The difference is how you think of the information. "Today we will discuss animal behavior." This is just a simple statement about the future. "Today we will be discussing animal behavior." This is more specific. It suggests that the future action will be a process. When you discuss something, it isn't a quick, momentary action. A discussion involves thought and listening, and it requires time to complete. By saying "will be discussing," it gives the sense that the action will take place over a period of time.

we use “will” to talk about future events in general, but we use “will be” + ing when we want to focus on a specific time or event in the future. For example: What will you do tomorrow? I’ll work tomorrow. What will you be doing at 2:00 p.m. tomorrow? I’ll be working at that time.

The sentence means the same. Just different ways of saying it by using different verb forms: "will be discussing" = 将会讨论 "will discuss" = 会讨论 1. Today we will be discussing animal behavior. = 今天,我们将会讨论动物行为 2. Today we will discuss animal behavior. = 今天,我们会讨论动物行为