Cliff Swallows may be evolving to dodge traffic (1 Viewer)

[Acrocephalus]

“Shorten your wings if you want to live near a heavy traffic road and want to have offspring “, another case of microevolution / contemporary adaptation (I am thinking about Blackcap migration and Egyptian Vulture from the Canary Islands for instances).

Brown, C. R., & Brown, M. B. (2013). Where has all the road kill gone? Current Biology, 23(6): R233–R234. doi:10.1016/j.cub.2013.02.023

Nature News reporting on the study:
Swallows may be evolving to dodge traffic

 

[Andrew Rowlands]

As the two researchers checked the roadside colonies, Brown, an amateur taxidermist, collected dead swallows for skinning and stuffing — gathering 104 vehicle-killed adults and 134 adults killed accidentally in nets used for the study.

I find this very disturbing :C

 

[fugl]

Makes sense considering the powerful selection pressures.

 

[Snapdragyn]

I find this very disturbing :C

I did too until I noted that this was a 30 year study. That averages out to 4-5 birds per year. I think that we had more than that during the 3 months of fall migration I did at LPBO in the 80s, including species killed (or dropped; it was often a mystery) in nets by predators (including chipmunks - woe to the bird caught too low in a net).

 

[njlarsen]

I have not had time to read this study, but how many birds were caught in the nets total? I think I remember an average saying 1/1000 for most ringing projects ...

Niels

 

[jurek]

Interesting study. But wasn't also the number of swallows killed by cars too small to create the selection pressure?

 

[KenM]

Interesting study. But wasn't also the number of swallows killed by cars too small to create the selection pressure?

I might be able to draw a human comparison?...St.Kilda off the NW coast of Scotland, which I believe was inhabited between c1700's until the 1920's.

Then all the inhabitants were taken off by the Royal Navy, as they required the island for training purposes.

The Islanders during their occupancy...existed primarily on cliff nesting Auks, which were harvested then ''salted'' and stored for consumption during the Winter months.

Upon returning to the mainland, the Islanders were given a medical, and it was found that all the adult male members, had developed thicker ankles and wrists, than their mainland counterparts.

I don't know how many generations their ''stay'' represented...c200 years..average life expectancy 40?..five generations?

Yes..the biometrics for both Cliff Swallow and Homo Sapien might be of some interest over their respective monitored periods.

 

[Daniel Philippe]

But wasn't also the number of swallows killed by cars too small to create the selection pressure?

Wouldn't the selection pressure be created by the many birds avoiding collision instead ?

 

[fugl]

In so far as natural selection is implicated in any of this, one might expect the swallows to become progressively harder to catch as well as more adept at dodging cars. And maybe even to roughly the same degree since the figures for car & net deaths (as per the study) are not that dissimilar.

 

[njlarsen]

Wouldn't the selection pressure be created by the many birds avoiding collision instead ?

Not according to the theories about selection I have read -- where selection pressure is the part of the population erased by the selection per generation (I think)

Niels

 

[fugl]

Not according to the theories about selection I have read -- where selection pressure is the part of the population erased by the selection per generation (I think)

Surely, just a matter of semantics, long wings being selected against (in the present example), short wings being selected for.

 

[KenM]

Remiss of me..but..I failed to point out in post 7..that the ''thicker'' wrists and ankles, were a direct result of ''rope holding'' and getting good ''foot'' grip on the cliff faces where the Auks were collected. Perhaps 3-4 men at the top holding, with probably the lightest individual going over the top..on sea cliffs that were up to 1200' high. Please ignore....If this was patently obvious.

 

[jaco]

That human/auk example sounds more like phenotypic plasticity than evolution. In your reference, was there any mention of inheritance?

A group of people subjected to a particular exercise regime will experience a set of morphological changes that another group will not. We all know that. I know that all too well (glances at belly).

 

[KenM]

That human/auk example sounds more like phenotypic plasticity than evolution. In your reference, was there any mention of inheritance?

A group of people subjected to a particular exercise regime will experience a set of morphological changes that another group will not. We all know that. I know that all too well (glances at belly).

I was attempting to draw an analogy (using the auk/human example), with the Cliff Swallow experience...ie circumstances altering behaviour, which in turn alters structure and confers an ''inherited edge'' to the survivors.

 

[Richard Klim]

10,000 Birds

Greg Laden, 10,000 Birds, 19 Mar 2013: It may be hard to swallow, but Bumpus could get bumped to the back burner.

PS. Another Cliff Swallow selection study by the Browns...

• Brown, Brown & Roche (in press). Fluctuating viability selection on morphology of cliff swallows is driven by climate. J Evol Biol. [abstract]

 

[jaco]

I was attempting to draw an analogy (using the auk/human example), with the Cliff Swallow experience...ie circumstances altering behaviour, which in turn alters structure and confers an ''inherited edge'' to the survivors.

I get it, but it's not really analogous at all.

Unless there was evidence of heritability of that feature, there was no evidence of selection in the human/auk example.

 

[Kirk Roth]

Not according to the theories about selection I have read -- where selection pressure is the part of the population erased by the selection per generation (I think)

Niels

There can be selection pressure AGAINST something and/or/but also selection pressure FOR something.

So swallows that bite the dust because their wings are too long to dodge the cars are selected AGAINST. Swallows with shorter wings who breed more successfully because because they are less busy spending energy dodging cars, being injured, dying, etc. are being selected FOR. In both cases, I believe the term "selection pressure" can be used.

About the number of swallows, it takes fewer than you'd think. If we accept the BIO 101 definition that evolution is simply a change in gene frequencies in a population, this can be done in a single generation - especially if your population is only those birds which breed under several bridges in a corner of Nebraska (I haven't read the study - don't really know the sample size). This could be even more rapid if vehicles are relatively efficient at killing long-winged swallows (gone in one fell swoop, if you will).

 

[Snapdragyn]

This could be even more rapid if vehicles are relatively efficient at killing long-winged swallows (gone in one fell swoop, if you will).

Or one swell coupe? 3

 

[ClarkWGriswold]

Or one swell coupe? 3

:-Cmy father would have been proud of that one SD3

Rich

 

[KenM]

I get it, but it's not really analogous at all.

Unless there was evidence of heritability of that feature, there was no evidence of selection in the human/auk example.

I beg to differ...both examples compare to species physically adapting to circumstances and becoming more equal to the ''situation'' with apparant respective ''shorter wings'' giving faster and greater lift capability..thus reducing the mortality rate and increasing the success rate of that individual colony.

By the same token..bigger joints (wrists/ankles) would have enabled the ''auk pickers'' to harvest the cliffs with ''greater'' success than perhaps they would have achieved..without, enabling the ''colony'' to survive in what must have been extremely ''trying'' circumstances to say the least.

As with the shorter wing..markedly stronger joints, evolving perhaps over 5 generations...is another example of successful adaptation under pressure.

My original surprise..was the apparant, relatively speaking ''short-time'' taken in both cases, to effect a material result.