Origin and Evolution of some Biological Characters of Anabarilius grahami As Referred To Geological Development of Fuxian Lake

Based on data collected in Fuxian Lake from November,1988 to March,1991,the habits in living spaces,feeding and breeding of Anabarilius grahami (Regan) have been described.From the view of organic evolution and geological development of the lake,the origin and evolution of these biological characters have been further discussed.The biological characters of A.grahami are closely correlated to its origination.It shares a most recent common ancestor with A.andersoni and A.qiluensis (Yang et al.,1987).Their common ancestor would be a streamlived and omnivorous fish because the primitive extant species of Anabarilius are all stream-dwellers.A.grahami is endemic to Fuxian Lake.Some biological characters are also closely correlated to the geological development of the lake.Fuxian Lake was formed in late Pliocene as the result of Fault depressions (Nanjing Institute of Geography and Limnology et al.,1989;Yang,1984).Since its formation,the lake has generally followed a deepening and oligotrophic development.It is the unique origination of A.grahami and the deepening,oligotrophic development of the lake that produced profound eftects on the biological characters of A.grahami.1.A.grahami prefers to breed at outlets of cave springs or hill springs and the substrate and water current in the breeding sites are similar to hill streams.This breeding habit is common to the primitive species of Anabarilius and is supposed to be descended from the common ancestor and therefore should be a primitive character.2.The larvas and adults of A.grahami occupy different living spaces.The larvas smaller than 30 mm SL occur in shallow coastal region and adults occur in middle and upper layers of open water.Similar habits are possessed by Barbodes fuxianensis,B.chonglingchungi and percocypris pingi regani which live in the same lake.According to the recapitulation rule,the habit of larvas is supposed to be a primitive biological character.3.A.grahami shares a close phylogenetic relationship with A.andersoni and A.qiluensis (Yang et al.,1987).All of them feed mainly on planktons.They have undergone differentiations in gill rakers.A.grahami have 31-39 gill rakers,length of gill rakers 46.7%-55.6% of gill filaments and having numerous secondary gill rakers.By contrast,A.andersoni and A.qiluensis have 21-25 and 22-25 gill rakers,length of gill rakers 30.0%-54.0% and 35.4%-45.1% of gill filaments,having less secondary gill rakers.Comparison indicates that A.grahami have evolved a most developed filtering organ in corresponding to the oligotrophic environment.4.A.grahami has habits of a long annual breeding season and a temporally regular interval between two sequent spawning populations.These habits had evolved to ensure enough food for the larvas and full use of the limited breeding sites as the result of adaptations to the deepening and oligotrophic development of the lake.5.A.grahami has lower absolute and relative fecundities than A.andersoni which is endemic to Xingyun Lake.Interspecific differentiations in fecundities were resulted from adaptations to different geological developments of Fuxian and Xingyun Lakes.Xingyun Lake followed generally a shallowing and eutrophic development in corresponding to which A.ander soni evolved higher fecundities.Howerver food shortage from deepening and oligotrophic development of Fuxian Lake had led to lowering of fecondities of A.grahami.6.Population of A.grahami has many more females than males,females being 4.1 times of males.Dominant females can ensure a potentially high fecundity for the population.