The life-cycle and productivity of the land snail Theba pisana (Mollusca: Helicidae)
Cowie, R.H. (1984). The life-cycle and productivity of the land snail Theba pisana (Mollusca: Helicidae). J. Anim. Ecol. 53(1): 311-325. https://dx.doi.org/10.2307/4359
In: Journal of Animal Ecology. Blackwell Science/British Ecological Society: Oxford. ISSN 0021-8790; e-ISSN 1365-2656, meer
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| Trefwoord |
Theba pisana (O. F. Müller, 1774) [WoRMS]
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| Abstract |
1) The land snail Theba pisana was sampled over a 4-year period at Tenby, South Wales. Newly-hatched snails appeared in late summer and autumn; mortality was high during the first winter; maturity was attained after 2 years; hibernation occurred in both winters; and breeding occurred only once, with death soon afterwards. Samples from other localities covering the whole range of T. pisana suggest both annual and biennial life-cycles with breeding in summer and autumn in Britain and northern France, and later in autumn and in winter in the Mediterranean. (2) An adequate combination of warmth and humidity is necessary for growth. Snails aestivate when it is too hot or dry (in southern, Mediterranean localities), and hibernate when it is too cold (Britain and probably northern France). The length of the life-cycle (1 or 2 years) is probably determined by the duration of aestivation or hibernation, and this may show considerable local variation. (3) Thirty pairs of virgin snails were used to investigate lifetime production of eggs by T. pisana in the laboratory. T. pisana was confirmed as an obligate outcrosser. (4) The single laboratory breeding season lasted from July 1980 to March 1981; most snails died soon after this. Mean clutch production per pair was five, with a mean of seventy-seven eggs in each. Mean egg dry weight was 0.769 mg and was c. 16% of wet weight. Mean total production per pair was 368 eggs, and 678 eggs if pairs producing less than 100 were omitted. This may well under-estimate production in the wild. (5) Late-season clutches were smaller than early ones. Larger snails started to lay earlier and produced larger clutches. They may also have produced more clutches, and consequently more eggs in total |
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