Search
×

Sign up

Use your Facebook account for quick registration

Sign up with Facebook

OR

Create a Shvoong account from scratch

Create your account
Already a Member? Sign In!
×

Sign In

Sign in using your Facebook account

Sign in with Facebook

OR

Not a Member? Sign up!
×

Sign up

Use your Facebook account for quick registration

Sign up with Facebook

OR

Sign In

Sign in using your Facebook account

Sign in with Facebook
Shvoong Home>Science>Biology>chromosome study of Ethiopian Bulinus snails Summary

chromosome study of Ethiopian Bulinus snails

Book Summary   by:nabia     Original Authors: M.Sc thesis by Zekeria Yusuf Addis Ababa University ; Et
  • Summary rating: 2 stars (2 Ratings)
  • Visits : 524
  • words:900 
ª
 
Abstract: Freshwater snails of the genus Bulinus most frequently Bulinus truncatus/tropicus complex occur in Ethiopia as various ploidy levels which are other wise rare in other animal phyla (diploid, tetraploid, hexaploid and octoploid).The genus Bulinus has ,like the rest of the planorbidae, a basic haploid chromosomal complement of 18. This investigation provides data on occurrence and distribution of various ploidy levels in B. truncatus/tropicus complex based on meiotic prophase bivealent chromosomes and also emphasizes the role of chromosomes in identification of B. truncatus /tropicus group. Specimens were collected from fourteen different localities in Ethiopia. Twenty snails were taken as representative sample for each site. Snails were sacrificed and chromosome preparation has made from gonad tissue (ovotestis).Two slides were prepared for each specimen and analyzed for meiotic bivalent chromosomes. The result showed that diploid populations were observed in five sites mostly in low altitudes. Tetraploid populations in three sites, hexaploid population in two sites only and octoploid populations in four sites mostly high altitude areas. Tetraploid populations have found in all high, medium and low altitudes: Senkale (high altitude), Hora lake (medium altitude), low altitude region (Gerbi, Kemese zone). Unexpected result was found in Hora lake, as both diploid and tetraploid populations were occur together in the same microhabitat such cases had not been reported previously. A new occurrence for tetraploid population, which is not common in high altitude, in Senkale stream near Ambo was recorded. Key words: ploidy level, gonad tissue (ovotestis), microhabitat, Bulinus truncatus/tropicus complex, bivalent chromosomes 1. Introduction Phylum mollusca (L: soft) is one of the largest group all animal phyla including between 50,000-110,000 living species (Pechenick, 1996) and above 35,000 fossil species has had geological history, further the possession of mineral shell increases chances of preservation; has resulted in rich fossil record that dates their origin back to Cambrian (Barnes, 1974).Members of phylum mollusca include familiar forms: calms, oysters, squids, octopus, snails and slugs. These species are distributed among some extremely dissimilar or heterogeneous assemblage of organisms making molluscan body plan probably the most malleable in animal kingdom (Barnes, 1974; Pechenik, 1996). Phylum mollusca is distributed among seven classes. Among this, class Gastropoda is the largest comprising 40,000-75,000 living species and some 15,000 fossil forms of snails and slugs occupying diverse habitats marine, fresh water, terrestrial and conquered island: pulmonate gastropods with elimination of gills and conversion of mantle cavity into a lung (Barnes, 1974). 1.1 Class Gastropoda About 75%-80% of all living molluscs are gastropods (Barnes, 1974; Pechenik, 1996). Gastropods have undergone most extensive adaptive radiation of all major molluscan groups (Barnes, 1974). In many respects, gastropods exhibit least change from ancestral molluscan plan for they possess a well developed head, a shell of one piece and a broad flat creeping foot. The most significant modification, and the one to which most of other changes are related is anticlockwise through 1800 twisting, or torsion that the body had undergone during early development.
Torsion is not coiling of shell (Pechenik, 1996). Another change occurred in gastropod structure involved the shell. Although there are fossil species with planospiral shells, all existing gastropods possess asymmetrical shells; or if the shells are symmetrical, this symmetry has been secondary derived (Barnes, 1974). Planospiral shell had disadvantage of not being very compact; since each coil lay outside of preceding one the diameter of shell could become relatively great. This problem was solved with evolution of asymmetrical coiling in which coils were laid down around central axis called collumella and each coil lay beneath preceding coil such shell is more compact (Pechenik, 1996). According to pechenik (1996), Geastropod shell typically carried so that it leans to the left side of the body. The shell axis is thus oblique to the long axis of the body, balancing animal’s center of mass over foot. The shells of most gastropod species coil clockwise to the right that is the shells are “right-handed (dextral). Probably as a consequence of space limitations within the coiled shell ctenidium ,osphradium, kidney (nephridium) and heart auricle on the right side of the body tend to be reduced or absent; only primitive gastropods still exhibit paired structures. A relatively few snail species form shells that coil counter clockwise to the left and show a corresponding reduction of absence of ctenidium, osphradium, kidney and heart auricle on left side of the body such species are said to be ‘left handed’ (sinistral). It is also possible for a dextrally coiled snail to produce a shell that appears to be left handed; some gastropods exhibit such a pattern particularly during larval stage (Pechenik, 1996). Albrecht, et al., (2006) that stated phylogenetic relationships among the genera are confused and controversial. Traditionally, anatomical characters such as male copulatory organ structure or radulae were used to divide Planorbidae into different subfamilies and tribes. Hubendick (1978) found reduction of spire and coiling to be a common trend in Basommatophora, resulting in a more or less conical shell and a significantly enlarged aperture. General Objective - To study the chromosome of genus Bulinus from various localities in Ethiopia. Specific objectives - To determine ploidy levels existing among the Bulinus species in Ethiopia. - To determine the distribution of different ploidy levels among Bulinus population
Published: August 04, 2007   
Please Rate this Summary : 1 2 3 4 5
Write your own     Comment
View All  
Translate Send Link Print
X

Top 5

.