The document discusses heterochrony, the evolutionary process affecting developmental timing and morphological traits across species. It outlines various types of heterochrony, including paedomorphosis and peramorphosis, which describe how growth rates and timings of development differ between ancestors and descendants. The conclusion highlights the significance of heterochronic genes in the evolution of organisms, underscoring the interaction between development and evolution.

1. Heterochrony: the
Evolution of
Development
byKennethJ.McNamara
Prepared by Ahmet VARIS
1

2. OUTLINE
• Darwinian view
• Aim
• What is heterochrony?
• Types of heterochrony
• Relative Frequency of Heterochrony
• Heterochrony and Sexual Dimorphism
• Conclusion
2

3. Darwin’s view of Evo/Devo
• “Embryology rises greatly in interest, when we look at
the embryo as a picture, more or less obscure, of the
progenitor, either in its adult or larval state, of all
members of the same great class.’’
• ‘’This is one of the most important subjects in the whole
round of natural history.”(Darwin ,1878, p.396 and p.386)
3

4. AIM
• Understand how developmental stages evolve from
ancestor to next generation.
• Observe how species from a common ancestor have
different physiology as a result of their evolution of
development.
• Examples from species
4

5. Evolution & Development
• Within populations of a single species, individuals do not
all grow and develop at the same rate or for the same
duration.
• The same rule occur between closely related species, the
main morphological differences arise from variations to
the rate and duration of growth.
• It is now recognized that developmental genes, particularly
those regulating embryonic or larval development, play a
major role in evolution
5

6. HETEROCHRONY
• Earlier definition (1800s) ‘The term heterochrony was
used to describe cases in which the ontogenetic
sequence of events did not recapitulate or repeat the
sequence of events in phylogeny’.
• Ontogeny is recapitulation of phylogeny dependent on
the physiological functions of heredity (reproduction)
and adaptation (nutrition).
6

7. 7
Embryos of different vertebrates
share basic primitive features such
as gills (red) and tails (blue)
(The Earth Through Time, Harold L. 8th
edition, Chapter 6 - page 5)
(http://evolution.berkeley.edu/evolibrary/ar
ticle/side_o_0/ontogeny_01)
The course of a chick's development,
if recapitulation of phylogeny by
ontogeny is tottally true

8. • Today’sdefinition of heterochrony ‘the mechanism that
produces a parallel between ontogeny and phylogeny’.
• Heterochrony involves a shift in the timing of
developmental processes so an event occurs earlier, later,
or at a different rate in a taxon compared to its ancestor.
8
(Leonard & James, 1993)
Embryonic development and stripe patterns of the zebras Equus burchelli (top)
and grevyi (bottom). Illustration drawn by Carole B.

9. 9
HETEROCHRONY
Paedomorphosis
Progeneis
Neoteny
Postdisplacement
Peramorphosis
Hypermorphosis
Acceleration
Predisplacement

10. Paedomorphosis
• The evolutionary process in which larval or juvenile
features of an ancestral organism are displaced to the
adult forms of its descendants.
• If the period of growth of the descendant form is
stopped prematurely: progenesis
• If onset of growth is delayed: postdisplacement
• If the rate of growth is less in the descendant than in
the ancestor: neoteny
10

11. 11
Second stage of the
development is the last
stage anymore.
The rate of growth is
less when it compared
to ancestor.
The onset of growth is
delayed so the
organisms
development stop
when it become
mature and
differentiate from
ancestor.
(Kenneth J. 2012)
( https://www.geol.umd.edu
BSCI392,10-5-07)
X axis:time
Y axis: development

12. Peramorphosis
• Phylogenetic change in which individuals of a species
mature past adulthood and take on traits which havent
seen yet.
• if the period of growth in the descendant is extended:
hypermorphosis
• if the onset of growth occurs earlier in the descendant
than in the ancestor: predisplacement
• if the growth rate is increased: acceleration
12

13. 13
Maturation occur later
than ancestor
The speed of
development is faster
than ancestor
The structures begin
development earlier
than ancestor
(Kenneth J. 2012)
( https://www.geol.umd.edu
BSCI392,10-5-07)
X axis:time
Y axis: development

14. 14Differences in shape of
the skull between three
different breeds of dogs
Evolution of the domestic dog
from the wolf by paedomorphosis
(Kenneth J. 2012)

15. Relative Frequency of Heterochrony
• Amphibians show a dominantly paedomorphosis, which
may be related to their large cell size, causing a reduced
rate of cellular division.
• Paedomorphosis has occurred many times in frogs, for
example, resulting in the development of many
miniature species. The 29 smallest species (with the
smallest having an average body length of just 7.7
millimeters) are spread across five families and 11
genera.
• Peramorphosis may have been more frequent in
dinosaurs, in particular being a major contributing factor
to the evolution of very large body size
15

16. 16
Peramorphic evolution of protoceratopsian dinosaurs
(Kenneth J. 2012)

17. Heterochrony and Sexual Dimorphism
• Sexual dimorphism: The condition where the two sexes
of the same species exhibit different characteristics
beyond the differences in their sexual organs.
• Size and morphological variance arises from either
variations in growth rates or differences in the relative
times of onset of sexual maturity; in other words, it
arises from heterochrony.
17

18. 18
The adult female of the blue
boxfish, Stropiurichthys
robustus, is paedomorphic
compared with the male,
resembling the juvenile in
body shape and body
patterning.
Photocorynus males live
parasitically attached to the
female.
(Kenneth J. 2012)
(http://www.fishbase.org/summary/Photocorynus-spiniceps.html)

19. Conclusion
• The evolution of organisms mostly caused from
differentiation of heterechronic genes which influence
development of organisms
• We are (as homo sapiens) a classic example of
dissociated heterochrony, where some peramorphic
features are developmental trade-offs for other,
paedomorphic, features: some parts of our anatomy are
relatively retarded, compared with our ancestors, but
others have developed beyond.
• So heterochrony is the interaction between development
and evolution from ontegenetic and phylogenic
perspective.
19

20. Articles about Heterochronic
Genes
• Koen Geuten and Heleen Coenen, Heterochronic genes
in plant evolution and development.
• Carl S. Thummel, Molecular Mechanisms of
Developmental Timing in C. elegans and Drosophila.
• Eric G. Moss, Heterochronic Genes and the Nature of
Developmental Time.
20

21. REFERENCES
• Kenneth J. McNamara (2012), Heterochrony: the Evolution of
Developmen, DOI 10.1007/s12052-012-0420-3
• Kathleen K. Smith (2002), Sequence Heterochrony and the
Evolution of Development, DOI 10.1002/jmor.10014
• Timing is Everything: Morphogenesis, Heterochrony and
Evolution, 2016
• Homeotic Genes and Body Patterns,
http://learn.genetics.utah.edu/
• The Earth Through Time, Harold L. Levin, 8th edition, Chapter
6
• Ontogeny and phylogeny,
http://evolution.berkeley.edu/evolibrary/article/side_o_0/ont
ogeny_01
21

22. THANK YOU
22