Transcript How many species of cichlid fishes are there in

How many species of cichlid
fishes are there in Lake
Tanganyika?
By Andrew G Challingsworth
Lake Tanganyika?
• The endemic fishes of Lake Tanganyika are a
textbook examples of explosive speciation and
adaptive radiation.
• Their study promises to yield important insight
into the processes of speciation.
• Accurate estimates of species richness of lineages
in Lake Tanganyika will be a necessary
prerequisite for a comparative analysis of the
intrinsic and extrinsic factors influencing rates of
diversification.
Lake Tanganyika!
• On the basis of current estimates of species
richness, number of founding lineages and
age of radiations, it appears that these fishes
represent the most rapid known large-scale
radiation of species of any animal group in
a circumscribed area.
Lake Tanganyika!
• Thus, we suggest that the study of cichlid fishes
may offer unique opportunities to gain insight into
the reason underlying the taxonomic and
geographical distributions of species richness and
functional diversity.
• Molecular phylogenetic studies have suggested
that much of the radiation of species has occurred
within the present basins of Lake Tanganyika
Lake Tanganyika!
• Molecular studies have also provided
circumstantial evidence for within-lake
geographical isolation of populations,
confined to rocky shores of Lake
Tanganyika.
• This suggests a possible role of
intralacustrine allopatric speciation among
such habitat specialist taxa.
Lake Tanganyika!
• Recent theoretical studies have suggested that
sympatric speciation is a more plausible process
than previously believed, and that it might be
driven by disruptive natural or sexual selection or
by a combination of both.
• Divergence under natural selection, or at any rate
coexistence in sympatry, may be facilitated by the
legendary functional plasticity of the cichlid
feeding structures.
Lake Tanganyikan feeding
structures!
Tanganicodus irsarcae an insectivorous carnivore also
awfusch feeder.
Tanganicoudus irsarcae
• Tanganicoudus irsarcae feeds on invertebrates
found with in the algae layer found on the rocky bi
cover or commonly known awfusch layer.
• It also has pharyngeal teeth for extracting
cellulose out of the algae.
• Also with reduced swim bladder for surge type
environment.
• The functional plasticity of the cichlid is a surge
zone rock feeding fish.
Conspecifics that have also
adapted to the surge type
environment.
Eretmodus cyanostictus southern variation feeds
predominately on the Awfusch bi cover.
What is Awfusch
Awfusch is the algae bi cover that encrusts rocks in the photic zone.
Awfusch
Provides nutrients in the form of cellulose
for many fish species that have pharyngeal
teeth for extracting the nutrients out of the
algae cell.
Pharyngeal teeth
• A good representation in identifying fishes
is by there tooth structure, the picture below
is the pharyngeal teeth of Eretmodus
cyanostictus.
Conspecifics Eretmodus
cyanostictus
• Also feeds on the awfusch bi cover.
• Is not an insectivore feeds solely on the Awfusch
bi cover.
• Mimicry in its display pattern to Tanganicodus
irsarcae.
• Also has a reduced swim bladder for surge type
environment.
• Plasticity evolving to fill niche areas that are under
utilized by other species.
Morphological traits
• Until the 1980s, most cichlid species were
defined on the basis of morphological traits
likely to be amenable to study in preserved
museum specimens.
Feeding structures in Lake
Tanganyika.
• Although what seems to dominate the feeding
structure in the cichlids of Lake Tanganyika is
space.
• The utilization of every available area of space has
been utilized by the cichlids.
• This can be tested true due to the fluctuations of
the water level of lake Tanganyika particularly the
surge biotope as the water level increases the
surge biotope expands and hence as the water
level decreases the surge biotope contracts.
Feeding structures in Lake
Tanganyika.
• Due to the expansion of water as the lake level
rises we can see new habitats created
predominately rocky algae based habitats which is
then exploited by the species, often forming
another new species to utilize the abundance of
food resources.
• This ideology the expansion and contraction
theory has predominated speciation in much of
Lake Tanganyika’s faunal environment.
Where there seems to be
allocation of space we have the
representation of a species.
Living in the desolated shell beds of the snail genus Neothauma
is another cichlid taking advantage of the utilization of space.
Shell dwellers
• These are a diminutive species of cichlid
that have utilized the empty snail shells of
the genus Neothauma which accumulate in
masses on the lake floor.
Utilization of space
• In this tropical lake where optimum a biotic
and biotic factors such as high water
temperature, calcium riched environment
abundant food supply create patterns of
speciation which can be viewed in respect
to other working evolutionary systems
representing other lineages of fish from
other lakes in the Rift lake system.
Other examples of the utilization
of space.
• Almost every example in species
diversification in Lake Tanganyika can be
described as the utilization of space.
• But what makes the utilization of space
such a promising agent for speciation.
• It is because it is accompanied by such
successful biotic and a biotic factors that
make speciation so successful.
Utilization of Zooplankton!
• Due to the enriched sunlit waters and the
high amounts of solar radiation penetrating
Lake Tanganyika there is a massive
production of zooplankton which
specifically identifies species into certain
feeding guilds one such species is
Cyprichromis leptosoma.
Once again the utilization of
space.
• It seems that where we have a food resource
or even a habitat resource in Lake
Tanganyika we have a species utilizing that
niche to become evolutionary successful.
Cyprichromis feeding on the
zooplankton!
• An open water swimmer utilizing the
abundant zooplankton resources is
Cyprichromis leptosoma which actually
spaces itself out in shoals and the defined
space are considered the species territory
although constantly moving thus the
utilization of space has been taken one step
further into a moving territorial existence.
Recent surveys of Lake
Tanganyika!
• Increasing estimates of cichlid species
richness in Lake Tanganyika has risen the
number of cichlids from 173 species to
more than 200 species with a recent field
guide listing approximately 213 species.
• Although to get a good rough estimate the
total is most likely to be 250.
Why such a species richness!
• Two ancient lake wide lineages have each
been subdivided into clades conforming
approximately to the outlines of the three
ancient basins which were split apart by
documented falls in the water level.
Conclusion
• Species diversification has been the agents
of:
• The utilization of space by the Cichlid
species.
• The biotic and a biotic factors as mentioned
that have influenced such a high rate of
success in species speciation and
diversification.
Bibliography
• Graduate Certificate of Aquaculture Deakin
University.
• The Aquanet Place Research Center 14161422 RO Malvern Rd Glen Iris 3146.