Science and sensibility

Any regular readers of Science and Sensibility will by now have worked out that I have done my usual trick of getting busy with my real life and letting these pages go to seed. One of the things I’ve been doing quite a lot of in my long absence is poking around spider webs with my camera. Our flat has a ‘garden’ which might be better described as a small grassy fallow land. We are hardly going to be part of a garden festival but the patch does seems to make a nice home for any number of gnats, flies and aphids and by extension the wasps, birds and spiders that make a meal of such things. So, in my first post in I don't know how many months, I am going to introduce to a few of my gardern's hunters. (If you happen to be one of my arachnophobic flatmates and you don't want to know what happens between you and the washing line may I suggest you make a run for it now).

I have found just about the hardest thing to in photographing spiders is actually finding them. It's simple enough to find their webs erected between shrubs or even (optimistically) attached to the house, but actually connecting a web to its maker can be hard work. For all their fearsome reputation as predators (there are no vegetarian spiders) spiders also make a tasty treat for birds and there are native wasps that give their young the best possible start in life by carrying off an anesthetised spider to their nest and laying eggs in the still living body. With those sorts of fates to avoid and prey to lure it is no surprise that spiders are masters of camouflage, the spiders depicted above and below are probably from the widespread genus Eriophora they are certainly both lying in wait.

You can see in the next photo (my favourite for what it’s worth) a thread of this spiders’ web is attached to its leg.

Through this thread the spider feels the tension of the web and in the words of John Davies

If aught do touch the utmost thread of it,
She feels it instantly on every side.

Other people mark the first appearance of swallows as the great turning point of the year, me, I like my winged messangers a litte smaller. This afternoon I spied my first bumble bee since winter started. Past experience suggests we're still months away from the emergence of most of this year's queens put it's an exciting event all the same.

Sadly when I spotted the early messanger I bereft of camera so I will mark this event with a pic from last summer, one of the very first I took with the camera my dad gave me to play with and I have since effectively stolen, hopefully I'll get some better ones this year!

A bumble bee is caught, with its tongue out and just out of focus as it makes its way between foxglove flowers

Remember last month when all the heavy weights of the science blogging world were talking bout Heliconius heurippa - the Andean butterfly that appears to have arisen by hybridisation between two other Heliconius butterflies? Yeah, if I wanted to be big deal blogger that's probably when I should have put my two cents in. Of course being a big deal is hardly my motivation so I have no shame in arriving late to this particular party.

The basic story is certainly available from all the usual outlets, in summary Jesus Mavarez and his colleagues have used molecular genetics and lab crosses to show that a rather pretty tropical butterfly has arisen from interspecific hybridisation between two closely related species. Most commentators have understandably highlighted how this story contrasts with the usual lineage splitting modes of speciation but there is more to this story than that. One of the things I'm really interested in is studying the processes and events that have occurred during the evolution of different groups to generate their current day distributions. So, rather than rehash what has been so excellently explained elsewhere lets see what this research has to say about the events that have generated the unique distribution this group of butterflies display

The hybrid species H. heurippa surrounding by examplesof the parent species that generated it

Scientists have been talking about Heliconius butterflies for well over 100 years. They are interesting because individual species are highly polymorphic across their range with different geographic 'races' each bearing a different wing pattern. This polymorphism is important because the wing patterns are warning signals to potential predators that these butterflies are not palatable. These isolated populations do occasionally interbreed but the progeny of these crosses bare kaleidoscopic wing patterns that give no clear signal to predators which, unaware of their prey's chemical defences, will make hybrids into a disappointing lunch.

Interesting biogeographical distributions like the one that the Heliconius present us generate interesting hypotheses to test. What sort of evolutionary processes could generate disjunct populations bearing distinct colour polymorphisms in tropical America? Most people would argue this is another example of the ubiquitous and lasting effects the last ice age generated. They would argue a formally continuous population of each species was broken into subpopulations as glaciers generated 'forest islands' separated by uninhabitable ice. During this isolation warning signals drifted apart in different populations so that when the ice finally receded hybrids generated by interbreeding between the formally separate populations were met with fitness costs (ie getting eaten). The cost of being eaten generates a selective pressure to maintain the most common wing pattern (as a clear signal to predators) in each region so the geographical races each maintain their unique colour patterns.

A model for the generaton of disjunct populations following glaciation

The glacial hypothesis is certainly a reasonable suggestion, molecular evidence from New Zealand invertebrates (and in fact flightless birds) seems to tell a similar story and the effects of the ice age in the northern hemisphere are very well documented. Still, there are other interpretations that could be made by the present day Heliconius distributions. Some argue that the distribution could equally well be described by an ongoing series of 'peripatric' speciation events. In this hypothesis there will occasionally be dips in the predator driven selective pressure to have a common wing pattern (perhaps a new predator invades an area but doesn't immediately learn the signal). Following such a dip hybrids won't be so strongly selected against and a polymorphic population may arise. Of course eventually the selection pressure will return, predators will steer clear of the most common of the wing patterns which will be driven to fixation at the cost of all the other patterns. The end result here is something very much like we see in nature, populations broken into geographic races, each bearing a different wing pattern that is recognised by the local predators.

A model for the generation of disjunct populations as a result of peripatric events

So how are we to choose between these two hypotheses, neither of which is obviously silly? The answer is, as always, by getting more evidence. The one piece of evidence that the glacial hypothesis needs (and that some may have overlooked) is something to say the Mesoamerican forest was fragmented during the last ice age. The best way to study past distributions of forest is 'stratigraphical palynology' which amounts to looking for pollen grains in different layers of soil or lake beds. The most recent palynological evidence suggests that Mesoamerican forests actually survived the ice age intact. If story holds up then the glacial hypothesis will need to be discarded or radically reworked.

On the other hand Mavarez et. al's revelation that H. heurippa is a hybrid species provides support for the peripatric hypothesis. The peripatric model requires that occasionally selection pressures can be loosened to the extent that wing patterns other than the most common one can prosper and that once one of these patterns is finally fixed (by the return of selective pressure for the most common wing type) a mechanism exists to isolate the population from its parents. Mavarez et. al tell us that a Venezuelan Heliconius population they have studied contains 8% hybrids as proof hybridisation happens and then go on to conclusively prove H. heurippa is the result of hybridisation. So what stops these hybrids from falling back into their parent lineages? One of the most exciting (and rather under reported) results of the paper was that the wing patterns generated by hybridisation can themselves be isolating mechanisms. H. heurippa males studied for this paper showed marked preference for their own wing pattern when it came to choosing mates. It is possible that this preference comes as a package with the wing pattern (a paper published this year suggests wing colour and mate preference are the result of two linked genes or pleiotropic effects of one gene in one of H. heurippa's parents) or that mate preference evolves once selection for the most common wing type builds up and canny males select their mates in an attempt to ensure their offspring also have the common wing pattern.

The evidence that hybrid phenotypes which are usually so strongly selected against can occasionally forge viable new populations not only helps understand the details of how new species arise but also shines light on how variations within species may arise and be maintained

Some more reading

Aydin Örstan on the same stuff

Mavarez et. al on the hybrid origin of H. heurippa

Palynological evidence that andean forests weren't fragmented in the last ice age

Radagast has found an amazing group of photos shortlisted for this year's Kongsberg Underwater Image Competition.

There are stunnig photos in all the catergories but have to check out the images of microspopic specimens which include the photo at the top of this post. That photo might look like it's come to you curtousey of Buckminster Fuller (or perhaps an adenovirus) but it's actually the product of an protozoa. The Radiolarians are an ancient group (they in fact beat Human architects to this particualr structure by about 600 million years) of planktonic protozoa that form minerlised skeletons . Many of Ernst Haeckel's famously elaborate drawings come from his book on the Radiolarians

Welcome along to the 10th time the Circus of the Spineless has preformed for the blogosphere. I have decided to take hat you might call a systematic approach to presenting the submissions I've received ( and a few posts I hunted down too). The idea behind this presentation is that you will not only get to see pretty pictures of insects (and, oh there are some pretty ones this month) but that you might also be confronted with some of the very different ways life on earth gets on with living. Of the two and a half million animals so far described considerably less than 60 000 fall into the sub-phylum Vertebrata - that is less than three percent of described animals build there bodies in the same way we do. Even that number is a great under estimation, there are probably at least 10 million arthropods and very few vertebrates not yet known to man.

Below is a tree representing some of groups of animals. Clicking on the picture of a group will take you to table of links about group for you to peruse, of course if you'd rather just scroll down do that(and whatever you do be sure to read the last paragraph announcing the next host and all that.

(The basis of this image is kindly provided by the Berkeley understanding evolution site)

Aramoana is a tiny settlement (home to 260 people) on the mouth of the Otago Harbour - about 20 minutes drive from my flat in Dunedin. In New Zealand the settlement's name is almost completely synonymous with a tragedy that played out there 16 years ago. On November 13th 1990 David Gray, a reclusive, gun collecting schizophrenic shot and killed 13 people before he was himself killed by armed police.

The Aramoana tragedy was unlike anything we had ever experienced in our own country and I imagine the settlement of Aramoana will be associated with the events of that day for a long while yet. It would be a shame though, to let this be the limit of Aramoana's impact on the New Zealand psyche. Aramoana is a wonderful place, home not just to 260 people but to scores of wading birds, shags, penguins, seals, insects and most importantly no aluminium smelters.

You see, back in the 1980s a group of New Zealand and Australian corporations wanted to come into Aramoana and build a new smelter to turn Australian mined bauxite into valuable aluminium. The problem was their plan involved, destroying the settlement and much of the salty mudflats that are the basis of its unique biological abundance. The government of the day had a very interventionist economic policy and was keen on paving the way for major projects to go ahead with little regard for their environmental impact. Thankfully the people of Aramoana (including local artistRalph Hotere who produced a series of paintings in protest) weren't so lapse - a grassroots movement developed that spread through the country . In December of 1980 the people or Aramoana officially seceded from New Zealand. The publicity their moves bought allowed them to sell official stamps and passports for their new independent state to help fund their opposition to the proposed smelter. Eventually the movement grew strong enough that it's voice was heard, the government decided the proposed smelter was unlikely to commercially viable and not worth the damage it would cause. With no government backing one of the Australian corporation chose to back out and the was off for good.

With this, other story of Aramoana in mind I have made a few trips out to the settlement in recent weeks, and even remembered to bring a camera once. This first pic I am going to share with you about sums up the 'other' Aramoana story to me - that with a little effort humans can actually make a positive impact on the environment

That's just one of the dozen or so New Zealand Kingfishers (Kotare or Halcyon sanctus vagans) I saw in about a hundred metre stretch of mudflats. These guys would perch upon a stump or a sign looking downwards before they lurched at some target below them, freefalling until they were a few metres above the ground at which point their brilliant blue wings would flap slowing their descent and finally pulling them back up, occasionally with a fish or crustacean in tow. The slat marsh and mudflats are the jewel in Aramoana's crown - as well as the kingfishers there are godwits which undertake a remarkable migration from China, oystercatchers like those photographed below, stilts, herons and over 80 species of moth (about 7% of all the species described in New Zealand)

The other biological extravaganza at Aramoana comes in the form of the 1.2 km long man-made break water that just in the ocean (protecting the harbour from storms and the like. As well as making a permanent home for any number of molluscs ( several species of limpets, chitins and snails to my count) it also marks a spot where sea birds can get a feed.

That's a shag, probably a little shag ( Kawaupaka, or Phalacrocorax melanoleucos brevirostris) like the star of Pete's rather more spectacular photos. Driving out to Aramoana you see almost every mooring post in the harbour is a sunning point for some shag or other, there are four species of shag commonly in the harbour and one of them (the Stewart Island Shag) has two colour morphs so their is a great deal of diversity. While I was inexpertly stalking the bird you see above my eye was caught by a flash of white plunging into the sea. The flash was a bird that looked a little like a small sea gull pinning its wings back and diving a break neck speed into the water, returning to the air almost immediately. Try as I might I couldn't get a photo of it in action but just as I was cursing my inabilities the bird in question, a white fronted tern (Tara or Sterna striata) chose to alight on a post about twenty metres away from me

All of the photos I have shown you so far are form the second of my recent trips to Aramoana. On my first trip I was lucky enough to be accompanied by my beautiful girlfriend but not my camera (I have to say the first trip had the better company.) Thankfully my girlfriend is much more clever than me and brought along her digicam and was able to snap the image I am going to leave this post with. As we stood at the very end of the breakwater looking out at a few of the shags diving underwater in pursuit off a meal we spotted another bird swimming in an entirely different manner - with almost all of it's body submerged. It wasn't until this bird came ashore that we could see that it was one of the rarest penguins in the world (about 500 pairs breed here in the South Island and another 2000 on offshore islands)- the Yellow Eyed (Hoiho or Megadyptes antipodes). Yellow-eyed Penguins are famous for being very shy birds, usually scurrying from the sea to their nests (which are made in forest and scrub beside the sea) and quick to catch fright and return the water if they see people. For some reason this one was a little more gregarious, it surely must have seen us but was content to hop about from rock to rock for a little while and hold out it wings to the sun. Just another of the really special encounters all those people worked together to secure in the 80s