Investigating Genetic Variation and Selection in Starfish Species Piaster ochraceus

Stephanie Budhan ’21

Figure 1. The sea star species Piaster ochraceus.

Extreme environmental disturbances, such as a natural disaster or epidemics, dramatically impact animal population survival. These events have the potential to eliminate entire species, and affect the gene pool or the frequency of certain genes within the population. However, scientists observing these natural disasters and their subsequent effects can be difficult due to their sporadic occurrence.

A study conducted by Dr. Lauren Schiebelhut and her team at University of California, Merced, analyzed a recent epidemic among the starfish species Piaster ochraceus. In 2013, a disease known as Sea Star Washing Disease decimated the starfish population. This epidemic created a rare opportunity for scientists to study genetic variation evolution in post- epidemic sea stars. The researchers used ecological surveys to quantify abundance, size, and mortality of starfish. In addition, tissue samples from starfish were collected and DNA was sequenced. Statistical analysis tests helped to determine any genetic change or shifts in allele frequency. Furthermore, the current study, coupled with a previous study that collected data on pre- epidemic P. ochraceus, analyzed genetic variation between the pre- and post- epidemic sea stars.

Researchers found that the sea star wasting disease decimated population by about 81%. Statistical analysis revealed significant genetic differences between pre- epidemic and post- epidemic sea stars, suggesting that the epidemic affected the gene pool of the population. Post- epidemic sea had a favorable genetic make-up that made them adapted to survive the epidemic and so were naturally selected to survive. Three specific loci or genes displayed a shift in allele frequency between pre- and post- epidemic sea stars. However, more gene modeling must be performed to determine why these specific genes were targeted but they may play a role in the immune system of sea stars.



  1. M. Schiebelhut, J. Puritz, & M. Dawson, Decimation by sea star wasting disease and rapid genetic change in a keystone species, Pisaster ochraceus. Proceedings of the National Academy of Sciences, (2018). 2018. doi:10.1073/pnas.1800285115.  
  2. Image retrieved from:

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