RESUMEN
OBJECTIVES: Skeletal asymmetries reflect developmental stability and mechanical, functional, and physiological influences on bone growth. In humans, researchers have documented the greatest limb bone bilateral asymmetry in diaphyseal breadths, with less asymmetry in articular and maximum length dimensions. However, it remains unclear as to whether the pattern observed for humans is representative of nonhuman primates, wherein bilateral loading may minimize directional asymmetry. This study adds to the small body of asymmetry data on nonhuman primates by investigating patterns of long bone asymmetry in a skeletal sample of Saguinus oedipus (cotton-top tamarin). MATERIALS AND METHODS: Humeri, radii, ulnae, femora, and tibiae of 76 adult captive cotton-top tamarin skeletons (48 males, 28 females) were measured bilaterally. We included maximum length, midshaft diaphyseal breadths, and at least one articular measurement for each bone to assess directional (DA) and fluctuating asymmetry (FA) in each dimension. RESULTS: Most dimensions exhibit significant FA, and very few have significant DA; DA is limited to the lower limb, especially in knee dimensions. Overall, the magnitudes of asymmetry in tamarins have a consistent ranking that follows the same pattern as found in humans. DISCUSSION: This first study of DA and FA among multiple dimensions throughout the limbs of a non-hominoid primate suggests that previously-reported patterns of human bilateral asymmetry are not exclusive to humans. The results further indicate potential underlying differences in constraints on variation within limb bones. While processes shaping variation await further study, our results argue that different long bone dimensions may reflect dissimilar evolutionary processes.
Asunto(s)
Huesos/anatomía & histología , Huesos/patología , Saguinus/anatomía & histología , Animales , Antropología Física , Femenino , MasculinoRESUMEN
Quatro clones do pulgão Myzus persicae (Sulzer) foram utilizados para se avaliar a magnitude de suas respostas plásticas em sete condições de temperatura 15,0; 17,5; 20,0; 22,5; 25,0; 27,5 e 30,0°C. Um índice multivariado de tamanho foi obtido por ACP, a partir de cinco caracteres morfológicos. Quatro desses caracteres foram medidos bilateralmente para quantificação da Assimetria Flutuante (AF). A fecundidade foi estimada pelo número de ninfas presentes do trato reprodutivo das fêmeas. A variabilidade atribuída aos componentes ambientais e genéticos de variação foi estimada com o auxílio de um modelo de genética quantitativa. A maior parte da variabilidade fenotípica morfológica na população estudada ocorreu como resposta à temperatura (componente ambiental), mas componentes genéticos de variação também foram detectados. Acredita-se que o potencial plástico descrito seja adaptativo, contudo um ambiente a 30°C não permitiu a sobrevivência. Pequena variabilidade no comprimento do rostro com relação aos demais caracteres pode ter resultado de seleção estabilizadora, considerando seu valor adaptativo para a obtenção de alimento. Os pulgões apresentaram AF em alguns dos caracteres medidos. Entretanto, não foi detectada relação linear dos níveis de AF com valores de temperatura, nem houve um padrão geral de variação para este caráter. Os dados corroboram a hipótese de que adversidades do meio afetam mais efetivamente o tamanho dos organismos e que, portanto, este seria um indicativo de estresse mais eficiente do que a AF de um caráter propriamente dito.
Four clones of the aphid Myzus persicae (Sulzer) were used to assess the magnitude of their responses to seven different temperatures (15.0, 17.5, 20.0, 22.5, 25.0, 27.5 and 30.0°C). A multivariate index of size was obtained using five morphological characteristics simplified by PCA. Among these characteristics, four were measured bilaterally both sides in order to evaluate the fluctuating asymmetry (FA). Fertility was estimated according to the number of nymphs in the reproductive female apparatus. The variability attributed to the environmental and genetic components was estimated using a genetic quantitative model. A large part of the total variability found for size distribution was attributed to differences in temperature (environmental component), but genetic components of variation were also detected. The plastic potential was considered adaptive, since it increases clone survival in unstable environments and allows new habitat exploitation. However, 30°C temperature did not permit clone development and survival. Lower variability in one morphological character, the rostrum, in comparison with the other traits may be the result of a stabilizing selection, in relation to its adaptive value to obtain food. The aphids presented FA in some of the measured characteristics. However, no linear relation was detected for the levels of FA and temperature values and no general pattern of variability was found. The data corroborate the hypothesis that size is more effectively affected than FA by external influences, and consequently, is a much more efficient indicator of environmental stress.
RESUMEN
Phenotypic variations on developmental period, size and fluctuating asymmetry (FA) of Musca domestica L., induced by larval competition for food were described and correlated. Ten densities, varying from 100 to 1000 larvae per 75 g of wheat medium, were established in the laboratory and observed until adult emergence. The adjusted curve of survival was similar to a hyperbola. The developmental period extended with increasing densities, and the size was inversely proportional to the degree of larval crowding. Males and females responded differently to the selection pressures of competition, being size of the males much more variable than those of the females. Although morphological and physiological adjustments caused by environmental interaction were detected, the levels of fluctuating asymmetry remained invariable. Genetic correlation between these types of phenotypic variation was not detected. It can be supposed, however, that levels of FA, which are stress indicative, were minimized by the considerably plastic potential of the species. Thus, physiological and morphological adjustments reduced developmental difficulties and promoted survival of a greater number of individuals.
Foram descritas e correlacionadas as variações fenotípicas no período de desenvolvimento, tamanho e variações causadas por assimetria flutuante em Musca domestica L., induzidas por seleção para competição larval por alimento. Dez densidades de 100 a 1000 larvas por 75 g de farelo de trigo umedecido foram estabelecidas em laboratório e acompanhadas até a emergência dos adultos. A curva ajustada de sobrevivência foi semelhante a uma hipérbole. O período de desenvolvimento se estendeu com o aumento da densidade, mas o tamanho foi inversamente proporcional ao grau de agregação larval. Machos e fêmeas respondem de modo distinto às pressões de seleção para competição, sendo machos mais variáveis que fêmeas quanto ao tamanho. Embora ajustes morfológicos e fisiológicos provocados por ação ambiental tenham sido detectados, os níveis de assimetria flutuante permaneceram invariáveis. Não foram, portanto, detectadas correlações genéticas entre estes tipos de variações fenotípicas. Pode-se supor, entretanto, que níveis de assimetria flutuante, que podem ser indicativos de estresse, tenham sido minimizados pelo grande potencial plástico da espécie. Assim, ajustes fisiológicos e morfológicos estariam diminuindo dificuldades no desenvolvimento e promovendo a sobrevivência de maior número de indivíduos.