No abstract

Recent years have seen an increase in the number of studies that use DNA sequence information in addition to morphological methods, as the latter alone can be inadequate for morphologically similar, cryptic species. Marine onchidiid slugs (Mollusca: Gastropoda: Onchidiidae), which commonly inhabit intertidal environments and have a near-global distribution, comprise 11 genera and 86 described species. Singapore has 19 recorded species of onchidiids with Peronia verruculata (Cuvier, 1830) being the most abundant. Here we present mitochondrial DNA sequence data from 63 P. verruculata-like specimens to show that they constitute two closely-related clades with distinct sequence signatures and a clear barcode gap. Intraclade distances are 0–1.8% while interclade distances range from 4.7 to 6.0%. Scanning electron microscopy of internal copulation organs reveals that the two clades have distinct penial and accessory gland spine structures, which also differ in size. Using an integrative taxonomic approach, we propose that what was initially thought to be P. verruculata in Singapore, actually are two different species of Peronia.

Environmental DNA (eDNA) with metabarcoding or metagenomics will likely become a major biomonitoring tool in the 21st century, perhaps even more so in the face of increased coastal urbanization and its associated effects such as pollution, land reclamation, and seabed dredging. Together, these impacts and the consequent high turbidity pose severe challenges to traditional survey techniques that rely heavily on visual observations. We here demonstrate that eDNA can be used for biomonitoring in turbid waters, using Singapore as a case study. The cytochrome c oxidase subunit I (COI) locus was used to detect 525 metazoan molecular operational taxonomic units (MOTUs) based on eDNA obtained from 52 L of filtered seawater. Of these, 130 MOTUs (24.7%) were identifiable to species, including ecologically significant species that in some cases were invasive or rarely observed. Metazoan signals also enabled discrimination of discrete, but connected, environments from intertidal and subtidal zones. Taxa with known habitat preferences were found to have left trace eDNA at sites that matched putatively suitable habitats. Moreover, no coast-specific signals were detected in open water samples, which suggest that intermixing of water was limited. The study confirms that eDNA metabarcoding is a viable biomonitoring tool for coastal areas with highly sedimented waters.

Sea anemones are sedentary marine animals that tend to disperse via planktonic larvae and are predicted to have high population connectivity in undisturbed habitats. We test whether two sea anemone species living in two different tidal zones of a highly disturbed marine environment can maintain high genetic connectivity. More than 1000 loci with single-nucleotide polymorphisms (SNPs) were obtained with double-digest RADseq for 81 Stichodactyla haddoni and 99 Entacmaea quadricolor individuals to test for population genetic structure. We find evidence that both species predominantly propagate via sexual reproduction, and asexual reproduction is limited. We observe panmixia that indicates the absence of effective dispersal barriers for these species living in a highly anthropogenically disturbed environment. This is positive news for both species that are also found in the aquarium trade. More fundamentally, our results suggest that inhabiting different parts of a shallow reef may not affect a species’ population connectivity nor favour asexual reproduction.