Disentangling genetic from environmental effects on phenotypic variability of Southern rock lobster (Jasus edwardsii) postlarvae

Environmental conditions experienced during larval dispersal of marine organisms can determine size-at-settlement of recruits. It is, therefore, not uncommon that larvae undergoing different dispersal histories would exhibit phenotypic variability at recruitment. Here we investigated morphological differences in recently settled southern rock lobster (Jasus edwardsii) recruits, known as pueruli, along a latitudinal and temporal gradient on the east coast of Tasmania, Australia. We further explored whether natural selection could be driving morphological variation. We used double digest restriction-site associated DNA sequencing (ddRADseq) to assess differences in genetic structure of recently settled recruits on the east coast of Tasmania over three months of peak settlement during 2012 (August, September and October). Phenotypic differences in pueruli between sites and months of settlement were observed, with significantly smaller individuals found at the northernmost site. Also, there was a lack of overall genetic divergence; however, significant differences in pairwise FST values between settlement months were observed at the southernmost study site, located at an area of confluence of ocean currents. Specifically, individuals settling into the southernmost earlier in the season were genetically different from those settling later. The lack of overall genetic divergence in the presence of phenotypic variation indicates that larval environmental history during dispersal of J. edwardsii could be a possible driver of the resulting phenotype of settlers.

Methods
Four ddRADseq libraries were prepared from genomic DNA of Jasus edwardsii pueruli samples.

Libraries were sequenced at the Australian Genome Research Facility (AGRF) on the Illumina HiSeq 2500 platform using a 100 bp single-end kit

海洋生物幼体扩散过程中所经历的环境条件，可决定其幼体补充时的体型大小。因此，具有不同扩散经历的幼体在补充阶段表现出表型变异的情况并不罕见。本研究聚焦澳大利亚塔斯马尼亚东海岸沿纬度与时间梯度分布的新近定居南方岩龙虾（Jasus edwardsii）幼体补充群（该阶段个体又称pueruli）的形态差异，并进一步探究自然选择是否为该形态变异的驱动因素。我们于2012年的三个定居高峰期（8月、9月及10月），采用双酶切限制性位点关联DNA测序（ddRADseq）技术，对塔斯马尼亚东海岸新近定居的幼体补充群的遗传结构差异进行评估。研究观察到不同采样位点与定居月份的pueruli存在表型差异，其中最北端采样点的个体体型显著偏小。整体遗传分化并不显著，但在位于洋流交汇区的最南端研究位点，不同定居月份间的成对FST值存在显著差异。具体而言，该位点早期定居的个体与后期定居的个体在遗传上存在分化。表型变异存在但整体遗传分化缺失的结果表明，南方岩龙虾（Jasus edwardsii）幼体扩散阶段的环境经历可能是导致其补充群表型差异的潜在驱动因素。
方法
本研究从南方岩龙虾pueruli样本的基因组DNA中制备了4个ddRADseq文库。文库由澳大利亚基因组研究设施（AGRF）依托Illumina HiSeq 2500平台，采用100 bp单端测序试剂盒完成测序。