Search

Allozymes present several classical examples of divergent selection, including the variation in the cytosolic aspartate aminotransferase (AAT) in the intertidal snails Littorina saxatilis. AAT is a part of the asparate-malate shuttle, in the interidal molluscs involved in the anaerobic respiration during desiccation. Previous allozyme studies reported the sharp gradient in the frequencies of the AAT 100 and the AAT 120 alleles between the low and high shores in the Northern Europe and the differences in their enzymatic activity, supporting the role of AAT in adaptation to desiccation. However, the populations in the Iberian Peninsula showed the opposite allele cline. Using the mRNA sequencing and the genome pool-seq analyses we characterize DNA sequences of the different AAT alleles, report the amino acid replacements behind the allozyme variation and show that same allozyme alleles in Northern and Southern populations have different protein sequences. Gene phylogeny reveals that the AAT 100 and the northern AAT 120 alleles represent the old polymorphism, shared among the closely related species of Littorina, while the southern AAT 120 allele is more recently derived from AAT 100 . Further, we show that the Aat gene is expressed at constitutive level in different genotypes and conditions, supporting the role of structural variation in regulation of enzyme activity. Finally, we report the location and the structure of the gene in the L. saxatilis genome and the presence of two additional non-functional gene copies. Altogether, we provide a missing link between the classical allozyme studies and the genome scans and bring together the results produced over decades of the genetic research., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kerstin Johannesson reports financial support was provided by Swedish research council Vetenskapsrådet., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)