Question

Which of the following statements is/are accurate?

Answer 1

Answer and explanation:

In nature there are different mechanisms that prevent the crossbreeding between different species, what in biology is called reproductive barriers. Some mechanisms that act by preventing hybridization between different species are:

• Hybrid breakdown
• Gametic isolation.
• Mecanical isolation.
• Temporary isolation.
• Ethological aislaminet.
• Ecological insulation.

These mechanisms are responsible for preserving the genetic integrity of each species by preventing hybridization between different species.

A. One species of sea urchins can not fertilize another closely related species because the eggs do not have a receptor for the sperm. This is a good example of a hybrid breakdown.

This is not accurate. In the case of sea urchins, the encounter of gametes requires two chemical mechanisms:  

• The first mechanism is called chemotaxis, which consists of the presence of a chemical signal on the surface of the egg, for which only sperm has a receptor.  
• Another mechanism is that - once the sperm and egg are found - the membrane of the egg releases substances that interact with receptors in the sperm, allowing the sperm to enter it.

These two chemical mechanisms ensure that gametes of two different species cannot be joined and fertilized, which is an example of gametic isolation.

B. Horses and Mules can be bred but their offspring is typically sterile. This could be an example of a hybrid breakdown.

This is accurate. Horses and donkeys belong to two different species, with a different chromosomal load:

• Horses have 32 pairs of chromosomes.
• Donkeys have 31 pairs of chromosomes.

Both species can be bred, but their descendant, mules (Equus africanus x ferus), have an odd number of chromosomes (63) and are infertile. This represents an exact example of hybrid breakdown.

C. Damselflies have sensory receptors that are sensitive to touch (tactile cues). Two related species of damselflies are unable to mate because their touch cues are not compatible. This is a good example of gametic isolation.

This is not accurate. The sensitivity to the touch of damselflies is specific to individuals of the same species, preventing mating between male and female of different species.

This, like courtship, is a mechanism that prevents crossbreeding between different species, establishing an example of mechanical isolation.

D. One species of sea turtle mates during the early spring and a closely related species mates during late spring. This is an example of temporal isolation.

This is accurate. When two related but different species - such as turtles - have their mating period at different times of the year, there is talk of temporal or seasonal isolation.

Temporal isolation is a reproductive barrier that prevents crossing between different species, due to their mating habits at different times.

E. One sponge species releases its gametes during the night and another species releases its gametes during the day. This is an example of ecological isolation.

This is not accurate. In sponges, like some coral species, periods of release of gametes and fertilization vary throughout the day, with some synchrony between individuals of the same species.

The fact that some sponges release their gametes by day and other species do it at night is an example of the reproductive barrier called temporal isolation.

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