Friday, January 18, 2013

Murder and Deceit: Just Another Day In The Life Of Golden Algae

Nobody likes a cheater, but from humans to bacteria almost every community has their share of freeloaders.

Cooperation is essential for the survival of many organisms, but there are always those who are willing to reap the benefits of a community and use up collective resources without ever making their own contribution. According to a recent study published in the journal Evolution, golden algae  (Prymnesium Parvum) are no exception.

Live culture of Prymnesium Parvum. Image credit:  Unviersity of Liverpool Harmful Plankton Project

Prymnesium Parvum are found worldwide in extensive blooms blanketing the surface of marine and inland waters. Golden algae blooms produce toxic substances meant to kill off other algal species, but these same substances can be highly destructive as they are also toxic many fish species. When present at high enough concentrations, these toxins have been known to decimate nearby fish populations. It has been estimated that golden algae blooms in 33 reservoirs in Texas alone have killed almost 30 million fish, causing tens of millions of dollars in revenue to be lost.

For a single cell, toxin production is largely useless as the toxic substances would drift away before reaching concentrations high enough to be lethal. For this reason it is beneficial for the algal cells to band together: many cells producing the toxins all at once permit toxin levels to accumulate to sufficiently high levels. The toxin produced by one cell would exert most of its protective effect on neighboring cells, but those same neighboring cells ensure that cell is covered.

In a study published in the journal Evolution, researchers at the University of Arizona reported finding freeloaders in golden algae populations. These cells grow faster than their peers because they never actually produce any toxins. Instead, the resources that would normally be used in toxin production are redirected to ensuring their own propagation.

As hard times fall upon the algae, however, the toxic cells adopt a new approach. Normally, when nutrients are abundant the toxic cells use photosynthesis to generate energy. As nutrients become scarce, however, toxic cells stop growing and begin attacking other cells. They swim up to their prey using their flagella and latch on, and in some cases a struggle ensues. Other cells may join in the melee, surrounding the victim and producing more toxin before consuming their victim.

Toxic golden algae attacking and devouring a green alga. Image credit: William Driscoll, PhysOrg

Roving packs of carnivorous cells may seem like quite a departure from our perception of mild-mannered algae. The ‘cheaters’ never adopt this behavior, however; they just keep on growing. One would expect that because cheaters have an advantage when conditions are favorable they would eventually take over the population, but the authors of the study believe that because the cheaters are unresponsive to changing environmental conditions this doesn’t happen.

Next, scientists in the laboratory of Jeremiah Hackett at the University of Arizona have set out to determine the difference between toxic and non-toxic cells. They have found that stress-related genes are regulated differently between the two types of cell. Ultimately they hope that their work will lead to the identification of ways in which the behavior of golden algae cells can be exploited to restrict the growth of golden algae blooms, and that finding the golden algae's 'Achilles heel' may ultimately reduce the threat this species poses to their local ecosystems. 

1 comment:

  1. I wonder why the "cheaters" are unable to adopt hunting behaviour? There must be something that prevents this trait evolving in cheater cells.