| Title | Reconstructing long-term changes in Daphnias body size from subfossil remains in sediments of a small lake in the Himalayas |
| Abstract | A combined analysis of modern zooplankton and fossil Cladocera assemblages from a Himalayan lake,
Lake 40, revealed that the endemic Daphnia tibetana disappeared in the late-1980s, after persisting as the
only Daphnia species for almost 3000 years. Daphnia head shields, which are rarely recovered from the
sediments, were the most abundant Daphnia remains in the lake. The remains were of the Ctenodaphnia type;
the smaller ones had a large central hole. Head shields of the same type were also found in zooplankton water
samples, rich in exuviae as well as of intact specimens of D. tibetana, from a nearby lake. Small individuals
had a distinct nuchal organ in the dorsal region of the head. We therefore postulated that the head shields
with the hole were from young (newborn or individuals in the two first moults). Up to now, the nuchal organ
has been described in laboratory populations of D. (Ctenodaphnia) magna, where it disappears quite early in
life. It probably functions as an osmoregulatory organ, essential for the survivorship of late embryos and
early juveniles. On the other hand, as far as we know, head shields with a hole have never been recorded in
plankton or in sediments. In view of the fact that head shields were representative of Daphnia abundance, we
used them to reconstruct changes in density and body size during ca. 3000 years. In fishless mountain lakes,
mean Daphnia body size tends to increase toward the end of the productive season. The number of moults
and maximum body size depend mainly on the duration of the ice-free period, and on summer temperatures.
In cold years, when the productive season is short, the number of moults will be low, and the range of
Daphnia body size will be narrow. We used Daphnia body size and abundance estimates, in addition to an
analysis of changes in the Cladocera assemblage, to reconstruct past environmental conditions. |
| Source | Journal of paleolimnology 32, pp. 95–107 |
| Keywords | Cladocera remainsDaphnia body sizeFishless lakesRemote lakesSediments |
| Journal | Journal of paleolimnology |
| Editor | Kluwer Academic, Boston, Paesi Bassi |
| Year | 2004 |
| Type | Articolo in rivista |
| DOI | 10.1023/B:JOPL.0000025295.04832.77 |
| Authors | Manca M.; Comoli P. |
| Text | 52831 2004 10.1023/B JOPL.0000025295.04832.77 ISI Web of Science WOS 000220995200007 Cladocera remains Daphnia body size Fishless lakes Remote lakes Sediments Reconstructing long term changes in Daphnias body size from subfossil remains in sediments of a small lake in the Himalayas Manca M.; Comoli P. CNR ISE, Verbania A combined analysis of modern zooplankton and fossil Cladocera assemblages from a Himalayan lake, Lake 40, revealed that the endemic Daphnia tibetana disappeared in the late 1980s, after persisting as the only Daphnia species for almost 3000 years. Daphnia head shields, which are rarely recovered from the sediments, were the most abundant Daphnia remains in the lake. The remains were of the Ctenodaphnia type; the smaller ones had a large central hole. Head shields of the same type were also found in zooplankton water samples, rich in exuviae as well as of intact specimens of D. tibetana, from a nearby lake. Small individuals had a distinct nuchal organ in the dorsal region of the head. We therefore postulated that the head shields with the hole were from young newborn or individuals in the two first moults . Up to now, the nuchal organ has been described in laboratory populations of D. Ctenodaphnia magna, where it disappears quite early in life. It probably functions as an osmoregulatory organ, essential for the survivorship of late embryos and early juveniles. On the other hand, as far as we know, head shields with a hole have never been recorded in plankton or in sediments. In view of the fact that head shields were representative of Daphnia abundance, we used them to reconstruct changes in density and body size during ca. 3000 years. In fishless mountain lakes, mean Daphnia body size tends to increase toward the end of the productive season. The number of moults and maximum body size depend mainly on the duration of the ice free period, and on summer temperatures. In cold years, when the productive season is short, the number of moults will be low, and the range of Daphnia body size will be narrow. We used Daphnia body size and abundance estimates, in addition to an analysis of changes in the Cladocera assemblage, to reconstruct past environmental conditions. 32 Reconstructing long term changes in Daphnia s body size from subfossil remains in sediments of a small lake in the Himalayas Manca_Comoli_JOPL.pdf Articolo in rivista Kluwer Academic 0921 2728 Journal of paleolimnology Journal of paleolimnology J. paleolimnol. marinamarcella.manca MANCA MARINA MARCELLA TA.P02.006.002 Processi evolutivi in ambienti estremi dell area Himalaiana |
