Data from: A biting commentary: integrating tooth characters with molecular data doubles known species diversity in a lineage of sea slugs that consume “killer algae”

Predicting biotic resistance to highly invasive strains of “killer algae” (Caulerpa spp.) requires understanding the diversity and feeding preferences of native consumers, including sea slugs in family Oxynoidae. Past studies reported low algal host specificity for Oxynoe (6 spp.) and Lobiger (4 spp.), but these taxonomically challenging slugs may represent species complexes of unrecognized specialists that prefer different Caulerpa spp. Here, we assess global diversity of these genera by integrating gene sequences with morphological data from microscopic teeth and internal shells, the only hard parts in these soft-bodied invertebrates. Four delimitation methods applied to datasets comprising mtDNA and/or nuclear alleles yielded up to 16 species hypotheses for samples comprising five nominal taxa, including five highly divergent species in Lobiger and five in Oxynoe. Depending on the analysis, a further four to six species were recovered in the O. antillarum-viridis complex, a clade in which mitochondrial divergence was low and nuclear alleles were shared among lineages. Bayesian species delimitation using only morphological data supported most candidate species, however, and integrative analyses combining morphological and genetic data fully supported all complex members. Collectively, our findings double the recognized biodiversity in Oxynoidae, and illustrate the value of including data from traits that mediate fast-evolving ecological interactions during species delimitation. Preference for Caulerpa spp. and radular tooth characteristics covaried among newly delimited species, highlighting an unappreciated degree of host specialization and coevolution in these taxa that may help predict their role in containing outbreaks of invasive algae.

预测针对‘杀手藻’（Caulerpa spp.）高入侵株系的生物抗性，需明确本地消费者的多样性与取食偏好，其中包括鞘海牛科（Oxynoidae）的海蛞蝓。既往研究显示，海牛属（Oxynoe，6个有效种）与拟海牛属（Lobiger，4个有效种）对藻类宿主的特异性较低，但这类分类学上颇具挑战的海蛞蝓类群，实则可能是多个未被认知的特化物种复合群，各自偏好不同的蕨藻属（Caulerpa）物种。本研究通过整合基因序列与微观齿舌、内部贝壳（这类软体无脊椎动物仅有的硬质结构）的形态学数据，对这两个属的全球多样性展开评估。针对包含线粒体DNA（mitochondrial DNA，mtDNA）和/或核等位基因的数据集，我们采用4种物种界定方法进行分析，对包含5个名义分类群的样本共得到至多16个物种假说，其中拟海牛属与海牛属各包含5个高度分化的物种。根据不同分析方案，在安的列斯海牛-绿色海牛（O. antillarum-viridis）复合群这一演化支中，还可进一步区分出4至6个物种；该类群的线粒体分化程度较低，且不同谱系间共享核等位基因。不过，仅使用形态学数据的贝叶斯物种界定方法可支持绝大多数候选物种；而结合形态学与遗传学数据的整合分析，则完全支持该复合群内的所有类群。综合而言，本研究的发现使鞘海牛科（Oxynoidae）的已知生物多样性翻倍，同时证实了在物种界定过程中纳入介导快速演化生态互作的性状数据的重要价值。新界定的物种中，对蕨藻属（Caulerpa spp.）的取食偏好与齿舌（radular tooth）特征存在共变异现象，这凸显出这类类群中未被认知的宿主特化与协同演化程度，或可为预测它们抑制入侵藻类暴发的作用提供依据。