Mating system variation in the eelgrass, Zostera marina

<p>Genetic diversity can modulate a population's response to a changing environment and plays a critical role in its ecological function. While multiple processes act to maintain genetic diversity, sexual reproduction remains the primary driving force. The eelgrass (<em>Zostera marina</em>) is an important habitat forming species found in temperate coastal ecosystems across the globe. Recent increases in sea surface temperatures have resulted in shifts from a perennial to a largely annual life-history strategy at its southern edge-of-range. Given that mating systems are intimately linked to standing levels of genetic variation, understanding the scope of sexual reproduction can illuminate the processes that shape genetic diversity. To describe and characterize edge-of-range eelgrass mating systems, developing seeds on flowering <em>Z. marina </em>shoots were genotyped from three meadows in Topsail, North Carolina. In all meadows, levels of multiple mating were high, with shoots pollinated by an average of 8 sires (range: 3 – 16). The number of fertilized seeds (i.e., reproductive success) varied significantly across sires (range: 1 – 25) and was positively correlated with both individual heterozygosity and self-fertilization. Outcrossing rates were high (approx. 70%) and varied across spathes. No clones were detected and kinship among sampled flowering shoots was low, supporting observed patterns of reproductive output. Given the role that genetic diversity plays in enhancing resistance to and resilience from ecological disturbance, disentangling the links between life-history, sexual reproduction and genetic variation will aid in informing the management and conservation of this key foundation species. </p>