Physella acuta: atypical mitochondrial gene order among panpulmonates (Gastropoda)

Abstract

Mitochondrial (mt) sequences are frequently used for phylogenetic reconstruction and for identification of species of molluscs. This study expands the phylogenetic range of Hygrophila (Panpulmonata) for which such sequence data are available by characterizing the full mt genome of the invasive freshwater snail Physella acuta (Physidae). The mt genome sequences of two P. acuta isolates from Stubblefield Lake, New Mexico, USA, differed in length (14,490 vs 14,314 bp) and showed 11.49% sequence divergence, whereas ITS1 and ITS2 sequences from the nuclear genome differed by 1.75%. The mt gene order of P. acuta (cox1, P, nad6, nad5, nad1, D, F, cox2, Y, W, nad4L, C, Q, atp6, R, E, rrnS, M, T, cox3, I, nad2, K, V, rrnL, L1, A, cytb, G, H, L2, atp8, N, nad2, S1, S2, nad4) differs considerably from the relatively conserved gene order within Panpulmonata. Phylogenetic trees show that the 13 protein-encoding mt gene sequences (equivalent codons) of P. acuta group according to gastropod phylogeny, yet branch lengths and dN/dS ratios for P. acuta indicate elevated amino acid substitutions relative to other gastropods. This study indicates that mt sequences of P. acuta are phylogenetically informative despite a considerable intraspecific divergence and the atypical gene order in its mt genome.

RETRACTED ARTICLE: The complete mitochondrial genomes of two freshwater snails provide new protein-coding gene rearrangement models and phylogenetic implications

“…These data are in accordance with previous findings from different gastropod clades [2, 4, 9, 14]. Most of PCGs were inferred to use TAA/TAG as stop codons except for T ( P. corneus : cox 1 and cox 2), which frequently occurred in protein-coding genes of most gastropod mt genomes [5, 6, 8, 13]. The incomplete stop codon was thought to be complemented via post-transcription alpolyadenylation [36].…”

“…Similar to most of the other pulmonate mt genomes [4, 5], the location of rrnL is between tRNA-Val (V) and tRNA-Leu (L1), while that of rrnS is between tRNA-Glu (E) and tRNA-Met (M) in both R. swinhoei and P. corneus mt genomes (Fig. 1).…”

“…Many of these freshwater snails are intermediate hosts for flatworm parasites and transmit infectious diseases of human and veterinary importance such as fascioliasis, cercarial dermatitis and schistosomiasis [3–5]. Accurate identification of species and analysis of genetic variation within populations is essential for studying molecular epidemiology and controlling parasite infection.…”

“…Owing to the unique features such as maternal inheritance, lack of extensive recombination, a relatively high evolutionary rate and abundantly available marker types [6], mitochondrial (mt) genomes have been widely used for species identification, population genetics and evolutionary relationships studies in metazoans including pulmonates [4, 5, 8]. In general, the metazoan mt genome is a single circular DNA molecule of about 14–17 kb in size, typically containing 37 genes [9]: 13 protein-coding genes (PCGs) [cytochrome c oxidase subunits 1–3 ( cox 1- cox 3), apocytochrome b (cyt b ), ATPsynthase subunits 6 and 8 ( atp 6 and atp 8), NADHdehydrogenase subunits 1–6 and 4 L ( nad 1-6 and nad 4L)], two ribosomal RNAs [small and large subunit ribosomal RNA (rrn S and rrn L )] and 22 transfer RNA (tRNA).…”

Positive selection on panpulmonate mitogenomes provide new clues on adaptations to terrestrial life

“…The particular demographic pattern of land snails that produces highly structured populations (hypothesis 4), i.e., “islands” of isolated demes, affects the probability of reciprocal monophyly of two samples and the chance that a gene tree matches the species tree [42], and explained the persistence of ancestral polymorphisms and the extreme divergence in Achatinella [43], Systrophia [44], and Xerocrassa [45]. In addition, in the case of Hygrophila, some studies found high divergence rates in Physella [46], and Radix [47], although no clear hypothesis has been proposed to explain this pattern.…”