Lemon sharks are cartilaginous fishes that live near coasts of tropical and subt

Question

Lemon sharks are cartilaginous fishes that live near coasts of tropical and subtropical oceans. There are two species of lemon sharks, the Atlantic lemon shark, Negaprion brevirostris, and the sicklefin lemon shark, Negaprion acutidens. Lemon sharks take 12-15 years to mature, have a gestation period of 1 year, and have a life span of about 25 years. Female lemon sharks give live birth to their pups and can have between 4-20 pups every other year. Once born, the newborn lemon sharks stay in shallow, well-protected nurseries until they grow large enough to move to deeper water. Hypothesis 1: There was a single common ancestor to both current species of lemon sharks that existed more than 30 million years ago. When the Tethys sea closed, this ancestral species was separated into two populations-Indo-Pacific and Atlantic. The Indo-Pacific population became the modern day sickle fin lemon sharks. The Atlantic population separated into Western and Eastern Atlantic Coast populations as the continents of North American and Africa drifted apart. The closure of the Isthmus of Panama split some of the Western Atlantic Coast Population into the Pacific Mexico Coast population. Hypothesis 2: The common ancestor to both current species lived in the Indo-Pacific and some individuals swam across the Pacific Ocean to form the Pacific Mexico Coast population. The Pacific Mexico Coast population continued to spread into the Atlantic Ocean before the Isthmus of Panama closed. The individuals that were in the Western Atlantic Ocean then swam across the Atlantic Ocean to form the Eastern Atlantic Coast population that resides along the coast of Africa. A recent molecular DNA analysis of the lemon shark genus Negoprion showed that for a specific gene, LS30, there were 7 possible alleles: Al, A2, A3, A4, A5, A6, and A7. The PMC population showed no variation for the gene LS30, all individuals were homozygous for the allele Al. Individuals in the WAC population contained only the alleles A5 and A6. Individuals in the EAC population contained alleles A2, A3, and A4. All individual of the species N. acutidens were homozygous for the A7 allele. What do these molecular data tell us about gene flow between the 3 populations of N. brevirostris? Do the molecular data support Hypothesis 1 or 2? Justify your answer with one sentence.

Explanation / Answer

3 populations of N. brevorotric from the PMC, WAC and EAC has different alleles for the same gene LS30. From the data we know that Indo Pacific population has always had the parental population with Lemon sharks ( Negaprion acuitidens). This original species was detached from the later developed species and the other Negaprion species were in different places, so the molecular data also tells us that there is a variation in their gene, so they must have migrated to different places. Thus the variation has come, while mating the population of the different place. Here the gene flow we need to recall, the transfer of one population of genes from one population to another, the Indo Panama population have travelled and separated across the sea.

All the 3 population genes have evolved from their ancestral types, and their migration of gene and its flow has got the variation in those alleles.

Hypothesis two looks stronger, as there is the allele variation, which is because of gene flow. Showing from the recent data.

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