A botanist is studying two closely related plants. She extracts nuclear DNA and finds out one individual has two copies of each chromosome (diploid) and the other has four copies of each chromosome (tetraploid). Based on this information, she determines they are separate species. In making this determination, which species concept was used?

Question

BlackTom AI · Accepted Answer

The question asks which species concept is applied when two closely related plants are found to have different ploidy levels (diploid vs. tetraploid) and are considered separate species based on this observation.
Option 1: Morphological species concept. This concept defines species primarily by observable physical traits and morphology. While chromosome number can influence form, the core criterion here is not morphological similarity or difference, but reproductive compatibility, so this option is not the best fit for explaining speciation due to ploidy.
Option 2: Biological species concept. This concept centers on reproductive isolation—species are groups that can interbreed and produce viable, fertile offspring. The diploid and tetraploid individuals would have trouble producing normal offspring together due to mismatched chromosome sets, effectively isolating them reproductively. This is a classic route to speciation when polyploidy creates barriers to interbreeding, making this the most fitting concept for the scenario.
Option 3: Phylogenetic species concept. This defines species based on the smallest diagnosable monophyletic group in a phylogenetic tree. While polyploidy can be used in phylogenetic analyses, the key point in the scenario is the reproductive barrier due to chromosome differences, not the reconstruction of a phylogeny.
Option 4: Molecular species concept. This approach uses genetic differences to delineate species, often focusing on DNA sequence divergence. Although ploidy changes do affect genetics, the decisive factor highlighted here is reproductive isolation rather than merely molecular divergence.
Option 5: Ecological species concept. This concept defines species by occupying distinct ecological niches. The scenario emphasizes chromosomal differences and potential reproductive barriers rather than niche differentiation, so this is not the central explanation.
In summary, the core idea demonstrated by diploid versus tetraploid individuals leading to separation into distinct species through hindered interbreeding aligns most closely with the Biological species concept, which centers on reproductive compatibility and isolation.

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