Wake Tech BIO 112 - Evolution A Case Study in Speciation

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A Case Study in SpeciationQuestions:A Case Study in Speciation Hawthorn trees are native to North America. Hawthorn fruitsrange between 5 mm and 20 mm in diameter, with anaverage of 12.6 mm. The hawthorn fruit is eaten by thelarvae of the hawthorn maggot fly, Rhagoletis pomonella.The female lays fertilized eggs in the fruit. Maggots (larvae)emerge from the egg, feed on the fruit, and grow throughseveral molts. To stay safe these maggots burrow into the fruit as they grow. Healthy maggots drop from the tree with the fruit and burrow in thesoil. Pupation takes place in the soil. Adult maggot fliesemerge from the soil and fly to fruit trees, where they mateon the surface of the fruit. Hawthorn maggot flies are parasitized by parasitoid waspsthat lay eggs in the maggot’s body, paralyzing and ultimatelykilling the maggot. One way the flies avoid these parasitoidwasps is by burrowing into the fruit. Domesticated apples (Malus domesticus) were introduced toNorth American in the 1600s. They are the most widelygrown frui t in North America. A typical commercial apple hasa diameter of 70 mm. When apples were introduced to NorthAmerica, the larva of Rhagoletis pomonella started feedingon them. The large apple fruit provides 220 times more foodthan hawthorn fruit, but nutritionally the quality of hawthornfruit is superior. However, the apples are larger so the fliescan make deeper burrows to avoid parasitoid wasps. It hasbeen observed that apple maggots carry fewer parasitoidwasp eggs than hawthorn maggots do. One study shows that52% of hawthorn maggots (those that live on the hawthornfruits) survive while only 27% of maggots raised on applessurvive.Scientists studying the hawthornmaggot flies have found thatHawthorn and apple maggot flies arephysically indistinguishable.However, they are geneticallydistinct, with different geneticprofiles. While there is nogeographic isolation or physicalseparation between hawthorn andapple maggot flies, they do prefer tomate with other flies from the sametype of fruit. For example, flies bornon apple trees will usually mate withother flies born on apple trees.There is only a 4-6% hybridization rate between hawthorn and apple maggot flies and there are no post zygotic barriers that have been observed. Apple trees and hawthorn trees have fruit hat ripen at different times of year, which leads to temporal separation of apple and hawthorn flies.Questions: 1. Based on your initial reaction, are these flies two species?No, they are the same species, they are just born and raised within different environments. 2. Which information is relevant to the morphological species definition? (choose all that apply)a. Hawthorn and apple maggot flies are physically indistinguishable.b. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.c. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.d. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs inhawthorns and apples, respectively.3. According to the morphological species concept, are hawthorn and apple maggot flies separate species? Explain.They technically are because they prefer to breed with their own [maggots that were raised within their environment] and they have genetic differences .4. Which information is relevant to the biological species definition? (choose all that apply)a. Hawthorn and apple maggot flies are physically indistinguishable.b. There is a 4-6% hybridization rate between hawthorn and apple maggot flies.c. Hawthorn and apple maggot flies are genetically distinguishable and have a distinct genetic profiles.d. Hawthorn and apple maggot flies strongly prefer to mate and lay fertilized eggs inhawthorns and apples, respectively.5. What reproductive barrier limits interbreeding between hawthorn and apple maggot flies?The fruit that they breed in. 6. According to the biological species concept, are hawthorn and apple maggot flies separate species? Explain. Technically yes because they mate within their respective fruit. 7. Based on the information provided in this case study, are hawthorn and apple maggot flies separate species? Explain your thoughts. Which species concept are youusing?By the biological concept, their reproductive behavior is different therefore they are different. The mating within their respective fruit separates them and they can also create hybrids while the Hawthorne flies cannot. 8. Is this an example of allopatric speciation or sympatric speciation? Explain your reasoning.Sympatric speciation because they are within the same vicinity but it is there reproductivebehavior or their sexual selection to reproduce with flies that are like them that separates


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Wake Tech BIO 112 - Evolution A Case Study in Speciation

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