, Volume 132, Issue 1, pp 87-93
Date: 07 Oct 2012

Is formalin fixation and ethanol preservation able to influence in geometric morphometric analysis? Fishes as a case study

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Geometric morphometric analysis has increased in the recent years, turning into a powerful tool to explore shape and size variation. Several biological studies use specimens that have been through some kind of preservation, mainly formalin preservation, commonly used in biological collections. This study analyzed the effect of preservation in shape on two fish species: Eucinostomus argenteus and Pomadasys corvinaerformis. Twenty-nine individuals of E. argenteus and twenty-five of P. corvinaeformis were collected, photographed twice, preserved in 10 % formalin for 1 week, and then transferred to 70 % ethanol for 83 days. We evaluated three levels of error: (1) error of landmark digitalization, (2) error of taking the picture and storage in JPEG format, and (3) the formalin and ethanol fixation error using Procrustes ANOVA, Discriminant Analysis, and Principal Component Analysis. Significant difference between treatments was observed on both species with Procrustes ANOVA and Discriminant Analysis. In addition, Principal Component Analysis showed a separation between groups of treatment on both species. These results represent the first evidence of preservation effects in studies of geometric morphometrics and show that according to the statistical test utilized, the fixation could affect the shape variations in different ways and could lead the researcher to false results or wrong conclusions. Other methods to explore the shape variation of organisms previously fixed should be tested in order to assess their influence in geometric mophrometric studies.

Communicated by A. Schmidt-Rhaesa.