Penguins are unique, flightless aquatic birds that live primarily in the harsh conditions of the Antarctic. In a research article published by Cai Li et. al, the scientists discussed the adaptations of male emperor and Adelie penguins that allow them to survive such harsh habitats. These two species of penguins are very similar, with few slight differences. One similarity is that these penguins have evolved flipper-like wings that aid them in underwater flight. The researchers built a phylogeny to evaluate the similarities between the two penguin species. Some other adaptations they noticed that were similar between emperor and Adelie penguins were their unique feathers, visual sensitivity, and a thick epidermis. Penguins’ feathers are particularly useful to prevent heat loss; the researchers found that these two species have the most feather-associated proteins of all penguins. The major difference that the researchers found between emperor and Adelie penguins was their lipid metabolism ability. A gene involved in lipid metabolism has been selected for in Adelie penguins, but not in emperor penguins.
Genome sequencing of these two penguin species provides important insight into how animals adapt to survive extreme environments.
In addition to lipid metabolism and the major epidermal and forelimb features that have evolved in the two penguin species, the researchers also discussed the light-sensing abilities of emperor and Adelie penguins that we were unable to cover in the podcast.
Adaptations to the emperor and Adelie penguins transduction abilities have also enabled them to live an aquatic lifestyle in the harsh Antarctic climate. To understand this adapted light-sensing ability, opsin genes (RH1, RH2, SWS1, SWS2, LWS, OPN3, OPN4, OPN5 and OPSP) between different avian species were analyzed. More specifically, the researchers decided to use protein sequences of these genes from the chicken genome as a reference. Knowing that chickens live in extremely different habitats compared to penguins, we found this particularly interesting, and reached out to the lead researcher to ask why they chose to use the chicken genome as a reference. They reassured us that despite their different habitats, the chicken genome is our most understood avian model, which is comparable enough to the penguin genome.
The average avian species showed to have four classes of cone opsin genes whereas the two penguins the researchers studied had three classes of cone opsin genes. The OPSP or pinopsin gene, expressed in the pineal gland, was found to be pseudogenized in the two penguin species. Pseudogenization is a process that occurs in a genome where some genes are non-functional. This pseudogenization was caused by two frameshift mutations in the gene of the emperor penguin and one frameshift and one premature stop codon in the Adelie penguin. Being in different codon locations, it can be expected that pseudogenization occurred independently between the two lineages. Positive selection expressed between the other phototransduction related genes suggests the two penguin lineages developed different light transduction adaptations to better suit their needs in the extreme Antarctic environment.
Citation: Cai, L., Yong, Z., Jianwen, L., Lesheng, K., Haofu, H., and et.al. (2014). Two Antarctic penguin genomes reveal insights into their evolutionary history and molecular changes related to the Antarctic environment, GigaScience, Volume 3, Issue 1, 2047–217X–3–27, https://doi.org/10.1186/2047-217X-3-27