The last wild Spix’s Macaw and an Illiger’s Macaw produced a hybrid. A report by Cristina Miyaki, Patricia Faria, Richard Griffiths, João Araujo and Yara Barros. Published in Conservation Genetics.2: 53-55, 2001

(Website editor: This paper is very interesting in it shows how DNA analysis showed that a Spix's macaw could reproduce successfully with an Illiger's Macaw. Sadly the last known remaining Spix's Macaw in the wild disappeared between the completion of the paper and its publication.) 

Abstract

The one remaining wild male Spix’s macaw (Cyanopsitta spixii) chose a female Illiger’s macaw (Propyrrhura maracana) as a mate. Eggs were found in the nest used by the couple and one of them contained an embryo. Sequence variation in CHD1-Z and CHD1-W genes showed that it was a natural hybrid.

Introduction

The Spix’s Macaw (Cyanopsitta spixii) is one of the world’s most endangered animal species. There are only 60 individuals in captivity and one bird in the wild. This last free living Spix’s Macaw is a male (Griffiths and Tiwari 1995) and is paired to an Illiger’s Macaw (Propyrrhura maracana, previously known as Ara maracana) in Bahia State, Brazil. Even though Grant and Grant (1992) estimated that 7.5% parrot species hybridize in nature, this pair is unique due to the rarity of the Spix’s Macaw. An International Committee was organised to try to preserve this species in situ and in captivity. Some of the questions it raised are: (1) is this hybrid pair able to incubate Spix’s Macaw’s eggs produced in captivity and raise chicks? and (2) can this wild male display effective reproductive behaviour?

The hybrid pair has been monitored by the Spix’s Macaw’s committee field team. Until 1996, the content of the hybrid pair’s nest was not examined. During the 1996/1997 breeding season, Y.M. Barros and J.C.C. Araújo found eggs in the nest but chicks never hatched (personal communication). During following reproductive seasons the eggs were removed for artificial incubation although no fledgings were obtained. The brood was replaced by wild Illiger’s Macaws eggs and chicks. In 1997 one of the removed eggs was broken and it contained an apparently perfect embryo. The mixed pair proved to have parental abilities and successfully raised Illiger’s Macaw chicks during the 1998/1999 breeding season. However, it still remains unproven as to whether the Spix’s Macaw male is fertile.

To answer this question, we studied the embryo found in the hybrid couple’s nest. We sexed it as a female, since it had two PCR products of the CHD 1 genes (“Chromo-Helicase DNA binding gene 1”). These genes are located on the Z and W sex chromosomes (Griffiths et al. 1998). Thus, if hybridization took place, the embryo should hold a CHD1-Z indistinguishable from the Spix’s Macaw’s whilst its CHD1-W should be identical to the maternal Illiger’s Macaw’s. We attempted to recognise this by using DNA sequencing.

Methods

DNA was extracted from muscle tissue or blood following standard procedures (Bruford et al. 1992). The PCR products of the CHD1 genes (Miyaki et al. 1998) from the embryo and two females from each species (C. spixii and P. maracana) were electrophoresed in a 3% agarose gel. The bands were purified from the gel either by collection into PEG 15% (Zhen and Swank 1993) or using the GFX kit (Amersham Pharmacia Biotech). These products were directly sequenced or cloned into pGEM (Promega) and then sequenced in an ABI 377. The sequences were aligned and compared.

Results and discussion

We aligned 229 bp of the CHD1-Z and 231 bp of the CHD1-W (Figure 1) from the embryo and the 4 other individuals. There were no differences between individuals from the same species. In contrast, a comparison between species revealed 1.75% and 0.86% differences between their CHD1-Z and CHD1W genes, respectively. The embryo’s and the Spix’s CHD1-Z sequences were identical and the same CHD1-W sequence was shared by the embryo and the Illiger’s Macaws.

As the capture of the embryo’s potential parents was too risky, we had to extract DNA from two alternative females from each species. The Spix’s Macaws’ samples were obtained from wild born, captive birds. The two sampled Illiger’s Macaws were taken from the same population as the breeding female. The comparison of the CHD1-Z and CHD1-W sequences between species revealed interspecific differences that would allow hybridization to be identified. Examination of the embryo showed a Spix’s CHD1-Z derived from the father and an Illigers CHD1-W from the mother. This proved it was a hybrid and showed that the last wild Spix’s Macaw is fertile.

This result justifies a future release of a female as a potential mate to help establish a wild population again.

Acknowledgements

We thank A. Wajntal for invaluable discussions and M. I. Bampi for her support. This work was supported by FAPESP, CAPES, CNPq (Brazil) and BBSRC (UK).

References

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