Animal Molecular Breeding 2015, Vol. 5, No. 1, 1-8
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The dendrogram obtained from the average linkage
cluster analysis showed that the accessions studied
were grouped into five clusters which can be classified
into two main groups (A and B). The first main group A
consists of Accessions C32, C33, C23 and C21 in
Cluster1, C11, C14, and C12 in Cluster 2 and B52 in
Cluster 3. These accessions were characterized by lack
of pigmented skin and brown shell colour. While
accessions in Cluster 1 completely lacked the albino
pigmentation (that is, the light yellow skin colour),
those in Cluster 2 were all albinos with the light yellow
skin colour. Although accession B52 fell into this
group, it was characterized by light brown skin
pigmentation. The second main group B consists of
accessions A22, A33, A42 in Cluster 4 and B22, B32,
B42 and B11 in Cluster 5, respectively. This group was
characterized by strong black pigmentation in skin and
had black shell colour. While accessions in Cluster 4
generally had brown skin colour, those in Cluster 5 had
black or brown skin colour.
3 Discussion
Information on sizes of populations and levels of
genetic diversity of species of interest is important for
the development of the appropriate natural resource
management and conservation schemes for different
groups of plants and animals. Land snails, including
A.
marginata
, typically live in discrete populations often
isolated from one another with low dispersal ability
(Denny, 1980; Fearnley, 1993). This suggests that they
are prone to effects of population differentiation with
reduced gene exchanges between them, leading
presumably to strong local differentiation (Schilthuizen
and Lombaerts, 1994; Pfenninger et al. 1996).
Moreover, habitat fragmentation and instability of
human-disturbed environments may impose severe
restrictions on gene flow and increase random genetic
drift. Extinction and recolonization dynamics in local
populations may also modify the distribution of genetic
variability, leading to a decrease or an increase of
variation among populations (Schilthuizen and
Lombaerts, 1994; Ruckelshaus, 1998).
In the present study, morphometric analysis of
A.
marginata
was carried out using 5 morphological
characters (shell height, shell width, spire height,
aperture height, and aperture width), and
biogeographic differentiation was observed in all the
samples examined with samples from Akwa Ibom and
Cross River States, respectively, showing great
heterogeneity in the width and aperture height of the
shell, thus resulting in major differences in the shell
shapes between the different snail accessions. On
account of this, molecular approaches were also
applied to characterize the genetic diversity of
A.
marginata
. In this case, RAPD-PCR was used to
identify DNA segments exhibiting high evolutionary
rates using 3 different primers. A large number of
scorable RAPD fragments (84) were obtained from
only fifteen (15) samples using 3 selected primers and
79 of the fragments were polymorphic. The percentage
of polymorphic bands ranged from 50 to 94.04%.
These results are in tandem with those reported
previously by
Tassanakajon et al. (1998) during their
examination of genetic variation in wild black tiger
shrimp and Thaewnon-ngiw et al. (2003), who studied
the genetic diversity of introduced golden apple snail in
comparison with four native apple snails in Thailand by
RAPD analysis. The morphometric and genetic
diversity of
A. fulica
from 10 geographical locations in
Thailand and Malaysia was examined by Pattamarnon
(2004) using RAPD, RFLP and SSCP analysis.
Seventy two (72) polymorphic fragments were
generated across all investigated samples (n = 215)
using RAPD while RFLP revealed limited genetic
diversity and lack of genetic heterogeneity. The low
number of RAPD patterns and the low percentage of
polymorphic RAPD fragments found in
A. fulica
compared with those found in
A. marginata
in the
current study and other local species described above
are further confirmations of the status of high genetic
diversity of
A. marginata
. A point of great significance
from these results is the fact that inter- and
intra-population genetic diversity can enhance
adaptation to a particular habitat and also expand the
boundary of colonization and distribution, enabling a
species to survive in a wide variety of conditions
(Williamson, M. (1996). Consequently, the high
genetic diversity observed amongst
A. marginata
accessions collected from the southern part of Nigeria
can possibly be related to environmental differences.
Another point of interest from the data presented here
is the fact that though one of the primers used in the
