Sean P. Mullen, Ph.D.
Assistant Professor
Evolutionary Genetics

111 Research Dr., D216
Bethlehem, PA 18015

(610) 758-5569

sem307@lehigh.edu

Fig. 1a - photo courtesy of Will Cook (2006)

Fig. 1b

Fig. 2

Fig. 3a

Fig. 3b

Research

My research focuses on understanding how adaptive phenotypic variation arises and is maintained in natural populations.  In particular, I am interested in the link between divergent natural and sexual selection on traits involved in sexual signaling and mate recognition and the origins of barriers to gene exchange between closely-related populations.  Hybrid zones are ideal settings to address such questions because they present opportunities to study the effects of gene flow, selection, and recombination in nature and, thus, provide insights into the genetic, behavioral, and phenotypic changes that occur early in speciation.

Although I have studied the origins of adaptive phenotypes in a number of evolutionary systems (predominantly insects), much of my previous work has been aimed at understanding the origins of mimicry and wing pattern variation among hybridizing populations of mimetic and non-mimetic admiral butterflies in the Limenitis arthemis-astyanax species complex (Figures 1a and 1b).

Current efforts in the lab are directed towards identifying the genes underlying the mimicry polymorphism is this system using a combination of functional genetic and genomic approaches.  Ongoing projects include: 1) QTL and association mapping to identify genome regions underlying wing pattern differences between mimetic and non-mimetic phenotypes, 2) functional genetics of larval wing discs (cDNA library construction, EST sequencing, and, ultimately, gene expression studies) to identify candidate patterning loci, and 3) Analyses of SNP variation associated with previously identified patterning genes from Drosophila and other lepidopteran systems (e.g. - Heliconius, Bicyclus). In addition, we are conducting no choice mating trials to test for evidence of assortative mating and/or reinforcement.

Other projects in the lab:

• Molecular phylogenetics of the Neotropical butterfly genus Adelpha (Figure 2), in collaboration with Dr. Keith Willmott (FMNH).
• Hybridization and species boundaries in two western North American admiral species (L. lorquini and L. weidemeyerii) (Figures 3a and 3b).

Students interested in working in my lab please click here.

Recent publications:

Ries. L., Mullen, S.P. 2008 A rare model limits the distribution of its more common mimic: A twist on frequency-dependent batesian mimicry. The Society for the Study of Evolution.

Mullen, S. P., Dopman, E. B., & R. G. Harrison. 2008. Hybrid zone origins, species boundaries, and the evolution of wing-pattern diversity in a polytypic species complex of North American admiral butterflies (Nymphalidae: Limenitis). Evolution 62:1400-1417.

Mullen, S. P., Millar, J.C., Schal, C. & K. L. Shaw. 2008. Identification and characterization of cuticular hydrocarbons from a rapid species radiation of Hawaiian swordtailed crickets (Gryllidae: Trigonidiinae: Laupala) .J. Chem. Ecol 34:198-204

Mullen, S. P. * & J. A. Andres*. 2007. Rapid evolution of sexual signals in sympatric Calopteryx damselflies: reinforcement or “Noisy-neighbor” ecological character displacement. Journal of Evolutionary Biology. 20:1637-1648. *-both authors contributed equally

Mullen, S. P., Mendelson, T. C., Schal, C., & K. L. Shaw. 2007. Rapid evolution of cuticular hydrocarbons in a species radiation of acoustically diverse Hawaiian crickets (Gryllidae: Trigonidiinae: Laupala). Evolution 61(1):223-231.

Danley, P. D., S. P. Mullen, F. Lui, J. Quakenbush, & K. L. Shaw. 2007. Generation and analysis of large scale cricket expressed sequence tags (EST’s) derived from a normalized, nerve chord cDNA library. BMC Genomics 8:109.

Reudink, M. W., S. G. Mech, S. P. Mullen, & R. L. Curry. 2007. Structure and dynamics of a chickadee hybrid zone. The Auk 124:463-478.

Mullen, S. P.  2006. Wing pattern evolution and the origins of mimicry among North American admiral butterflies (Nymphalidae: Limenitis). Molecular Phylogenetics and Evolution. 39 (3):747-758.

Lovejoy, N.*, Mullen, S. P.*, Sword, G. A., Chapman, R. F., & R. G. Harrison. 2006. Ancient trans-Atlantic flight explains locust biogeography. Proceedings of the Royal Society Biological Series B. 273:767-774. *-both authors contributed equally

Book Review

 "Conservation and the Genetics of Populations", Reviewed for Copeia 2007.

Field work on the Big Island of Hawaii in collaboration with Dr. Kerry Shaw, Cornell University

top