Patterns of population genetic structure and connectivity of squat lobsters associated with vulnerable marine ecosystems
Authors:   , Yan Ruo-Jin 
Published: December 2021

<p>Vulnerable marine ecosystems (VMEs) are susceptible to the impact of intense or long-term anthropogenic activities (e.g., bottom trawling). Networks of marine protected areas (MPAs) can help facilitate the conservation and restoration of biodiversity and ecosystem function provided by VMEs. An understanding of the connectivity amongst populations of deep-sea organisms is crucial for informing the management of VMEs, by assessing the effectiveness of existing MPAs and informing the placement of new MPAs. Genetic evaluation of population structure is one of the most commonly used indirect approaches for interpreting connectivity. In contrast to corals or sponges, which are typically habitat-forming organisms as VME-indicator taxa, squat lobsters are often found in close association with VMEs and can be considered to be VME-associated taxa. Nowadays, population genetic studies of deep-sea fauna mainly focus on VME-indicator taxa, whilst relatively few studies have focussed on VME-associated taxa, such as squat lobsters, whose distribution is not exclusively limited to VMEs. In this study, three deep-sea squat lobster species, Munida isos Ahyong & Poore, 2004, Munida endeavourae Ahyong & Poore, 2004 and Munida gracilis Henderson, 1885, were selected based on their association with VMEs (e.g., cold-water coral reefs and seamounts), wide distributional ranges across the southwest Pacific Ocean, and sample availability.  The overall aims of this research are to evaluate patterns of population structure and genetic connectivity of three squat lobster taxa in the southwest Pacific Ocean and consider how the acquired genetic information can contribute to the management and conservation of VMEs in the southwest Pacific Ocean. A general introduction of VMEs, MPAs, connectivity of deep-sea fauna, High-Throughput Sequencing (HTS), study area and study taxa are presented in Chapter 1.  To provide background information for this research, a review was conducted of the molecular-based studies of the systematics, taxonomy and phylogenetics of marine squat lobster taxa (Chapter 2). Recent molecular-based studies have dramatically increased our understanding of squat lobster phylogenetics and systematics, and thereby the taxonomy of this diverse and challenging group, which provide a valuable starting point for evaluating hypotheses concerning speciation, biogeography, adaptation and co-evolution (e.g., squat lobsters and corals). Notably, accurate taxonomy is critical for population genetic studies and consequently supports the conservation efforts of VMEs.  A range of molecular genetic markers, including the mitochondrial COI region, nuclear microsatellites and single nucleotide polymorphisms (SNPs), were utilised to evaluate the genetic connectivity amongst populations of three VME-associated taxa (Munida isos, M. endeavourae and M. gracilis). In addition to this, universal invertebrate primers were used to yield partial COI fragments of 649 bp (DNA barcoding) for the three Munida species to confirm the taxonomic identity and to exclude the possibility of cryptic species. Due to limited genetic information for the three Munida species, novel microsatellite loci were developed for M. isos based on the HiSeq 2500 sequencing platform and used for cross-species amplification in M. endeavourae and M. gracilis (Chapter 3). Additionally, a Genotyping by Sequencing (GBS) protocol and the Universal Network Enabled Analysis Kit (UNEAK) pipeline were employed to develop novel SNPs for M. isos samples from the southwest Pacific Ocean (Chapter 5).  A spatially explicit hierarchical testing framework (Northern-Southern biogeographical provinces, North-Central-South regions, and individual geomorphic features) was employed for the evaluation of connectivity amongst populations of the three deep-sea squat lobster taxa across their distributional range in the southwest Pacific Ocean (Chapter 4). The level of genetic diversity was high as revealed by variation at the COI region, and moderate based on microsatellite markers across the three Munida species. With more than 96% of the variance being attributed to differences within populations in the three Munida species, based on both marker types, no genetic subdivision was detected in M. endeavourae, whilst little genetic differentiation was observed in M. isos and M. gracilis based on microsatellite variation. For M. isos, populations from the Tasmanian slope were potentially genetically different from all other populations and may act as source populations, whereas populations from the Kermadec Ridge may be sink populations. Robust evidence of recent demographic expansions was detected in the three Munida species, based on COI and microsatellite marker types. The estimated time of demographic expansions for the three Munida species was ca. 16.1 kya, 24.4 kya and 21.6 kya for the M. isos, M. endeavourae and M. gracilis, respectively, coinciding with the late Pleistocene. The results are discussed in the context of the distribution of existing MPAs, and contribute new information useful to the management of VMEs within national and international waters in the region.  To further investigate patterns of connectivity in deep-sea squat lobster populations and provide valuable information for the design of management strategies to protect VMEs, newly developed SNPs were utilised (Chapter 5). The results showed that the Tasmanian slope and Macquarie Ridge populations were genetically different from all other populations, both within New Zealand’s exclusive economic zone (EEZ) and the high seas beyond, with little gene flow derived from Tasmanian slope populations to Macquarie Ridge populations. The results are discussed in the context of existing MPAs, and highlight the complexity of the endeavour to maintain population diversity and gene flow across multiple national jurisdictions as well as international waters, all of which employ different spatial protective measures.  The findings of this research are summarised and discussed in relation to the usefulness of genetic studies to provide new and valuable information about the genetic diversity and connectivity of VME-associated species, and to highlight what additional genetic research is needed to assist in the management and conservation of VMEs in the southwest Pacific Ocean (Chapter 6).</p>