Crossing the pond: genetic assignment detects lobster hybridisation

Abstract

American lobsters (Homarus americanus) imported live into Europe as a seafood commodity have occasionally been released or escaped into the wild, within the range of an allopatric congener, the European lobster (H. gammarus). In addition to disease and competition, introduced lobsters threaten native populations through hybridisation, but morphological discriminants used for species identification are unable to discern hybrids, so molecular methods are required. We tested an array of 79 single nucleotide polymorphisms (SNPs) for their utility to distinguish 1,308 H. gammarus from 38 H. americanus and 30 hybrid offspring from an American female captured in Sweden. These loci provide powerful species assignment in Homarus, enabling the robust identification of hybrid and American individuals among a survey of European stock. Moreover, a subset panel of the 12 most powerful SNPs is sufficient to separate the two pure species, even when tissues have been cooked, and can detect the introduced component of hybrids. We conclude that these SNP loci can unambiguously identify hybrid lobsters that may be undetectable via basic morphology, and offer a valuable tool to investigate the prevalence of cryptic hybridisation in the wild. Such investigations are required to properly evaluate the potential for introgression of alien genes into European lobster populations. Genetic introgression due to hybridisation with non-native species is a major consequence of human-facilitated introductions that threatens endemic species with reduced fitness and local replacement 1,2. Even where hybridisation between native and introduced species is rare, rapid and extensive genetic introgression can arise 3. Population-level introgression and genetic admixture are not necessarily undesirable-managed interbreeding has been proposed to enhance resilience in key species threatened with extinction 4-but invasive hybridisation is often associated with profoundly harmful effects, including loss of genetic variation and adaptation 1,5. Nevertheless, assessing the conservation threat posed by hybridisation is not straightforward, and is especially challenging when hybrids themselves are fundamentally difficult to identify 5,6. Investigation of hybridisation and management of its impacts require tools to distinguish hybrids from pure species strains, and the increasing availability of molecular markers presents a powerful resource to assess the extent of crossbreeding and introgression in wild populations subject to introductions 7,8. The European lobster (Homarus gammarus) is renowned for its high value as a seafood commodity, but stock collapses have severely diminished the productivity of fisheries throughout extensive portions of the species' range 9. In Europe, recent annual landings of H. gammarus of ~5,000 tonnes are dwarfed by those of its transatlantic congener, the American lobster (H. americanus), which supports vast harvests of >150,000 tonnes per year 10. To satisfy European demand for lobster that native H. gammarus landings cannot fulfi...

Interspecific hybridization of decapod crustacean species with commercial interest—A review

“…10,54 Hybridization research and management of its consequences has necessitated the search for various tools used in distinguishing hybrids from pure species and the increasing availability of molecular markers provides a powerful tool for evaluating the extent of crossbreeding and introgression in wild populations affected by introduction. 10,55 Based on analysis of mitochondrial DNA haplotypes, mitochondrial cytochrome oxidase I (COI) and nuclear microsatellite data, the hypothesis of an hybrid origining from invasive species population can be substantiated. 52 Kim et al 56 also reported accurate identification of hybrid between snow crabs using a genotyping assay based on a single nucleotide polymorphism (SNP) in the ITS-1 (internal transcribed spacer) region and the COI gene.…”

“…52,55,[91][92][93][94][95][96][97][98][99] Invasive hybridization is frequently associated with profoundly negative consequences, such as loss of genetic variation and adaptation. 10,55,92,100 Interspecific hybridization between introduced and native species has thus raised concerns about the genetic integrity and evolutionary viability of native taxa, particularly those under threat from other stressors. 52,92 Genetic introgression from hybridization with non-native species is a major consequence of human-facilitated species introductions, endangering endemic species through decreased fitness and local replacement.…”

“…5,6 Interspecific hybridization between two different species usually produce more productive progenies 1,9 although some may be infertile. 10 In interspecific breeding programme, typically, each species has several superior traits 9,11 and the programme is expected to produce hybrids with faster growth rates and greater disease resistance than the parental species. 1,5,12,13 While hybridization holds significant promise for aquaculture by combining desirable traits from different species, it also presents challenges and potential drawbacks, such as reproductive sterility, 14 unpredictable traits, 15 accumulation of deleterious variation, 16 outbreeding depression, 16 genetic swamping, 16 genetic pollution (where hybridized organisms could potentially disrupt local ecosystems and result in negative ecological consequences if they interbreed with wild populations) 17 and ethical and moral concerns (including changes in the natural order, animal welfare issues and the possibility of unintended consequences).…”

Shell disease syndromes of decapod crustaceans

“…There are reports of non-native American lobsters exhibiting symptoms like those of ESD housed in a public aquarium in Europe (van der Meeren, 2008) showing the apparent presence of this condition in European waters (these animals were caught locally). The susceptibility of hybrids of H. americanus x gammarus (Ellis et al, 2020) to ESD is also undetermined.…”

Genome-wide SNPs in the spiny lobster Panulirus homarus reveal a hybrid origin for its subspecies

“…In marine organisms, genome-wide SNP discovery has been of considerable assistance in improving our understanding of the degree of population genetic differences [ 12 , 13 ], detection of secondary contact [ 14 ], and the effect of local environmental adaptation [ 15 ]. The joint allele frequency spectrum (AFS) from genome-wide SNP data has recently been used successfully to investigate historical demography of several non-model marine species (e.g., [ 16 ]).…”