Population structure of many marine organisms is spatially patchy and varies within and between years, a phenomenon defined as chaotic genetic patchiness. This results from the combination of planktonic larval dispersal and environmental stochasticity. Additionally, in species with bi-partite life, postsettlement selection can magnify these genetic differences. The high fecundity (up to 500,000 eggs annually) and protracted larval duration (12-24 months) and dispersal of the southern rock lobster, Jasus edwardsii, make it a good test species for chaotic genetic patchiness and selection during early benthic life. Here, we used double digest restriction site-associated DNA sequencing (ddRADseq) to investigate chaotic genetic patchiness and postsettlement selection in this species. We assessed differences in genetic structure and diversity of recently settled pueruli across four settlement years and between two sites in southeast Australia separated by approximately 1,000 km. Postsettlement selection was investigated by identifying loci under putative positive selection between recently settled pueruli and postpueruli and quantifying differences in the magnitude and strength of the selection at each year and site. Genetic differences within and among sites through time in neutral SNP markers indicated chaotic genetic patchiness. Recently settled puerulus at the southernmost site exhibited lower genetic diversity during years of low puerulus catches, further supporting this hypothesis. of spawning (Hendry, Berg, & Quinn, 1999), individual reproductive success (Hedgecock, 1994), pelagic larval duration (PLD) (Palumbi, 1994), larval behaviour (Raimondi & Keough, 1990) and natural selection (Cowen et al., 2000). Variability in the interaction of all those factors means that ephemeral fine-scale genetic heterogeneity or chaotic genetic patchiness could occur rather than the expected homogenous genetic diversity (Johnson & Black, 1982).Selective processes taking place before and after settlement can also lead to temporal genetic variation in the allele frequencies of a population (Johnson & Wernham, 1999). and 24 months in this phase before metamorphosing into a postlarva, known as puerulus (Booth, 1994). Phyllosoma experience up to 98% mortality during their protracted PLD (Lesser, 1978). This is not uncommon in marine invertebrates, and in the case of a sea urchin, although 2% of survivors were found to be sufficient to replenish a population, they carried a smaller representation of the overall genetic diversity of the adult population (Flowers, Schroeter, & Burton, 2002). Once pueruli settle, they remain sedentary and short distance migration is restricted to nocturnal foraging or retreating to protected areas during moulting (George, 2005).
Settlement of J. edwardsii pueruli in southeastern Australia ishighest between the months of July and February and peaks during winter months (Gardner, Frusher, Kennedy, & Cawthorn, 2001).Puerulus settlement has been monitored in southeastern Australia for the past four d...