Question

Two morphs of the marine snail Littorina saxatilis have been identified on rocky intertidal shores in Galacia, Spain. Johannesson et al (1995) made the following observations about these snails:

• One morph consists of snails with smooth, unbanded shells. These snails are found in the blue mussel zone, low in the intertidal. The other morph consists of snails with ridged, banded shells. These snails are found high in the intertidal, in the barnacle zone.
• All snails feed on algae, but algal species differ between the two zones.
• The two morphs overlap in a narrow midshore band at the border of the blue mussel and barnacle zones.
• Mating in the midshore band is not random. Females prefer to mate with males of the same morph, and only 8% of the snails in the midshore band are hybrids.
• Some female hybrids have been observed with embryos in their brood pouches, indicating that they are not sterile. However, the survival rates of hybrids relative to the survival rates of pure morphs are unknown.

Consider the information provided in this case study in addressing the questions below.

Are the two morphs separate species:

• According to the biological species concept?
• According to the morphospecies concept?

• According to the ecological species concept?

For each species concept, define the species concept, explain what information you used to answer the question, and suggest one piece of additional information that would be relevant in helping you to decide if the two morphs are separate species.

Answer should show an understanding of the species concepts and a defensible use of evidence

• Correct definition of species concept
• Selection of evidence that is relevant to the species concept and good explanation of how the evidence is used.
• Clear description of additional evidence that is relevant to the species concept

Answer 1

By considering the information provided in the above case study, we can answer the questions:-

1. The two morphs of the marine Snail Littorina Saxatilis are not the seperate species, rather they are show the two polymorphism of one species.

According to biological Species concept, the two morphs are different becauseof the biological species concept , the species or member of population that actuallly or potentially interbreed in nature, not according to similarity of appearance. Mating in the midshore band is not random. Female prefer to mate with males of the same morphs.

According to morphospecies concept, the species or members of population uses different morphological character to sepearte morphs. Both the sanil are morphologically different. One morphs contains of snails with smooth, unbanded shells , other morphs consist of snail with ridged , banded shell.

According to ecological species concept, the species or member of population uses different geographical condition to reside. one snail live in blue mussel zone, low in intertidal while other live in barnacle zone, high in intertidal.

Definiton of species concept:- The species concept is a concept of groups in which the actually or potentially interbreeding population reproductivly isolated from eachother. They are seperated under biological species concept, ecological species concept , morphological species concept (Morphospecies concept).

The above given exapmple is a very good evidence of species concept because species concept is basically define by biological species concept as they are actually or potentially intertreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species , it does not define species. organism may appear to be alike and be different species.

Another evidence of Biological Species concept is the dogs came of all shape and sizes- from tiny Chihuahuas to massive great Danes- but they belong to same species.