What induces multicellularity in a choanoflagellate species? A) the presence of the preferred prey/food source in the environment B) the developmental signal molecules that induce differentiation C) the presence of predators in the environment D) the cell migrations that take place during the developmental phases of growth

What the question is really asking

This is testing what external cue can trigger a normally single-celled choanoflagellate to form a multicellular colony. The key is that, in choanoflagellates, colony formation is often an environmentally induced life stage, not an internally programmed animal-style development.

The known trigger in choanoflagellates

In well-known experiments, choanoflagellate multicellularity (rosette colony development) is induced by the presence of certain bacteria associated with their food supply. Those bacteria release chemical cues that cause the choanoflagellates to stay attached after cell division and form a multicellular rosette.

Why the other options do not fit

• B) Differentiation signals are central to animal embryonic development, but the classic choanoflagellate example is induced by environmental bacterial cues tied to feeding.
• C) Predator-induced colony formation is seen in some microorganisms, but it is not the standard choanoflagellate multicellularity trigger referenced in this context.
• D) Cell migration during developmental phases describes processes in multicellular embryos, not what initiates colony formation in choanoflagellates.

Correct choice

So the best answer is A, because the presence of the prey/food-associated bacteria in the environment is what induces multicellularity in the commonly cited choanoflagellate case.