Research presentation by Hanna Bensch on "the monoculture effect" on April 4

For next week's EXEB-meeting, I am pleased to welcome one of our most beloved and loyal co-workers: Hanna Bensch. Hanna has been working for many summers now with us in the damselfly project, and she also participated in our recent field sampling expedition to Cameroon in Central Africa, during January and February 2017. Hanna's skills as a field assistant are amazing, and we are so happy that she has been working with us for so long time.

Hanna will give a presentation of her Master's-thesis work that she has done under the supervision of Charlie Cornwallis on ostriches (Struthio camelus) in South  Africa. The title is:

The monoculture effect: a meta-analysis and experiment on ostrich chicks

Abstract:

Increased genetic diversity of a population can decrease pathogen and parasite transmission and prevalence within the population, a phenomenon known as the monoculture effect. This diversity-disease hypothesis has been studied within many different host systems. However, the overall generality of the monoculture effect has been debated and not systematically investigated. I therefore tested the strength and generality of the monoculture effect by conducting a meta-analysis on the relationship between within group genetic diversity and pathogen prevalence or mortality. My meta-analysis confirmed the monoculture effect to be a general phenomenon, finding a significant negative relationship between group genetic diversity and rates of host infection and mortality. However, a majority of the studies included were on insects and further studies on a broader range of taxa is of interest to increase the understanding of the monoculture effect. To complement my meta-analysis, I therefore conducted an experimental study on ostrich chicks, testing group genetic diversity’s effect on growth and survival. 

 

 

If you want to know if chicks from groups of high diversity did better than chicks from groups of low diversity, then you have to come to my presentation! :)

 

 

Along the same topic as Hanna's presentation above, I suggest that we also have a discussion about a recent paper in Science about the relationship between resistance and tolerance evolution, that challenges the common view that these two forms of defense are redundant to each other. You can find the paper here, and the Abstract is below:

Antibiotic tolerance facilitates the evolution of resistance

1. Irit Levin-Reisman¹,
2. Irine Ronin¹,
3. Orit Gefen¹,
4. Ilan Braniss¹,
5. Noam Shoresh²,
6. Nathalie Q. Balaban¹,*

Abstract

Controlled experimental evolution during antibiotic treatment can help to explain the processes leading to antibiotic resistance in bacteria. Recently, intermittent antibiotic exposures have been shown to lead rapidly to the evolution of tolerance—that is, the ability to survive under treatment without developing resistance. However, whether tolerance delays or promotes the eventual emergence of resistance is unclear. Here we used in vitro evolution experiments to explore this question. We found that in all cases, tolerance preceded resistance. A mathematical population-genetics model showed how tolerance boosts the chances for resistance mutations to spread in the population. Thus, tolerance mutations pave the way for the rapid subsequent evolution of resistance. Preventing the evolution of tolerance may offer a new strategy for delaying the emergence of resistance.

 

Time: Tuesday, April 4, 10.00

Locale: "Darwin", 2nd floor (Ecology Building)

 

Optimal initial and adult size in animals

A few weeks ago, Erik picked a classical and highly-cited American Naturalist paper to celebrate the journal’s 150th anniversary. 

For this week’s meeting, we will read a less classical, and much less cited, paper from the treasure trove that is AmNat:

Kozlowski, J. 1996. Optimal Initial Size and Adult Size of Animals: Consequences for Macroevolution and Community Structure. The American Naturalist 147:101–114.

I’ve been reading this paper several times lately as I have been preparing my VR application. Every time, I have found it to be thought-provoking and stimulating. In the paper, Jan Kozlowski asks, using somewhat different terms, the question: what determines the number of unique adaptive peaks for body size on the macroevolutionary adaptive landscape? He does this by combining life history optimization models for optimal age and size at maturity, with models on optimal offspring size, and some really neat ecological reasoning about size-selective interactions. IThe end result is fascinating. Can’t believe this paper has only been cited 41 times! 

/Viktor Nilsson-Örtman

Where? Darwin
When? Tuesday 10.00  

There will be fika!

Abstract

Evolution of adult size and offspring size is considered with the aid of an optimal energy allocation model in which, in contrast to existing allocation models that apply a purely energetic definition of fitness, the amount of energy allocated to reproduction is divided into quanta dependent on offspring size, and net reproductive rate is maximized. This approach enables the connection between adult and offspring size to be identified: larger offspring make it optimal for their mothers to have larger adult size. Optimal offspring size exists in the range of sizes for which the ratio of production rate to mortality rate is concave upward with respect to body size. If such a range does not exist, it is optimal to produce the smallest viable offspring. Optimal adult size exists in the range of sizes for which the ratio of production rate to mortality rate is concave downward. If such a range does not exist, it is optimal to have the largest viable adults. The shape of the function representing the ratio of these two rates changes if a new size-specific predator invades the system: then, a macromutation abruptly changing either initial size or adult size can be preferred by natural selection. Possible mechanisms of such macroevolutionary changes are discussed. In the modern world, in which many small and large species with various offspring sizes exist, replacement of one species by another is expected after invasion by a size-selective predator.

Modularity: Genes, Development, and Evolution

Inspired by the discussion last week, I thought it would be nice to read a conceptual paper about the importance of modularity for evolutionary processes. If you are interested in how genetic and developmental organization shapes phenotypic evolution don't miss the next lab meeting!

Where? Darwin
When? Tuesday 10.00  

Expect fika!

 Modularity: Genes, Development, and Evolution

Diogo Melo, Arthur Porto, James M. Cheverud, and Gabriel Marroig

Abstract
Modularity has emerged as a central concept for evolutionary biology, thereby providing the field with a theory of organismal structure and variation. This theory has reframed long-standing questions and serves as a unified conceptual framework for genetics, developmental biology, and multivariate evolution. Research programs in systems biology and quantitative genetics are bridging the gap between these fields. Although this synthesis is ongoing, some major themes have emerged, and empirical evidence for modularity has become abundant. In this review, we look at modularity from a historical perspective, highlighting its meaning at different levels of biological organization and the different methods that can be used to detect it. We then explore the relationship between quantitative genetic approaches to modularity and developmental genetic studies. We conclude by investigating the dynamic relationship between modularity and the adaptive landscape and how this relationship potentially shapes evolution and can help bridge the gap between micro- and macroevolution

The Evolutionary Origins of Hierarchy, or how networks organize themselves

A few adaptationist arguments assume that organization is always a result of direct selection, so I thought it would be interesting to discuss a paper on how a few simple constraints can cause evolving systems to organize themselves regardless of what they're selected for.

As usual, Tuesday at 10:00 am in Darwin (with fika).

The Evolutionary Origins of Hierarchy

Mengistu H, Huizinga J, Mouret JB, Clune J (2016). PLOS Computational Biology 12(6): e1004829. doi: 10.1371/journal.pcbi.1004829

Hierarchical organization—the recursive composition of sub-modules—is ubiquitous in biological networks, including neural, metabolic, ecological, and genetic regulatory networks, and in human-made systems, such as large organizations and the Internet. To date, most research on hierarchy in networks has been limited to quantifying this property. However, an open, important question in evolutionary biology is why hierarchical organization evolves in the first place. It has recently been shown that modularity evolves because of the presence of a cost for network connections. Here we investigate whether such connection costs also tend to cause a hierarchical organization of such modules. In computational simulations, we find that networks without a connection cost do not evolve to be hierarchical, even when the task has a hierarchical structure. However, with a connection cost, networks evolve to be both modular and hierarchical, and these networks exhibit higher overall performance and evolvability (i.e. faster adaptation to new environments). Additional analyses confirm that hierarchy independently improves adaptability after controlling for modularity. Overall, our results suggest that the same force–the cost of connections–promotes the evolution of both hierarchy and modularity, and that these properties are important drivers of network performance and adaptability. In addition to shedding light on the emergence of hierarchy across the many domains in which it appears, these findings will also accelerate future research into evolving more complex, intelligent computational brains in the fields of artificial intelligence and robotics.

Extinction can be estimated from moderately sized molecular phylogenies

There has been some debate as to whether extinction rates can be estimated from phylogenies alone. This paper claims that it is still possible with some caveats. Even though this paper seems sort of niche, I think it is important to be caught up on this debate J. I will try to frame the debate at the beginning of the lab meeting, if some people feel lost. 

We are meeting in Darwin now Tuesday 10.00. I will bring fika. 

Link to paper.