Genetics 9
Origins of the black bee
In the next 6 pages some ideas regarding the origins of the black bee Apis mellifera mellifera are investigated, in particular its evolution and relationship to the other three honeybee species.

Apart from making honey the four honeybee species have something else in common - they sting. The polypeptide melittin is the main toxin in bee venom. The chemical structure of melittin is shown on the left.
melittin amino acid sequence
Kreil used this data to deduce the phylogenetic relationships between these four species:

The sequences for mellifera and cerana are identical showing that these two species are very closely related which suggests that they diverged only relatively recently on a geological scale.

The sequence of dorsata differs from the mellifera/cerana sequence by only 3 amino acid residues but a difference of 5 residues is found between dorsata and florea.
On this basis a phylogenetic tree can be proposed where the line of descent of florea is the first to branch off from the line traced back to the common ancestor of the honeybee. This is followed by the branching off of dorsata. Followed by cerana and mellifera at a much later date.

Estimates of the dates of the branching of florea and dorsata has been difficult to find. But recent work has estimated that the mellifera/cerana split occurred about 6 to 9 million years ago.

The geographical distribution of these four honeybee species is shown on the next page.
Next page: Genetics 10.
phylogenetic tree
melittin structure
In a series of experiments published in 1973-75 G. Kreil(1)
G. Kreil(2) found the amino acid sequence in the four species of Apis: mellifera; cerana; dorsata; and florea. All four melittins are composed of 26 amino acids in a straight chain with differences among the species only at positions 5, 10, 15, 22, 25 and 26. The amino acids at the other positions are identical.

In the diagram below the 4 amino acid sequences are draw with the amino group (the N-terminal) on the left. The differences in the amino acids residues for each adjacent sequence is shown by the coloured boxes.
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