a SciTechnol journal Letter To Editor Barreiros, J Biodivers Manage Forestry 2017, 6:1 DOI: 10.4172/2327-4417.1000172 International Publisher of Science, Technology and Medicine Journal of Biodiversity Management & Forestry All articles published in Journal of Biodiversity Management & Forestry are the property of SciTechnol, and is protected by copyright laws. Copyright © 2017, SciTechnol, All Rights Reserved. Why Flightless Birds are ‘Condemned’ to Lay Eggs João P Barreiros* Abstract Birds evolved very fast and are the only vertebrate group that never turned to ovoviviparity. While this is explainable as an evolutionary pressure for feathered fight and reduced size, their fast evolution apparently caused the disappearance of a signifcant proportion of genes. However posterior evolutionary trends of Aves to become fightless and with increased body sizes were not accompanied by an ‘expected’ turn to ovoviviparity, something known for a number of reptile taxa (e.g. some constrictor serpents). This impossibility is particularly noted in marine fightless birds from which penguins are certainly the best extant example having to endure seasonal extreme energy losses when coming ashore to lay eggs. This same limitation was most certainly the major cause for the extinction of the largest marine bird in the Northern Hemisphere – The Great Auk Pinguinus impennis. Here we discuss why ovoviviparism is probably an impossibility for birds while proposing lines of research that could prove, or disprove, our hypothetical and speculative view. Keywords: Ovoviviparity; Aves; Evolutionary constraint; Feathered fight *Corresponding author: CE3C – Centre for Ecology, Evolution and Environmental Changes / Azorean Biodiversity Group and Universidade dos Açores - Faculdade de Ciências Agrárias e do Ambiente, 9700-042 Angra do Heroísmo, Portugal, Tel: (+351)295402200; E-mail: joao.ps.barreiros@uac.pt Received: January 27, 2016 Accepted: February 02, 2017 Published: February 09, 2017 Avian evolution is a fascinating subject that was recently exten- sively discussed in Science’s Special Section “A Flock of Genomes” (12 December 2014 issue 346). One of the many key points in this special section is pointed out when referring that avian genomes consistently contain fewer genes and the ancestral avian lineage has distinctly lost a large number of genes by means of large segmental deletions afer their divergence from other extant reptiles [1]. Is it in here the cause for birds had never ever turned to ovoviviparity? If so, then how may the study of bird’s genomes give an answer to this ‘riddle’? The section “A Flock of Genomes” does not offer a response to this question although it gives us important clues on how to investigate it. It is known that a sustained size reduction was essential for the origin of birds and fight [2]. However, it is precisely that selection and the mechanical characteristics of feathered fight that probably caused the evolutionary impossibility of a modern bird – especially large, heavy bodied fightless species - turning to ovoviviparity. In fact, the evolutionary trend to miniaturization did happen at a rate of ca. 150 times faster than normal [3]. According to Benton [2] a move to tree dwelling is a crucial driver to the above changes although this does not explain how large sized birds, even before the K-T boundary event, adopted the opposite trend of becoming heavier and flightless (e.g. Cretaceous Hesperornis). All amniotes produce eggs but birds just had to ‘get rid of them’ very quickly in order to keep their low weight for flight. In fact, this evolutionary pressure for reduced weight might have ‘erased’ the genes that would allow birds to develop an alternate way of reproducing by turning to ovoviviparity. As explained almost all birds develop only a single functional ovary on the left side as a result of the evolutionary loss of the right ovary during the transition from nonavian theropods to birds [1]. It has been hypothesized that this loss represents an adaptation to reduce weight during flight [4]. Together with their very fast evolution, the disappearance of two genes related with ovary development is the probable key to the impossibility of ovoviviparism in birds [2]. While there is no evidence that non-avian dinosaurs and Pterosaurs, small or big, turned to ovoviviparity, it is certainly more probable than not that giant marine reptiles such as Pliosaurs, Plesiosaurs and Mosasaurs were ovoviviparous as Ichthyosaurs certainly were. Penguins have to endure enormous energy consuming eforts to lay eggs and for parental care. Being exclusively marine, ovoviviparity should have been the ‘logical’ evolutionary step for a high metabolic animal that does need to lay eggs on land. Of course, marine turtles also have to lay eggs on beaches but their lower metabolic rates are certainly more compatible with the effort and only females do it. Besides, turtles, while not having parental care, only come ashore a few times while both members of a penguin breeding pair do have to endure this effort several times. Therefore, the genes that would allow a transition to ovoviviparity have most probably disappeared. We can speculate that one of the most iconic recent Aves extinction, the Great Auk Pinguinus impennis, the only fightless marine bird in the Northern Hemisphere together with the lesser known and also extinct Spectacled Cormorant Phalacrocorax perspicilliatus, could still be amongst the extant species if ovoviviparity had developed since, especially the former, was probably hunted to extinction only because of their need to aggregate in breeding colonies where they became an easy target [5]. Modern birds are now better known but this key evolutionary aspect should and can be thoroughly studied in order to explain why ovoviviparity is absent or even ‘impossible’. If possible, a new window for understanding Aves evolution would become an important step of vertebrate evolution studies. References 1. Zhang G, Li C, Li Q, Li B, Larkin DM, et al. (2014) Comparative genomics reveals insights into avian genome evolution and adaptation. Science 346: 1311-1320. 2. Benton MJ (2014) How birds became birds. Science 345: 508-509. 3. Puttick MN, Thomas GH, Benton MJ (2014) High rates of evolution preceded the origin of birds. Evolution 68: 1497-1510.