Aspectos biológicos e histológicos da reprodução de Leptinaria unilamellata (d’Orbigny, 1835) (Mollusca, Pulmonata, Subulinidae)

Abstract

Most of the studies on snails reproduction were realized with species of temperate climate. This knowledge is important to development of management strategies of snails populations, so as to controlling parasites. The present work aimed to compare aspects of reproductive biology and development of reproductive system of Leptinaria unilamellata maintained isolated and grouped, besides to ascertain if this snail species when exposed to unfavorable humidity conditions retain its offspring in their reproductive tract. Two experimental groups were made to assess reproduction. One with 30newly hatched individuals, maintained isolated and other with 30 individuals in pairs. Every fifteen days, the Shell length was measured. To verify the sexual maturity it was observed the presence of juveniles in the terrariums. Daily observations were realized too verify the number of reproductive events, the number of individuals in each event and the interval between reproductive events. To determinate the reproductive investment of snails from both groups, after birth, the parental snails and its offspring were heighted to provide data in order to calculate this index. With regard to shell growth, it was observed that in juveniles maintained in pairs showed higher growth rates in comparison to isolated ones. After maturity, the growth rates of isolated and paired snails were alike, with a trend to establishment in the course of time. Paired snails reached sexual maturity before isolated. Moreover, paired individuals presented more reproductive events and a larger number of juveniles when compared to isolated snails. The fecundity of isolated snails presented a mean significantly higher in relation to paired (F=16.3585; p<0,0010). During the observation period paired individuals showed mean reproductive investment significantly lower when compared to isolated individuals (8,15% and 12,28% respectively) (ANOVA p=0;F=34.0539). To assess the development of reproductive system, 30 individuals maintained isolated and 30 paired (with 6 individuals separated to the study of each age) at the ages of 15, 45, 75, 90 and 105 days were utilized in histological study. It was observed that there is no difference in reproductive system in the different ages and among snails maintained isolated and paired. The ovotestis was observed in15 days only in paired snails, which can indicate that this gland is formed lately in isolates snails. To verify the behavior of retention of the offspring it were made two groups, each one with 30 isolated snails. The group 1 was maintained under favorable humidity conditions, while in the first phase of the assay the group 2 was submitted to unfavorable humidity conditions. It was observed that snails exposed to water stress are capable to retain its offspring in the oviduct, realizing oviposition as soon as the humidity conditions improve. It was observed that L. unilamellata, besides aestivation they also can produce an epiphragm that sealing the shell and avoiding the water loss to the environment.