1a. What species concept should be used in this case? b. Are apple maggot flies

Question

1a. What species concept should be used in this case?

b. Are apple maggot flies distinct as a species from hawthorn maggot flies?

c. Propose a biologically reasonable scenario that explains how apple maggot flies evolved.

d. How did you weigh the different pieces of evidence to reach a conclusion to questions (2) and (3)? What evidence was most important, what was least important, etc.?

e. What further information would you need to increase your confidence in the conclusions you reached?

Hawthorn trees grow throughout North America and they produce a small fruit which is eaten by a small fly larva. In 1864, apple growers discovered an unknown maggot had started feeding on apples. Through the years, hawthorn and apple maggot flies have progressively become more distinct. Below I present evidence taken from the original scientific literature for you to consider and evaluate From what may be incomplete and ambiguous data, I hope you will be able to answer what appear to be two simple questions 1. Do hawthorn maggot flies and apple maggot flies belong to the same species? If not, and if apple maggot flies belong to their own species, what would be a biologically reasonable scenario for how the speciation occurred? 2. Facts about Hawthorn and Apple Maggot Flies (Rhagoletis pomonella) The Organisms The apple maggot fly (Rhagoletis pomonella, Walsh) is native to eastern North America. It originally bred in the large fruits of hawthorn trees (Reissig. 1991). Apple maggot flies are about 5 mm long. The tip of a female's abdomen is more narrowly pointed than a male's Hawthorn and apple maggot flies are assigned to the same VAtaxonomic species (Rhagoletis pomonella) (Bush, 1966 2002) Figure 1: Apple maggot flies (male -left, female -right) . Hawthorn maggot flies and apple maggot flies are physically indistinguishable . There is no geographic isolation or physical separation between adult maggot flies . As host-races of the same species, these flies are not typically given different common names

Explanation / Answer

Answer (a): This is an example of microevolution. Since both Hawthorn maggot fly and apply maggot fly deviated from a common ancesteral origin, they represent Sympatric speciation. In Sympatric speciation, the parental species developes into two different species, merely due to exploitation of new niche. Gene flow between them reduces because of the adaptation of reproduction cycle according to the new niche.

(b): However, hawthorn maggot fly and Apple maggot fly are physically indistinguishable, genetically they are different and are easily distinguishable. Their choice of fruit for laying eggs has reduced the fidelity between them. Although, they have evolved as distinct species and have different common name but they are considered as different 'race' and are denoted by same scientific name.

(c): In ancient time, the ancestors of Apple maggot flies used to lay their eggs on hawthorns, but recently, they lay eggs on Hawthorn trees (native to North America) and Apples (introduced to North America by immigrants). Females lay their eggs on the fruit they grew, and males look for mates on the fruit they grew. Therefore, Hawthorn flies end up mating with other hawthorn flies and so does apple flies. This reduced the gene flow between the population that mate on different fruit. The timing of ripening of fruits and reproductive cylcle of flies also played a great role in the shift from hawthorns to apples and consequently towards sympatric speciation.

(d): Although both the flies are physically indistinguishable but their genetic variation leads to the conclusion of their evolution as sympatric species over a period of time. Since the time period is not as long as it requires for complete evolution of a species, they is referred to as different 'race' of same species and have been designated same scientific name 'Rhagoletis pomonella'.

The most important evidence of speciation are the genetic variation among them, their separate niche, reduced reproductive fidelity. The least important was their physical resembelance. The reproductive fidelity will reducO to nill in future. owing to the time period required for complete evolution, these flies evolved in last 100 years only, hence this speciation is in process of evolution.

(e): We all are evolving with time. The only thing that distinguishes one species from another is their gene pool. A complete knowledge of genetic variation between the species and the change in genetic frequency over the time will help us understand the evolution.

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