Development of twenty-three novel microsatellite markers for the seagrass, Zostera muelleri from Australia

Seagrasses are one of the most productive and economically important habitats in the coastal zone, but they are disappearing at an alarming rate, with more than half the world’s seagrass area lost since the 1990s. They now face serious threat from climate change, and there is much current speculation over whether they will survive the coming decades. The future of seagrasses depends on their ability to recover and adapt to environmental change—i.e. their ‘resilience’. Key to this, is understanding the role that genetic diversity plays in the resilience of this highly clonal group of species. To investigate population structure, genetic diversity, mating system (sexual versus asexual reproduction) and patterns of connectivity, we isolated and characterised 23 microsatellite loci using next generation sequencing for the Australian seagrass species, Zostera muelleri (syn. Z. capricorni), which is regarded as a globally significant congeneric species. Loci were tested for levels of variation based on eight individuals sampled from Lake Macquarie, New South Wales, Australia. We detected high to moderate levels of genetic variation across most loci with a mean allelic richness of 3.64 and unbiased expected hetrozygosity of 0.562. We found no evidence for linkage disequilibrium between any loci and only three loci (ZosNSW25, ZosNSW2, and ZosNSW47) showed significant deviations from Hardy–Weinberg expectations. All individuals displayed a unique multi-locus genotype and the combined probability of identity across all loci was low (PID = 1.87 9 10-12) indicating a high level of power in detecting unique genotypes. These 23 markers will provide an important tool for future population genetic assessments in this important keystone species.Craig D.H. Sherman, Annalise M. Stanley, Michael J. Keough, Michael G. Gardner and Peter I. Macreadi

Genetic relationships within and between populations of the endangered grass Lachnagrostis limitanea (Gramineae)

Allozyme electrophoresis was used to examine the genetic relationships within and between four naturally occurring populations of the endangered Spalding blown grass (Lachnagrostis limitanea (J.M.Black) S.W.L. Jacobs (syn. Agrostis limitanea)) from the mid north of South Australia. five polymorphic markers were detected during a screen of 34 putative allozyme loci, and used to assess population structure in the species. As karyotype analysis of seedlings derived from all populations confirmed that the species is polyploid (octoploid, with 2n = 8x = 56), allozymic interpretation and population genetic assessment were limited to the assignment of “whole genotypes” at each polymorphic marker for each plant. despite this restriction, the genetic data indicate that (1) sites displayed the low levels of allozymic divergence typical of conspecific populations, (2) each population was genetically distinct, (3) none of the three sites with small population sizes displayed any within‐site genetic variability, and (4) most of the genetic diversity present in the species resides within the largest natural population (Yakkalo). Parent/progeny comparisons demonstrated an absence of apomixis and inferred that out‐crossing was common in the Yakkalo population, suggesting that inbreeding rather than selfing perse is the most likely cause of the severe reduction in genetic variability observed at the other three sites. The implications of these results for conservation management of remnant L. limitanea populations are discussed.Mark Adams, Manfred Jusaitis, Amber Clark

Biogeography of Australian seagrasses: NSW, Victoria, Tasmania and Temperate Queensland

This chapter presents an introduction to the biogeography of southeastern Australian seagrasses, explaining the distribution and basic ecology of the 22 species that inhabit this 10,000 km stretch of coastline, from the northern limit of Queensland's temperate zone through to Tasmania. The chapter draws on 25 years of new information (peer-reviewed literature, books, personal communications, etc.) that has been generated since the previous biogeography chapter of its kind was written by Larkum et al. (Biology of Seagrasses-a treatise on the biology of seagrasses with special reference to the Australian region. Elsevier, The Netherlands, 1989). The influence of local (e.g. geomorphic environment) and large-scale (e.g. temperature) factors on the distribution of species are discussed. Also, we present up-to-date information on the status (declining, increasing, or no change) of each species from a conservation point of view on a state-by-state basis. Not surprisingly, many species are reported to have declined for a variety of reasons, including: flood events, boat moorings, and coastal development (e.g. dredging). Fortunately, there are also reports of recovery. Thanks to developments in genetic sequencing we have been able to present new data on genetic connectivity, gene flow, and source-sink populations for a handful of species. In the coming years we expect and hope that improvements in remote sensing technology will allow for more accurate, more frequent, and higher resolution mapping of seagrasses along this stretch of coast