Экологический кризис прибрежной зоны. Тезисы Верищагинской конференции

UNEXPECTEDLY HIGH SPECIES DIVERSITY REVEALED IN AN ENDEMIC GASTROPOD GENUS (PARAMELANIA) FROM LAKE TANGANYIKA: THE COMPLEMENTARY ROLE OF OLD AND NEW

COLLECTIONS Todd J.A., Burgon J.D., Michel E. department of Earth Sciences, Natural History Museum, London, UK 2Institute of Biodiversity, Animal Health and Comparative Medicine,

University of Glasgow, UK
department of Life Sciences, Natural History Museum, London, UK
j .todd@nhm.ac.uk

Lake Tanganyika’s endemic ‘superflock’ of cerithioidean snails is perhaps the most diverse (>100 species) and morphologically disparate (18 genera) extant gastropod radiation within Ancient Lakes worldwide. Known generic diversity was discovered early and has grown little over the past century. Until now species diversity has been considered to be well known, excepting the single hyper-diverse genus, Lavigeria, One moderately diverse genus, the iconic Paramelania, has been known for 130 years and historically has been considered to comprise 2-5 morphologically variable species or ‘forms’; but it has long been recognised that the genus is in need of revision. We decided to undertake a detailed re¬examination based on the following materials:

-historic collections, 19th and early 20th century, Brussels (RBINS), London (NHM), Tervuren (MRAC) (mostly shells only): 321 lots, 6414 specimens
-A. Cohen research collection (shells): 69 lots, 1382 specimens
-E. Michel research collection (shells, EtOH specimens): 87 lots, 529 specimens
-Our aim was to answer the following questions:

1. Do finely divided shell-based groups (species) coincide with molecular clades based on sequencing COI and 16S gene fragments?
2. How do the species composition of historic and modern collections using a variety of methods (e.g. dredging, SCUBA) compare over 147 lake-wide collections?
3. Are within-site collections of living and dead (shell) specimens comparable?

We obtained DNA sequences (16S, COI) from specimens comprising five a priori, finely divided, shell-based species; robust molecular clades proved to be consistent with shell morphology. We used this correspondence to assess species diversity in the three major historic collections comprising shells only, including samples from the currently inaccessible Congo coast. We also re-assessed the two modern research collections (including radulae, opercula), largely from the Tanzanian coast, in the light of insights gained from historic samples.

The combined historic and modern collections comprised over 8395 shells from 147 lake-wide locations, with a marked difference in collection method, maximum depth and substrata between historic and modern collections. Geographic sampling was uneven, historically focused in Congo and Zambia, while modern samples were largely restricted to Burundi and Tanzania. Twenty-one species were separable using shell morphology (16 undescribed) - another two species are found in collections elsewhere. Historic and modern collections showed similar total diversity, 16 and 14 species respectively, but shared only 9 in common. High levels of sympatry were seen. Both wide-ranging species and short- ranged local endemics are present (n=7; undescribed) and evidence exists for extensive range shifts between dead and living populations.
Historic and modern collections give complementary views of diversity and distribution of Paramelania, capturing differences in geographic ranges and ecology. Unexpectedly high levels of ‘hidden’ diversity were found: 21 species, 16 undescribed. The value of fine-scale shell morphology in delimiting species within this genus was revealed here through strong molecular-morphological congruence. Our results emphasise that in systems with high local endemism, historic collections may contain undocumented diversity only revealed in a modern interpretive context. In such cases, species discovery needs to be undertaken on both modern and historical collections to get the most accurate view of biodiversity.