Life cycle and population dynamics of Helicodonta obvoluta (O. F. Müller, 1774) (Gastropoda: Pulmonata: Helicidae)

Abstract

Life cycle of Helicodonta obvoluta (O. F. Müll.) was studied in the field and in laboratory. Mating lasts 2-3 hrs and includes: meeting of the partners, recognition, courtship dance, copulation, resting phase and parting. No spermatophores were observed upon dissection of a total of 90 adult individuals which seems to indicate that H. obvoluta does not produce them. The egg-laying snail embeds anterior part of its body 4-6 mm deep in rotting timber. The egg-laying lasts from about a dozen hours to two days. Freshly laid eggs are white, calcified, slightly translucent and get opaque in a few days. They are slightly oval, of 2.10-2.85 mm major and 2.00-2.60 mm minor diameter. In laboratory, eggs are laid in spring (March-June) and autumn (August-November), in the field, the egg-laying periods are somewhat shorter (April-beginning of June, end of August-beginning of October). Most laboratory snails laid eggs only once in their lifetime, the maximum number of egg-laying periods was four. The percentage of hatching eggs in laboratory is ca. 59%. The number of eggs per clutch ranges from 9 to 27. The incubation period ranges from 14 to 31 days, and is shorter for spring (14-18 days) compared to autumn (19-23 days) clutches. Hatching is asynchronous, lasting from 1 to 4 days. With approaching hatching, the white colour of the egg disappears, so that the young snail is surrounded only by a translucent membrane, which gets broken as a result of its movements. Newly-hatched snails have shells of 1 whorl, devoid of periostracal hairs. No egg cannibalism was observed. Out of 174 young hatched in laboratory, 159 reached maturity. During numerous dissections of adult individuals no eggs were found in the reproductive tracts; if there is an egg-retention, it must be very short-lasting. Placing eggs in rotting timber and covering them with mucus protects them from drying-out, ensures a more favourable temperature and limits accessibility to predators. The number, relative and absolute size of eggs, number of clutches per year and per lifetime, and the life span seem to be correlated with size rather than with phylogenetic position of the species. No uniparental reproduction was observed. In laboratory the time elapsing between hatching and maturity (lip completely formed) ranged from 140 to 624 days; it varied between individuals hatched in particular years and seasons, e.g. young of the spring 1997 grew much faster (mean 354 days) than those of the spring 1999 (mean 442 days). The time required to reach full size was not correlated with the ultimate number of whorls. The growth shows three distinct phases: a quick initial phase of 3-4 months, a slow phase, and a short quick phase preceding lip formation. The monthly increment depends on the growth phase: 1.15 whorl in phases 1 and 3, 0.30 whorl in phase 2. The growth rate in the field is similar to that observed in laboratory, though with a wider scatter within growth phases and some differences between years and seasons. Depending on weather conditions, the youngest...

Molluscan fauna of abandoned crystalline limestone quarry in Rogóżka (Lower Silesia, Krowiarki Range, Stronie Śląskie commune)

“…C. parvula is exceptional in that it is abundant in various microhabitats, such as litter, tree trunks, stones or rock ledges. These observations are confirmed by the studies on the seasonal dynamics of abundance, age structure and species composition of malacofauna in litter samples taken during various seasons of the year in the nature reserve Muszkowicki Las Bukowy (KUZNIK-KOWALSKA 1998), or population dynamics of Helicodonta obvoluta (MALTZ 2003) -a snail staying mainly on logs and descending to the litter only in early spring and late summer.…”

Field and laboratory studies on the life-cycle, growth and feeding preference in the hairy snail Trochulus hispidus (L., 1758) (Gastropoda: Pulmonata: Hygromiidae)

“…In Punctum pygmaeum (Draparnaud, 1801) (Baur 1989), Helicodonta obvoluta (O.F. Müller, 1774) (Maltz 2003) or Perforatella bidentata (Kuźnik-Kowalska & Roksela 2009) similar variation has been observed. In P. pygmaeum it can be explained by possible egg retention, but T. hispidus and the latter two species are considered strictly oviparous species.…”

“…The growth phases recorded in T. hispidus (fast phase followed by slow phase) seem to be typical for helicids and hygromiids (Maltz 2003;Kuźnik-Kowalska & Roksela 2009). The slow growth phase in such species is associated with a development of a reproductive system which has been discussed in Maltz (2003) and Maltz & Sulikowska-Drozd (2008). In the case of growth in the field, environmental factors such as variable temperature or humidity associated with a particular season should be considered.…”

Life cycle and population dynamics of Discus perspectivus (Megerle von Mühlfeld, 1818) (Gastropoda: Pulmonata: Endodontidae)

“…Carychium tridentatum (Risso), MORTON 1954, BULMAN 1990. Possible reasons and implications of such differences, as well as mechanisms of regulation of the onset of reproduction have been discussed by MALTZ (2003b).…”

“…Life cycles and population dynamics of most European terrestrial pulmonates still remain unknown (for review see KUZNIK-KOWALSKA 1999, MALTZ 2003b. On the other hand, such data are of great importance for evolutionary inferences (reproductive strategies), systematics and phylogeny (though life history parameters are only rarely used as characters), or ecology and protection of endangered species and communities of which they form a part.…”