Biology

04 September 2015: Neither one thing nor the other

P. myojinensis

P. myojinensis. The blue structure is the nucleus, the red structures the endosymbionts.

A remarkable creature discovered in the ocean southeast of Japan – that doesn’t quite seem to belong to any of the three known domains – may provide evidence of how complex multicellular life evolved on Earth.

In 2010, a scientific expedition to the Myojin Knoll, about 35 kilometres southeast of the Japanese island of Aogashima, collected biological samples from a hydrothermal vent more than 1,200 metres below the surface.

The samples were frozen and then embedded in epoxy resin; the resin was then prepared for study by being sliced into ultrathin sections.

That’s when the researchers discovered they had collected one truly remarkable specimen, a single-celled organism that lays somewhere between prokaryotes, organisms like bacteria and archaea, and eukaryotes, the basis of complex organisms such as fungi, plants and … well … us.

The main differences between prokaryotes and eukaryotes are that the former do not have a nucleus surrounded by a membrane, or any membrane-bound organelles such as mitochondria or chloroplasts.

As described in the journal Microscopy, the cell, dubbed Parakaryon myojinensis, was discovered on one of the bristles of a type of Polychaete called a scale worm. It was 10 micrometres long and three wide, much larger than most bacteria. Inside the cell the researchers discovered a nucleus with a membrane. As well, they discovered three endosymbionts, organisms that live symbiotically inside another, also surrounded by membranes. Obviously, then, the cell was not a prokaryote.

However, the nucleus of P. myojinensis was surrounded by a single membrane and consisted of DNA fibres, whereas a nucleus in a eukaryote cell has a double membrane and consists of chromosomes.

The endosymbionts also had only a single membrane. Mitochondria in eukaryotes, like the nucleus, have a double cell wall. As well, the endosymbionts closely resembled bacteria rather than mitochondria.

This last point is what makes the discovery of P. myojinensis so important.

There are two major theories about how eukaryotes evolved. The autogenesis theory proposes that a eukaryote’s structures developed from primitive prokaryotic features. The symbiogenesis theory – first properly described by Russian Konstantin Mereschkowski in 1910 and subsequently advanced by Lynn Margulis in 1967 – proposes that eukaryotes evolved from a symbiotic relationship after a bacteria was absorbed by larger achaean, eventually becoming an integral and working part of the cell.

P. myojinensis seems to be an organism that has incorporated endosymbionts into its structure but not yet developed the full range of eukaryotic functions.

As the authors of the paper suggest, “ … it may even be a conservative descendant of the transitional lineage between prokaryotes and eukaryotes.”

For a fuller description of the possible implications of the discovery, read this article on ABC online by British scientist Nick Lane, whose latest book The Vital Question: Why is life the way it is?, is a rewarding and thought-provoking read.

12 May 2015: Dinosaurs and birds

Archaeornithura meemannae

Archaeornithura meemannae (Credit: Zongda Zhang)

Remarkable new finds announced by China’s Institute of Vertebrate Paleontology and Paleoanthropology includes the earliest date yet established for a true bird and a bird-related dinosaur with leathery wings.

In a summary report on their website, Michael Balter said a team of paleontologists led by Min Wang and Zhonghe Zhou found 130 million year old fossils of two ancient wading birds in northeast China. The two remains of Archaeornithura meemannae show many features that belong to modern birds, including fan-shaped tail feathers and “the U-shaped wishbone familiar to anyone who has carved a roast chicken.” The fossils, dating back 130 million years, pushes “back the lineage that led today’s birds by at least 5 million years.” The report suggests this means the origins of true birds is older still. In an article in Nature, scientists from the Institute described a new species of scansoriopterygidae dinosaur they called Yi qi (pron. ‘yee chee’). Not only is this the shortest binomial ever given to a dinosaur, it’s also the first dinosaur found with striking evidence of ‘bat-like’ wings. Although other species of scansoriopterygidae were first described as early as 2002, this is the first fossil found with convincing evidence of membranous wings. Sometimes defined as ‘avian dinosaurs’, the scansoriopterygidae group belongs to a clade that ultimately lead to true birds. While it is not believed the group are direct ancestors of birds, they are examples of yet another evolutionary experiment in flight. Institute palaeontologist Corwin Sullivan said the while the dinosaur probably did not fly like a bird, “our guess would be that Yi qi was gliding or maybe combining gliding with some relatively inefficient flapping.”

06 November 2014: Dragonflies

Sp. unknown (pos. Neurothemis fulvia?). Photo: Simon Brown

Sp. unknown (pos. Neurothemis fulvia?).
Photo: Simon Brown

Small blog on dragonflies. Just because.

And because they are incredibly beautiful. And because they are incredibly ancient, among the first flying insects. Extinct proto-dragonflies, sometimes called griffenflies, could have up to 70cm wingspans. They lived from the late Carboniferous to the late Permian.

Dragonflies are also the fastest insects, and can fly backwards, which is pretty cool.

Also I’ve got this photo I took in Phuket. Not quite a griffenfly, but pretty nonetheless.