Inter-specific hybridization underlies phenotypic variability in Daphnia populations

Area of Science:

• Ecology
• Evolutionary Biology
• Limnology

Background:

• Three Cladocera species (Daphnia hyalina, D. galeata, D. cucullata) commonly coexist in Palaearctic glacial lakes.
• Populations often include morphologically intermediate individuals alongside typical species forms.

Purpose of the Study:

• To investigate the genetic basis of morphological intermediacy in coexisting Daphnia populations.
• To determine the role of interspecific hybridization in generating these intermediate phenotypes.

Main Methods:

• Electrophoretic analysis of allozyme patterns was used to assess genetic variation.
• Allozyme data were compared between morphologically typical and intermediate individuals.

Main Results:

• Morphologically typical species were fixed for different alleles at the GOT locus.
• Intermediate individuals were heterozygous for alleles of the species they resembled, indicating hybridization.
• Allozyme patterns supported interspecific hybridization as the source of intermediate phenotypes.
• Limited backcrossing and no gene flow were detected between D. cucullata and the other two species.

Conclusions:

• Morphological intermediates in these Daphnia populations are primarily the result of interspecific hybridization.
• Hybridization occurs mainly between Daphnia hyalina and Daphnia galeata.
• There is restricted gene flow between the studied Daphnia species, particularly involving D. cucullata.