Podcast 142 - The LDG

The gang discusses two papers that look at the origins of the latitudinal diversity gradient, the tendency for higher species diversity in the tropics and lower diversity closer to the poles. Specifically, these studies use comprehensive phylogenetic analyses of modern taxa to try and determine if the current diversity gradient is caused by increased speciation or decreased extinction at the equator. Meanwhile, Amanda shares diseases with her cat, James decides to "treat" himself to a Lime-A-Rita, and Curt just re-enacts scenes from other media.   Up-Goer Five (James Edition): The group looks at two papers that are interested in where animals live. They are looking at a well known thing where more animals live near the middle of the world than at either end. However, it is not clear whether there are more animals in the middle of the world because they have been there longer and so the number of animals has just built up over time, or whether animals in these areas make more types of animals more quickly. The first study looks at animals that have no legs and live in the water that you can not drink and breath water. This study finds that animals that live in the middle of the world actually make other animals slower than animals that live at either end of the world do, so the reason there are more animals in the middle of the world is probably because they have been there longer. The second study looks at animals with hard outer skin that have six legs and live in big families. This study finds that there is no change across the world in how quickly these animals make more animals, which is different from the first study. However, this does mean that the reason there are more animals in the middle of the world is because they have been there longer, so this agrees with the first study!   References:   Economo, Evan P., et al. "Macroecology and macroevolution of the latitudinal diversity gradient in ants." Nature communications 9.1 (2018): 1778.   Rabosky, Daniel L., et al. "An inverse latitudinal gradient in speciation rate for marine fishes." Nature (2018): 1.