Question

A short hike through the Sandia Mountains from early spring to late summer will often reveal several different species of penstemon. The Rocky Mountain penstemon blooms in the spring while the very similar inflated penstemon blooms in late summer. As a result, hybrids are rarely encountered.

Answer 1

Complete question:

Categorize the following situation as either a pre- or postzygotic isolating mechanism and then specify which type of pre- or postzygotic isolating mechanism it is.

A short hike through the Sandia Mountains from early spring to late summer will often reveal several different species of penstemon. The Rocky Mountain Penstemon blooms in the spring while the very similar inflated penstemon blooms in late summer. As a result, hybrids are rarely encountered.

Answer:

• pre-zygotic isolating mechanism
• Type: seasonal or temporal

Explanation:

There are different mechanisms of reproductive isolation. These are barriers that inhibit or interrupt the genetic flux between different species. These mechanisms are about the biological characters of each species that prevent the reproduction with other species.  

The reproductive isolation mechanisms might be either prezygotic or postzygotic.

1. Pre-copulatory or pre-zygotic:

• Ecological or due to habitat isolation;
• seasonal or temporal;
• Sexual or ethologic;
• Mechanical;
• Gamete incompatibility.  

  2. Post-copulatory o post-zygotic:

• Hybrid inviability
• Hybrid sterility
• Hybrid with diminished viability and or fertility
• Cytoplasmatic interactions.

The exposed situation is an example of prezygotic isolation due to seasonal or temporal barriers. Penstemon blooms in the spring, while the very similar inflated penstemon blooms in late summer. Probably, if they had the same reproductive season, they would produce hybrids. But as they are isolated by different reproductive seasons, they do not.  As they can not even fertilize, they are considered to be prezygotic isolated species.