Final answer:
If a fungus is well-suited to its environment, it will likely reproduce asexually, as this is faster and can occur under stable conditions. Sexual reproduction is beneficial under changing conditions as it increases genetic variation. A fungus unable to produce a minus mating type can still reproduce asexually.
Step-by-step explanation:
If a fungus is perfectly suited for its environment, it is likely to reproduce through asexual reproduction. Asexual reproduction, including mechanisms like budding in yeasts or spore production in other fungi, allows for rapid population increases, particularly when environmental conditions are stable and favourable. This form of reproduction is quick and efficient, enabling fungi to proliferate and dominate their ecological niche. However, when environmental conditions are variable or challenging, sexual reproduction can be advantageous. Sexual reproduction in fungi introduces genetic variation, which is crucial for adapting to new or changing environments. This occurs through the fusion of spores from two different mating types, typically denoted as plus (+) and minus (-), forming a zygospore. If a mutation occurs so that a fungus can no longer produce a minus mating type, it can still reproduce asexually. However, its ability to undergo sexual reproduction and hence its potential for genetic diversity would be compromised. Some fungi are homothallic and can mate with themselves, but those that are heterothallic require two compatible individuals to reproduce sexually.