I got off of the plane in
Lilongwe, exhausted after my journey from Canada. I was met by a smiling man
who I was to drive with for the next five hours north to the village of Kande,
on the shores of Lake Malawi. We drove through the beautiful countryside and
countless villages that all had their little hub of shops and restaurants
nestled around the main road. We reached Kande at around 7:30; it was dark, and
only the bright stars and the fireflies lit the road.
I was asleep as soon as my head
hit the pillow in my cozy cabin. The next morning I was up and at it, taking a new
diver out to explore the reef. It was my first dive in the lake as well. Right away fish of many different shapes and
colours surround me. I know Lake Malawi is known as the most biologically
diverse lake on the planet, but wow! The manifestation of this diversity astounds
me.
The cichlid fishes are one of the
largest animal groups on the planet. The group itself is thought to predate the
continental drift events that separated Africa and South America around 140
million years ago as they are found in Africa, Latin America, Madagascar, and some
parts of South East Asia. However, the
African cichlids represent one of the most striking examples of adaptive
radiation (rapid evolutionary divergence) in the animal kingdom.
There are over 600 identified
species, and many more unidentified species that live only in Lake Malawi! The lake
basin is thought to be around 8.6 million years old, yet the majority of the
cichlid species have been thought to have diverged from each other much more
recently than the origin of the lake. To give you an idea of that insane speed,
it is thought that we diverged from our closest living relative, the
chimpanzee, around 13 million years ago!
There are many hypotheses as to
how this group of fish has diversified so spectacularly. The geological history
of the African lakes and their rising and falling cycles have given rise to
many smaller lakes that have disconnected and reconnected over evolutionary
time. This has allowed for many separate, but startlingly parallel,
evolutionary trajectories. There are many highly behaviourally similar species
that live in different regions or lakes, yet share less genetic similarity with
each other than with the other species in close range.
Like Darwin’s finches of the
Galapagos Islands the Cichlids of Africa have all specialized to specific
ecological niches. There are species that remove parasites from the skin of
catfish, and another that eats the catfish skin itself. There are scale eaters,
fin-biters, sediment sifters, and zooplankton feeders. There is a group that
inhabits snail shells, another that eats snails, crabs, or flies on the
surface, and yet another that flips rocks to find insect larvae hidden
underneath. Some species have evolved huge eyes to enable them to see in the
dim lights at depths of over 100 meters, and others have evolved lateral line
systems to enable them to find creatures in the mud.
These different morphological and
behavioural adaptations are associated with changes in body shape and colour,
jaw structure and orientation, and teeth size and form. As I float through this
underwater realm I can see these novel adaptations in action. The evolutionary
history of this lake, and the resulting diversity amaze me.
It is one of the many reasons that I chose to come to
Malawi, and I am looking forward to my time here amongst these crazy fish!
