Please direct questions and comments to: Hope
Hollocher
Morphological Divergence:
Insect pigmentation is a very promising model system for understanding the genetic and developmental basis of morphological change. Pigmentation is under direct selection in response to different ecological conditions and evolves rapidly in many different organisms. Generally speaking, 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. Our research focuses on the evolution of abdominal pigmentation among 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 Central and South American mainland as well. Such clines imply the action of natural selection operating 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 the lab aims to unravel the development, evolution and adaptive significance of pigmentation in these Caribbean and South American Drosophila.
Reproductive Divergence:
When Sturtevant first discovered that Drosophila melanogaster was
actually
two closely related species, Drosophila melanogaster and Drosophila
simulans,
he was thrilled with the prospect of being able to use these two
species
to understand the genetic basis of species differences, in particular,
reproductive isolation. Although the prospects were high, reality
turned
out to be not so kind. The differences that had evolved between these
two
species proved to be genetically intractable since crosses yielded
offspring
that were either completely sterile or inviable (a geneticist’s
nightmare).
With the recent discovery of naturally occurring strains that rescue
inviability
and sterility defects of hybrids, we are now able to fully realize
Sturtevant’s
original desire to use the genetic tools available in a species such as
D. melanogaster to understand the evolution of reproductive isolation.
This project uses a combined developmental, molecular, and evolutionary
approach to look at how germline development has diverged between the
two
species leading to hybrid sterility. Most recently we have turned to
microarray analysis to target
genes involved in reproductive isolation.
We use immunofluorescence and confocal microscopy to track
germ cell migration during early stages of Drosophila embryonic
development.
In this image, wild type germ cells destined for larval gonads are
colored
bright green.
Landscape
Epidemiology:
In collaboration with
Agustin Fuentes in Anthropology,
my lab examines how spatial and social
structuring of natural populations of macaques, Macaca fascicularis, are important
for understanding biodiversity and disease dynamics on the Indonesian island of Bali. In
spite of dramatic changes to overall forest cover on the island over
the last few centuries, a large and self-sustaining population of
macaques remains in a high-density human environment. Co-existence of
humans and macaques appears possible because of the high resource
availabilty associated with agricultural-religious land-use patterns in
Bali. Given the distribution of macaque sites across the island and
their potential interconnection via riverine corridors, macaques are
exploiting the human landscape, moving along riverine corridors and
acting as units of gene flow across these sites/populations. Given this
connectivity, pathogens, along with genetic markers, may be transported
in this same pattern to differing macaque sites. Our research combines
population genetics, evolutionary biology, anthropology and
virology/parasitology to try to link individual infection to how
disease flows through macaque host populations and so influences
disease dynamics.
Hollocher, H. 1996. Island hopping in Drosophila: patterns and processes. Philosophical Transactions of the Royal Society: Biological Sciences 351:735-743.
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.
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.
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.
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 Evolution18:384-392.
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 57:2566-2579.
Wilder,
J. A., E. G. Dyreson, R. J. W. O’Neill, M. L. Spangler, R. Gupta, A. S.
Wilder, and H. Hollocher 2004.
Contrasting
modes of natural selection acting on pigmentation genes in the
Drosophila
dunni subgroup. Journal of Experimental Zoology (Mol Dev Evol)
302B:1-14.
To contact lab: hope.hollocher.1@nd.edu
Last updated: 12/09/05
Return to Hollocher Lab Members Page
Return to Hollocher Lab Home Page