A few years ago, I had taken a class called Macroevolution. During the class we read several seminal papers on the subject and discussed the implications of these topics. At the end of the class, we set up on the white board some of the principle topics in macroevolution. The discussion involved how the topics were linked and specifically what they could be/were linked to. The class ended with a bunch of evolutionary topics that were heavily interacting and influencing each other.
I though this was fascinating and I ended up taking pictures of the board after we had finished the class. Below is a cleaned up version of that work session with the appropriate terminology defined and/or discussed below. Keep in mind that the interactions depicted in the diagram are not all of the possible interactions, they are just the most prevalent ones that we happened upon during our discussion.
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| Macroevolutionary concepts. Click for a larger version. |
Terminology
The descriptions and definitions below are taken or paraphrased directly from the source literature as cited.
Adaptation – Any change in the
structure or functioning of successive generations of a population that makes
it better suited to its environment. (Oxford
Dictionary of Biology)
Burden - Evolutionary constraints
caused by functional interdependency and maintained by internal selection or in
other words hierarchically nested interdependence of characters within the
organism (Schoch, 2010). Basically these are genes that are hard wired into the
genome and passed down through generations that are really difficult, if not
impossible, to get rid of. For instance, almost all tetrapods have four limbs
since the first tetrapod.
Constructional Morphology – Phylogenetic,
functional, and morphogenic constraints and their dynamic relationship which help
to explain a variety of evolutionary phenomena such as sub-optimal structures,
convergence, parallel evolution, channeled evolutionary pathways, and the
geometrical patterns that characterize organic structure (Reif et al, 1985).
Deep Homology – the sharing of the
genetic regulatory apparatus that is used to build morphologically and
phylogenetically disparate animal features. Homology, as classically defined,
refers to a historical continuity in which morphological features in related
species are similar in pattern or form because they evolved from a
corresponding structure in a common ancestor. Deep homology also implies a
historical continuity, but in this case the continuity may not be so evident in
particular morphologies; it lies in the complex regulatory circuitry inherited
from a common ancestor (Shubin et al, 2009).
Developmental
Constraint – The theory that during development the systems within an individual organism will develop a limited and discrete subset of phenotypes,
regardless of the environmental variance or experimental manipulation. In other
words, regularities and trends observed in phylogeny are a reflection of a
conserved set of pattern-generating rules. These internal rules of development
define the realm of possible variation and place limits on the process of
adaptation (Alberch, 1989).
Disparity (Morphological
Disparity) – The total amount of
the dissimilarities among all and any kinds of biological groups of organisms
(Pavlinov, 2011).
Diversity (Taxonomic
Diversity, Biodiversity) – The existence of a wide variety of species
(species diversity) or other taxa of plants, animals, and microorganisms in a
natural community or habitat, or of communities within a particular environment
(ecological diversity), or of genetic variation within a species (genetic
diversity). The maintenance of a high level of biodiversity is important for
the stability of ecosystems (Oxford
Dictionary of Biology).
Exaptation – A
morphological or physiological character that predisposes an organism to adapt
to a changed environment or lifestyle. (Oxford
Dictionary of Biology)
Extinction Rate – The
number of extinctions during a given period of time.
Gradualism (Phyletic
Gradualism) - It holds that new species arise from the slow and steady
transformation of entire populations. Under its influence we seek unbroken
fossil series linking two forms by insensible gradation as the only complete
mirror of Darwinian processes; we ascribe all breaks to imperfections in the
record (Eldredge and Gould, 1972).
GRNs (Gene Regulatory Network) – GRNs
are large networks that determine the course of animal development. These networks consist largely of the functional linkages
among regulatory genes that produce transcription factors and their target
cis-regulatory modules in other regulatory genes, together with genes that
express spatially important signaling components. They have a modular
structure, consisting of assemblies of multigenic subcircuits of various forms.
Each such subcircuit performs a distinct regulatory function in the process of
development. GRNs have been attributed to being the reason why there is little
change in the phylum and superphylum-level body plans since the Early Cambrian
(Davidson and Erwin, 2006).
Mass Extinctions – The
extinction of a large number of species within a relatively short interval of
the geological time scale. (Oxford
Dictionary of Biology)
Natural Selection – The
process that, according to Darwinism, brings about the evolution of new species
of animals and plants. Darwin noted that the size of any population tends to
remain constant despite the fact that more offspring are produced than are
needed to maintain it. He also saw that variations existed between individuals
of the population and concluded that disease, competition, and other forces
acting on the population eliminated those individuals less well adapted to
their environment. The survivors would pass on any heritable advantageous
characteristics to their offspring and in time the composition of the
population would change in adaptation to a changing environment. Over a long
period of time this process could give rise to organisms so different from the
original population that new species are formed. (Oxford Dictionary of Biology)
Punctuated
Equilibrium – An evolution hypothesis that states in evolutionary history
the development of new species occurs very rapidly in short bursts (lasting
typically less than 100,000 years), which are separated by long periods in
which little evolutionary change occurs (Oxford
Dictionary of Science).
Red Queen Hypothesis
– An evolutionary theory that describes how the coevolution of competing
species creates a dynamic equilibrium, in which the probability of extinction
remains fairly constant over time. Hence, evolution is seen neither as
‘progressive’ – with a species’ chances of survival improving over time – nor
as ‘escalatory’ – with increasing vulnerability to extinction over time.
Instead, as one species evolves improvements that make it more competitive, its
competitors experience selection pressures that force them to evolve in order
to keep pace with it. Ones that lag too far behind will become extinct (Oxford Dictionary of Biology).
Rock Record – The
availability of the information on the fossil record, which is correlated with
the availability of rocks during a particular time period. The absence or
presence of rocks, which have the possibility of containing a set of fossils
could have an influence on how scientists perceive the evolution of a
particular group (evolutionary rate, extinction rate, diversity, etc.) (Barrett
et al., 2009).
Signor-Lipps Effect – This effect is
where for most organisms, it is unlikely that the
true last occurrence of an extinct species or family will be recorded.
Therefore, almost all observed time ranges are truncated. This causes a
"smearing" of the record of an extinction event backward in time (Raup, 1986). In
other words, a fundamental problem with using biostratigraphic last
occurrences to infer patterns of extinction is that, barring reworking, last
occurrences nearly always underestimate time of extinction. Signor and Lipps
(1982) showed that a random distribution of errors at biostratigraphic range end-points
can produce apparent gradual decline preceding a sudden extinction boundary
(Meldahl, 1990).
Species Selection – Selection
is one of two process of origination and persistence of clades that has been
proposed. Selection encompasses those interactions between heritable, emergent
character variation and the environment that cause differences in rates of
birth or death among varying individuals (Vrba and Gould, 1986). Species
selection requires that species be units of selection, and thus there must be
properties of the species, rather than the sum of the properties of individuals,
upon which selection can act (Erwin, 2000).
Species Sorting – Sorting
is one of two process of origination and persistence of clades that has been
proposed. In Darwinian Theory, evolutionary change is the product of sorting
(differential birth and death among varying organisms within a population).
Sorting is a simple description of differential representation; it contains, in
itself, no statement about causes. As its core, Darwinism provides a theory for
the causes of sorting- natural selection acting upon organisms in the “struggle
for existence.” However, other processes (genetic drift, for example) produce
sorting as well (Vrba and Gould, 1986).
Stasis – An evolutionary
theory where there is zero rate of evolution and no extinction of speciation;
evolutionary change occurs only in response to changes in the physical environment
(Stenseth and Smith, 1984).
References
2008, in Hine, R. S., ed., Oxford Dictionary of Biology: Oxford, Oxford
University Press.
2010, in Daintith, J., and Martin, E., eds., Oxford Dictionary of
Science: Oxford, Oxford University Press.
Alberch, P., 1989, The logic of
monsters: Evidence for internal constraint in development and evolution:
Geobios, v. 22, no. Supplement 2, p. 21-57.
Barrett, P. M., McGowan, A. J., and
Page, V., 2009, Dinosaur diversity and the rock record: Proceedings of the
Royal Society of London. Series B: Biological Sciences, v.
10.1098/rspb.2009.0352, p. 1-8.
Davidson, E. H., and Erwin, D. H.,
2006, Gene Regulatory Networks and the Evolution of Animal Body Plans: Science,
v. 311, no. 5762, p. 796-800.
Eldredge, N., and Gould, S. J., 1972,
Punctuated equilibria: An alternative to phylogenetic gradualism, in Schopf, T. J. M., ed., Models in
Paleobiology: San Francisco, Freeman, Copper and Company, p. 82-115.
Erwin, D. H., 2000, Macroevolution is
more than repeated rounds of microevolution: Evolution & Development, v. 2,
no. 2, p. 78-84.
Meldahl, K. H., 1990, Sampling,
species abundance, and the stratigraphic signature, of mass extinction: A test
using Holocene tidal flat molluscs: Geology, v. 18, no. 9, p. 890-893.
Pavlinov, I. Y., 2011, Morphological
Disparity: An Attempt to Widen and to Formalize the Concept, INTECH Open Access
Publisher.
Raup, D. M.,
1986, Biological extinction in earth history: Science, v. 231, no. 4745, p.
1528-1533.
Reif, W.-E.,
Thomas, R. D. K., and Fischer, M. S., 1985, Constructional morphology: The
analysis of constraints in evolution dedicated to A. Seilacher in honour of his
60. birthday: Acta Biotheoretica, v. 34, no. 2, p. 233-248.
Schoch, R. R.,
2010, Riedl's burden and the body plan: selection, constraint, and deep time:
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution,
v. 314B, no. 1, p. 1-10.
Shubin, N.,
Tabin, C., and Carroll, S., 2009, Deep homology and the origins of evolutionary
novelty: Nature, v. 457, no. 7231, p. 818-823.
Signor, P. W.,
III, and Lipps, J. H., 1982, Sampling bias, gradual extinction patterns and
catastrophes in the fossil record Geological Society of America Special Paper,
v. 190, p. 291-296.
Stenseth, N.
C., and Smith, J. M., 1984, Coevolution in Ecosystems: Red Queen Evolution or
Stasis?: Evolution, v. 38, no. 4, p. 870-880.
Vrba, E. S.,
and Gould, S. J., 1986, The Hierarchical Expansion of Sorting and Selection:
Sorting and Selection Cannot Be Equated: Paleobiology, v. 12, no. 2, p.
217-228.
