Using cone beam CT scans to reveal headfirst ingestion and possible prey manipulation tactics in sawsharks

Prey manipulation through headfirst ingestion is a common foraging tactic in predatory taxa. Sawsharks possess a toothed rostrum that is thought to assist in prey capture, but the process from prey contact to ingestion is unknown. This study provides evidence of headfirst ingestion and possible prey orientation in situ through the use of cone beam CT scans in the common sawshark (Pristiophorus cirratus). CT scans provide an efficient method for assessing ingestion and proposing plausible behavioural tactics for food manipulation in a species difficult to observe in the wild or maintain in captivity.     

Meta-Fish-Lib: A generalised,dynamic DNA reference library pipeline for metabarcoding of fishes

The accuracy and reliability of DNA metabarcoding analyses depend on the breadth and quality of the reference libraries that underpin them. However, there are limited options available to obtain and curate the huge volumes of sequence data that are available on public repositories such as NCBI and BOLD. Here, we provide a pipeline to download, clean and annotate mitochondrial DNA sequence data for a given list of fish species. Features of this pipeline include (a) support for multiple metabarcode markers; (b) searches on species synonyms and taxonomic name validation; (c) phylogeny assisted quality control for identification and removal of misannotated sequences; (d) automatically generated coverage reports for each new GenBank release update; and (e) citable, versioned DOIs. As an example we provide a ready-to-use curated reference library for the marine and freshwater fishes of the U.K. To augment this reference library for environmental DNA metabarcoding specifically, we generated 241 new MiFish-12S sequences for 88 U.K. marine species, and make available new primer sets useful for sequencing these. This brings the coverage of common U.K. species for the MiFish-12S fragment to 93%, opening new avenues for scaling up fish metabarcoding across wide spatial gradients. The Meta-Fish-Lib reference library and pipeline is hosted at https://github.com/genner-lab/meta-fish-lib .     

A Permian nurse log and evidence for facilitation in high‐latitude Glossopteris forests

The biology of trees that grew in high‐latitude forests during warmer geological periods is of major interest in understanding past and future ecosystem dynamics. As we study the different plants that composed these forests, it becomes possible to make comparisons with ecosystem processes that occur today. Here we describe a silicified late Permian (Lopingian) glossopterid (seed fern) trunk from Skaar Ridge, central Transantarctic Mountains, Antarctica, with evidence of glossopterid rootlets growing into its wood. The specimen is interpreted as a nurse log similar to those seen in some extant forests. Together with evidence of glossopterid roots growing within the lacunae of older roots, this new specimen suggests the existence of facilitative interactions among the glossopterid trees that dominated the high‐latitude forests of Gondwana during the late Permian. More generally, the existence of self‐facilitation might have favoured the expansion of glossopterids within various environments, especially those at high palaeolatitudes, during the Permian icehouse to greenhouse transition.     

A QTL on the Ca7 chromosome of chickpea affects resistance to the root-lesion nematode Pratylenchus thornei

Molecular Breeding - Plant height is vital for crop yield by influencing plant architecture and resistance to lodging. Although lots of quantitative trait loci (QTLs) controlling plant height had...     

Nitrogen,water, and phosphorus uptake as functions of fine-root mass in greenhouse microcosms of Poa pratensis

Plant Ecology - Understanding resource uptake as a function of fine-root mass is important for both basic ecological theory and applied biogeochemical cycling models. We measured plant population...     

Evolutionary history of nematodes associated with sweat bees

Organisms that live in close association with other organisms make up a large part of the world’s diversity. One driver of this diversity is the evolution of host-species specificity, which can occur via reproductive isolation following a host-switch or, given the correct circumstances, via cospeciation. In this study, we explored the diversity and evolutionary history of Acrostichus nematodes that are associated with halictid bees in North America. First, we conducted surveys of bees in Virginia, and found six halictid species that host Acrostichus. To test the hypothesis of cospeciation, we constructed phylogenetic hypotheses of Acrostichus based on three genes. We found Acrostichus puri and Acrostichus halicti to be species complexes comprising cryptic, host-specific species. Although several nodes in the host and symbiont phylogenies were congruent and tests for cospeciation were significant, the host’s biogeography, the apparent patchiness of the association across the host’s phylogeny, and the amount of evolution in the nematode sequence suggested a mixture of cospeciation, host switching, and extinction events instead of strict cospeciation. Cospeciation can explain the relationships between Ac. puri and its augochlorine hosts, but colonization of Halictus hosts is more likely than cospeciation. The nematodes are vertically transmitted, but sexual transmission is also likely. Both of these transmission modes may explain host-species specificity and congruent bee and nematode phylogenies. Additionally, all halictid hosts come from eusocial or socially polymorphic lineages, suggesting that sociality may be a factor in the suitability of hosts for Acrostichus.     

Electron cryotomography of ESCRT assemblies and dividing Sulfolobus cells suggests that spiraling filaments are involved in membrane scission

The endosomal-sorting complex required for transport (ESCRT) is evolutionarily conserved from Archaea to eukaryotes. The complex drives membrane scission events in a range of processes, including cytokinesis in Metazoa and some Archaea. CdvA is the protein in Archaea that recruits ESCRT-III to the membrane. Using electron cryotomography (ECT), we find that CdvA polymerizes into helical filaments wrapped around liposomes. ESCRT-III proteins are responsible for the cinching of membranes and have been shown to assemble into helical tubes in vitro, but here we show that they also can form nested tubes and nested cones, which reveal surprisingly numerous and versatile contacts. To observe the ESCRT–CdvA complex in a physiological context, we used ECT to image the archaeon Sulfolobus acidocaldarius and observed a distinct protein belt at the leading edge of constriction furrows in dividing cells. The known dimensions of ESCRT-III proteins constrain their possible orientations within each of these structures and point to the involvement of spiraling filaments in membrane scission.