Reproductive isolation is just one aspect of speciation that attracts my attention. From a developmental point of view it is also important to determine how species evolve differences in morphology as well and insect pigmentation is one of the most promising model systems for understanding the genetic and developmental basis of morphological change. In Drosophila, pigmentation is well understood from a genetic and biochemical point of view. As a morphological trait, it is relatively simple to reconstruct as compared to three-dimensional structures. Pigmentation is also under direct selection in response to different ecological conditions; therefore, it is a trait that evolves rapidly. The second project in my lab focuses on the evolution of abdominal pigmentation between different species of the Drosophila cardini group. In this group, changes in abdominal pigmentation show a regular cline along the arc of the Caribbean islands with lighter species occurring in Puerto Rico and progressively darker species occurring southward through the Lesser Antilles. Parallel clines in abdominal pigmentation exist within various species in this group on the South American mainland as well. Such clines imply the action of natural selection during differentiation and make for interesting comparisons between the evolutionary processes affecting pigmentation differentiation on the islands (where gene flow between islands is absent) versus the mainland (where populations still exchange individuals regularly). Work in my lab focuses on unraveling the development, evolution and adaptive significance of pigmentation in the D. cardini group. What genetic differences underlie differences in pigmentation? Do differences in pigmentation correspond to changes in regulatory regions or coding regions of these genes? Are the same loci responsible for similar changes in pigmentation in all lineages in this group? To answer these questions, we are analyzing patterns of sequence variation from multiple genes involved in pigmentation and determining how these patterns correspond to changes in the developmental control of melanin synthesis and deposition in the different species of the group.
 

Selected Publications
Hollocher, H. and C.-I Wu. 1996. The genetics of reproductive isolation in the Drosophila simulans clade: X vs. autosomal effects and male vs. female effects. Genetics 143:1243-1255.

Hollocher, H., C.-T. Ting, F. Pollack, and C.-I Wu. 1997. Incipient speciation by sexual isolation in Drosophila melanogaster: Variation in mating preference among natural isolates. Evolution 51: 1175-1181.

Hollocher, H., C.-T. Ting, M.-L. Wu, and C.-I Wu. 1997. Incipient speciation by sexual isolation in Drosophila melanogaster: Extensive genetic divergence without reinforcement. Genetics 147:1191-1201.

Hollocher, H. 1998a. Island hopping in Drosophila: genetic patterns vs. evolutionary processes. pp. 124-141. In: Evolution on Islands. Edited by P. R. Grant. Oxford University Press, Oxford.

Wu, C.-I and H. Hollocher. 1998. Subtle is nature: the genetics of differentiation and speciation. pp. 339-351. In: Endless Forms: Species and Speciation. Edited by D. J. Howard and S. H. Berlocher. Oxford University Press, Oxford.

Hollocher, H. 1998b. Reproductive isolation in Drosophila: how close are we to untangling the genetics of speciation? Current Opinion in Genetics & Development 8:709-714. 

Colegrave, N., H. Hollocher, K. Hinton, and M. G. Ritchie. 2000. The courtship song of African Drosophila melanogaster. Journal of Evolutionary Biology 13:143-150. 

Hollocher, H. 2000. Theories of speciation. Vol. 5, pp. 383-396. In: The Encyclopedia of Biodiversity. Edited by S. A. Levin. Academic Press, NY.

Hollocher, H., K. Agopian, J. Waterbury, R. W. O'Neill, and A. W. Davis 2000. Characterization of defects in adult germline development and oogenesis of sterile and rescued female hybrids in crosses between Drosophila simulans and Drosophila melanogaster. Journal of Experimental Zoology (Mol Dev Evol) 288:205-218.

Hollocher, H., J. L. Hatcher, and E. G. Dyreson 2000a. Evolution of abdominal pigmentation differences between species in the Drosophila dunni subgroup. Evolution 54:2046-2056.

Hollocher, H., J. L. Hatcher, and E. G. Dyreson 2000b. Genetic and developmental analysis of abdominal pigmentation differences across species in the Drosophila dunni subgroup. Evolution 54:2057-2071.

Wilder, J. A. and H. Hollocher 2001. Mobile elements and the genesis of microsatellites in Dipterans. Molecular Biology and Evolution 18:384-392.

Wilder, J. A., T. Diaz, R. W. O’Neill, J. Kenney, and H. Hollocher 2002. Characterization and isolation of novel microsatellites from the Drosophila dunni subgroup. Genetical Research, Cambridge 80:177-185.

Sainz, A., J. A. Wilder, M. R. Wolf, and H. Hollocher 2003. Drosophila melanogaster and D. simulans rescue strains produce fit offspring, despite divergent centromere-specific histone alleles. Heredity 91:28-35.

Wilder, J. A. and H. Hollocher 2003. Recent radiation of endemic Caribbean Drosophila of the dunni subgroup inferred from multilocus DNA sequence variation (Evolution, in press).