Reproduction and genetic detection of veligers in changingDreissenapopulations in the Great Lakes

Abstract

Abstract. Dreissenid bivalves, Dreissena polymorpha (zebra mussel) and Dreissena bugensis (quagga mussel) are biofouling species that invaded the Great Lakes region of North America from source populations in Europe in the 1980s. Initially, D. polymorpha spread faster and farther; however, D. bugensis have recently displaced D. polymorpha in many areas of the Great Lakes and was the first to be found west of the Continental Divide. Early detection of dreissenids is important in anticipating and preventing potentially high economic impacts. To study population dynamics and to enhance detection methods, we assessed ''spawnability'' using a serotonin bioassay and developed a new, sensitive, multiplex PCR method to identify veligers and verify adult species. Contrasting riverine populations were identified in the Saginaw River (100% D. polymorpha) and the Detroit River at Belle Isle (100% D. bugensis in 2010), and mixed populations of mussels (10% to ;50% D. polymorpha) were found in Saginaw Bay, Lake Huron. In 1994, when the Detroit River population at Belle Isle was virtually all D. polymorpha (Ram et al. 1996), spawning could not be induced by serotonin until late May, and peak spawnability did not occur until early June. In 2010, D. bugensis at the same site could be induced to spawn in the first week of April, and reached near maximal spawning intensity by mid-May. In 2010, Detroit River veligers were first observed in April and, by PCR species-specific detection, were 100% D. bugensis. Veligers changed to a mixed population of both species later in May and rose to a peak, mixed population in early June. These experiments demonstrate a quantitative, species-specific detection of dreissenid veligers, and lay the groundwork for determining the role of early reproduction and other mechanisms in mediating the displacement of one species by a closely related ''cousin.''

Validated methodology for quantifying infestation levels of dreissenid mussels in environmental DNA (eDNA) samples

“…The traditional microscopic screening methods for veliger larvae detection2526 are labour intensive and time-consuming40, with a relatively high potential for false positive results. In addition, our method outperforms previous molecular methods aimed at determining only dreissenid DNA presence42829. To the best of our knowledge, this is the first method capable to differentiate specific dreissenid DNA levels from other bivalves in eDNA samples.…”

“…Several previous studies have developed detection methods based on molecular markers for dreissenid identification in environmental samples42829. However, to our knowledge, this study is the first published in which a method was developed for identification and quantification of the infestation level of invasive dreissenid species.…”

“…The latter is labour intensive and time-consuming, and can result in false positives due to the similar appearance between dreissenid larvae and those of other macroinvertebrates27. Alternatively, molecular markers have proven useful in species identification diagnostics, but these previous studies do not intend sample quantification42829. Thus, after optimization they offer a faster diagnosis without false positives but they do not allow the quantification of the dreissenid infestation.…”

Invasion genetics from eDNA and thousands of larvae: A targeted metabarcoding assay that distinguishes species and population variation of zebra and quagga mussels

“…However, those each required two separate markers (one for zebra mussels and another for quagga mussels) and neither discerned population genetic variability. Ram et al () used mt16S RNA for zebra mussel and mtDNA COI for quagga mussel, with the two targeted regions differing by 181 nt in length. Amberg et al () designed COI primers for the zebra mussel, with their future aspirations stated to develop a probe to differentiate quagga mussel eDNA.…”

Accuracy and reliability ofDreissenaspp. larvae detection by cross-polarized light microscopy, imaging flow cytometry, and polymerase chain reaction assays

“…larvae in plankton samples (Frischer et al 2002, Hoy et al 2010, Rochelle et al 2010, Ram et al 2011. PCR-based approaches extract total community DNA from the contents of a plankton net tow and use PCR amplification to detect genes unique to Dreissena spp.…”