Donnerstag 22.11.2007
16 Uhr 15 Hörsaal 1 (Zoologie)
Hans METZ
(Section Theoretical Biology, Institute
of Biology, Leiden University)
"Geometries of macro- respectively
meso-evolution: two lectures"
Abstract:
Lecture 1: Attempts to contribute to a postmodern synthesis: explorations in the interface between macro- and mesoevolution Evo-Devo and adaptive dynamics (AD) are two main postmodern contributions to the evolutionary synthesis.
Evo-Devo contributes to a predictive understanding of the evolutionary process by (1) telling how easily different
changes of morphologcal (s.l.) patterns are generated, and (2) outlining the selective pressures caused by the need for a
good, stable, developmental integration. AD explores the consequences of the changes in the finer features of the
fitness landscape caused by the community dynamics. AD techniques mainly use local properties of the fitness
landscape. Hence AD can only deal with meso-evolutionary timescales. From a larger perspective the low-dimensional
fitness landscapes occurring in most AD studies can be seen as surfaces at the top of ridges in a much higher
dimensional landscape of potential morphologies, with the abyss around the ridges created by the lacok of a proper
development or functioning. The location of the ridges and abysses is grossly the same for the variety of environmental
conditions that can be set by the community dynamics in the considered time windows. The high dimension and
ridgyness of fitness landscapes suggested by Evo-Devo and functional biology conspire in a number of ways:
1. Developmental systems leading to mutation distributions that are in some way aligned with the ridges evolve much
faster than systems where this is not the case.
2. The stabilizing selection in off-ridge directions should have a great robustness of the developmental system as
ultimate consequence. Yet, the high dimension of genotype space implies that this robustness can never lead to a lack
of suitable mutational variation, and thereby to the conservation of features. Hence, the fact that evolution largely
proceeds through the quantitative variation in the size and shape of homologous parts should be due to the stabilizing
internal selection that arises as a consequence of organismal organization.
3. So-called allopatric speciation supposedly occurs by separated populations wandering on the high fitness maze, so
that after a while their mixed offspring, having intermediate properties, ends up in the abyss. As random fitness
landscapes almost never engender allopatric speciation the question arises whether, and if so for what reason, evolved
genotype to phenotype maps may be more speciation prone.
4. Large mutational steps far more often than not make an individual land in the fitness abyss, and only the much rarer
very small steps keep it on the top. This may provide a theoretical justification for the AD assumption of effective
rareness and smallness of mutational steps.
Lecture 2 : Meso-evolutionary predictions derivable from the interplay between ecology and evolution Adaptive
Dynamics is a framework geared towards making the transition from micro-evolution to macro-evolution based on a
time scale separation approximation. This assumption allows defining the fitness of a mutant as the rate constant of
initial exponential growth of the mutant population in the environment created by the attractor of the resident
community dynamics. This definition makes that all resident types have fitness zero. If in addition it is assumed that
mutational steps are small, evolution can be visualised as an uphill walk in a fitness landscape that keeps changing
as a direct result of the evolution it engenders. One of the intriguing consequences from studying the singular points
of the resulting dynamical systems is the existence of a fairly ubiquitous type of singularity that engenders adaptive
diversification (including potentially speciation). Another type of singular points are so-called Evolutionarily Stable
Strategies, characterised by the fact that in the environment created by such a strategy no mutants has positive
fitness. Contrary to what is suggested by their name ESSs may still repel meso-evolutionarily; attracting ESSs are
called CSSs. Within the AD framework the following meso-evolutionary predictions follow from geometric genericity
arguments:
1. When an empty habitat is colonised and the physical environment stays roughly constant for a sufficiently long
2. time, initially speciation occurs very frequently but the overall speciation rate decreases quickly.
3. Initially in the directional selection phases in between speciation events a lot of non-adaptive variability is
incorporated, most of which will be weeded out at later stages. 3. Speciation is rare in environments that fluctuate
on time scales between that of directional evolution and speciation (the latter tends to be much slower than the
former).
4. Given the observed speeds of directional evolution we may expect that most slow change in the fossil record is
due to the tracking of changing adaptive equilibria, punctuated by rare short periods of fast directional evolution.
The punctuation events are of two types, coupled to speciation, when a CSS changes into a branching point, and
"just so", due to the collision of a CSS and an evolutionary repellor.
Biographical note
Hans Metz has been full professor of Mathematical Biology in Leiden, The
Netherlands, since 1986. He obtained his MA from Leiden University in
1971 (cum laude), and his PhD from Leiden University in 1981. His work
lies in Mathematical Biology, especially Adaptive Dynamics. Since 1996 he is
group leader and senior adviser of the Adaptive Dynamics Network Evolution and Ecology Program of the IIASA (Laxenburg, Austria). From 2006
to 2007 he was a visiting professor at the Ecole Normale Superieure and Paris VI.
From 2006 to 2007 he was a visiting professor at the University of Helsinki.
A follow-up discussion with the speaker takes place at the
Konrad Lorenz Institute for Evolution and Cognition
Research (KLI),
Adolf-Lorenz-Gasse 2,
A-3422 Altenberg,
the next day at 3.00 p.m.