Question 1. All the Single Ladies: Bdelloid Rotifers (Adapted from posts by Ed Yong, Not Exactly Rocket Science, 2009; Frances Farabaugh, Intern Invertebrate Zoology Department NMNH; and Hecox-Lea and Mark Welch BMC Evolutionary Biology (2018) 18:177) Bdelloid rotifers (pronounced with a silent “b”) are a class of rotifers (approximately 450 species!) entirely made up of females. That's right, there are no male bdelloids. These females have been around without male counterparts, and consequently sex, for about 80 million years! The bdelloids pose a problem for evolutionary biologists, who have struggled to explain how these animals could make do without a strategy that serves the rest of the animal kingdom very well. The reason for these animals' evolutionary longevity is an area of continuing investigation among scientists. Use what you know about how genetic diversity is introduced into a population to respond to the following questions: Explain why asexual reproduction is not particularly useful for introducing genetic variation into a population. a. b. Describe two ways through which genetic variation is introduced during meiosis that bdelloid rotifers do not benefit from. Bdelloids live in freshwater pools but can survive periods of drought by dehydrating and living in a dry and dormant state for a very long time, with no loss of fecundity or lifespan - much like the tardigrades we met earlier this semester! The intense selective pressure of desiccation, and the unique genomic diversity of bdelloid rotifers provide an exceptional opportunity to study the evolution of genes. Recently, scientists found a gene called lea, in bdelloid rotifers that has a version on two different chromosomes. While these genes are similar, they differ by about 14% of their sequence, and these differences translate to proteins with substantially different structures and functions. Version A acts as a molecular shield and prevents more sensitive proteins from balling together into useless clumps when they dry out. Its partner, version B, insinuates itself into the fatty membranes that surround all cells and helps to stabilize them. c. Explain how asexual reproduction brings selective advantage to the bdelloids with respect to the two versions of the lea gene being present on nonhomologous chromosomes.