Assessment+Activities

=Example Questions and Responses =

Question I
There are 2 species of the banded sea snake from Efate in Vanuatu, //Laticauda colubrina// and //L. frontalis//. They are almost identical except that //L. colubrina// grows much larger. There are no natural hybrids seen. Discuss what sort of speciation is demonstrated here and suggest reasons for this speciation. Read the responses below and try to identify which response would be awarded an excellence. Think about the question and what the key points that need to be addressed are. Post your choice on the wall and a key reason it deserves Excellence. **Answer 1)** The type of speciation I think is occuring between L. colubrina and L. frontalis is sympatric speciation. A definition of sympatric speciation is when a new species is formed even when there is no separationof the gene pool by physical barriers. There are 2 situations when this is thought to occur: 1)In the changing environment around Efate there is a diverse range of microhabitats. Some of the sea snakes may have preferred to occupy one particular habitat most of the time, only rarely coming into contact with fellow sea snakes who prefer other microhabitat. The seas snakes become dependent on the resources offered so they never meet up. This is called niche differentiation. 2)The individuals of L. colubrina and L. frontalis have remained genetically isolated for so long because of their niche differentiation become reproductively isolated. They have become new species that have developed subtle differences in behaviour, physiology, and structure (in this case L. colubrina grows much larger). This is all due to natural selection in which the organisms with traits most suited to the environment survive and reproduce. So therefore, the seasnakes are species of the same genus living together in the area as their ranges overlap.    **Answer 2)** As L. colubrina and L. frontalis are sea snakes, living in the ocean around the Vanuatu it is unlikely that there is a geographical boundary between the two species. This means that sympatric speciation is occuring, when there is two species live with overlapping ranges but do not interbreed due to reproductive barriers. This ofetn occurs if a population moves to a new area with very few selection pressures causing an increase in the size and diversity withtin the population. Different parts of the population then become separated and gene flow stops. With the sea snakes this could have occured due to a geographical barrier. If the water level dropped, a stretch of land that there before formed, isolating the population on either side of it. Another way the population could have been separated is through niche differentiation. The habitat of the population can contain microhabitats, where the environment was different. For the sea snakes different areas around the the island might ahve different depths of water, salinity, prey, or temperature. Due to the variety in populationsome members might prefer to inhabit a certain part of the environment and will only come in contact with other members inhabiting the same microhabitat. If the population is separated and the different areas have different selection pressures then the new populations will evolve differently to adapt to these pressures until their gene pools become so different they form new subspecies. For L. colubrina larger prey might have meant that the snakes evolved to be larger in order to make the prey easier to catch.Larger predators might also have meant the L. colubrina evolved larger to avoid being eaten. The L. frontalis may have evolved in an area where being small meant it could hide more easily from predators. If this continues, reproductive isolating mechanisms will emerge creating two new species that will not interbreed even if they share a habitat. The reproductive isolating mechanisms here could include both prezygotic and postzygotic. Prezygotic mechanisms might exist if the two snakes inhabited different habitats in the same general area around Efate. Other prezygotic mechanisms might include temporal, the fact that the snake might not recognize signals for mating from the other species. Also structural mechanisms might make it physically impossible for the snakes to mate because of their different size. Even if this is not the case and mating does occur the gametes of the two species might be incompatible. Postzygotic mechanism of hydrid inviability might mean that even if a gamete does form it does not develop so no natural hybrids are seen. **Answer 3)** Sympatric speciation is demonstrated here. This is when there are no physical barriers but speciation has occured through behavioural, structural, etc. barriers,. Whilst occupying the same area, the 2 different sea snakes could have different needs, e.g. food. By having different diets, it reduces the need for competition and ensures better chances of survival for each species as they do not have to compete with each other for the limited resources available. This could be the reason as to why they are separated. Due to different diets, the L. colubrina grows larger.

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