Analysis of "Selection on Phalanx Development from the Bird Wing" Article (Essay Sample)

📌Category: Articles
📌Words: 970
📌Pages: 4
📌Published: 16 June 2022

Abstract

The article titled “Selection on Phalanx Development from the Bird Wing” from De Bukker et al. (2021) provides new insights into the evolution of bird wings, which have made them more adaptable to their environment and their ability to fly longer distances. However, one of the more prominent points arising relates to the evidence that supports the association between Dinosaurs and Birds, with the association appearing to be much closer than it is with reptiles. The study utilises the frameshift and MAD hypotheses and implements these within its discussions and its role in determining how bird wings have evolved.

The root cause of the evolution of the bird wing has been a phenomena scientists have argued for centuries. The authors of “Selection on Phalanx Development from the Bird Wing” are no exception and have chosen to take a brand-new approach to understand the evolutionary process. This included examining cell death in the phalanx-forming region, which allowed a survey of the patterns of digit loss in adult amniotes to be made. Before the article was published, many hypotheses were suggested to determine the evolution of the bird's wing. Firstly, the frameshift hypothesis stipulated a shift in positional values or molecular-developmental identity, which caused a change in digit phenotype. The hypothesis predicts that if the genes expressed during development were studied, it would be possible to match the gene expression profiles of the fingers in the bird wing to the fingers developing in positions 1-3 in other limbs. This hypothesis has been well studied by researchers who have continued to search for genes that control the development of bird wings, with a primary focus on identifying genes that could be utilized to test the hypothesis. Specifically, the hypothesis posits that a homeotic shift occurred in the avian stem that the developmental programs once expressed in D1-D3 are now executed in the digitals that develop in positions D2-D4. As such, this allowed for conflicting data from developmental biology and paleoethology regarding the homologies of the wing digits to be reconciled. The evidence supporting the hypothesis includes a molecular signature, namely the lack of Hoxd11 and Hoxd12 stable across amniotes.  

A secondary hypothesis is the most anterior digit (MAD), which posits a lack of Hoxd10, Hoxd11 and Hoxd12 gene expression in digit I in amniotes. The hypothesis accounts for the transcriptional landscape of the mesopodium, which is a low-hox zone that suggests that digit I may have evolved from low-hox tissues through again in Hoxa13 expression and reinforced expression Hoxd13. Therefore, the hypothesis believes that the unique morphology of digit I occur due to a reduced dosage of HOXD proteins. A similarity between the hypotheses lies in their predictions regarding the evolution of developmental gene expression, specifically in the Hoxd13 in the MAD and the lack of Hoxd11 and Hoxd12 in the digit. However, prior to the article from de Bekker et al. (2021), there remained a lack of understanding of the applicability of this hypothesis and if these markers are key in the evolution of the bird's wing. This provides a key step forward in understanding and conserving biodiversity and how wings have evolved to support long-distance flight and the environment of the bird habitats.

The article from de Bekker and colleagues tested several hypothesizes, including that Hoxd13 is expressed in all five digits in amniotes and the propositions of the MAD and frameshift hypotheses. They studied a phylogenic sample of 18 amniotes, including crocodiles, ostrich, zebra finch and moles, whereby a wide variation in Hoxd 11,12 and 13 in digit I was identified. The study collected embryos from the samples, which was approved by the University of Melbourne Animal Experimentation and Ethics Committee and adhered to the Australian National Health and Medical Research Council guidelines. A key strength of the study was its in-depth and clear overview of the methods applied, as this enhances its retest ability, signifying that the experiment has a strong internal validity. 

 The study identified patterns of apoptosis, Sox9 expression and markers of the phalanx-forming region, which suggest that phalanges were lost from wing digit IV due to early arrest of the phalanx-forming region followed by cell death. Interestingly, the study found that the multiple amniote lineages lost phalanges with no frameshift, suggesting that the bird's wing evolved due to targeted loss of phalanges under natural selection, thus supporting the presence of a gradualist model of evolution based on a modification to the developmental gene expressions. This means that the results from the study are consistent with recent studies that eliminate the need to postulate a frameshift in the first place, and that the phenotype of the Archaeopteryx lithographica wing is consistent with phalanx loss. This provides the link between dinosaurs and a modern bird rather than the believed association with reptiles predominantly. However, a limitation of the article lies in its discussion of the findings and its lack of hypothesis on what they intended to identify from the samples. In this sense, while it is obvious that a focus was placed on identifying if the hypotheses were applicable, it fails to provide a distinct purpose that could allow the author to understand in greater detail what the study aims to find. This is further limited by the lack of clear discussion on the findings. 

Overall, the article must address the limitations noted within the previous section but further provide a definitive and clear discussion regarding the study findings. This could help enhance the level of clarity and understanding of the findings and provide an opportunity to address areas for future research and, ultimately, what the findings mean for the research field. Perhaps reducing the number of samples could allow the authors to be more specific and offer a more detailed insight into specific species and thus adding a greater understanding of such species rather than attempting to report on a significant proportion of samples which limited the ability to provide explanations of the findings in greater details. However, the study provides key insights into the possibility of how bird wings have evolved and provide support for the relationship between dinosaurs and birds.  

References

De Bakker, M. A., van der Vos, W., de Jager, K., Chung, W. Y., Fowler, D. A., Dondorp, E., ... & Richardson, M. K. (2021). Selection on phalanx development in the evolution of the bird wing. Molecular biology and evolution, 38(10), 4222-4237.

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