DNA analysis is certainly a big help.
A certain percentage difference in DNA/genetic material is set for diferentiation of species in mammal.
This have results in 2 species of Orang-utans, 2 of Gorillas, 3 of giraffes, 2 of Clouded Leopards, etc.
They can be differentiated superficially but are fully inter-fertile.
In the case of lesser animals like butterflies, different limits will need to be set, and I suspect the infertility barrier will be even more porous between sibling species.
A good species for DNA analysis is Papilio clytia.
In Malaya all forms occur until the halfway mark & roughly from Selangor southwards to Singapore only form dissimilis is known.
This suggest that f-dissimilis is acting on its own ie. as a good separate species.
I don't whether anyone has done any breeding experiments to show all the forms can arise from a batch of eggs.
TL Seow![]()