Influence of soil physicochemical parameters on the abundance of Paracoelophrya polymorphus (Ciliophora: Radiophryidae) commensal of earthworms (Annelida: Glossoscolecidae) collected in Bambui (NorthWest Cameroon)
Résumé
Earthworms of the genus Alma nilotica belonging to the family Glossoscolecidae, lodges an abundant fauna of astomatous ciliates in its
digestive tract. Each species is located in a well-defined portion of the gut and the reasons for this stratification still remain unclear. In
order to assess the influence of physico-chemicals parameters of the soil on the distribution of one of these astomatous ciliates
(Paracoelophrya polymorphus Fokam, 2012) along the digestive tract of Alma nilotica, a study was carried out from April to
September 2013 in Bambui on the banks of Fansaah river. The volumic density (VD) of worms (number /dm3 soil) was examined. A
total of 60 worms were used for the counting of ciliates. The observation of Paracoelophrya polymorphus was done after staining with
methylene blue. Twelve physico-chemicals parameters of the soil from the site of collection of worms were analyzed. The degree of
binding between the VD of worms, the abundance of ciliates and physico-chemicals parameters was performed for different portions of
the digestive tract. VD of the earthworms shows a positive and significant correlation with the Cation Exchange Capacity CEC (r =
0.771; P < 0, 05) and with Mg (r = 0.886; P < 0, 01). Paracoelophrya polymorphus is located in the foregut and midgut of its host but,
its preferential zone is the foregut. In the foregut, a negative and significant correlation was found between available phosphorus (P)
and P. polymorphus abundance (r = -0,943; P < 0, 01). In the midgut, a positive and significant correlation was obtained between the
Cation Exchange capacity (CEC) (r = 0.754; P < 0, 05), magnesium (r = 0.812; P < 0, 05), calcium (r = 0.754; P < 0, 05) and P.
polymorphus abundance. These chemical parameters influence directly the density of the earthworms and indirectly the stratification
of P. polymorphus