Australasian Science 11

(Jacob Rumans) #1
APRIL 2016|| 17

S


ix closely related species of rock-wallaby from north-
east Queensland have long been considered a classic
example of chromosomal speciation. Each of these
species is similar in almost every way, yet each differs
in the shape and number of their chromosomes.
These chromosome differences should make gene low
between these species almost impossible, since hybrids would
have reduced fertility due to their chromosome differences.
However, contrary to expectations, we have found no rela-
tionship between the degree of chromosome differences and
the amount of gene low among these species. For example, we
found relatively high levels of gene low between some species
that differ by multiple chromosome changes, and alternatively

we found low gene low between species with similar chromo-
somes.
This indicates that the mechanisms driving species forma-
tion are much more complex than just the incompatibilities
caused by chromosome rearrangements. It appears then that
complex interactions between the way genetic material is pack-
aged into chromosomes and how the chromosomes differ in
their shape, number and arrangement is driving species forma-
tion.
Chromosomes are the long molecules of deoxyribonucleic
acid (DNA) found in each cell that contain all the genetic infor-
mation each organism requires to function. For example, each
human cell contains about 2 metres of DNA, separated into

Wallabies Rock the


Basis of Speciation


SALLY POTTER & MARK ELDRIDGE

Six rock-wallaby species in Queensland have different numbers of chromosomes, yet gene
flow somehow occurs between them. What does this tell us about how new species form?

Credit: Henry Cook

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