Tuesday, 26 July 2011

Cool critter of the month; Wolbachia, not one for the boys (plus why all men are doomed!)

Wolbachia is a type of bacteria that infects insects and mites, and it’s one of those weird little creatures that you couldn’t make up if you tried. (Wolbachia is the little bright dots within the egg cell)

Wolbachia is an intracellular parasite; it lives inside the main body cells (somatic) of both males and females but only the germ line cells of females (the female’s eggs). Being only found in female eggs, not male sperm, it has a vested interest in ensuring that the insects give birth to more girls than boys. As such the tiny bacterium goes about its absolute best messing about in a range very nasty ways with male insects.

Wolbachia will stoop to any level in its war against the male gender (not in humans...for now), here is short list of the tricks it has up its sleeve (and easy to read pictures to boot!):

It kills males during larval development, basically meaning that more females will be born each generation and hence there will be more wolbachia.

It turns males into females, the process of feminisation, resulting in either full blown females or the even less appealing infertile pseudo female.

It manages to let females get pregnant and have female babies without any men involved! This process has the awe inspiring name of parthenogensis. In the Trichogramma wasp, this has been so successful that males aren’t needed at all, the wasps population is now made up nearly all females, the males are redundant and only a few are born each generation.

Using a trick known as cytoplasmic incompatibility, uninfected male bugs are unable to breed with infected females. This cunning trick means that uninfected males have a lower fitness than infected ones, and hence more infected offspring are produced each generation and again wolbachia wins out by spreading its evil man hating ways through the population.

Some strains can prevent reproduction entirely if it is not present. The insects have become so reliant on the wolbachia parasite that they simply cannot live without it. Some species of wasps are now obliged to have this nasty critter in their systems; if you experimentally remove wolbachia from these wasps with antibiotics then they can’t have anymore offspring.

Wolbachia illustrates a general trend across much of evolutionary history, the trend towards feminisation and eventually asexuality. Wolbachia is a super charged version of this principle that is crushing populations of male insects around the world as we speak, but other animals are far from free of similar effects. Humans are also showing a trend towards feminisation.

Basically having different sexes is hard work, it takes a great deal of time and energy. If you need to have lots of gene shuffling (what all the kids are calling it these days) it is a good idea as it produces lots of variation, but it’s not nearly as efficient as good old fashioned asexual reproduction (but substantially more fun!). Over time species that have become established in a particular environment tend to move towards asexuality (as they don’t need all the variation). This is where we come in, we are doing well and released from large areas of natural selection (due to our good diets, modern medicine and lack of man eating tigers), and so we don’t need as much variation. So it seems that males are a waste of valuable resources, all we do is generate variation, we are not needed for producing new offspring. Selection has kicked in and has begun to whittle away at the Y chromosome (which is tiny by comparison to the X anyway). Y chromosome size has declined dramatically over the last few million years. The data is staggering today 7% of males are infertile and ¼ of these cases are new and not traceable to their fathers. This is getting worse, one by one the 27 remaining active Y chromosome genes will disappear, reduced by the relentless onslaught of mutation, and then men will become extinct!

Indeed there is the distinct possibility of humans becoming parthneogentic in the future, with females capable of producing cloned or slightly genetically reshuffled offspring. In addition it would only take a few choice mutations to get females to reproduce sexually with other females. There are incompatibility issues at present, but it is entirely possible for the nuclei of two female eggs to fuse to produce female only offspring. With some clever artificial insemination this trick could be closer than we think.

To put it bluntly males may well be doomed, fortunately for us guys this is a long term problem (some people predicting 125,000 years for total elimination of human males), but spare a thought for our insectiod man friends, who may well be on the out much sooner.

Wednesday, 6 July 2011

The big fish review: part three, the open ocean

The slightly overdue third and penultimate part of my sweeping survey of all things fishy. There are two remaining ecological disaster zones that are as yet unmolested by my withering gaze, the open ocean fisheries (us fishy types call them pelagic) that hold our swordfish, tuna and marlin as well as the silty mangrove swamps in which baby fish and coastal prawns grow up before commuting out to the big sea. Both are critical ecosystems in slightly different ways, and both are being decimated by two very different types of fishing practice. Todays focus is on the open ocean so here's the scoop (or should I say trawl...oh dear):

1) Blue and yellowfin tuna...not so dolphin friendly

A rare shot of a bluefin tuna that isnt rushing past at 20 knots

These are the big guys of the fish world, the top predators in a similar way to wolves in Europe and lions in Africa. Sleek fast, hydrodynamic, with fast metabolisms to keep them active when hunting. Indeed tuna have warm blood and control their temperature in similar ways to land mammals. Being at the top of many open ocean food chains, these rapid hunters act as keystone predators. They influence the numbers and diversity of nearly all other smaller fish in the ecosystem.

Now sadly for these fish they taste great (although that can be said for most animals depending on who you ask) and we have been fishing them for as long as we had boats capable of getting out to their mid ocean hunting grounds (and for as long as we have had nets and lines capable of catching them). The issue here is similar to that discussed with sharks, these are large slow growing top predators, as such it takes time for them to recover from population losses caused by fishing. Now tuna due produce millions of eggs (as opposed to the handful of shark pups) , but as they are released into the open ocean, only a tiny fraction don't become a whale snack.

As such we have seen dramatic declines in these species. I would also like to point out the folly of buying dolphin friendly tuna, which is a sad story showing that having your heart in the right place doesn't always mean that you get the intended results.

People like dolphins, especially environmentalist types. The traditional method of catching tuna was with a purse siene net, it looks like a big coin purse, and is pulled around a shoal of tuna before being zipped up by another boat, just as you would pull the cord on such a purse. The best way to target the shoal of tuna was actually to follow the pods of dolphins that ate the same small fish as the tuna. The sad fact that a few dolphins were being caught prompted Greenpeace and a few other charities to campaign to get people only to eat dolphin friendly tuna. Purse siening was a very selective method of fishing, apart from the fact it caught a few dolphins, the replacement method long lining was much worse.

Long lines are similar to regular pole and line fishing, the idea is the same, put out a baited hook and wait for the fish to take the bait.
The difference is in scale, long lines are kilometres long and hang millions of baited hooks in the water. These are towed slowly or simply left to wait in the sea, they subsequently catch anything and everything (except dolphins, who don't really go in for baited hooks), this includes critically endangered turtles, regular old endangered sharks, hordes of non target species that are thrown back as bycatch and oceanic birds such as the albatross. Long lining bycatch rates range from 30-60%, much less selective and ultimately much more damaging than the original method! So while dolphins were saved (a collection of species that were not threatened in most of their ranges ) everything else in the sea suffers.

Fortunately we have started to realise the error of our ways and sustainable pole and line caught tuna is making a comeback. If you can't live without it go for skipjack, albacore or blackfin (American south east asian readers should also avoid pacific bigeye) and try to make sure it is pole and line caught. Do this and fish everywhere will thank you, furthermore, you will no longer be an accessory to turtle murder!

2) Swordfish, king mackerel and marlin...heavy death metal

Beautiful animals these guys...and shown with spiffingly brillinat British accents in finding nemo

These charismatic chaps follow very much the same rules as tuna, indeed they are top predators and have been decimated by the practices of long lining. Yet there is an extra piece to fit in this puzzle box, poisonous mercury.

Mercury is a rather nasty heavy metal, in liquid form it looks cool, but inside your body even in relatively small amounts it does some serious harm. Hair loss, seizures, trembling, loss of liver function and kidney shutdown, in extreme doses brain damage and death heads up a symptom list aggressive cancer would be proud of.

Top predators such as swordfish naturally build up mercury in their systems, each tiny fish eaten has a small amount, and as it takes a very long time to get out of their (and our) bodies it builds up. When We eat swordfish steak we get a big dose of this mercury. Indeed swordfish is so loaded with the stuff, one portion puts a regular man up to his weekly safe mercury threshold and is considered a risk to an unborn child. The food and agriculture organisation for the UN recommends that pregnant and breast feeding mothers consume absolutely no swordfish, marlin or king mackerel, as even one portion is loaded with this poison.

Now this problem has been around for a while, but it is getting worse. Incidents of mercury poisoning are increasing year on year in Japan (eat lots of fish) and there have been cases reported of new York lawyers losing their hair and having seizures due to a steady diet of high grade sashimi. The problem stems from our increased industrial activity. Mining for gold and platinum produces mercury waste that ends up being dumped into rivers and then slowly makes its way to the sea. Mercury pollution is also driven by sales of batteries, so if you want to help out the swordfish (and maybe one day eat one that's not loaded with a deadly poison) switch to rechargeable batteries.

If unsure about the levels of mercury in fish you can consult this handy chart, if you are pregant or breast feeding (or thinking about it), this list if quite important.