Article review : “Emergence of an evolutionary innovation: Gene expression differences associated with the transition between oviparity and viviparity”

I read “Emergence of an evolutionary innovation: Gene expression differences associated with the transition between oviparity and viviparity” for the primary literature review. The researcher’s question was to understand if the long egg retention of the three-toed skink Saiphos equalis was an “intermediate” phenotype between true oviparity and viviparity. The skink S. equalis has bimodal parity modes meaning there are two populations of S. equalis in Australia, one which births viviparous neonates in a clear membrane that is broken during or shortly after hatching. The other exhibits long egg retention with a short incubation period (3-5 days) before the hatchlings emerge and this phenotype is believed to illustrate how oviparity transitions to viviparity. The two populations are found in different locations with the viviparous populations being found in Mummel Gulf National Park, NSW, Australia, and the oviparous populations being found near the city of Sydney, Australia and there are no geographic barriers that would prevent gene flow. The gene expression in the uterine tissue was analyzed as the researchers hypothesized that differences in behavior, physiology, gestational tissue morphology or gene expression between the populations would be related to parity mode.

         The results indicated there were distinct gene expression profiles between oviparous and viviparous populations of Saphios equalis. The uterine gene expression between parity modes was significantly different yet and PCA delineated groups by both parity mode and stage in reproduction (gravid or nongravid). The genes uniquely expressed in gravid individuals are related to physiological functions such as metabolism, enzymes involved in uterine remodeling, and transport of ions. Different parity modes had differentially expressed genes in nongravid individuals related to metabolism. The genes found in viviparous S. equalis are similar to those found in the uterine remodeling of other viviparous skinks and mammals. The majority of differentially regulated genes related to immune function and this reflects the common need in both parity modes to avoid maternal rejection of the embryo during prolonged retention and development. The other main difference was genes related to calcium ion transport were significantly upregulated in viviparous individuals and this is consistent with prior studies that suggest that the eggshell of oviparous organisms supplies the embryo with calcium. The findings support the researcher’s hypothesis that the long egg retention of oviparous S. equalis more than likely is a transitional from between the parity modes of oviparity and viviparity.
Besides being really interesting these kinds of study can shed light on how viviparity evolves in certain organisms and is really important for evolutionary biologist. 
Authors: Charles S. P. Foster Michael B. Thompson James U. Van Dyke Matthew C. Brandley Camilla M. Whittington

Journal: Molecular Ecology Volume29, Issue7 April 2020 Pages 1315-1327
Citation:
Foster, CSP, Thompson, MB, Van Dyke, JU, Brandley, MC, Whittington, CM. Emergence of an evolutionary innovation: Gene expression differences associated with the transition between oviparity and viviparity. Mol Ecol. 2020; 29: 1315– 1327. https://doi.org/10.1111/mec.15409
Link:https://onlinelibrary.wiley.com/doi/10.1111/mec.15409