Naturally occurring hybrid zones have been studied for decades because inferences can be drawn from observable patterns of genetic variation to characterize underlying ecological and evolutionary phenomena such as selection across environmental gradients, frequency-dependent selection against hybrids, and Wright’s shifting balance theory. The dynamics of hybrid zones have also been studied to evaluate the stability of range boundaries.  


Members of the lab have carried out research on the stability and formation of butterfly hybrid zones in Central and South America. This research continues the long standing (100+ years) tradition of utilizing tropical butterflies (such as Heliconius erato) as model species for studying ecological and evolutionary phenomena. By integrating traditional and molecular genetic approaches with GIS analysis of satellite imagery, it has been possible to demonstrate that concordant hybrid zones at parapatric range boundaries idiosyncratically shift in response to regional land cover change such as deforestation. Unlike studies of shifting range boundaries that focus almost entirely on distributional data, this approach facilitates understanding of how genetic and ecological processes interact to alter species distributions.

 

The stability and formation of

Neotropical butterfly hybrid zones

Related links

  1. •www.heliconius.org

  2. •www.stri.org

  3. •Bermingham Lab- http://striweb.si.edu/bermingham/

  4. •McMillan Lab- http://www4.ncsu.edu/~womcmill/index.html

  5. •Jiggins Lab- http://heliconius.cap.ed.ac.uk/butterfly/home.php

  6. •Mallet Lab- http://www.ucl.ac.uk/taxome/jim/

  7. •Gilbert Lab- http://uts.cc.utexas.edu/%7Egilbert/

  8. •Joron Lab- http://zeldia.cap.ed.ac.uk/joron/

  9. •Reed Lab- http://reedlab.org

  10. •Instituto de Genetica- p://cienciasbiologicas.uniandes.edu.co/genetica/

  11. •ButterflyBase- http://heliconius.cap.ed.ac.uk/butterfly/db/

  1. •Blum, M.J. 2002. Rapid motion of a Heliconius hybrid zone: Evidence for phase III of Wright’s shifting balance theory? Evolution 56 (10): 1992-1998.

Abstract- It has been proposed that a moving hybrid zone can be a mechanism for the spread of adaptive traits in

phase III of Wright’s shifting balance model of evolution. Here I present an example of a moving hybrid zone in

warningly colored Heliconius butterflies, a system which is considered to be a possible case of shifting balance

evolution. Having moved approximately 47 km in 17 years, the hybrid zone shift has led to the H. erato hydara color

pattern rapidly displacing the adjacent H. erato petiverana pattern. The movement is potentially due to dominance

drive augmenting a slight selective advantage of H. erato hydara over H. erato petiverana, which is largely consistent

with theoretical conditions favoring the success of phase III.

  1. •Dasmahapatra, K.K., Blum, M.J., Aiello, A., Hackwell, S., Davies, N., Bermingham, E.P., Mallet, J. 2002. Inferences from a rapidly moving hybrid zone. Evolution 56(4): 741-753.

Abstract- Anartia fatima and Anartia amathea (Lepidoptera: Nymphalidae) are sister taxa whose ranges abut in a narrow hybrid zone in eastern Panama. At the center of the zone, hybrids are abundant, although deviations from

Hardy-Weinberg and linkage disequilibria are strong, due in part to assortative mating. We measured differences

across the zone in four wing color-pattern characters, three allozyme loci, and mitochondrial haplotype. Wing pattern,

allozyme, and mitochondrial clines were coincident (i. e. , had the same positions) and concordant (i. e. , all markers

had similar cline shapes, about 28 km wide). Repeated samples demonstrated that the hybrid zone has been moving

eastwards at an average rate of 2. 5 km/year over the past 20 years, accompanied by an equivalent movement of the

mtDNA cline. No introgression of mtDNA haplotypes were found in the ‘‘wake’’ of the moving cline, as might be

expected for a neutral marker. The concordance of morphological and mtDNA clines between 1994 and 2000, in spite of hybrid zone movement, suggests strong epistasis between the mitochondrial genome and nuclear loci. Cline movement is achieved mainly by pure fatima immigrating into amathea populations; hybrids had little effect, and were

presumably outcompeted by fitter pure fatima genotypes. This movement can be explained if random dispersal of 7–

19 km. gen 1/ 2 is coupled with a competitive advantage to A. fatima genomes of 2–5%. Hybrid zone motion is equivalent

to Phase III of Wright’s shifting balance. Hybrid zone movement has rarely been considered likely in the past, but

our results show that it may be more important in biogeography and evolution than generally realized.

  1. •Blum, M.J.  2008. Ecological and genetic associations across a Heliconius hybrid zone. Journal of Evolutionary Biology 21(1): 330-341.

Abstract- Differences in habitat use can bridge early and late stages of speciation by initiating assortative mating.  Heliconius color pattern races might select habitats over which each color pattern confers a relative fitness advantage because signal efficacy of wing patterns can vary by environment. If so, then habitat preferences would serve to promote the evolution of mimetic color patterns for mate choice. Here I compare color pattern genotype and phenotype frequencies to environmental variation across the H. erato hydara x H. erato erato hybrid zone in French Guiana to determine whether races exhibit habitat preferences. I found that genotype and phenotype frequencies correspond to differences in land cover moreso than to other environmental factors. Temporal shifts in color pattern genotypes, phenotypes and forest cover were also found to covary at individual sample sites, which further suggests that H. erato races differ in habitat use and that habitat preferences may promote speciation among Heliconius butterflies. 

  1. •Blum, M.J., Bermingham, E.P., Dasmahapatra, K.K. 2003.  A molecular phylogeny of the neotropical butterfly genus Anartia (Lepidoptera: Nymphalidae). Molecular Phylogenetics and Evolution 26: 46-55.

Abstract- While Anartia butterflies have served as model organisms for research on the genetics of speciation, no phylogeny has been published to describe interspecific relationships. Here, we present a molecular phylogenetic analysis of Anartia species relationships, using both mitochondrial and nuclear genes. Analyses of both data sets confirm earlier predictions of sister species pairings based primarily on genital morphology. Yet both the mitochondrial and nuclear gene phylogenies demonstrate that Anartia jatrophae is not sister to all other Anartia species, but rather that it is sister to the Anartia fatima–Anartia amathea lineage. Traditional biogeographic explanations for speciation across the genus relied on A. jatrophae being sister to its congeners. These explanations invoked allopatric divergence of sister species pairs and multiple sympatric speciation events to explain why A. jatrophae flies

alongside all its congeners. The molecular phylogenies are more consistent with lineage divergence due to vicariance, and range expansion of A. jatrophae to explain it’s sympatry with congeners. Further interpretations of the tree topologies also suggest how morphological evolution and eco-geographic adaptation may have set species range boundaries.

  1. •Flanagan, N., Blum, M.J., Davison, A.., Alamo, M., Albarran, R., Faulhaber, K., Peterson, E., McMillan, W.O. 2002. Characterizaton of microsatellite loci in neotropical Heliconius butterflies. Molecular Ecology Notes 2(4): 398-401 (cover article)

Abstract- The Heliconius butterflies offer exceptional opportunities for the study of the ecology and evolution of mimicry. Despite previous reports of difficulties in the development of microsatellite loci in Lepidoptera, we characterize 15 polymorphic loci in H. erato that show promise for genetic mapping and population studies in this and other species. Levels of variation were high, in both numbers and size ranges of alleles. The loci showed broad amplification success across the genus and in two other genera. All loci that amplified in a population of H. melpomene were polymorphic.