Same Species or Not?

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We were hired to help save the rodent population in St. Kitts. Originally, we planned to take rodents from Nevis, a neighboring island with a healthy population of the species, but this proved to have a few setbacks. We quickly realized that our plan was failing; in nearly 240 attempts to bring a Nevis animal into the St. Kitts population, we were not able to observe a single successful reproductive event. We then introduced the idea that they were different species, despite looking identical. As we conducted research, we were able to confirm our suspicions. We’ve traced the cause of this to three different events: natural selection, allopatric speciation and the founder effect, and prezygotic reproductive isolation due to habitat isolation.

Separate Islands Equals Separate Species?

Upon looking into the maps of St. Kitts and Nevis, we have concluded that they may have once been together as one island. Due to this conclusion, we have realized that the rodents were once one species; however, due to habitat isolation as the islands grew apart a phenomena called prezygotic reproductive isolation has occurred. This happens when two species are in the same general area but are on different enough terrain that they form different breeding requirements, causing the two species not to be able to mate with one another. This would explain why after so many attempts we were unable to witness a successful reproductive event.

An Act of Nature?

Diversifying selection may have begun to occur before the islands split into their own separate habitats. This occurs when a habitat begins to favor traits in a certain population’s genetics; there becomes an increase in the amount of different traits in a population and over time the species splits into two separate groups. As the habitat began to change and split off into two islands, the terrain may have begun to favor some traits over others. These different traits can be shown in our data chart (attached below) we have collected in the sections that pertain to size, speed, and leap height. The rodents that didn’t hold these traits declined over a long period of time, causing us to be left with two different species on St. Kitts and Nevis.

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Gene Pool Picking?

One last final explanation on the theory of the two different rat species would be Allopatric Speciation. Allopatric speciation only occurs during geographic isolation, which would tie into the theory that the two islands were once one. As everyone knows the founder effect is part of Allopatric speciation, obviously when the two islands split up there was only so many genes left in the gene pool for the rodents to reproduce out of. We also seemed to have found that the rodents on St. Kitt island are in the sciurus genus, the genus that the common European, North, South, and Central American squirrel is in. On the other hand the squirrel on Nevis island is in the Heteromys genus, the genus of most Central America rodents. We currently are finalizing scientific names for the species, leave ideas in the comments.