Analysis of reticulate relationships within the <i>Daphnia longispina</i> species complex. Allozyme phenotype and morphology

Abstract

Abstract A two‐step method is proposed to get reliable associations between morphology and genotype in clonal assemblages in which more than two predominantly parthenogenetic species are thought to coexist with hybrids. In dataset 1, the genetic relationships among clones of the Daphnia longispina hybrid complex from seven prealpine lakes in southern Germany were studied based on the variation at 21 enzyme loci. The spatial arrangement in the multidimensional scaling plot revealed a reticulate pattern among three presumably parental species, D. cucullata, D. galeata and D. hyalina , and three hybrid groups, D. cucullata/galeata, D. cucullata/hyalina and D. galeata/hyalina . The Got1 locus was believed to be a discriminating factor between species and hybrids (cf. Wolf and Mort, 1986). However, this locus is more variable, and 57% of the clones would have been misidentified using it. Moreover, the morphological variation within genetically defined groups is also higher than previously assumed. In dataset 2, the revision of morphological and genetic markers greatly improved the association between morphology and genotype in newly collected animals. The spatial arrangement of clones in multidimensional scaling plots and morphological asymmetries to parents suggest both, different degrees of introgression and bidirectional hybridization. Most unexpected genotypes were found in the cxh hybrid group, suggesting that F1‐hybrids are fertile. The results showed (1) that the clonal diversity was very high (2) that detailed analyses of multiple morphological and allozyme markers are necessary to resolve taxonomic relationships within clonal assemblages consisting of multiple species, hybrids and differently introgressed backcrosses, and (3) that the three original species seem to have sufficient within‐species recombination and a low enough rate of backcrossing to allow taxonomic identification. It must remain undecided if the present situation is locally restricted, if it is stable or represents a transient situation which could lead to either a consolidation of the three species by gradual elimination of the hybrids, to a taxonomic breakdown, or to hybrid speciation.