As a child, Mendel explored the nearby forests of Michoacán, a state in Mexico, with his older brother Vicente. The trees there are filled with massive, beautiful clusters of monarch butterflies. Their metamorphosis fascinated him throughout his life and, today, he studies the evolution of their wing design as a research scientist in New York City. Finding a balance between the land of his birth and his promising future abroad is at the heart of Alexis Gambis’ dazzling new drama “Sons of Monarchs,” which screened at this year’s Sundance Film Festival.