Verspreiding en habitats van <i>Lymnaea natalensis</i>, tussengasheerslak van die lewerbot <i>Fasciola gigantica</i>, in Suid-Afrika

Abstract

Hierdie artikel fokus op die geografiese verspreiding en die habitats van Lymnaea natalensis, die slaktussengasheer van die lewerbot, Fasciola gigantica, soos gereflekteer deur die vindplekke van sy 4 552 monsters wat tans in die Nasionale Varswaterslakversameling (NVV) van Suid-Afrika op rekord is. Alhoewel hierdie spesie in’n verskeidenheid van waterliggame aangetref is, was die meerderheid van die monsters (±70%) afkomstig vanuit riviere, spruite en damme en is die water in 70.8% van die gevalle as standhoudend en in 71.8% van die gevalle as stadigvloeiend, of staande beskryf.  Die resultate van lewenstabeleksperimente deur verskeie outeurs het daarop gedui dat temperatuur ’n minder belangrike bepalende faktor in sy geografiese verspreiding blyk te wees, maar dat die beskikbaarheid van standhoudende water deurslaggewend vir sy voorkoms in ’n gegewe habitat mag wees. Hierdie resultate strook met die bevinding dat slegs 7.5% van die monsters van hierdie spesie in die NVV in habitats wat as seisoenaal beskryf is, versamel is. Verder bied dit’n logiese verklaring vir die sporadiese voorkoms, of totale afwesigheid van hierdie spesie in die droër streke van Suid-Afrika.  Opgaardamme en besproeiingsnetwerke dra grootliks by tot die skepping van permanente habitats wat geskik sou wees vir L. natalensis.  As tussengasheer vir een van die lewerbotspesies wat reeds ’n ekonomiese faktor in Suid-Afrika is, is dit ’n aspek waarmee beslis rekening gehou behoort te word in die beplanning en konstruksie van nuwe besproeiingsprojekte.

Abstract

Distribution and habitats of Lymnaea natalensis, snail intermediate host of the liver fluke Fasciola gigantica, in South Africa

This paper focuses on the geographical distribution and the habitats of Lymnaea natalensis, the snail intermediate host of the liver fluke, Fasciola gigantica, as reflected by the collection sites of its 4 552 samples currently on record in the National Freshwater Snail Collection (NFSC) of South Africa.  Although this species was represented in a variety of waterbodies, the majority of samples (±70%) came from rivers, brooks and dams and in 70.8% of the cases the water was described as permanent and in 71.8% as slow flowing or standing.  The results of life-table studies conducted by various authors indicated that temperature should be a relatively unimportant factor in determining its geographical distribution, but that the availability of permanent water should be decisive for its presence in a given habitat.  These results are in agreement with the finding that only 7.5% of the samples of this species in the NFSC were collected in habitats which were described as seasonal.  Furthermore, it gives a logical explanation for the sporadic occurrence, or total absence of this species in the more arid regions of South Africa. Water impoundments and irrigation networks contribute to a large extent towards creating perennial habitats which would be suitable for L. natalensis.  As intermediate host for one of the liver fluke species which already is an economic factor in South Africa, this certainly is an aspect which ought to be reckoned with in the planning and construction  of new irrigation schemes.