Document: STE-3-71-7

Revelations on the structure of Bosmina populations in Lake Kinneret, Israel.

SCHWARTZ, S.S.* ^1,2 and K.D.HAMBRIGHT ²

Oklahoma State University, Stillwater, OK ¹
Kinneret Limnological Laboratory, Tiberias, Israel ²

Abstract:
It has been know for more than four decades that in Lake Kinneret Bosmina longirostris occurs as two forms, B.l. longirostris with relatively straight antennules and B.l. cornuta, with sharply curved antennules. Our study was prompted by an analysis of a core from the lake revealing a dramatic change in the relative frequency of the two morphs over the last 100 years. Typically the cornuta morph constituted <30% of the individuals found, but in sediments dating from 1916 and 1980, the cornuta morph constituted >50%. The cornuta morph constitutes ~40% of all individuals from sediments deposited in the 1990's. Given the observed change we wanted to know more about the nature of the differences between the morphs. Using cellulose acetate electrophoresis methodology to examine allozymes we determined that the cornuta morph is a fixed heterozygote at the GPI locus whereas the longirostris morph is a fixed homozygote for the fast allele. We found no evidence of individuals with the slow allele. The two morphs shared the same fixed allele at each of the other five loci examined. This seemingly simple result has profound implications for our understanding of the Bosmina population in the lake. First, the morphs are not simply extremes of phenotypic plasticity. While there is some morphological variability within each morph, they remain visually distinct. Secondly, it is likely that the cornuta morph is actually a hybrid with one parent now absent from the lake. Hybridization has been described previously in the genus so this is not unusual. Finally, the simplest explanation for an entire population of heterozygous individuals is that the cornuta form is obligately parthenogenetic. This has only been observed in arctic populations of polyploid individuals. B.l. cornuta is found across Europe and more populations will need to be sampled to determine the breadth of our result.

Keywords: Bosmina, Lake Kinneret, population genetics, breeding system

This abstract is being presented at: 9:00 AM in session:
Oral Session #54: Lake Ecology.