Analysis of reticulate relationships within the Daphnia longispina species complex. Allozyme phenotype and morphology

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 Daphniu 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. cucullatu, D. galeuta and D. hyulinu, and three hybrid groups, D. cuculhta~guleata, D. cucullutal hyulinu and D. guleuta,'hyulinu. 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 Fl-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 87 88GieBler 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.

On the presence of Daphnia galeata in Lake Orta (N. Italy)

“…D. galeata is fixed for F (fast) alleles, whereas D. longispina is fixed for S (slow) alleles at this locus, therefore making the distinction between the two very easy. Lately, Gießler (1997) reported AO as a second diagnostic marker, as D. galeata appeared to be fixed for F (fast) alleles at this locus, while D. longispina was fixed for the S (slow) alleles. These two diagnostic markers typically enable a discrimination of the species, and of the backcrosses and second generation's hybrids as well.…”

“…In particular, the presence of allele M can be interpreted in different ways. It has been suggested (Gießler 1997) that this allele is indicative of the presence of Daphnia cucullata genes. According to what we know on the ecology of this species, this is not a reliable interpretation for Lake Orta because D. cucullata is considered a "lowland" species, typical of well buffered water bodies (Fryer 1985).…”

The coexistence of hybrid and parentalDaphnia: the role of parasites

“…AO and AAT are diagnostic markers for D. galeata and D. hyalina (Wolf & Mort 1986;Gießler 1997). Specimens were differentiated into six genealogical classes (taxa): 'pure' parentals, both hybrid generations, and first generation backcrosses (see table 1 in ).…”

Gene flow in the Daphnia longispina hybrid complex (Crustacea, Cladocera) inhabiting large lakes

“…Within the first few hours, the daphnids were picked out and subjected to morphological identification (GieBler, 1987(GieBler, , 1997 population sizes in some of the lakes allowed the analysis of only a few individuals. To gain a broader perspective on the spatial scale of the population structure, the results were compared with those from a different study.…”

“…Deviations from H-W expectations appear to be highly variable, which might be partly the result of taxonomic confusion. Molecular methods revealed interspecific hybridization and improved taxonomic identification (Hebert, 1985;Taylor & Hebert, 1993;GieBler, 1997). F1-hybrids may become extremely abundant and sometimes outcompete one or both parental species (Taylor & Hebert, 1992).…”