most of the cranial bones have complex structures generated by a unique mechanism termed intramembranous ossification and originate from the cranial neural crest cells. The unique and innovative nature of the neural crest and cranial bone is also reflected in the morphogenic processes that create diversity in craniofacial shape throughout the course of vertebrate evolution, exemplified in the bird lineage. In this thesis, I seek to expand our knowledge of the development and evolution of craniofacial elements, by developing a 3-D platform to generate cranial bone in vitro and investigating the evolution of beak and tooth loss in birds. In the first chapter, I introduce the first system for generating intramembranous bone with mouse cranial neural crest cells in 3-D hydrogel culture. The flexibility of the platform will allow it to be utilized for generating 3-D cranial bones from neural crest cells using various sources...

Ecosystems are being altered on a global scale by the extirpation of top predators. The ecological effects of predator removal have been investigated widely; however, predator removal can also change natural selection acting on prey, resulting in contemporary evolution. Here we tested the role of predator removal on the contemporary evolution of trophic traits in prey. We utilized a historical introduction experiment where Trinidadian guppies (Poecilia reticulata) were relocated from a site with predatory fishes to a site lacking predators. To assess the trophic consequences of predator release, we linked individual morphology (cranial, jaw, and body) to foraging performance. Our results show that predator release caused an increase in guppy density and a "sharpening" of guppy trophic traits, which enhanced food consumption rates. Predator release appears to have shifted natural selection away from predator escape ability and towards resource acquisition ability. Related diet and mesocosm studies suggest that this shift enhances the impact of guppies on lower trophic levels in a fashion nuanced by the omnivorous feeding ecology of the species. We conclude that extirpation of top predators may commonly select for enhanced feeding performance in prey...