Abstract
Sexing of birds is indispensable for scientific, breeding and conservation programs but is difficult in many species and is particularly problematic in the case of nestlings showing no sexual dimorphism. Most useful and efficient methods of sex determination are based on unique features of the Z and W sex chromosomes detected via PCR to distinguish males (ZZ) and females (ZW). During the last twenty-five years researchers searched for the universal marker capable of sexing a maximally wide spectrum of species in a single PCR assay. We screened the phylogenetically representative set of 135 Psittaciformes species including 59 species sexed for the first time. Two known (P2P8, CHD1iA) PCR markers and four additional W/Z polymorphisms (CHD1iE, CHD1i16, CHD1i9 and NIPBLi16) located within the Chromo Helicase DNA binding CHD1 or the Nipped-B homolog NIPBL genes were applied. We present the electrophoretic patterns obtained for the PCR products of the analyzed markers including most typical and atypical patterns allowing sex determination, as well as those obtained when the given marker failed in sexing. Technical aspects of molecular sex determination are discussed: the optimization of amplification conditions, direct PCR and potential misinterpretations. A truly universal marker has not been found, and therefore, we propose a sexing strategy based on multiple CHD1i16, NIPBLi16, CHD1i9 and CHD1iE markers. This new strategy confirms the sex of a given bird with at least two markers detecting independent Z/W polymorphisms, reduces the number of necessary PCR reactions and minimizes the risk of sex misidentification.
Highlights
We have addressed this issue in the Psittaciformes order by testing six W/Z polymorphisms, including two well-known markers (P2/P8; CHD1iA)
We did not find a universal marker, and we evaluated the potential risks of sex misidentification associated with the application of only one marker
Markers tion within the CHD1 or Nipped-B homolog gene (NIPBL) genes in the chicken (Gallus gallus) sex chromosomes (FigTo illustrate the genomic localization of the analyzed markers, we show their position ure 1)
Summary
According to the Red List Index, parrots have the highest extinction risk compared to other avian orders. The extinction risk will likely rise, as many parrot species are large-bodied and slow-breeding, and most taxa are ecologically specialized, which is known to be associated with extinction [1]. Parrots have become the most captivating avian group [2]. Increased demand for captive-bred companion parrots increases their illegal trapping from the wild, which strongly influences their extinction risk, along with such threats as habitat loss or degradation, a biased sex ratio in adults and low female breeding participation (reviewed by Heinsohn et al [3]). The breeding, monitoring and conservation of endangered parrot populations are important and require an efficient sexing method
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