Rate of evolutionary change in cranial morphology of the marsupial genus Monodelphis is constrained by the availability of additive genetic variation.

We tested the hypothesis that the rate of marsupial cranial evolution is dependent on the distribution of genetic variation in multivariate space. To do so, we carried out a genetic analysis of cranial morphological variation in laboratory strains of Monodelphis domestica and used estimates of genetic covariation to analyse the morphological diversification of the Monodelphis brevicaudata species group. We found that within-species genetic variation is concentrated in only a few axes of the morphospace and that this strong genetic covariation influenced the rate of morphological diversification of the brevicaudata group, with between-species divergence occurring fastest when occurring along the genetic line of least resistance. Accounting for the geometric distribution of genetic variation also increased our ability to detect the selective regimen underlying species diversification, with several instances of selection only being detected when genetic covariances were taken into account. Therefore, this work directly links patterns of genetic covariation among traits to macroevolutionary patterns of morphological divergence. Our findings also suggest that the limited distribution of Monodelphis species in morphospace is the result of a complex interplay between the limited dimensionality of available genetic variation and strong stabilizing selection along two major axes of genetic variation.

Punçäo de tireóide: valor da associaçäo de duas técnicas / Thyroid biopsy: value of the association of two techniques

Os nódulos tireoidianos têm elevada prevalência na populaçäo geral. O objetivo desse estudo foi avaliar o grau de associaçäo das técnicas de punçäo aspirativa e näo-aspirativa e comparar a citologia obtida pelas duas técnicas. Foram selecionados 61 pacientes portadores de nódulo tireoidiano, que foram submetidos à punçäo pelas duas técnicas, guiadas por ultra-sonografia. Os esfregaços foram analisados por dois citopatologistas independentes, conforme 5 critérios que avaliam a qualidade do material. Näo houve diferença significativa entre as técnicas quanto à soma dos pontos dos critérios, quando estes foram analisados juntos ou isoladamente (p>0,05). A concordância entre as técnicas foi muito baixa (k=0,13). Näo houve diferença entre as técnicas quando foram comparadas as somas dos critérios conforme os dois patologistas (p>0,05). A técnica näo-aspirativa foi superior à técnica aspirativa nos nódulos hiperecogênicos (p<0,05). As técnicas fornecem material de qualidade semelhante e a associaçäo das duas técnicas diminui falhas diagnósticas.