Behavioral consequences of polyploidy in hyla chrysoscelis treefrogs : implications for speciation and underlying mechanisms

Abstract

Polyploidy occurs when organisms have more than the typical two copies chromosome sets. Polyploidy has occurred many times throughout plant and vertebrate evolution, and recently in diverse families of frogs. Male treefrogs produce acoustic advertisement-calls to attract females. Females reliably choose males of their own species on the basis of their advertisement-calls, which allows two gray treefrog species to live and breed amidst each other. To investigate the effects of polyploidy on behavior, I created artificial polyploids of the diploid gray treefrog, Hyla chrysoscelis. Polyploid males produce advertisement calls with slower pulse-rates, and consisting of pulses with slower rise-times, both in the direction of the tetraploid species, H. versicolor. Polyploid females also demonstrate a preference for calls with slower pulse-rates, and demonstrate weak preference for slow rise-time pulses, as do females of H. versicolor. These parallel effects of polyploidy undoubtedly contributed to the rapid establishment of early polyploids. I also documented differences in cell size and number between the two species. Cells of polyploids are larger, and fewer in number, than those of the diploids. Environmental temperature can also influence cell size: frogs grown at cooler temperatures have larger cells, similar to polyploids grown at normal temperatures. By comparing the behavior of diploid frogs grown in cooler temperature, polyploids, and wild type diploids, I can further determine the relative effects of cell size and other consequences of polyploidy, such as gene copy number.