Título:
Eco-Evo-Devo - do we need a new "Modern Synthesis" in evolutionary biology?
area de concentraçâo:
biológicas
autor:
Klaus Hartfelder
Professor Associado
Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
In the Darwin year 2009 several publications asked questions alike the one posted in the title
of this presentation. It is essentially a question on whether current knowledge obtained from
advanced developmental biology and ecology research programs is in line with the postulates
of the “Modern Synthesis” of evolutionary biology. This was a major research program that
unified evolutionary biology in the 1940s by setting it on the firm foundations of population
genetics based on mathematical models. The founders of the Modern Synthesis then
integrated these models with contemporary knowledge from paleontology and taxonomy of
extant organisms. In line with Darwinian theory, the proponents of the Modern Synthesis
were unanimous in the assumption that Natural Selection is the major player in evolution,
selecting from mutation-generated allelic variation within populations. Some of the biological
assumptions implicit in the mathematical models were, however, soon seen to be violated, as
shown by results emerging in the 1970s from biochemical genetics and subsequently by
analyses of whole genomes. These indicated that many mutations could be selectively neutral,.
Furthermore, population genetic studies on islands (especially Hawaii) showed that effective
population size can be small and, thus, genetic drift can play a major role in the genetic
composition of populations. Nevertheless, speciation continued to be seen as a result of
genetic differentiation of populations driven by natural selection, this resulting in
reproductively isolated units (species). Whether species differed in their morphologies
(phenotype) or were similar was a secondary problem, and major changes in shape were seen
as a gradual accumulation of microevolutionary steps.
Practically untouched by “Modern Synthesis” , developmental genetics gradually
reached maturity in the 1980s disclosing astounding similarities in the “genetic toolkit” that
different groups of organisms use to build widely divergent body plans from simple structures,
the eggs. The dramatic changes in morphology seen in mutants of the fruit fly, Drosophila
melanogaster, where minor mutational changes in a single gene could turn an antenna into a
leg (homeotic mutant), or where a complete eye could be induced ectopically, in place of a
wing, caused a major impact in biological thinking, even more so because in some of these
experiments the fly’s genes could be substituted by their equivalents (homologs) from other
organisms, e.g. the mouse. These findings essentially led to the surge of a research program
called evolutionary developmental biology, or tenderly just “evo-devo”. The fact that minor
mutations within the coding regions of a gene, or even mutations within the regulatory regions
of a small number of genes, could have such major phenotypic effects was seen as evidence
that similar mutational changes, in the past, could have driven the divergence of the body
plans of the major groups of animals. In effect, this brings us back to the controversy of
microevolution versus macroevolution, never really settled, but , in the 1940s, at least
temporarily won by the Modern Synthesis proponents.
These results from developmental biology, which showed how major gene effects can
dramatically affect the morphology of animal groups, soon caught the attention of ecologists
working on major phenotypic variation within species, such as seasonal morphs of butterflies,
exaggerated horns of dung beetles, castes of social insects, wing polymorphism in aphids and
locusts, and others. In these species, morphological variation can either have a genetic basis,
or even be simply driven by environmental parameters, such as temperature, photoperiod,
nutrition or population density. This means that environmental effects acting on gene
regulatory networks within a single genotype can generate major phenotypic differences
within a species and, consequently, there now are strong voices calling for a need for a new
research program on unifying principles in evolutionary biology. Tenderly calling this new field
“eco-evo-devo” would, however, not be of much use if its three legs continued to march
merely in parallel.
Clearly, I would be overestimating my insights and sound foolish if promising to
provide unifying principles at this workshop, but reviewing the essentials of the Modern
Synthesis and, especially trying to grasp as to what is the meaning of micro- and
macroevolution in terms of functional genomics in a population context may be a
step towards this goal.