Case Study Instructions

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Feb 20, 2024

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Something’s fishy in Lake Paxton: Speciation in Sticklebacks In this case study, we are going to be talking about the origin of species – where new species come from. In order to do so, I want to provide you with a few concepts and definitions. First of all what is a species? There are many possible ways to answer this question, but perhaps the most popular and widely used definition is defined below, along with other important terms: The Biological Species Concept ( BSC ) defines a species as: a population or group of populations whose members have the potential to interbreed in nature and produce viable and fertile offspring, but who cannot successfully interbreed with members of other species. Population : a group of individuals of the same species living in the same area at the same time When new species form, we call the process speciation. Essentially, speciation is when a population of organisms diverges (evolves differences) from another population to such a degree that the two populations no longer act like a single species, but rather act like 2 species. If we’re thinking of the BSC , it means the 2 populations no longer can produce viable and fertile offspring. Speciation may occur by two different mechanisms, allopatric speciation and sympatric speciation , though allopatric speciation is thought to be much more common than sympatric. Allopatric speciation is speciation that occurs when two populations become separated by a geographic barrier, such as a river, mountain, or any other type of unsuitable habitat between the populations. Allopatric speciation can also occur when members of a single species disperse into a new isolated habitat, creating two geographically separated populations. Once isolated, the two populations diverge. Sympatric speciation is speciation that occurs without a geographic separation between the two populations. In sympatric speciation, members of the same population undergo divergent or diversifying selection, eventually resulting on two distinct populations occupying the same general geographic range.

For Today: 1. Discuss with your group what questions you could test experimentally to determine if the two Stickleback types are a single species or two species. Specifically: a. Is gene flow being disrupted? b. Is there a difference in fitness? c. Is there evidence of reproductive isolating mechanisms? 2. Develop a hypothesis and post your idea to the class discussion board. Here are some terms to help identify generations in a population: a. P generation – the parents b. F1 – first generation offspring c. F2 – second generation offspring 3. Plan your experiment and add these details to your discussion post. Be sure to include the following: a. How many of each type of stickleback you will require? b. Where your experiments will take place (in the lab, in the field or both locations)? c. What type of data you would collect during your experiment? d. What are the independent & dependent variables? e. What do you expect to get as results if your hypothesis is valid? 4. Once your group has posted a plan – your plans will then be open for peer review. 5. Individually, peer review at least one group’s proposal. You should comment on the following: a. Does the experimental design match the question and hypothesis? b. Questions you have about the experimental plan. 6. Evaluate the lab data provided & complete the worksheet below.

Experiment # Hypothesis Supported (1 species/2 species/ in transition) Why according to the Biological Species Concept? 1 1 species This successfully became a single species since there were children between Bethnic and Limnetic, and they effectively reproduced in their natural environment. According to the data, the F2 hybrids are in the middle of the two in terms of both body depth and measures of the rest of the body. 2 2 species Benthic and Limnetic Sticklebacks have very varied feeding success rates in various settings, which raises the possibility that these two groups may be two unique species. 3 Transition There was a production of the F2 hybrids, but they were at such a small rate, that seemed as if they were trying to go away from it. 4 2 species Though they only desired matings between individuals with the same names, such as Limnetic male to Limnetic female, and vice versa, they nonetheless attempted to mate the Limnetic with the Bethnis. 5 2 species The stark disparities in nest cover preferences between limnetic and benthic sticklebacks reveal ecological and perhaps behavioral differences, which raises the possibility that they are two distinct species or that speciation is taking place. 6 1 species A 95% success rate was achieved by the Betbois and Limnetic F1 hybrids when they mated, compared to 97% for Bethis and Bethnic and 96% for Limnetics. This demonstrates that they have success reproducing.

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7 2 species Data on courtship behavior suggests that Benthic and Limpetic sticklebacks may belong to different species. A potential reproductive barrier is suggested by the lack of positive female responses in the benthic male and limnetic female combo. 8 2 species According to the data on the various growth rates of benthic, limnetic, and F1 hybrid sticklebacks in various zones, it's possible that they are two independent species that are currently going through speciation. 9 2 species Due to signs of reproductive isolation, such as the restricted mating reference, the sticklebacks may represent two distinct species. Only a tiny percentage of emetic remakes sawn with hybrid males, and the majority of them prefer to sawn with limnetic males, suggesting the prospect of restricted interbreeding and the possibility that these two groups may be separate species or in the process of speciation. 10 1 species The F1 hybrid stickleback from Paxton lake introduced to second lake are showing viability as they have successfully formed a population with intermediate anatomic features between the benthic and limnetic stickleback. 11 2 species The field observations of courtship and mating between two species sticklebacks where interspecific courtships were observed but never completed Write your group’s conclusion about the question “Are the two Stickleback types a single species or two different species?” using data from the above experiments to support your conclusion .

Based on the data and observations from our experiments, we conclude that the two Stickleback types are likely two different species rather than a single species. Here are the key findings that support our conclusion: Mating Behaviors and Hybridization: In the laboratory experiments, we observed mating behaviors and even successful hybrid offspring between the two Stickleback types. This suggests that there is a lack of reproductive isolation between them, as they can interbreed and produce viable offspring. Field Observations: In their natural habitats, we also observed mating behaviors and a lack of geographical barriers preventing interaction between the types. This reinforces the notion that they are behaving as two distinct populations rather than a single, interbreeding one. Considering these findings, it is reasonable to conclude that the two Stickleback types meet the criteria of the Biological Species Concept, which defines a species as populations capable of interbreeding and producing viable and fertile offspring. Therefore, we suggest that they should be classified as two different species.

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