Which of the following is believed to be the primary reproductive isolation mechanism for causing sympatric speciation in North American apple maggot flies (Rhagoletis pomonella)? Group of answer choices autopolyploidy allopolyploidy habitat isolation sexual selection
The correct answer and explanation is:
The correct answer is habitat isolation.
Explanation:
The North American apple maggot fly, Rhagoletis pomonella, is a well-studied example often cited in discussions of sympatric or parapatric speciation. Historically, these flies primarily laid their eggs in the fruits of hawthorn trees. However, with the introduction and widespread cultivation of domesticated apples (a non-native host) in North America, a new population of Rhagoletis emerged that began utilizing apples as a host plant.
The primary reproductive isolation mechanism driving the divergence between the apple-infesting and hawthorn-infesting populations is habitat isolation, specifically tied to their host plant preference. Flies tend to mate on or near the fruit where they emerged. Females strongly prefer to lay their eggs on the type of fruit they developed in. This strong preference for either apples or hawthorns creates a significant barrier to gene flow between the two groups, even though they exist in the same geographic areas (sympatric).
While other factors like temporal isolation (apples ripen earlier than hawthorns, leading to different breeding seasons) also contribute to reducing gene flow, this temporal difference stems from the host plant choice itself. Therefore, the choice of host plant acts as the fundamental mechanism separating the populations for mating and reproduction, effectively isolating their “habitats” in terms of breeding substrate.
The other options are not considered the primary mechanism for Rhagoletis speciation: Autopolyploidy and allopolyploidy involve changes in chromosome number, which is not the process observed here. Sexual selection, while potentially playing a minor role in mate choice on the fruit, is not considered the primary driver of the initial and main reproductive isolation barrier, which is established by the host-fidelity behavior.