EFFECT OF CONTROLLED TEMPERATURES ON GAMETOGENESIS IN THE GASTROPODS PHYSA ACUTA (PHYSIDAE) AND BULINUS TROPICUS (PLANORBIDAE)

Abstract

The effects of a range of constant temperatures on gametogenesis were investigated in two freshwater snail species which occur sympatrically in the Umsin-dusi River, Natal, South Africa, Physa acuta (invasive) and Bulinus tropicus (endemic). Both were shown to be simultaneous hermaphrodites with slight protandry. An increase in temperature accelerated the process of gametogenesis but P. acuta responded more rapidly to these changes than B. tropicus. This, coupled with the greater fecundity and shorter incubation period of P. acuta, gives it a reproductive advantage over the endemic species, providing a possible explanation for the invasive's success in rapidly repopulating disturbed riverine habitats.