Traveling trapdoor spider may have dispersed across the ocean from Africa to Australia
Darwin proposed that long-distance dispersal explained the evolutionary history of many groups of organisms. However, the distances across Southern Hemisphere oceans are so great that species there were generally postulated to be the products of the separation of Gondwana, the ancient supercontinent that incorporated present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica. With the advent of modern molecular techniques, however, this debate is now being revisited.
One test case in this debate is an Australian trapdoor spider (Moggridgea rainbowi). This spider is sedentary and settles within a few meters of where it hatched. However, in a recent PLOS ONE study scientists confirmed that this arthropod belongs to an otherwise African genus. This finding suggests that the Australian trapdoor spider may have crossed the ocean from Africa rather than being the product of geographical separation.
Cell fate decision may not be a programmed event
From the moment of fertilization, building a human body involves a series of choices where cells generated by cell division must elect which of the myriad types of cell they will become. How does this decision occur?
A new study from French researchers suggests that cell fate decision is not a unique programmed event, as was believed, but the outcome of a very dynamic process. The authors used a time-lapse video recording coupled to single-cell molecular analyses to study the process step-by-step.
They found that the whole process is reminiscent of trial-and-error learning in which each cell explores — at its own rhythm and independently of cell division — different molecular possibilities (i.e. different genes turned on or off). The authors observed that some cells seem to “hesitate” and change morphology many times before reaching a stable state.
This study’s findings can be found in PLOS Biology and departs from the view that cell differentiation follows step-by-step instructions.
Image credit: Dr Jeremy Cosette, image from manuscript e2001867. Trapdoor spider image by Nick Birks.
Harrison SE, Harvey MS, Cooper SJB, Austin AD, Rix MG (2017) Across the Indian Ocean: A remarkable example of trans-oceanic dispersal in an austral mygalomorph spider. PLoS ONE 12(8): e0180139. https://doi.org/10.1371/journal.pone.0180139
Moussy A, Cosette J, Parmentier R, da Silva C, Corre G, Richard A, et al. (2017) Integrated time-lapse and single-cell transcription studies highlight the variable and dynamic nature of human hematopoietic cell fate commitment. PLoS Biol 15(7): e2001867. https://doi.org/10.1371/journal.pbio.2001867