Análise comparativa entre técnicas morfométricas aplicadas a Odontesthes bonariensis (Valenciennes) e Odontesthes humensis De Buen (Osteichthyes, Atherinopsidae) Comparative analysis among two different morphometric techniques used in Odontesthes bonariensis and Odontesthes humensis (Atherinopsidae)

<abstract language="eng">The objective of this study was to compare two different morphometric methodologies - traditional measurements and truss networks - based on two species of silversides, Odontesthes bonariensis (Valenciennes, 1835) and O. humensis De Buen, 1953, to determine which of the methods results in more reliable distinction between groups. The traditional measures do not represent the true fish form because it does not take into account alometric variations or distinct growth stages. The measures with truss networks extend over the fish form thoroughly resulting in complete representation of the fish's body when homologous morphologic points are connected. The two sets of measures used in the principal components analysis resulted in two groups. The first principal component presented similar positive coefficients, being interpreted as a variation of "size", due to different stages of fish growth. The second component presented positive and negative coefficients, with different values that were interpreted as changes in the "shape" of the organisms. As the groups overlapped partially on the second component axis (the one that represents shape), data were adjusted to exclude the size effect. The first component, then, presented positive and negative coefficients that were related to changes in the shape of organisms. The variables with positive coefficients were related to the anterior area of the body, while the negative coefficients were associated with the caudal peduncle. These variables were the same ones found in both the adjusted and non-adjusted analysis. This study showed that measures with truss networks represented more clearly the difference between groups of O. bonariensis and O. humensis, than with the traditional measures

Orthogonal projections and bootstrap resampling procedures in the study of infraspecific variation

The effect of an increase in quantitative continuous characters resulting from indeterminate growth upon the analysis of population differentiation was investigated using, as an example, a set of continuous characters measured as distance variables in 10 populations of a rodent species. The data before and after correction for allometric size effects using orthogonal projections were analyzed with a parametric bootstrap resampling procedure applied to canonical variate analysis. The variance component of the distance measures attributable to indeterminate growth within the populations was found to be substantial, although the ordination of the populations was not affected, as evidenced by the relative and absolute positions of the centroids. The covariance pattern of the distance variables used to infer the nature of the morphological differences was strongly influenced by indeterminate growth. The uncorrected data produced a misleading picture of morphological differentiation by indicating that groups of populations differed in size. However, the data corrected for allometric effects clearly demonstrated that populations differed morphologically both in size and shape. These results are discussed in terms of the analysis of morphological differentiation among populations and the definition of infraspecific geographic units.<br>A influência do aumento em caracteres quantitativos contínuos devido ao crescimento indeterminado sobre a análise de diferenciação entre populações foi investigado utilizando como exemplo um conjunto de dados de variáveis craniométricas em 10 populações de uma espécie de roedor. Dois conjuntos de dados, um não corrigido para o efeito alométrico do tamanho e um outro corrigido para o efeito alométrico do tamanho utilizando um método de projeção ortogonal, foram analisados por um procedimento "bootstrap" de reamostragem aplicado à análise de variáveis canônicas. O componente de variância devido ao crescimento indeterminado dentro das populações foi significativo para a maioria das medidas de distâncias, o que não influenciou a ordenação das populações, conforme evidenciado pela posição relativa dos centróides. O padrão de covariância entre as variáveis de distância que foi utilizado para inferir a natureza das diferenças morfológicas foi, no entanto, fortemente influenciado pela variação nas medidas de distâncias dentro das populações. O conjunto de dados não corrigido resultou em uma interpretação errônea sobre a natureza da diferenciação morfológica, sugerindo que as populações diferiram somente em tamanho. O conjunto de dados corrigido para o efeito alométrico, por sua vez, demonstrou claramente que as populações diferiram, não somente no tamanho, mas também na forma. Os resultados são discutidos em termos da diferenciação das populações em forma e tamanho no contexto da definição das unidades geográficas infraspecíficas