REPRODUCTIVE BIOLOGY OF ASOLENE PULCHELLA

TIECHER M.J.; BURELA S; MARTIN P.

Tucuman

Taller; IV taller Internacional "Biologia de Ampullariidae"; 2010

Asolene pulchella is a freshwater snail whose range extends from Paraguay to the north-eastern Buenos Aires province (Argentina). The aims of the present study were to investigate its reproductive biology, including mating, oviposition and embryonic development. The snails used in the present study were born and reared in the laboratory from field snails obtained from a population in Lago de Regatas (Buenos Aires, Argentina). The snails were maintained in 20 l aquaria with CaCO3 saturated tap water at 25 ± 2 °C,  14:10 (light:dark) photoperiod and fed on fresh lettuce. The copulations occur under water at any time of the day or night, its duration was 3.384 ± 1.672 h (mean ± SD, n = 58); homosexual matings were frequently observed. The males produce uniflagellated euesperm with an helicoidally shaped head and also fusiform paraesperm with 7-9 flagella. After a single copulation a female can lay up to seven egg masses with more than six hundred embryonated eggs during a period of 80 days, indicating a significant capacity of sperm storage. Oviposition occurs under water and more often at night; the right nuchal lobe of the female forms a channel through which packs of up to three eggs emerge sequentially and stuck one to each other; a different sticky secretion attaches the whole egg mass to the substratum. A high degree of cannibalism of the egg masses by both males and females has been observed. The eggs masses contain an average of 98.087 ± 29.192 spheroidal eggs (n = 23). Each egg is composed of two visible layers, the inner layer contains a yellowish perivitellin gum with a central clear fluid zone, where the embryo and a certain amount of euesperm is located. The outer layer is in contact with the gel that binds eggs of each package and that bears calcite microcrystals 20-30 ìm-long. The diameter of newly deposited eggs was 2.25 ± 0.285 mm (n = 70) but increased by 37.8% to hatching; at this time the perivitellin gum has been totally consumed by the embryo, which perforates the inner layer with the radula, causing it to collapse, and then goes through it by action of the foot. The development time was 10.82 ± 2.49 days (n = 28) and the percentage of hatched eggs per egg mass was 80 ± 0.0587 (n = 11). At the time of hatching the embryos measured 1.69 ± 0 71 mm long; the hatchlings lack a lung, that appears and becomes functional several weeks later. Our observations indicate that, even within the group of species that lay gelatinous egg masses, the details of their structure and of the development process may constitute a rich source of traits for comparative and taxonomic studies.