First EXEB-meeting in 2016: on speciation, ecological opportunity and latitude

                                



















Crab spider (Misumenia vatia) with prey. Photo: Erik Svensson

Posted by Erik Svensson 

"Evolution in Sweden 2016" is now over, and in my opinion it was a great success. You can see photos from this meeting here, and we can also briefly summarize our general reflections about this meeting on the first EXEB-meeting, which I post information about below. 

On this first EXEB-meeting of 2016, I want to discuss a recent paper published as a "Presidential Adress" in American Naturalist by Dolph Schluter, entitled "Speciation, ecological opportunity and latitude". 

I saw Dolph give a talk about this last year at a speciation-meeting in California, and I think that he is a very thoughtful scientist who has stimulated my thinking and influenced many other ecologists and evolutionary biologists. Hopefully, we will have a good discussion about this paper. But as usual, we will start the meeting with some general reflections, summary of impressions of "Evolution in Sweden 2016" and we can also hear a bit from Tobias and Nathalie's trip to Australia, as well as mine, Katie's and John's trip to Argentina. I might even bring some pictures to show. 

Time: Tuesday, January 19, at 10.00

Where: "Argumentet", 2nd floor, Ecology Building

Abstract: Evolutionary hypotheses to explain the greater numbers of species in the tropics than the temperate zone include greater age and area, higher temperature and metabolic rates, and greater ecological opportunity. These ideas make contrasting predictions about the relationship between speciation processes and latitude, which I elaborate and evaluate. Available data suggest that per capita speciation rates are currently highest in the temperate zone and that diversification rates (speciation minus extinction) are similar between latitudes. In contrast, clades whose oldest analyzed dates precede the Eocene thermal maximum, when the extent of the tropics was much greater than today, tend to show highest speciation and diversification rates in the tropics. These findings are consistent with age and area, which is alone among hypotheses in predicting a time trend. Higher recent speciation rates in the temperate zone than the tropics suggest an additional response to high ecological opportunity associated with low species diversity. These broad patterns are compelling but provide limited insights into underlying mechanisms, arguing that studies of speciation processes along the latitudinal gradient will be vital. Using threespine stickleback in depauperate northern lakes as an example, I show how high ecological opportunity can lead to rapid speciation. The results support a role for ecological opportunity in speciation, but its importance in the evolution of the latitudinal gradient remains uncertain. I conclude that per capita evolutionary rates are no longer higher in the tropics than the temperate zone. Nevertheless, the vast numbers of species that have already accumulated in the tropics ensure that total rate of species production remains highest there. Thus, tropical evolutionary momentum helps to perpetuate the steep latitudinal biodiversity gradient.

Lab-meeting on multiple adaptive peaks and predator-mediated natural selection

Posted by Erik Svensson

On Tuesday (April 30, 10.30) I was thinking that we should discuss a short paper that was recently published in Science, showing an empirical example and application of the Adaptive Landscape concept. I choose this paper to demonstrate that the idéa of the adaptive landscape is not just a theoretical construct, but could actually stimulate empirical and experimental studies. This was also the main rationale for the publication of our book on the topic last year, which is cited in the current paper. You will find the Abstract below, and the paper can be reached here. 

As another example of how "landscape thinking" and fitness surfaces can guide empirical work, I will also send around a manucript draft about predator-mediated natural selection in Calopteryx-demoiselles, that stems from the field work former postdoc Shawn Kuchta did in our lab between 2007 and 2009. We would both love to get some input on this manuscript, short or long, either during the lab-meeting or before or after (if you cannot attend). I will send you an e-mail with this paper attached well before the lab-meeting, but if you do not receive it and wish to have a copy, please do not hesitate to send me an e-mail (erik.svensson@biol.lu.se).

Any fika-volunteer?

Science 11 January 2013: 
Vol. 339 no. 6116 pp. 208-211 
DOI: 10.1126/science.1227710

• REPORT

Multiple Fitness Peaks on the Adaptive Landscape Drive Adaptive Radiation in the Wild

1. Christopher H. Martin*, 
2. Peter C. Wainwright

• ABSTRACT

The relationship between phenotype and fitness can be visualized as a rugged landscape. Multiple fitness peaks on this landscape are predicted to drive early bursts of niche diversification during adaptive radiation. We measured the adaptive landscape in a nascent adaptive radiation ofCyprinodon pupfishes endemic to San Salvador Island, Bahamas, and found multiple coexisting high-fitness regions driven by increased competition at high densities, supporting the early burst model. Hybrids resembling the generalist phenotype were isolated on a local fitness peak separated by a valley from a higher-fitness region corresponding to trophic specialization. This complex landscape could explain both the rarity of specialists across many similar environments due to stabilizing selection on generalists and the rapid morphological diversification rate of specialists due to their higher fitness.

On density-dependent diversification and speciation in birds

Posted by Erik Svensson


This coming Wednesday (March 21 at 13.30 NOTE TIME!!!!), we will discuss a paper about the (possible) density-dependent slowdown of cladogenesis in birds with the progress of adaptive radiation. It is a paper that was published relatively recently, although it is not entirely new, in PLoS Biology by Albert Phillimore and Trevor D. Price. The title of the paper is:
"Density-Dependent Cladogenesis in Birds"
The authors have used molecular phylogenies from various avian groups to test the hypothesis that diversification rates decline with the progress of adaptive radiation, and as we are approaching the present. Here is the Abstract to the article, which can be downloaded here (PLoS Biology is a "Open Acess"-publisher, which makes everything easier):

Abstract 

A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stronger slowdowns than small clades, even if the probability of speciation and extinction remains constant through time. This is a consequence of exponential growth: clades, which, by chance, diversify at above the average rate early in their history, will tend to be large. They will also tend to regress back to the average diversification rate later on, and therefore show a slowdown. We conducted a meta-analysis of the distribution of speciation events through time, focusing on sequence-based phylogenies for 45 clades of birds. Thirteen of the 23 clades (57%) that include more than 20 species show significant slowdowns. The high frequency of slowdowns observed in large clades is even more extreme than expected under a purely stochastic constant-rate model, but is consistent with the adaptive radiation model. Taken together, our data strongly support a model of density-dependent speciation in birds, whereby speciation slows as ecological opportunities and geographical space place limits on clade growth.

We meet at 13.30 (not 13.00!) to discuss this interesting article.