Dynamic reticulate evolution in a Daphnia multispecies complex.

Area of Science:

• Evolutionary Biology
• Genetics
• Zoology

Background:

• Genomic data increasingly highlight hybridization's significant role in evolutionary processes.
• The Daphnia longispina group serves as a model system to investigate species differentiation and reticulation due to its complex evolutionary history.

Purpose of the Study:

• To examine species-specific differentiation and signatures of reticulation within the Daphnia longispina complex.
• To analyze the sequence variation of ITS1 (a part of the nuclear ribosomal DNA) in key species and ecotypes.

Main Methods:

• Combined examination of mitochondrial DNA (mtDNA), allozymes, and ITS1 sequence variation.
• Focus on two unambiguous species (D. galeata, D. cucullata) and two ecotypes (hyalina, rosea) within D. longispina.
• Analysis of ITS1 types (S, L, XL) and their distribution across taxa.

Main Results:

• Two main ITS1 types (S and L) were identified, along with intra-individual and intra-specific polymorphisms.
• D. galeata and D. cucullata, differentiated by mtDNA and allozymes, showed minimal distinction in S-ITS1 (S(cg)).
• Reticulate evolution facilitated the spread of the S(cg) ITS1 variant across species boundaries, indicating species-specific introgression.

Conclusions:

• Hybridization and gene flow significantly impact species differentiation and can obscure phylogenetic signals in multi-species complexes.
• The spread of ITS1 variants like S(cg) demonstrates reticulate evolution's dynamic role, challenging traditional views of species boundaries.
• Findings have critical implications for phylogenetic and phylogeographic surveys, emphasizing the need to consider reticulate evolution.