Population Genetics of the Southern Rock Lobster: Is Translocation Genetically Viable? Erin Morgan

Introduction Translocation: The human-mediated movement of a species to maintain population number, connectivity and genetic diversity. Uses: Conservation, agriculture, repopulation/restocking [1, 2]. Risks: Misinterpretation of biological, behavioural or genetic backgrounds, leading to replacement of local populations, population competition and size reduction, introduction of disease, loss of localized adaptations (fitness) and loss of genetic diversity [3, 4]. Many marine species are assumed to be panmictic, meaning a single population with random mating, having no physical, behavioural or genetic barriers to connectivity. However, recent research is showing finer scale population subdivision is more common than previously assumed [5, 6, 7, 8]. Translocations have already been undertaken by commercial industry for the southern rock lobster, Jasus edwardsii, to maintain populations for fishing [9, 10]. Around Tasmania, lobsters are translocated from deeper water to shallow water areas currently over-exploited by agriculture. There are important phenotypic (or physical) differences between shallow and deep water populations, where shallow water phenotypes are more desirable due to a rich red shell colour, larger size and faster growth rate (Figure 1) [9]. These lobsters exhibit phenotypic plasticity, being able to change phenotype based on their environment, as Figure 1. Southern rock lobster, Jasus edwardsii, translocated individuals change to the more desired red phenotype after their first moult. red phenotype (left) and pale phenotype (right). This study aims to use microsatellite markers, or variations in short tandem repeats of DNA sequences, to investigate genetic differentiation among Tasmanian populations of the southern rock lobster. This study will determine whether assumptions made by the fishing industry of a panmictic population is true, and reveal potential patterns in connectivity across larger oceanic distances.

Methodology Lobsters were sampled from six sites across the southern Tasmanian coast (Figure 2), three from shallow water (<30m) sampling the red phenotype, and three deep areas (>60m) targeting pale phenotype. One population was sampled from New Zealand, to provide a larger scale of genetic connectivity. Sampling was conducted by taking a clip from the pleopod (swimming limb) of lobsters for genetic analysis. The Institute for Marine and Antarctic Studies (IMAS), provided capture- release permits as per the Australian Government National Health and Medical Research Council code of practice for care of animals for scientific purposes. DNA was extracted from a large sample of 460 lobsters, using 8 microsatellite markers designed for Jasus edwardsii [11]. DNA was amplified using Polymerase Chain Reaction, and PCR products were sent to the Australian Genome Research Facility (AGRF) for separation into microsatellite repeat lengths. Results were repeatedly analysed using population genetic computer software, providing probability values and standard error. A population genetics technique using F-statistics was used, based on the frequency of microsatellite marker alleles Figure 2. Sample sites [12]. Red shows shallow water phenotypes, of a population. Data analysis was considered significant at the level of p<0.002, with Fst values above 0.004 demonstrating white deep water. TAR, Taroona Reserve; MBI, Mutton Bird Island; genetic difference between marine populations [13].Computer analysis determined genetic connectivity as well as the level HI, Hobbs Island; MAT, Maatsyuker Island; CQE, Cape Queen Elizabeth; EP, East Pyramids; NZ, New Zealand. and directionality of migration or gene flow. Results TAR MBI HI MAT CQE EP New Table 1 showed a consistent significant genetic difference between New Zealand Tasmania and Tasmanian sites of around 0.03. Overall, populations of Tasmania showed no MBI 0.0002 Zealand genetic differences either between shallow and deep water sites, or between 0.9987 0.0013 HI 0.0005 0.0010 Tasmania geographically separate sites, however, on a larger scale, a clear genetic difference (0.0012) (0.0012) MAT 0.0016 0.0024 0.0030 exists between populations of lobsters around Tasmania compared to the New 0.3208 0.6792 CQE 0.0003 0.0021 0.0015 0.0004 population from New Zealand. Zealand (0.0121) (0.0121) Table 2 shows the rate of migration between now combined populations of EP 0.0012 0.0026 0.0005 0.0008 0.0002 Table 2. Migration rates (% probabilities). Tasmania and the population in New Zealand, based on microsatellite NZ 0.0292 0.0320 0.0342 0.0342 0.029 0.0312 Bold values show self recruitment, left frequencies. 32% of New Zealand lobsters sampled were migrants from Tasmania. Table 1. F-statistics across all populations. Bold indicates significant column indicates where migrants travelled Alternatively, 99% of Tasmanian lobsters were self recruited, or originated from values of p value <0.002. to, top row where migrants originated Tasmanian populations. Gene flow was in the order of 10 to 30 times more from., standard deviation in brackets common from Tasmania to New Zealand, than in the reverse direction. Discussion Conclusion Translocations of lobsters from deep to shallow water sites around Tasmania have already been conducted and shown to be No significant genetic difference was biologically beneficial [10, 14]. Assumptions about what is biologically meaningful should be treated with great care, as small levels identified between Tasmanian of statistically significant genetic difference found in some marine species may not be a true reflection of an entire population populations of different phenotypes, structure [5]. F-statistics suggest translocating lobsters in this manner is viable on a genetic level, as no significant genetic suggesting small scale translocation of differences were found between Tasmanian lobsters of different phenotypes. Therefore, assumptions of a panmictic population of lobsters from deep to shallow waters the southern rock lobster around Tasmania is true. around Tasmania are genetically viable. Large scale patterns of genetic difference based on isolation by oceanic distance have been found in marine species like the Analysis rejects the assumption of a southern rock lobster [4, 5, 8]. This study was limited by a single New Zealand population sampled, indicating further exploration of panmictic population over larger population connectivity across greater oceanic distances would better reveal migration patterns and genetic connectivity. The most geographical distances, highlighting the complicated barrier to migration for marine species is ocean currents, with 2,000 kilometres of open ocean between Tasmania and biggest limitation and the best direction New Zealand, predicted success of migration is low [15]. Results showed successful migration and genetic exchange of populations forward, to use a wider number of in Tasmania into New Zealand was much more likely than New Zealand populations traversing ocean currents into Tasmania. This is genetic measures to investigate highly important in consideration of fishing exploitation of lobsters, as New Zealand may rely on Tasmanian migrants as a source of population genetic structure of the new genetic diversity, in what is known as a source-sink relationship. Over-exploitation of lobster populations in Tasmania may southern rock lobster across larger have a flow-on effect, reducing populations of lobsters in New Zealand which rely on Tasmanian stocks for numbers. oceanic distances.

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