Integrating horn development with patterns of horn evolution

Horns appear to have arisen repeatedly within the scarabs, and in numerous lineages these structures have attained extreme proportions.  Today, the geotrupids (“dor” beetles), the scarabaeids (“dung beetles”) and the dynastines (“rhinoceros beetles”) are predominated by species with exaggerated horns.  Within each of these clades, horn morphologies are surprisingly evolutionarily labile (e.g. a recent phylogenetic analysis of 48 species from one scarab genus revealed 25 changes in the physical location of horns, and extensive interspecific variation in horn size and shape; PDF).  A close examination of this variation suggests that in addition to gains or losses of horns, there have been four principle axes, or trajectories of horn evolution (Figure).  Species differ in the physical location of their horns (e.g. head versus thorax, center versus sides of the thorax).  Species differ in horn shape (straight, curved, branched, etc.).  They also differ in horn allometry – a reflection both of the relative size of the horn, and of the developmental coupling of horn growth with among-individual variation in body size.  Finally, species differ in the presence/ absence, and the nature of dimorphism in horn expression, either male dimorphism (large versus small males) and/ or sexual dimorphism (males versus females).  (Dimorphism Figure)

Categorizing these among-species patterns into biologically meaningful trajectories allows us to consider how these changes are generated – which physiological and developmental pathways are involved, and even which specific genes in these pathways are involved (PDF).  Our long-term goal is to study the developmental mechanisms underlying all four of these trajectories in order to better understand the genetic bases for adaptive morphological evolution.  Laura Corley (Washington State University) and I are currently studying two pathways now known to be involved with the control of horn development, and that we suspect are likely mechanisms for the evolutionary diversification of horn form. (Figure)

The Limb-Patterning pathway and the evolution of horn location and shape
            Patterning and the origin of beetle horns 
            Patterning and the evolution of horn location and shape

The insulin pathway and the evolution of allometry

The fourth trajectory: evolution of horn dimorphism

Current Projects & Future Directions

 

Links to Other Evo-Devo and Developmental-Genetic Labs:
Laura S. Corley (Washington State University)
http://entomology.wsu.edu/personal/laura_corley/index.html

Ian Dworkin (North Carolina State University)
http://www.iandworkin.net/

H. Frederik Nijhout (Duke University)
http://www.biology.duke.edu/nijhout/

Thomas Flatt (Brown University)
http://www.brown.edu/Departments/EEB/research/flatt.htm

Alex Shingleton (Michigan State University)
http://www.msu.edu/%7Eshingle9/

Anthony Frankino (Princeton University)
http://www.princeton.edu/~frankino/

Armin Moczek (Indiana University)
http://www.bio.indiana.edu/~moczeklab/

Lisa Nagy (University of Arizona)
http://www.mcb.arizona.edu/nagy/default.html

Bicyclus Evolutionary Biology Group
http://biology.leidenuniv.nl/ibl/S6a/index.shtml

Greg Wray (Duke University)
http://www.biology.duke.edu/wraylab/

Elizabeth Jockusch (University of Connecticut)
http://hydrodictyon.eeb.uconn.edu/people/jockusch/jockuschlab/research.html

Jeffrey Marcus (Western Kentucky University)
http://asm.wku.edu/faculty/Marcus/default.html

Toru Miura (Hokkaido University)
http://noah.ees.hokudai.ac.jp/%7Emiu/miura_lab_eng.html

Bruce Edgar (Fred Hutchinson Cancer Research Center)
http://www.fhcrc.org/science/labs/edgar/index.htm

Sally Leevers (London Research Institute)
http://science.cancerresearchuk.org/research/loc/london/lifch/leeverss/?version=1

Peter J. Bryant (UC Irvine)
http://mamba.bio.uci.edu/~pjbryant/dbc/bryantp.htm

Beetlebase (Tribolium Genome Database)
http://www.bioinformatics.ksu.edu/BeetleBase/

Susan Brown (Kansas State University)
http://www.ksu.edu/biology/bio/faculty/brown/brown.html

Kansas State Tribolium Genetics Program
http://www.k-state.edu/tribolium/

Sean B. Carroll (University of Wisconsin)
http://www.molbio.wisc.edu/carroll/

Grace Boekhoff-Falk (University of Wisconsin)
http://www.anatomy.wisc.edu/faculty_boekhoff-falk.html