Evolution__3rd_Edition

198 PART 2 / Evolutionary Genetics
Figure 8.1
Two species of the butterfly Heliconius form parallel mimicry
rings in South America. At each site indicated, both H. erato
and H. melpomene are present and mimic each other; in
Heliconius also exists in multiple
forms, ...
. . . but its genetics differ from
Papilio memnon
Heliconius
melpomene
Heliconius
erato
different places the two species vary, in parallel, in appearance.
Both species are poisonous. Redrawn, by permission of the
publisher, from Turner (1976).
linked. When two morphs of a Heliconius species are crossed, the offspring contain a
kaleidoscopic variety of non-mimetic recombinant forms that resemble neither parent
nor any known morph of the species.
Why do the genetics differ in Heliconius and P. memnon? The reason is probably
geographic. At any one site in the range of P. memnon, several morphs are often living
side by side. Crosses between them will happen with high frequency naturally. But
in Heliconius only one morph is usually living at any one place. The different morphs
are mainly geographically separated and will not interbreed in nature. Moreover, in
Heliconius, the areas of overlap between neighboring morphs are probably due to
recent range expansions: in the past the ranges were probably completely separate.
The non-mimetic recombinant forms of Heliconius are usually generated only when
morphs from different places are put together in the lab. In Heliconius it does not matter
if the mimicry genes are scattered around the chromosomes, because the non-mimetic
progeny are not usually produced. In P. memnon it does matter. If the mimicry genes
were not linked, the recombinants would be produced a and be killed by predators.
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