Extremely divergent COI sequences within an amphipod species complex: A possible role for endosymbionts?

• Published in: Ecology and evolution 2022-10, Vol.12 (10), p.e9448-n/a
• Main Authors: Park, Eunji, Poulin, Robert
• Format: Article
• Language: English
• Subjects: Amphipoda; cryptic species; Divergence; Endosymbionts; Evolution; Genetic engineering; Genetic testing; Haplotypes; intracellular parasites; Mitochondrial DNA; morphological conservatism; Morphology; Phylogenetics; Population; Rickettsia; Species; species delimitation; substitution saturation
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.9448

Some heritable endosymbionts can affect host mtDNA evolution in various ways. Amphipods host diverse endosymbionts, but whether their mtDNA has been influenced by these endosymbionts has yet to be considered. Here, we investigated the role of endosymbionts (microsporidians and Rickettsia) in explaining highly divergent COI sequences in Paracalliope fluviatilis species complex, the most common freshwater amphipods in New Zealand. We first contrasted phylogeographic patterns using COI, ITS, and 28S sequences. While molecular species delimitation methods based on 28S sequences supported 3–4 potential species (N, C, SA, and SB) among freshwater lineages, COI sequences supported 17–27 putative species reflecting high inter‐population divergence. The deep divergence between NC and S lineages (~20%; 28S) and the substitution saturation on the 3rd codon position of COI detected even within one lineage (SA) indicate a very high level of morphological stasis. Interestingly, individuals infected and uninfected by Rickettsia comprised divergent COI lineages in one of four populations tested, suggesting a potential influence of endosymbionts in mtDNA patterns. We propose several plausible explanations for divergent COI lineages, although they would need further testing with multiple lines of evidence. Lastly, due to common morphological stasis and the presence of endosymbionts, phylogeographic patterns of amphipods based on mtDNA should be interpreted with caution. We contrasted phylogeographic patterns and species delimitation results shown by COI and 28S sequences in an amphipod species complex and explored the potential influence of endosymbionts in mtDNA patterns. Amphipod individuals infected and uninfected by Rickettsia comprised divergent COI lineages in one of four populations tested, suggesting a potential impact of endosymbionts, but further investigation is needed since several alternative scenarios exist.