‘Hydrogen is an energy source for hydrothermal vent symbioses’

doi:10.1038/nature10325

Authors: Jillian M. Petersen,Frank U. Zielinski,Thomas Pape, Richard Seifert, Cristina Moraru,Rudolf Amann, Stephane Hourdez,Peter R. Girguis,Scott D. Wankel,Valerie Barbe,Eric Pelletier, Dennis Fink, Christian Borowski,Wolfgang Bach & Nicole Dubilier

Abstract: The discovery of deep-sea hydrothermal vents in 1977 revolutionized our understanding of the energy sources that fuel primary productivity on Earth. Hydrothermal vent ecosystems are dominated by animals that live in symbiosis with chemosynthetic bacteria. So far, only two energy sources have been shown to power chemosynthetic symbioses: reduced sulphur compounds and methane. Using metagenome sequencing, single-gene fluorescence in situ hybridization, immunohistochemistry, shipboard incubations and in situ mass spectrometry, we show here that the symbionts of the hydrothermal vent mussel Bathymodiolus from the Mid-Atlantic Ridge use hydrogen to power primary production. In addition, we show that the symbionts of Bathymodiolus mussels from Pacific vents have hupL, the key gene for hydrogen oxidation. Furthermore, the symbionts of other vent animals such as the tubeworm Riftia pachyptila and the shrimp Rimicaris exoculataalso have hupL. We propose that the ability to use hydrogen as an energy source is widespread in hydrothermal vent symbioses, particularly at sites where hydrogen is abundant.

Presented by Taylor Heyl on 2011/09/07

‘Caterpillars evolved from onychophorans by hybridogenesis’

PNAS (2009): 0908357106v1-pnas.0908357106

doi:10.1073/pnas.0908357106

Author: Donald I. Williamson

Abstract: I reject the Darwinian assumption that larvae and their adults evolved from a single common ancestor. Rather I posit that, in animals that metamorphose, the basic types of larvae originated as adults of different lineages, i.e., larvae were transferred when, through hybridization, their genomes were acquired by distantly related animals. “Caterpillars,” the name for eruciforms with thoracic and abdominal legs, are larvae of lepidopterans, hymenopterans, and mecopterans (scorpionflies). Grubs and maggots, including the larvae of beetles, bees, and flies, evolved from caterpillars by loss of legs. Caterpillar larval organs are dismantled and reconstructed in the pupal phase. Such indirect developmental patterns (metamorphoses) did not originate solely by accumulation of random mutations followed by natural selection; rather they are fully consistent with my concept of evolution by hybridogenesis. Members of the phylum Onychophora (velvet worms) are proposed as the evolutionary source of caterpillars and their grub or maggot descendants. I present a molecular biological research proposal to test my thesis. By my hypothesis 2 recognizable sets of genes are detectable in the genomes of all insects with caterpillar grub- or maggot-like larvae: (i) onychophoran genes that code for proteins determining larval morphology/physiology and (ii) sequentially expressed insect genes that code for adult proteins. The genomes of insects and other animals that, by contrast, entirely lack larvae comprise recognizable sets of genes from single animal common ancestors.

Also to be discussed, responses to this paper:

http://www.pnas.org/content/106/52/E141.full

http://www.pnas.org/content/106/47/E131.full

http://www.pnas.org/content/106/47/E132.full

http://www.pnas.org/content/106/47/19906.short

Presented by Santiago Herrera and Catriona Munro on 2011/09/02