Local adaptation of Daphnia to protease inhibitors in cyanobacteria

• Applicant: Professor Eric von Elert, Ph.D.
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262323731

Man-made eutrophication of lakes has caused increasing frequencies of cyanobacterial blooms, which goes along with a reduction in abundance of Daphnia, the major herbivore of phytoplankton. This reduced abundance of Daphnia is a major cause for only short term improvement of water quality by food web manipulations. Although it has repeatedly been shown that Daphnia that coexist with cyanobacteria show increased tolerance to cyanobacteria, the genetic basis of this tolerance is entirely unknown. Among the most frequently reported inhibitors of cyanobacterial blooms are protease inhibitors (PIs), which have been demonstrated to specifically inhibit digestive proteases in Daphnia. In previous work, we have shown that a population of Daphnia magna that coexists with cyanobacteria is locally adapted to these cyanobacterial PIs: The animals themselves and their gut proteases are more tolerant to the PIs than animals from a population that exists without cyanobacteria. Haplotype analyses of the genes of the digestive proteases in the adapted population revealed that these loci have been under site-specific selection. This suggests that protease alleles with these selected sites are coding for proteases with increased inhibitor tolerance. However, it remains to be demonstrated that these prevalent non-synonymous mutations in digestive proteases have led to proteases that are more tolerant to PIs. Furthermore, an increased expression of protease genes might contribute to the enhanced tolerance in the adapted population. Here we are going to test whether or not plasticity in protease expression and differences in amino acid sequence in the digestive proteases contribute to the enhanced tolerance to dietary protease inhibitors in the adapted population.D. magna clones established from adapted and non-adapted populations will be compared for changes in gene expression of the digestive proteases in response to cyanobacterial protease inhibitors. The adaptive value of protease sites that have been under selection in the adapted population will be assessed by heterologous expression of chosen alleles and by enzyme-kinetics of the resulting proteins with respect to their tolerance to protease inhibitors. These data will be used for optimizing models for the prediction of 3D-structures of the digestive proteases and their tolerance to PIs in Daphnia. These 3D-structures will be used to predict tolerance to PIs at the population level of D. magna. Overall, the project aims at for the first time understanding the evolutionary adaptation of populations of Daphnia to cyanobacterial inhibitors. The findings might be relevant for understanding the evolution of resistance against host plant toxins in insects.

• DFG Programme: Research Grants
• Participating Persons: Professor Dr. Kay Hofmann; Dr. Thomas Petzoldt