This study examined the phylogeny and evolution of the genus Adansonia, which includes baobab species found across Africa and Australia, using the internal transcribed spacer (ITS) region. Twenty samples from six Adansonia species were used to construct a phylogenetic tree. The results showed that species located closer together geographically, like those within Madagascar, were more closely related on the tree. This supports the hypothesis that geographic proximity leads to greater genetic similarity between species over time due to shared ancestry and limited gene flow across large distances.

1.
Phylogeny and evolution of Adansonia across Continental Africa and Australia examined through the ITS region
Raveena Gupta
University of Wisconsin Madison1
David Baum Lab, Botany Department 2
SELECTED REFERENCES:
Baum D.A., Small, R.L., & Wendel J.F. (1998) Biogeography and
Floral Evolution of Baobabs (Adansonia , Bombacaceae)
as Inferred From Multiple Data Sets. Syst. Biol . 47(2) :
181± 207, 1998
Baum, D. A. (1995). The comparative pollination and oral biology of
baobabs (Adansonia Ð Bombacaceae). Ann. Mo. Bot.
Gard. 82:322± 348.
Chirwa M, Chithila V, Kayambazinthu D, Dohse C (2006).
Distribution and Population
473 Structures of Adansonia digitata in Malawi. FRIM,
Zomba, Malawi
De Smedt, S., Alaerts, K., Kouyate, A.M., Van Damme, P., Potters,
G., and Samson, R. (2011). Phenotypic variation of
baobab (Adansonia digitata L.) fruit traits in Mali.
Agroforestry Systems 82, 87-97.
Jack D. Pettigrew FRS, Karen L. Bell, Adhil Bhagwandin,& Eunice
Grinan, Ngalla Jillani,& Jean Meyer, Emily Wabuyelea
& Claudia E. Vickers (2012). Morphology, ploidy and
molecular phylogenetics reveal a new diploid species
from Africa in the baobab genus Adansonia (Malvaceae:
Bombacoideae). 1240-1250
ACKNOWLEDGEMENTS:
The David Baum Lab, Botany Department, at University of
Madison, supports this work. I would like to thank the David Baum
Lab for all the help and encouragement to complete this project.
ABSTRACT:
A phylogeny of the genus Adansonia, family Malvaceae was created by use of the ITS (internal transcribed spacer) region; 20 samples from six of the Adansonia species were utilized. Genus Adansonia consists of 9 species and is found (A.
digitata, A. suarezensis, A. za, A. perrieri, A. madagascariensis, A. grandidieri, A. rubrostipa, A. gregorii, A. killma) in continental Africa (this includes mainland Africa and Madagascar) and Australia. In the experiment, at least all the species from
Madagascar had a sample except for the two species from Africa and one from Australia. This analysis was carried out using the ITS region. The reads were assembled in Geneious and a phylogenetic tree was created by MEGA by bootstrapping it. A
maximum likelihood and maximum parsimony shows a possible explanation to understand the phylogeny of the Adansonia. Through the investigation, the phylogeny has given a lot of evidence regarding the evolution of the Adansonia species through
discrepancies in geographical distributions. This has ultimately led to the plausible hypothesis that species that are close together would have similar ancestors and would be more closely related. The species such as A.gregorii and A. digitata would be less
related to the rest of the species in Madagascar as they are far apart from each other. However the African species would be more related to the Madagascar species, but would be less parsimonious with the Australian species as it is further away.
Methods:
1) DNA Extraction using the modified Malvacea method
2) PCR of the ITS region using the LEU and 2 primers. (These are
custom made at the David Baum Lab)
3) Sanger sequencing was performed using all the four primers that
make up the region (two forward LEU and 3b and two reversed 2
and 4). Sanger sequencing was completed at the UW Madison
Biotechnology Center, Madison, WI.
4) Use Geneious to extract genomic sequence by manually aligning
them and editing the sequences.
5) The MEGA program was used to measure maximum likelihood and
parsimony. The bootstrap consensus tree was also created.
INTRODUCTION:
Adansonia species are extremely important. They belong to the Malvacea
family and the Bombacoideae subfamily (Munthali et al., 2012). This plants
of this genus is very useful for medical uses and as a food source in many
parts of the world especially, Africa where it is abundantly found (Munthali
et al., 2012).
The common name for the each of the nine species of the Adansonia is
Baobab. The Adansonia genus is found throughout the Indian Ocean region.
(Munthali et al., 2012). Baum et al. (1998) and his team argue that
Adansonia was originally found in Madagascar and migrated to Africa by
long- distance dispersal. This dispersal happened before the breaking of the
West Gondwana during the beginning of the crustaceous period (Baum et al,
1998). The Africa baobab trees are usually associated with the savannah,
more importantly the drier parts. Of the nine species, six are native to
Madagascar, two are native to Africa and the Arabian Peninsula, and one is
native to Australia (Baum et al, 19950). Some of the other species may also
be found in other parts of the world but that is due to human dispersal (Baum
et al, 1995).
DISCUSSION:
The diagram shows a total of eight species. This is where there is
geographical difference in the species, which is an influential factor that has
caused mutations within the plant. By analyzing the tree, it is visible that
within the eight species of Adansonia diversities emerged; this causes more
variance in the genetic material of the Adansonia and increases the diversity,
making the Adansonia more adaptable and environmentally fit to survive a
variety of conditions. Through the experiment we see that because the
Adansonia has travelled to so many places around Africa, it has adapted and
therefore the genes have mutated. This creates variability as it only build up
over time from gene mutations and polyploidy.
When the tree is compared to the map there are a lot of similarities to the
map as there is evidence indicating that the species that are close together in
the map have similar genetics as they are sister taxas in the phylogenetic tree.
For example A. madagascariensis is more similar to A.za, A. perrieri and A.
suarezensis. The possible explanation for this is that they are geographically
very close. A.za is present both in the south and north of Madagascar hence
allowing many of the species to similar to each other. However there is
distinct separate of species in Madagascar as indicated in the map. Also in
the map it is quite evident that the distribution of the A.za is very prevalent
towards the north and southwestern part of Madagascar. It is perhaps the
most available species distribution in Madagascar, which may suggest as to
why a lot of the other species relate more to the za specie.
RESULTS:
The phylogenetic tree was generated using the MEGA program. As soon as the results
from the Biotech Center arrived, the samples were run through the Geneious
application. The tree shows how the samples have diverged overtime in Madagascar.
The out-group, Pseudobombax (a taxon outside of the group or genera being
examined), has diverged away from the rest of the samples confirming the liability of
the data.
Figure 1: This is the most parsimonious
tree that was generated through the
MEGA program. With the
Pseudobombax as an out-group the tree
above shows the divergence of the
species with the Pseudobombax
confirming this. The samples above
show that all the samples derive from
the same ancestor and due to climate
and geographical constraints have
diverged. As a result successful gene
flow and speciation has occurred.
Figure 2: The geographical
presentation and distribution of the six
Adansonia species that exist in
Madagascar. Out of the nine species
only the six that are native to
Madagascar are: suarezensis, za,
perrieri, madagascariensis, grandidieri,
and rubrostipa. This image has been
retrieved from : Leong Pock Tsy, J.-M.
et al., 2011