Literature Review: Evo-Devo

by Carl Strang

One of the most fascinating biological disciplines to emerge in recent years is evo-devo, the study of the genetic regulation of embryological development, with the goal of understanding the role of evolution. Most of the work to date has been done in animals, and the connections between distantly related species often are amazing, as several studies cited below reveal. Plants are increasingly subjects of this form of study, and the general patterns often prove to be similar to those in animals, as illustrated in the Vlad et al. study. Humans don’t escape this type of scrutiny, and we prove to have very similar vocal controls to those of songbirds. Fossil studies often are brought into these researches, as shown in the studies of breathing in turtles and the evolutionary relationships of daddy longlegs (harvestmen). Even the electric organs of various groups of fishes are subject to this kind of analysis.

The first study goes into the development of leaves, which in some species results in their division into separate leaflets as in this buckeye leaf.

The first study goes into the development of leaves, which in some species results in their division into separate leaflets as in this buckeye leaf.

Vlad, Daniela, et al. 2014. Leaf shape evolution through duplication, regulatory diversification, and loss of a homeobox gene. Science 343:780-783. They looked at developmental regulation of leaflet formation. A particular protein produced through homeobox activity represses growth in areas that end up being between leaflets. The associated gene evolved within a duplicated section of DNA. They found a species in which the duplicate was lost, resulting in simple leaves.

Pfenning, Andreas R., et al. 2014. Convergent transcriptional specializations in the brains of humans and song-learning birds. Science 346:1333. They studied genomes of a variety of birds and primates, and found that song-learning birds and humans share genes that produce connections between their brains and vocal apparatus, genes that are inactive in bird and primate groups that do not sing or speak. Thus brain structure and circuitry features associated with song learning in birds and vocal learning in humans are analogous and similar, and homologous at the level of brain regions. Genetic underpinnings for these structures likewise are similar. “The finding that convergent neural circuits for vocal learning are accompanied by convergent molecular changes of multiple genes in species separated my millions of years from a common ancestor indicates that brain circuits for complex traits may have limited ways in which they could have evolved from that ancestor.”

Lyson, Tyler R., et al. 2014. Origin of the unique ventilatory apparatus of turtles. Nature Communications 5: 5211. DOI: 10.1038/ncomms6211  Described in ScienceDaily. They did a detailed study of modern and fossil turtles, focusing on breathing, because turtles are the only air-breathing vertebrates that cannot employ the ribs. Turtles breathe with a ring of muscles surrounding the lungs. This system was in place in the early (260mya, Permian Period) African turtle Eunotosaurus africanus. They found that the system evolved gradually, the body wall stiffening as ribs broadened (for reasons still to be determined), and the musculature gradually developing to take more and more of the load.

Gallant, J. R., et al. 2014. Genomic basis for the convergent evolution of electric organs. Science 344:1522-1525. They studied the genetic and developmental aspects of electric fishes, 6 separate groups of which independently evolved the ability to produce electricity. They found that the same genetic basis and developmental pathway evolved to the same endpoint in all these different lines. Certain muscle cells lost their contraction ability and increased their membrane’s ability to manipulate ions and build up charge. They are set up in series down the length of the fish, increasing the voltage. The most powerful is the Amazon’s electric “eel” (more like a catfish), which one of the researchers characterized as “in essence a frog with a built-in five-and-a-half-foot cattle prod.” These fishes all live in murky waters, and use their electric capability to sense their surroundings, communicate, stun prey, and defend themselves.

Nuño de la Rosa, Laura, Gerd B. Müller, and Brian D. Metscher. 2014. The lateral mesodermal divide: an epigenetic model of the origin of paired fins. Evolution & Development 16 (1): 38. DOI: 10.1111/ede.12061  From a ScienceDaily article. They looked at the fossil record and the genetics of development, and found that the body cavity prohibits development of limbs in the region of body axis where it occurs. The result is a single pair of limbs in front, and a single pair behind that region.

Garwood, Russell J., Prashant P. Sharma, Jason A. Dunlop, and Gonzalo Giribet. 2014. A Paleozoic stem group to mite harvestmen revealed through integration of phylogenetics and development. Current Biology, DOI: 10.1016/j.cub.2014.03.039  From a ScienceDaily article. They studied a rare early harvestman fossil with x-ray scanning which provided unusual 3D detail. The fossil was 305 million years old (Pennsylvanian Period), from France. It showed an extra pair of eyes, set laterally, which subsequent study revealed appear in vestigial form at a point in embryo development (mature present-day harvestmen have only a single pair of eyes). The authors mentioned that harvestmen are more closely related to scorpions than to spiders.

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