The life history of the diving beetle, Lancetes angusticollis (Curtis) (Coleoptera: Dytiscidae), on sub-Antarctic South Georgia |
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Authors: | Rodney J Arnold Peter Convey |
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Institution: | (1) British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK Fax: 44-1223-362616, GB |
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Abstract: | Two populations of the world's most southerly diving beetle (Lancetes angusticollis) were studied on sub-Antarctic South Georgia between November 1995 and April 1996. Parallel observations were made on laboratory
cultures of each life stage. All juvenile stages of L. angusticollis are voracious predators, preying mainly on the herbivorous copepod Boeckella poppei. Adult beetles additionally predate benthic ostracods. Laboratory predation rates and field population densities found in
this study suggest that L. angusticollis has a more significant impact on its prey than recognised in recent studies of South Georgian lakes. Spring field samples
contained only a few individuals of larval instar IV and adults. Young larvae were present from December onwards, with a rapid
progression through juvenile instars during the summer months. Fourth instar larvae left the water for pupation between mid-December
and at least mid-February. Combining these observations with known developmental threshold temperatures for each life stage
implies that L. angusticollis has a complex biennial (minimum) life-cycle, with overwintering possible in three life stages aquatic larvae, terrestrial
pupae (not proven) and aquatic adults]. L. angusticollis may be a suitable indicator species in the context of climate warming studies: a small (1°C) rise in mean environmental temperatures,
comparable to that already observed at several sub-Antarctic and maritime Antarctic localities, would allow completion of
an annual (univoltine) life-cycle, with concomitant rapid population increase, and serious implications for trophic interactions
in these simple lake ecosystems.
Received: 24 November 1997 / Accepted: 12 April 1998 |
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