First Bugs of Spring!

We had our first day above 40 degrees since February 7, and our first day with above-average temps since February 11th. A midday hike at Van Patten Woods Forest Preserve produced one of these guys:

Diplocladius cultriger, 3/6/2012, Illinois Beach State Park

Well, maybe not this species -- today's wouldn't hold still long enough for a photo, and midges are difficult enough to ID with a good close look. On the other hand, the date's about right (this species appears to be an early riser, so to speak), so Diplocladius is probably as good a guess as any.

Most of the papers I can find on these guys are simple descriptive or taxonomic works (1) , but midges are so ubiquitous that they occasionally prove useful for more theoretical work. For instance, Broderson & Lindegaard used subfossil chironomids to examine the history of shallow lakes in the Netherlands. (2)

In an echo of my last post, Krosch & Cranston used chironomids to test the Gondwanan vicariance model of biogeography. (3) They were basically refining earlier work on dates of speciation and rates of evolution, and for the most part they confirmed that this group fits the vicariance model quite well. (Midges are very small and not very long-lived. They don't handle salt water well. Overall, it hardly seems surprising that they'd be poor candidates for long-distance dispersal events. Having said that, other truly surprising dispersals have been documented, so this wasn't a sure thing.) But they also found an oddity with regards to New Zealand. Speciation events seem to put the last colonization of New Zealand after its separation from Gondwana (favoring a dispersal scenario) but before the proposed "drowning" of the islands. If true, that would strongly suggest that the drowning wasn't complete, although the authors propose other possibilities as well.

Lofty thoughts, I think, over such a humble little critter.

(1) Saether, O. A. (1973). Four species of Bryophaenocladius Thien., with notes on other Orthocladiinae (Diptera: Chironomidae). The Canadian Entomologist, 105(01), 51-60.

(2) Brodersen, K. P., & Lindegaard, C. (1997). Significance of subfossile chironomid remains in classification of shallow lakes. In Shallow Lakes’ 95 (pp. 125-132). Springer Netherlands.

 

(3) Krosch, M., & Cranston, P. S. (2013). Not drowning,(hand) waving? Molecular phylogenetics, biogeography and evolutionary tempo of the ‘Gondwanan’midge Stictocladius Edwards (Diptera: Chironomidae). Molecular phylogenetics and evolution, 68(3), 595-603.

A Rare Sight on a Snowy Afternoon

This little beauty showed up in downstate Quincy, IL last week:

Ivory Gull (Pagophila eburnea),
Quincy, IL 1/5/2015

This is an adult Ivory Gull (Pagophila eburnea). It's an arctic bird, normally spending the winter on the ocean north of Alaska over to Labrador! Every once in a while, one wanders south to delight all the birders within reach. (Which includes a good bit of the continent, for a bird like this!)

I didn't put his picture up just to brag, of course. His arrival here is a very small data point in a rather large argument in the field of biogeography. Namely, is the distribution of living things largely the result of continental drift and evolution within those continents (vicariance) or the result of rare, random occurrences of long-distance travel, followed by evolutionary radiations within the new location (dispersal).

Here's some poster children for the vicariance argument:



Ostrich (Struthio camelus)
Brookfield Zoo, 1/10/2012

Double-wattled Cassowary (Casuarius casuarius),
Nashville Zoo, 3/29/13

Emu (Dromaius novaehollandiae),
Cheyenne Mt. Zoo, Colorado Springs,
12/27/2013
 

These 3 species are all ratites, or large, flightless birds with no keel on the breastbone. The Ostrich is, of course, from Africa, the Emu from Australia, and the Cassowary from Australia and New Guinea. (Well, these individuals are all from zoos here in the US, but you get the idea.) 2 more species, the Rheas, hail from South America. All of these continents were united into the supercontinent Gondwana, which started to split around 185 million years ago, after separating from Laurasia to the north. Many species seem to share the generally southern distribution that indicates that they likely radiated from a Gondwanan origin.




Here's another example:

Rock Wallaby, (Petrogale concinna), Omaha Zoo, 12/30/2011

This is a Rock Wallaby (Petrogale concinna), from Australia. Everyone with a passing interest in mammals knows that Australia is the home of the marsupials. Turns out, though, that South America has quite a few of them as well, namely various species of Opossum. Several have moved north into Central America, and one (the Virgina Opposum, Didelphis virginiana) has colonized most of North America. We still see that southern distribution that indicates a Gondwanan background.

And then there's this guy:

Callimico, (Callimico goeldii),
Milwaukee County Zoo, 3/30/2007

This is a Callimico, or Goeldi's Monkey (Callimico goeldii). It's small, and like many relatives, it's found exclusively in South America. Given that Africa is the center of primate diversity, with additional species found throughout southern Asia, seems like a clear cut example of vicariance -- again we see the Gondwanan distribution. But.....

 

The earliest primate fossils anywhere date to less than 55 million years old, and the best molecular evidence for the split between the African monkeys and the S. American monkeys indicates an origin for the group at 40 million years ago. By that point, the south Atlantic had already opened, which means that those early monkeys would have had to take a long raft trip just to reach S. America! The total lack of earlier primate fossils in South America also supports this idea.

And this is where that Ivory Gull comes in. Opponents of dispersal ideas in biogeography make much of the fact that you can't possibly predict rare events in particular, which makes them very hard to test. How did that species get there? If we're allowed to postulate a one in a million raft journey, then we can explain anything, right?

The problem with that argument, of course, is that when you have billions or trillions of individual animals, plants, etc., composing millions of species, million to one events are going to be commonplace when we look at the Earth as a whole. I find it very hard to be critical of the dispersal ideas when we can demonstrate historical examples of just those sorts of events. This gull isn't likely to stick around and breed (for one thing, finding a mate would be very, very difficult), but with only three records in Illinois history (and only this one for Missouri) it's clearly a rare event.

While we can't predict where and when the next rare event will happen, we can make pretty good estimates on how many will occur in a given time frame, and those predictions can be tested. We can also look at mechanisms of dispersal, and how the biology of different groups should impact their likelihood of establishing themselves once they end up somewhere new, thus allowing for more predictions. For instance, birds that travel in flocks should be more likely to spread over long distances than species that travel alone, since loners aren't likely to find a mate in a new spot. So, finches on oceanic islands, yes. Woodpeckers, no. (That particular prediction holds up quite nicely, by the way.) We can also use birder's observations of rare vagrants to build up our estimates of rates of dispersal events, which can only help biogeographers add to our knowledge of the long history of life on this small blue planet.

This argument is developed more fully and much more clearly in The Monkey's Voyage by Alan de Queiroz.