Search

Most efforts at improving accuracy in phylogenomic reconstructions have focused on improving tree‐building methods or orthology determination. Even though the use of whole genome sequence or transcriptome data is increasing, the degree to which accurate genome assembly and annotation influence phylogenetic inference has not been well explored. Here, we use low‐coverage whole genome sequencing of spionid annelids to explore the impact of different assemblers and annotation strategies on tree reconstruction. We also produce a phylogenetic hypothesis that spans the breadth of Spionidae, examining the current systematics of the group, which is based on morphological parsimony analyses and classical taxonomy. Our results show that both assembly and annotation can have important consequences for the pool of loci that may be available for tree reconstruction. When an identical phylogenomic pipeline is used, differences in assembly and annotation can account for variation in reconstructed topologies. Interestingly, the completeness and depth of the data used for training annotation software (i.e. data from model systems) appear to be more important, by some measures, than the degree of phylogenetic relatedness of the organism from which training data are drawn. Despite variation in recovered topologies, the recognised subfamily Spioninae is nested within Nerininae, suggesting that diagnostic characters of Nerininae (e.g. thick egg membrane, short‐headed sperm) are symplesiomorphies of Spionidae rather than apomorphies of a particular subclade. With the increased use of genomic data, our results advocate for a broader consideration of how assembly and annotation may impact data matrices used in phylogenomic analyses. [ABSTRACT FROM AUTHOR]

Assessing the enormous diversity of Southern Ocean benthic species and their evolutionary histories is a central task in the era of global climate change. Based on mitochondrial markers, it was recently suggested that the circumpolar giant sea spider Colossendeis megalonyx comprises a complex of at least six cryptic species with mostly small and non-overlapping distribution ranges. Here, we expand the sampling to include over 500 mitochondrial COI sequences of specimens from around the Antarctic. Using multiple species delimitation approaches, the number of distinct mitochondrial OTUs increased from six to 15-20 with our larger dataset. In contrast to earlier studies, many of these clades show almost circumpolar distributions. Additionally, analysis of the nuclear internal transcribed spacer region for a subset of these specimens showed incongruence between nuclear and mitochondrial results. These mito-nuclear discordances suggest that several of the divergent mitochondrial lineages can hybridize and should not be interpreted as cryptic species. Our results suggest survival of C. megalonyx during Pleistocene glaciations in multiple refugia, some of them probably located on the Antarctic shelf, and emphasize the importance of multi-gene datasets to detect the presence of cryptic species, rather than their inference based on mitochondrial data alone.

Benthic habitats harbour a significant (yet unexplored) diversity of microscopic eukaryote taxa, including metazoan phyla, protists, algae and fungi. These groups are thought to underpin ecosystem functioning across diverse marine environments. Coastal marine habitats in the Gulf of Mexico experienced visible, heavy impacts following the Deepwater Horizon oil spill in 2010, yet our scant knowledge of prior eukaryotic biodiversity has precluded a thorough assessment of this disturbance. Using a marker gene and morphological approach, we present an intensive evaluation of microbial eukaryote communities prior to and following oiling around heavily impacted shorelines. Our results show significant changes in community structure, with pre-spill assemblages of diverse Metazoa giving way to dominant fungal communities in post-spill sediments. Post-spill fungal taxa exhibit low richness and are characterized by an abundance of known hydrocarbon-degrading genera, compared to prior communities that contained smaller and more diverse fungal assemblages. Comparative taxonomic data from nematodes further suggests drastic impacts; while pre-spill samples exhibit high richness and evenness of genera, post-spill communities contain mainly predatory and scavenger taxa alongside an abundance of juveniles. Based on this community analysis, our data suggest considerable (hidden) initial impacts across Gulf beaches may be ongoing, despite the disappearance of visible surface oil in the region.