Similar Microglial Cell Densities across Brain Structures and Mammalian Species: Implications for Brain Tissue Function.

Microglial cells play essential volume-related actions in the brain that contribute to the maturation and plasticity of neural circuits that ultimately shape behavior. Microglia can thus be expected to have similar cell sizes and even distribution both across brain structures and across species with different brain sizes. To test this hypothesis, we determined microglial cell densities (the inverse of cell size) using immunocytochemistry to Iba1 in samples of free cell nuclei prepared with the isotropic fractionator from brain structures of 33 mammalian species belonging to males and females of five different clades. We found that microglial cells constitute ∼7% of non-neuronal cells in different brain structures as well as in the whole brain of all mammalian species examined. Further, they vary little in cell density compared with neuronal cell densities within the cerebral cortex, across brain structures, across species within the same clade, and across mammalian clades. As a consequence, we find that one microglial cell services as few as one and as many as 100 neurons in different brain regions and species, depending on the local neuronal density. We thus conclude that the addition of microglial cells to mammalian brains is governed by mechanisms that constrain the size of these cells and have remained conserved over 200 million years of mammalian evolution. We discuss the probable consequences of such constrained size for brain function in health and disease.SIGNIFICANCE STATEMENT Microglial cells are resident macrophages of the CNS, with key functions in recycling synapses and maintaining the local environment in health and disease. We find that microglial cells occur in similar densities in the brains of different species and in the different structures of each individual brain, which indicates that these cells maintain a similar average size in mammalian evolution, suggesting in turn that the volume monitored by each microglial cell remains constant across mammals. Because the density of neurons is highly variable across the same brain structures and species, our finding implies that microglia-dependent functional recovery may be particularly difficult in those brain structures and species with high neuronal densities and therefore fewer microglial cells per neuron.

Comparative morphology and scaling of the femur in yangochiropteran bats.

Better known by their remarkable forelimb morphology, bats are also unique among mammals with respect to their hindlimbs. Their legs are rotated through 180°, generally reduced in size, and in some extant taxa particular bones (e.g. fibula) can even be absent. The femur is the main leg bone, but to date few bat studies have considered its morphology in detail, none in a wide-scale comparative study. Yangochiroptera is the largest bat taxon, spans nearly three orders of magnitude in body mass, and is highly diverse both in ecology and behavior, representing a good model for comparative analyses. Here, we describe the anatomy of the femur in a large sample of yangochiropteran bats (125 species, 70 genera, and 12 families), and explore major trends of morphological variation and scaling patterns in this bone. We used 13 categorical characters in the anatomical description and five linear dimensions in the quantitative analyses. Based on the categorical data, each family studied here was diagnosed, and those from the Neotropical region were included in an identification key. From the phylogenetic principal component analysis (pPCA) we showed that, in addition to size, major axes of variation in bat femur are related to robusticity and head morphology, features that are clearly distinct among some families. We also generated a phylomorphospace based on pPCA scores, highlighting convergences in femur shape. Molossidae, Mystacinidae, and Desmodontinae were grouped based on their greater robusticity, a pattern that was also recovered from categorical data. In these families, we found anatomical features (e.g. presence of tubercles and posterior ridges on the greater trochanter, long or medially/distally displaced lateral ridges on the shaft) that are well-known from their functional link with quadrupedal locomotion. Using phylogenetic regressions, we found out that compared with body mass, femur length scaled with negative allometry, as expected, but that femur width scaled isometrically, counter to expectations. As a result, robusticity index (the ratio of width to length), scaled with positive allometry - larger bats tended to have more robust hindlimbs. At species level, our most remarkable finding was related to Myotis simus, which presented the most robust femur (for its size) among yangochiropterans. Our results reinforce the informative potential of the chiropteran femur from both taxonomic and functional perspectives. Furthermore, the allometric trends seen in this bone may help understand the strategies adopted by flying vertebrates to deal with the high energetic cost of flight and, at the same time, evolve diversified foraging behaviors.

Cellular Scaling Rules for the Brains of Marsupials: Not as "Primitive" as Expected.

In the effort to understand the evolution of mammalian brains, we have found that common relationships between brain structure mass and numbers of nonneuronal (glial and vascular) cells apply across eutherian mammals, but brain structure mass scales differently with numbers of neurons across structures and across primate and nonprimate clades. This suggests that the ancestral scaling rules for mammalian brains are those shared by extant nonprimate eutherians - but do these scaling relationships apply to marsupials, a sister group to eutherians that diverged early in mammalian evolution? Here we examine the cellular composition of the brains of 10 species of marsupials. We show that brain structure mass scales with numbers of nonneuronal cells, and numbers of cerebellar neurons scale with numbers of cerebral cortical neurons, comparable to what we have found in eutherians. These shared scaling relationships are therefore indicative of mechanisms that have been conserved since the first therians. In contrast, while marsupials share with nonprimate eutherians the scaling of cerebral cortex mass with number of neurons, their cerebella have more neurons than nonprimate eutherian cerebella of a similar mass, and their rest of brain has fewer neurons than eutherian structures of a similar mass. Moreover, Australasian marsupials exhibit ratios of neurons in the cerebral cortex and cerebellum over the rest of the brain, comparable to artiodactyls and primates. Our results suggest that Australasian marsupials have diverged from the ancestral Theria neuronal scaling rules, and support the suggestion that the scaling of average neuronal cell size with increasing numbers of neurons varies in evolution independently of the allocation of neurons across structures.

Occurrence of leucism in Eira barbara (Carnivora, Mustelidae) in Brazil / Ocorrência de leucísmo em Eira barbara (Carnivora, Mustelidae) no Brasil

Abstract The occurrence of anomalous coloration (albinism, leucism and melanism) in mammals is a rare phenomenon in nature, but this phenomenon has been reported for several species of mammals. In this study, we report on the occurrence of leucism in Eira barbara by examining three road-killed individuals and two sightings of live animals in Reserva Particular do Patrimônio Natural Santuário do Caraça, southeastern Brazil. In addition, we examined tayra specimens housed in mammal collections from Brazil and USA. The animals found dead and those sighted had a whitish yellow fur on the body and head, resulting in lighter coloration than the coloring pattern commonly observed in tayras. Despite these lighter color pattern, the specimens showed parts of soft tissue, such as iris and the skin, with pigmentation very similar to that present in individuals with the typical color pattern. This set of factors indicates the specimens recorded were in fact leucistic and not albino. Among the specimens examined in the scientific collections, we found nine individuals from different localities that presented the whitish yellow color pattern. Some studies attribute the higher frequency of cases of leucism due to small populations and / or with some mechanism of reproductive isolation. Thus, analysis of the genetic variability of populations containing individuals with such characteristics should be considered. On the other hand, the occurrence of polymorphic color phenotype in tayras indicates that hypotheses related to the fixation of recessive characteristics, or on possible environmental adaptive advantages of these phenotypes can be tested.

Resumo A ocorrência de coloração anômala (albinismo, leucísmo e melanismo) em mamíferos é um fenômeno raro na natureza, mas ela tem sido relatada para diversas espécies. Neste trabalho nós relatamos a ocorrência de leucísmo em Eira barbara por meio do exame de três indivíduos encontrados mortos atropelados por veículos e pela visualização direta de indivíduos vivos na Reserva Particular do Patrimônio Natural Santuário do Caraça, sudeste brasileiro. Em adição, nós consultamos coleções de mamíferos em museus do Brasil e dos Estados Unidos da América. Os animais encontrados mortos e os avistados apresentavam pelagem amarela esbranquiçada no corpo e na cabeça, resultando em uma coloração muito mais clara que o padrão de coloração comumente observado em iraras. Apesar deste padrão de coloração mais claro, os espécimes apresentavam partes do tecido mole, tais como a íris e a pele, com pigmentação muito semelhante àquela presente em indivíduos com padrão de coloração típico da espécie. Este conjunto de fatores indicou que os espécimes registrados eram de fato leucísticos e não albinos. Dentre os espécimes examinados nas coleções científicas, nós encontramos nove indivíduos de diferentes localidades que apresentavam o padrão de coloração esbranquiçado. Alguns estudos atribuem a frequência elevada de casos de leucísmo a pequenas populações e / ou com algum mecanismo de isolamento reprodutivo. Dessa forma, análises da variabilidade genética de populações contendo indivíduos com essas características devem ser consideradas. Por outro lado, a ocorrência de fenótipos de coloração polimórficos em iraras indica que hipóteses podem ser testadas tanto com relação à fixação de caraterísticas recessivas, quanto sobre possíveis vantagens adaptativas ambientais desses fenótipos.

Small mammals (Chiroptera, Didelphimorphia, and Rodentia) from Jaíba, middle Rio São Francisco, northern Minas Gerais State, Brazil / Pequenos mamíferos (Chiroptera, Didelphimorphia, and Rodentia) de Jaíba, médio Rio São Francisco, norte do estado de Minas Gerais, Brasil

We report the results of small mammals inventories conducted in the region of Jaíba, northern Minas Gerais state, southeastern Brazil, from 1990 to 1995. This region is located in the southern limit of the Caatinga biome, and harbors a unique set of natural ecosystems and extensive agricultural areas. With a total effort of 2964 trap-nights and 44 net sessions, we captured 893 small mammals from 46 species, including four marsupials, 13 rodents, and 29 bats. We report on species that are endemic to the Caatinga (Wiedomys pyrrhorhinos and Xeronycteris vieirai), and species that are new to the mammal fauna of the state of Minas Gerais (Tonatia saurophila, X. vieirai, and Myotis lavali). We also provide the first valid voucher-supported record of Micronycteris sanborni from southeastern Brazil, and extend the known range of X. vieirai 800 km southward. All bats highlighted here as endemic or representing new records were associated to limestone outcrops, suggesting that preservation of this kind of habitat may be particularly relevant to the conservation of these mammals.

Reportamos os resultados de inventários de pequenos mamíferos conduzidos na região de Jaíba, norte de Minas Gerais, sudeste do Brasil, entre 1990 e 1995. Essa região está localizada no limite sul do bioma Caatinga, e abriga um conjunto único de ecossistemas naturais e extensas áreas cultivadas. Com um esforço total de 2964 armadilhas-noite e 44 sessões de captura com redes de neblina, nós capturamos 893 pequenos mamíferos, que permitiram a identificação de 46 espécies, incluindo quatro marsupiais, 13 roedores e 29 morcegos. Nós reportamos espécies endêmicas da Caatinga (Wiedomys pyrrhorhinos e Xeronycteris vieirai) e espécies que são novas para a fauna de mamíferos de Minas Gerais (Tonatia saurophila, X. vieirai e Myotis lavali). Nós também fornecemos o primeiro registro válido, com material testemunho, de Micronycteris sanborni para o sudeste do Brasil, e estendemos a distribuição geográfica conhecida de X. vieirai em 800 km na direção sul. Todos os morcegos destacados aqui como endêmicos ou representando novos registros estiveram associados a afloramentos de calcário, sugerindo que a preservação deste tipo de hábitat pode ser particularmente relevante para conservação desses mamíferos.

Morphological variation in the appendicular skeleton of Atlantic Forest sigmodontine rodents.

Rodents of the subfamily Sigmodontinae comprise a highly diversified group in the Atlantic Forest, with semifossorial, terrestrial, semiaquatic, scansorial, and arboreal forms. In this study, we analyzed morphometric variation in humerus, scapula, ulna, radius, femur, tibia, and pelvis to investigate its possible relationship with the different types of locomotion recorded in the literature. Skeletal characters were measured in 321 specimens belonging to 29 species and 19 genera either restricted to or recorded in this ecoregion. Multivariate morphometric analyses (principal component and canonical variate analyses) arranged individuals of different genera in groups congruent with the different types of locomotion. This arrangement was more clearly defined when analyses included only forelimb measurements, indicating that most of the variation in appendicular traits associated with the different locomotor modes occurs in the forelimb skeleton. Semifossorial forms exhibited the most distinct appendicular morphology, as well as the greatest frequency of endemism among analyzed species. These results suggest that this mode of locomotion led to greater differentiation in semifossorial Atlantic forest sigmodontines than in terrestrial and arboreal forms, which were found to have more subtle differentiation and fewer endemics. Scansorial species could not be set apart from terrestrial ones in terms of appendicular morphology, suggesting that these two modes of locomotion are the most similar and generalized for the group, as they occur in most lineages in the subfamily. The results of this study corroborate previous observations on the relevance of appendicular characters in the differentiation of species and genera in the subfamily Sigmodontinae.

Anticuerpos naturales contra proteínas propias y no propias de la membrana eritrocitaria / Natural antibodies against self and non-self red cell membrane proteins

Fue observada la presencia de anticuerpos naturales contra las proteínas de la membrana eritrocitaria en sueros de origen humano y animal. Se demuestran, por medio del "Western blot", las reacciones de sueros de conejos adultos contra el estroma de auto-, alo- y xeno-antígenos (humano y mono rhesus) de las membranas de los hematíes. Los sueros de conejo estaban dirigidos principalmente contra las dos espectrinas (alfa + beta) y la proteína banda 3. No hubo reacción contra estromas de tres monos rhesus. Las comparaciones entre sueros tratados y no tratados con ditiotreitol (DTT) sugieren la presencia de anticuerpos IgG. Los animales fueron clasificados de acuerdo con éstas reacciones, mediante el método de agrupamiento UPGMA. Aunque existe cierta variabilidad, probablemente debida a fenómenos estocásticos, los resultados apuntan a un reconocimiento de estructuras químicas similares entre las proteínas banda 3 y entre las espectrinas de los hematíes de conejo, mono rhesus y humanos. Esta amplia reactividad plantea el tema de cuáles serían los epitopos reconocidos por éstos anticuerpos. El presente trabajo incluye también la descripción del peso molecular de las proteínas de la membrana de los hematíes de conejo

Natural selection, morphologic divergence and phenotypic evolution in Proechimys dimidiatus (Rodentia:Echimyidae)

Os modelos da genética quantitativa desenvolvidos por R. Lande (1976, 1979, 1988) foram aplicados em um estudo de diferenciaçäo na morfologia craniana de duas populaçöes do roedor equimídio Proechimys dimidiatus das localidades de Tijuca e Teresópolis no estado do Rio de Janeiro. Foram estimados o gradiente de seleçäo e as intensidades seletivas mínimas necessárias para causar as diferenças observadas entre as duas populaçöes. O vetor de coeficiente de seleçäo mostrou que alguns caracteres cranianos evoluíram na direçäo contrária à força da seleçäo natural que teria atuado para aumentar os valores médios das dimensöes cranianas na populaçäo da Tijuca. A mortalidade seletiva mínima por geraçäo foi baixa (10-3), sugerindo que seleçäo fraca agindo sobre diferenças quantitativas pode explicar as diferenças morfológicas observadas

Application of size-free canonical discriminant analysis to studies of geographic differentiation

A análise discriminante canônica (ADC) é um procedimento empregado em estudos de variaçäo geográfica, diferenciaçäo interespecífica e macroevoluçäo. Todavia, o emprego desta técnica, com organismos nos quais o tamanho dos indivíduos possa variar em funçäo da amostragem, pode originar resultados espúrios, pois a discriminaçäo entre as amostras será um artefato de amostragem. Apresentamos estatisticamente o efeito da variaçäo no tamanho dos indivíduos dentro das amostras. Neste procedimento, o efeito do tamanho é removido calculando a regressäo de cada caráter sobre uma estimativa multidimensional de tamanho, o primeiro componente principal. A análise discriminante canônica é entäo efetuada sobre os resíduos da análise de regressäo. A aplicacäo deste método é ilustrada em uma análise de diferenciaçäo geográfica no roedor Proechimys dimidiatus (Echimydiae). Uma lista de comandos do programa estatístico SAS-PC, necessários para a implementaçäo do método é também fornecida