Creationism in Crisis
How a Complex Process Evolved From Simplicity.
It's Those Blinking Mudskippers Again
How a Complex Process Evolved From Simplicity.
It's Those Blinking Mudskippers Again
Mudskippers Could Be Key to Understanding Evolution of Blinking | Research
Indian mudskipper, Periophthalmodon septemradiatus
Mudskippers are the thing of nightmares for creationists because, although not directly ancestral to terrestrial tetrapods, they show how fish left the water and moved onto land, to become the terrestrial vertebrates - amphibians, reptiles, mammals and birds - we have today.
Another thing creationists dread is evidence of complexity evolving naturally from simplicity, because that conflicts with another of their counter-factual dogmas.
So, news today that simple beginnings of the evolution of blinking can be seen in the way mudskippers keep their eyes clean when out of water, will need to be rigorously ignored or misrepresented by creationists who are too afraid to consider that they could be wrong.
The news comes in the form of an open access research paper published a couple of days ago in the online journal PNAS by researchers from Georgia Institute of Technology, Seton Hill University, and Pennsylvania State University, and an accompanying news release from the Georgia Institute of Technology (Georgia Tech):
Blinking is crucial for the eye. It’s how animals clean their eyes, protect them, and even communicate. But how and why did blinking originate? Researchers at the Georgia Institute of Technology, Seton Hill University, and Pennsylvania State University studied the mudskipper, an amphibious fish that spends most of its day on land, to better understand why blinking is a fundamental behavior for life on land.
Although mudskippers are distantly related to tetrapods, the group that includes humans and other four-limbed vertebrates, researchers believed studying the fish could unlock how blinking evolved as these animals began to move on land.
The research team, which included several undergraduates, published their findings in the paper, “The Origin of Blinking in Both Mudskippers and Tetrapods Is Linked to Life on Land,” in Proceedings of the National Academies of Science.
By comparing the anatomy and behavior of mudskippers to the fossil record of early tetrapods, we argue that blinking emerged in both groups as an adaptation to life on land. These results help us understand our own biology and raise a whole set of new questions about the variety of blinking behaviors we see in living species.
Professor Thomas A. Stewart, co-corresponding author
Assistant professor
Department of Biology
The Pennsylvania State University, State College, PA, USABreaking Down Blinking
Mudskippers blink by sucking their eye downward into their eye socket. The evolution of this behavior did not require the evolution of a lot of new parts such as new muscles or special glands, though. Instead, mudskippers use their existing set of eye muscles in a new way.
Next, the research team set out to determine why mudskippers blink. In a series of experiments, they found that mudskippers blink for three main functions: to wet, clean, and protect the eye. These functions are also why humans and other land-dwelling vertebrates blink.This is a very exciting result because it demonstrates that the evolution of a new, complex behavior can be achieved using a relatively rudimentary set of structures.
We find that a single behavior can be deployed to accomplish three complex, distinct functions. These results not only help humans understand our own history, but also help us reevaluate the adaptations necessary for major transitions in the evolutionary history of vertebrates, like moving from water to land.
Brett Aiello, first author
School of Biological Science
Georgia Institute of Technology, Atlanta, GA, USA
Now at Department of Biology
Seton Hill University, Greensburg, PA, USA.
Blinking isn’t just a unique research question, but also an important mechanism to understand, according to Saad Bhamla, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering and author on the paper.
Engaging UndergraduatesWe all blink without thinking, and understanding why we blink is just such a beautiful puzzle right in front of our eyes. Through our research on mudskippers and by conducting biophysical and morphological analyses, we expose how blinking serves a multitude of functions for adapting to life out of water.
Professor Saad Bhamla, co-author
Assistant professor
School of Chemical and Biomolecular Engineering
Georgia Institute of Technology, Atlanta, GA, USA
To explore such open-ended questions, the researchers engaged the Vertically Integrated Projects (VIP) program, which allows undergraduates to conduct long-term, large-scale research projects as part of their coursework at Georgia Tech.
The sad news for creationists continues in the team's description of the significance of their study and the abstract to their published paper in PNAS:
SignificanceTo make matters worse for creationists, there is no hint there that the researchers believe an explanation other than evolution is demanded by the evidence; just another casual and unintentional rebuttal of creationism and creationists' wackadoodle beliefs.
Most tetrapods blink, closing their eyes periodically with eyelids or a nictitating membrane, and blinking is critical for maintaining eye health. In humans, for example, the inability to blink regularly can lead to vision loss. However, how and why did blinking first evolve? It has been difficult to tackle this question from the fossil record alone. This study sheds light on the origin of blinking by considering a second lineage of fishes that have convergently evolved blinking behaviors: the mudskippers. By analyzing how blinking behaviors are performed and testing hypotheses of blink function in mudskippers, we show how anatomical systems can be tinkered with to achieve a novel behavior and argue that blinking is an adaptation to life on land.
Abstract Blinking, the transient occlusion of the eye by one or more membranes, serves several functions including wetting, protecting, and cleaning the eye. This behavior is seen in nearly all living tetrapods and absent in other extant sarcopterygian lineages suggesting that it might have arisen during the water-to-land transition. Unfortunately, our understanding of the origin of blinking has been limited by a lack of known anatomical correlates of the behavior in the fossil record and a paucity of comparative functional studies. To understand how and why blinking originates, we leverage mudskippers (Oxudercinae), a clade of amphibious fishes that have convergently evolved blinking. Using microcomputed tomography and histology, we analyzed two mudskipper species, Periophthalmus barbarous and Periophthalmodon septemradiatus, and compared them to the fully aquatic round goby, Neogobius melanostomus. Study of gross anatomy and epithelial microstructure shows that mudskippers have not evolved novel musculature or glands to blink. Behavioral analyses show the blinks of mudskippers are functionally convergent with those of tetrapods: P. barbarous blinks more often under high-evaporation conditions to wet the eye, a blink reflex protects the eye from physical insult, and a single blink can fully clean the cornea of particulates. Thus, eye retraction in concert with a passive occlusal membrane can achieve functions associated with life on land. Osteological correlates of eye retraction are present in the earliest limbed vertebrates, suggesting blinking capability. In both mudskippers and tetrapods, therefore, the origin of this multifunctional innovation is likely explained by selection for increasingly terrestrial lifestyles.
Aiello, Brett R.; Bhamla, M. Saad; Gau, Jeff; Morris, John G. L.; Bomar, Kenji; da Cunha, Shashwati; Fu, Harrison; Laws, Julia; Minoguchi, Hajime; Sripathi, Manognya; Washington, Kendra; Wong, Gabriella; Shubin, Neil H.; Sponberg, Simon; Stewart, Thomas A.
The origin of blinking in both mudskippers and tetrapods is linked to life on land
Proceedings of the National Academy of Sciences (2023) 120(18); e2220404120. DOI: 10.1073/pnas.2220404120
Copyright: © 2023 The authors.
Published by PNAS. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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