K. Schwenk, INTERSPECIFIC HYBRIDIZATION IN DAPHNIA - DISTINCTION AND ORIGIN OF HYBRID MATRILINES, Molecular biology and evolution, 10(6), 1993, pp. 1289-1302
Three coexisting Daphnia species belonging to the D. longispina group
(D. galeata, D. hyalina, and D. cucullata) form species-hybrid complex
es by producing interspecific hybrids in several lakes in Germany and
The Netherlands. To evaluate the genetic consequences of interspecific
hybridization, I studied the patterns of mitochondrial DNA (mtDNA) se
quence variation. The directionality of interspecific hybridization an
d divergence of hybrids from parental species was tested, using the DN
A sequences of a segment of mtDNA. Via the polymerase chain reaction,
it was possible to investigate single animals and even single resting
eggs. A species-specific marker was established, using restriction pat
terns of amplified cytochrome b segments. mtDNA genotypes of hybrids r
evealed unidirectional mitochondrial gene flow for two hybrids, which
were investigated by using multiple clones. No evidence for introgress
ion of mtDNA was found. On the basis of a phylogenetic analysis, the s
pecies exhibit considerable distinctness, whereas differences between
clones within species and between hybrids and maternal species tend to
be very low. These results indicate a recent origin of hybrids and su
ggest that the radiation of the D. longispina group occurred >5 Mya.