Melting ice reveals massive Daphnia genome gone awry


A student at the University of New Hampshire was astonished when she retrieved a plankton net from the melt water in the Old Durham Reservoir this week.  Amanda Murby, a PhD student at the UNH Center for Freshwater Biology, was taking the first spring samples in the on-campus reservoir, known among ecology students for its dense populations of Daphnia pulex, a unique clone of daphnids adapted to feeding on toxic cyanobacteria that abound in these nutrient-rich waters.

Murby, whose research focus is on the accumulation of cyanobacteria toxins in zooplankton such as Daphnia, was at first confused when she pulled the half-meter net out of the fridged water near the inlet to the reservoir, the only location free of ice at this time.  According to Murby, her first reaction was OMG.  The daphnid barely fit into the net and its head was extended into a peaked helmet, described in the Daphnia literature as a form of polymorphism induced through chemicals released by invertebrate predators.  “At first I thought the net had collected some debris that had fallen into the lake during the winter.” explained Ms. Murby, still somewhat hesitant to form any conclusions.  During the attempt to remove the giant daphnid from the plankton net, the thrashing meter-long crustacean appeared to thrust itself forward with its postabdomen freeing itself from the net and quickly disappearing into the bog-stained waters of the reservoir.  The only evidence of this strange encounter is a cell-phone video taken by Ms. Murby’s field assistant who was standing on the opposite side of the Old Durham Reservoir (click here to see video).

Realizing the unlikelihood of capturing such a creature, Murby and her PhD advisor Jim Haney sought the opinion of other daphnid specialists on campus.  In a brief, but candid interview, Dr. Kelly Thomas, Director of the Hubbard Center for Genome Studies stated “This is the largest Daphnia I have ever seen”. Thomas who is a member of a team of researchers, who recently succeeded in sequencing the genome of Daphnia pulex, added that gigantism has been linked to duplicate genes in biology and Daphnia are renowned for both the exceptional size of its genome as well as the large number of duplicate genes.  Thomas also remarked that Hubbard Center has much interest in following up on this unusual phenomenon and concluded “hopefully, there is more than one (of these giant) Daphnia in the Old Durham Reservoir, but not too many”.  (click here to see the interview with Dr. Thomas).