Biodiversity Data Journal :
Research Article
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Corresponding author: Donald Colgan (don.colgan@austmus.gov.au)
Academic editor: Cristian Altaba
Received: 26 May 2020 | Accepted: 16 Sep 2020 | Published: 29 Oct 2020
© 2020 Donald Colgan, Hugo Lumsdaine
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Colgan D, Lumsdaine H (2020) Genetic assessment of the variation and distribution of the species of Salinator (Panpulmonata: Amphibolidae) in south-eastern Australia. Biodiversity Data Journal 8: e54724. https://doi.org/10.3897/BDJ.8.e54724
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Amphibolidae is one of the most abundant families of gastropods in estuarine environments of south-eastern Australia. However, the range limits of the species of Salinator, one of the family’s two genera in the region, remain unclear partly due to uncertainty of identifications based solely on shell morphology. Insufficient data have been collected to address questions regarding the genetic variability of any of the species of Salinator. Here, DNA sequences from a segment of the cytochrome c oxidase subunit I and 28S ribosomal RNA genes were collected to investigate the distribution and variation of the three Salinator species in the region, these being S. fragilis, S. rhamphidia and S. tecta. The results demonstrate a large range extension in S. rhamphidia and suggest that S. tecta may have limited distribution in Tasmania. In contrast to previously-studied estuarine Mollusca in the south-eastern coasts of the mainland and Tasmania, S. rhamphidia has regional differentiation. There is evidence of genetic disequilibrium within S. fragilis, suggesting that it may presently comprise contributions from two distinct sets of populations.
28S ribosomal RNA, cytochrome c oxidase subunit I, Salinator fragilis, Salinator rhamphidia, Salinator tecta, Tasmania
The two genera of mudflat snails of the family Amphibolidae Gray, 1840 in southern and eastern Australia include some of the most abundant molluscs of estuarine environments in the region (
The morphologies of S. fragilis, S. rhamphidia and S. tecta are similar and the shell characters potentially distinguishing them are limited to the height of the spire and shell size (
This study was conducted to clarify the distribution and variation of the three south-eastern Australian Salinator species, S. fragilis, S. rhamphidia and S. tecta, using genetic data. The study utilised newly-collected sequences from the mitochondrial cytochrome c oxidase subunit I (COI) and the nuclear 28S ribosomal RNA (28S rRNA) genes and available COI sequences from GenBank.
Specimens were collected by hand and stored at -80°C or in 95% ethanol until use. Specimens were morphologically identified using a stereomicroscope according to the body pigmentation criteria specified in
Abbreviations
AMS: Australian Museum Malacology collection.
MAL#: designation of Australian Museum Malacology collection locality
CASIZ: California Academy of Sciences Invertebrate Zoology collection
New collection localities and population designations
See Fig.
Map of collection localities of Salinator specimens. Details of named locations are provided in the text. Localities indicated by filled squares are represented by genetic data. Those with unfilled squares were examined using the morphology of the animal and those with open circles only conchologically. The numbers of specimens of each species’ sequences at a site are indicated next to the species name.
New South Wales:
N1: Port Jackson, Exile Bay, Bayview Park (MAL# 88194),
N2: Cuttagee Lake, estuary to west of the road bridge (MAL#88542),
Pittwater, Careel Bay, (MAL# 88529),
Tasmania:
T1: Tamar River, west bank, mudflats at Deviot (MAL# 72693),
T2: Henderson Lagoon, south bank at Falmouth (MAL# 76559),
T3: Snug, mudflats, estuary immediately S of town, upstream of bridge (MAL# 76557),
GenBank Accessions
S. tecta: JF439218 (
S. fragilis: JQ228488: C.472898 (
S. rhamphidia: JN620539 (
S. rosacea: JQ228476 (AMS C.463440) and JQ228475 (AMS C.472902) both from
DNA was extracted using the QIAGEN DNeasy Blood and Tissue Extraction kit following the manufacturer’s instructions. PCR amplifications generally followed the procedures in
Data were collected from parts of the COI and 28S rRNA genes. COI was amplified using the universal primers of
Chromatograms were examined in Sequencher version 5.4.5 (Gene Codes Corporation, Ann Arbor, MI). The dataset, comprising new sequences and GenBank data, was aligned in ClustalX (
Various phylogenetic analyses were conducted, although only the Maximum Likelihood (ML) analyses are reported in detail below. These were performed on the CIPRES data portal (
Net pairwise Kimura 2-parameter genetic distances (
Statistical parsimony analyses of the COI data were conducted with TCS 1.21 (
The GenBank accession numbers for the newly-collected sequences are MT356194 – MT356226 for COI and MT348593 – MT348598 for 28S rRNA.
Suppl. material
The alignment of the cytochrome c oxidase subunit I sequences used here. Sequences are identified by the Australian Museum registration number or GenBank accession number.
Suppl. material
The alignment of the 28S ribosomal sequences used here. Sequences are identified by the Australian Museum registration number or GenBank accession number.
The alignment of COI sequences (Suppl. material
Maximum Likelihood phylogeny of the relationships between Salinator species from the RAxML analysis. Bootstrap percentages above 70% are shown above or below branches. Lines to the right of the sequence names specify groups 1 and 2, the two major sub-networks recovered amongst S. fragilis in the TCS analysis of the data. Sequences are identified by the GenBank accession number followed by a geographic locator. Sequences collected here are identified by N1 (see Materials and Methods for details) for individuals from Exile Bay, N2 for those from Cuttagee Lake, T1 from Deviot, T2 from Falmouth and T3 from Snug. Sequences from localities in other studies are located by an abbreviation of the name of the relevant State.
There was no geographic pattern of variation within S. fragilis, but there was one large clade within the species that received considerable bootstrap support (85%). TCS analysis revealed two large sub-networks in the species that were separated by three mutational changes (Fig.
TCS analysis of the COI sequences prepared by the PopART graphical interface. The figures beside branches specify the number of mutational steps between network elements. Branches lacking figures represent one step. The provenance of sequences is colour-coded according to the legend. Abbreviations in parentheses in the legend indicate the newly-collected localities, detailed in the Materials and Methods. The numbers of occurrences of a haplotype is proportional to the size of the circle representing it. All but three haplotypes occurred only once. The specimens with a haplotype found in multiple individuals (shown by larger circles) are indicated by the accession numbers in the box nearest their symbol.
Average pairwise distances within species were similar for S. tecta and S. rhamphidia, but somewhat lower for S. fragilis (Table
Estimates of pairwise genetic distance within species and net pairwise genetic distance between species. Analyses were conducted using the Kimura 2-parameter model. Standard error estimates are shown above the diagonal for inter-species comparisons and after the distance measure for intra-species comparisons.
Species |
S. fragilis |
S. rhamphidia |
S. tecta |
S. rosacea |
P. solida |
S. fragilis |
0.007 ± 0.002 |
0.244 |
0.021 |
0.028 |
0.027 |
S. rhamphidia |
0.028 |
0.014 ± 0.004 |
0.025 |
0.027 |
0.028 |
S. tecta |
0.203 |
0.225 |
0.012 ± 0.003 |
0.024 |
0.024 |
S. rosacea |
0.251 |
0.268 |
0.221 |
0.011 ± 0.003 |
0.025 |
P. solida |
0.224 |
0.243 |
0.206 |
0.212 |
0.055 ± 0.01 |
The genetic diversity measures (Table
Measures of genetic variability in Salinator species from south-eastern Australia. The columns specify the number of sequences from the species, the number of distinct haplotypes amongst these, the haplotype diversity (Hd) and the nucleotide diversity (Nd). The final two columns show the values of the Tajima’s D and Fu’s Fs statistics, with the probability that these values conform to the expectations of selective neutrality.
Species |
n |
Number of haplotypes |
Hd |
Nd |
Tajima’s D |
Fu’s Fs |
S. fragilis |
26 |
19 |
0.976 |
0.00757 |
-1.77465 0.10 > P > 0.05 |
-15.274 P = 0.000 |
S. rhamphidia |
11 |
7 |
0.818 |
0.01436 |
0.23394 P > 0.10 |
0.893 P = 0.684 |
S. tecta |
5 |
5 |
1.000 |
0.01063 |
-1.22485 P > 0.10 |
-0.875 P = 0.15246 |
The same sequence of the ribosomal RNA fragment (Suppl. material
The DNA sequencing results provide novel insights into the distribution of Salinator taxa in south-eastern Australia and confirm the unexpected presence of S. rhamphidia in Tasmania, representing a considerable extension of the species’ confirmed range. The strongly-supported inclusion of the unidentified GenBank sequence (GU331961) from Queensland in S. rhamphidia also represents a large extension of the genetically-confirmed range of the species. There is genetic divergence between Tasmania and mainland specimens of the species. This contrasts with previous comparisons of specimens of estuarine gastropods from Tasmania and the Australian mainland which have not identified regionally-restricted clades. The comparisons include studies of Austrocochlea constricta (Lamarck, 1822) (
Sympatry at the local level was observed for S. tecta and S. rhamphidia by
There is considerable genetic diversity within each of the three species of Salinator. Statistical tests show that, at least for S. fragilis, this differs significantly from the expectations of neutral evolution. The negative value of the Fu’s Fs statistic for this species suggests that it has undergone recent population expansion. Such a situation has also been observed in other Mollusca in south-eastern Australia (
The authors wish to thank Tina Reutelshöfer and Pam Da Costa for technical assistance. We also thank Tina for fieldwork and collection assistance.
The Australian Museum
The authors declare they have no conflicts of interest
The alignment of the cytochrome c oxidase subunit I sequences used here. Sequences are identified by Australian Museum registration number or GenBank accession number.
The alignment of the 28S ribosomal sequences used here. Sequences are identified by Australian Museum registration number or GenBank accession number.