Evaluation of interspecific DNA content variations and sex identification in Falconiformes and Strigiformes by flow cytometric analysis

Abstract

A high interspecific karyotype variability has been evidenced in birds especially in Falconiformes and Strigiformes. Avian cytogenetic analysis, conventionally used for this study, presents several difficulties. We used flow cytometric analysis in order to obtain further information on the DNA patterns of different species of birds belonging to the abovementioned orders. Our study was performed on blood samples while chicken erythrocytes and human lymphocytes, with known cytometric DNA content, were used as reference cells. The blood samples of the birds under study were stained, simultaneously to the reference cell, with a lysis-staining buffer containing propidium iodide. The nuclear DNA content of the bird samples was calculated as DNA index in relation to reference cells, and was expressed as nuclear DNA mass in picograms (pg) with respect to the standard value of 7.0 pg per human lymphocyte nucleus. The results obtained showed an interspecific variability of DNA content and evidenced the usefulness of FCM analysis as a rapid and easy tool for studying the DNA pattern of different species of birds. Moreover, our results have confirmed and extended the possibility of sex identification in species of birds characterized by sexual monomorphism by evaluating the small DNA content difference which exists between males and females. Key terms: DNA content, sex identification, birds of prey, Falconiformes, Strigiformes, flow cytometry, avian erythrocytes Nuclear DNA content determination in eukaryotic organisms is important for its evolutionary significance. While many studies are presently available on karyotype and nuclear DNA content for mammals, less data are available for other vertebrates. For birds, the few studies available, mainly regarding karyotype constitution, have revealed a high interspecific variability, especially evident in the orders of Falconiformes and Strigiformes. This variability essentially involves the 2n chromosome number and DNA content, and could be related to an evolutionary process which is in agreement with several evolutionistic models (1,7,19). Avian cytogenetic analysis, conventionally used for studying the genome, presents several difficulties including the scarceness of karyological data, the presence of microchromosomes (characteristic of birds), and a high number of chromosomes (2). For these reasons, we deemed it of interest to investigate the nuclear DNA content of several species of Falconiformes and Strigiformes, with the aim of obtaining further information on the DNA patterns of the different species belonging to each of the two orders. We performed our study on blood avian samples taken from some species of Falconiformes (Accipitridae and Falconidae families) and Strigiformes (Strigidae and Tytonidae) using Flow Cytometric (FCM) analysis. This technique allows rapid and accurate evaluation of cellular DNA content in thousands of interphase cells for each measurement and is advantageous with respect to both cytogenetics and static cytometry. In this study particularly, it...

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