Is a planet able to sustain life without a moon? What are the major effects of a natural satellite on a planet and its fauna and flora ?
Yes. There is no reason why a moon would be essential for life. Animals on Earth have adapted to the cycles of the moon. However, this would not be necessary on a planet without a moon.
Tides would probably be greatly affected without a moon. The sun would continue to exert force on the tides, but without a moon the tides would be much less extreme than they are today.
Nocturnal plants and animals would also be affected. Plants would not longer be able to do photosynthesis under moonlight. And animals that rely on the moonlight to hunt would no longer be able to do so. You might see more animals using echolocation like bats or heat sensing organs like pit vipers.
The moon also slows down earths rotation. Without a moon, earth would rotate a lot faster, which means the days and nights would be shorter. Plants and animals would therefore, have to adapt to shorter days and nights.
The greatest impact would be on earths axial tilt. The moon stabilizes earth's axial tilt, and without it, Earth's axis would wobble. This could have serious impact on earth's climate over time. However, it wouldn't prevent life from forming, as the tilt would only change over hundreds of thousands of years.
A planet would be able to sustain life, but chances of it evolving life would be smaller. How much smaller, nobody can say with any certainty.
a moon, especially a large moon, will result in a thinner, more fractured crust of its primary; this will significantly increase the radioactive background and possibly increase the rate of mutations that powers evolution. This theory was first advanced in the '60s and later found its way in Isaac Asimov's enlarged Foundation cycle (Robots and Empire) - it is indeed a key plot point since it is what enables Levular Mandamus' ploy to make Earth uninhabitable.
it is largely believed that life will originate in warm, shallow seas, and later colonize the land. This step will be greatly accelerated by the existence of so-called undertidal or intertidal environments, where conditions rapidly shift from marine to land. The first adaptations allowing organisms to survive a brief transition to a dry environment lead the way to organisms more and more adapted to air.