GENETIC ANALYSES OF FRESH WATER CRAB, Sudanonautes africanus IN ONDO STATE, NIGERIA

Abstract

Fresh water crabs are a cheap and important source of animal protein to human beings. They also serve as bio-indicators of ecosystem disruption and also conservation icons. This study is to observe the genetic variations (in terms of their morphometry and protein profiles) in Sudanonautes africanus from three different water bodies (Ala, Ogbese and Owena Rivers) in Ondo state, Nigeria. Thirty samples of fresh water crabs were collected from each of the study locations for morphometric and meristic studies. The samples were weighed and morphometric studies were carried out on each of the specimen in relation to their sexes and also for each of the population (Rivers). Thereafter 5mg of the chelae tissues were collected from 15 samples from each of the study locations. The study reveals that there were no significant differences in the morphological parameters of the male crabs. However, there were significant differences in the meristic characters (Episternum and Abdominal segment) of the male crabs. There were significant differences in the mandibular palp of the female crabs but there was no significant difference in the remaining morphological and meristic character of the female S. africanus. The morphometric studies of S. africanus in the three study locations showed that there are no significant differences in the morphological parameters of the crab. However, there are significant differences in the meristic characters (Episternum and Abdominal segment) of S. africanus in the three study locations. The morphometric studies did not show variations in S. africanus in the three study locations. The regression analyses of the crabs with respect to sex and population shows that the crabs exhibit a negative allometry growth (b < 3). The study also revealed that the crabs in the three study locations are healthy (K > 1). However, the female crabs in Ogbese River are healthier than the crabs in the other locations and the male crabs. For the combined sexes, S. africanus collected from Ogbese River is also healthier than the ones collected from the other two locations. From the study of the sexes of S. africanus in the three locations, the relationship between the Carapace length and Body weights of the male crabs in Ala River accounts for 36% while the Female crabs in Owena river had a strong relationship (71%) between the Carapace length and Body weights. For the combined sexes, crabs from Owena River exhibited the strongest relationship between the Carapace length and Body weights. Principal component analyses of the morphometric parameters of S. africanus revealed that Length of Right Chelae (LRC), the Length of left chelae (LLC), Carapace Length (CL) and the Abdominal Length (AL) contributed significantly to the morphological variations of S. africanus in the study locations, while the number of teeth on the right chelae (NTR) and the number of teeth on the left chelae (NTL) contributed significantly to the variations in the meristic characters of S. africanus. Cluster diagram from the canonical Variate analyses of the morphological characters of S. africanus in the study locations show that there are no variations in the morphological characteristics of S. africanus. Cluster diagram of the meristic characters show that there are little variations in the meristic characters of S. africanus in the three study locations. The mean quantity of proteins of S. africanus in the three study locations show that samples from Ogbese River have the highest quantity of protein (81.40±22.58mg/ml) followed by Owena (77.73±16.02mg/ml) and Ala (60.67±10.99mg/ml) Rivers respectively. The quantity of proteins of S. africanus collected from Ala River was significantly different (P < 0.05) from the other two rivers. SDS-PAGE of the chelae tissue of S. africanus shows intra specific variations in terms of the number of protein bands and their positions on the electrophoretic gels. Bands produced vary from one to eleven and their molecular weights vary between 5.19kDa to 237.88kDa. It was also observed from the protein profile that there was an overlapping in the molecular weights of some bands (30.35, and 135.25kDa). From the three study locations, the protein with the largest molecular weight was found in Ogbese River. The dendogram of the molecular weights of the crab population from the three study locations revealed that the specie of crab vary genetically to each other with respect to their sample populations. Therefore, the study revealed that S. africanus in Ondo State, Nigeria vary genetically, though, they exhibit similar morphological characters.