Identifying invasive Daphnia species by morphological analysis of postabdominal claws in Sierra Nevada alpine lakes

Abstract

Sedimentary postabdominal claws, among other remains, have been used successfully in paleolimnological studies to reconstruct past environmental conditions and the distribution pattern of certain Daphnia species. However, morphological analysis of postabdominal claws has not proven adequate for the clear taxonomic differentiation among species within a complex, such as the Daphnia pulex complex. The presence of the invasive North American (NA) D. pulex lineage was recently detected in an alpine lake in the Sierra Nevada mountain range (Southeast Spain). This lineage has spread throughout Africa and the Mediterranean basin, suggesting a trend towards its increased presence in Europe. The aim of this study was to examine whether this invasive lineage could be differentiated from the native European (Eu) Daphnia pulicaria lineage based on morphological differences in postabdominal claws recovered from three alpine lakes in the Sierra Nevada. The most useful differential variables were the postabdominal claw length (PCL), ratio of distal comb length to PCL (Cldist/PCL), and number of stout spines. Thus, NA D. pulex may be identifiable by a short PCL, low Cldist/PCL value and the presence of < 5 stout spines. Because of a wide variability in PCL within the Eu D. pulicaria species and an overlap in stout spine number between the species, morphological analysis results cannot unequivocally differentiate these lineages. However, they make a useful contribution to recognition of the possible presence of this invasive lineage. The present findings assist identification of the invasive NA D. pulex lineage in potentially affected regions, facilitating reconstruction of its historic dispersion and colonization.