June 13 2006: Drs. Arjan Borghuis
June 13th, 2006
Drs. Arjan Borghuis
(Department of Molecular Ecology, Radboud University)
Evolution at work: will host races ever become species?
Abstract
Darwin (1859) was the first to describe speciation as an ecological process based on adaptation and divergent natural selection, either in sympatry or in allopatry. But, the contrasting ideas of Walsh (1864) and Wagner (1841) have set the scene for a still ongoing debate on the way species can evolve. The allopatric model of Wagner, assumes that speciation is only possible when physical barriers prevent interbreeding between allopatrically occurring individuals of a species. In contrast, the model of Walsh describes a sympatric model of speciation based on intrinsic barriers that prevent interbreeding. Ever since, many have favoured the allopatric model of speciation, later worked out by Mayr, whereas others, among them many that are studying herbivorous insects, have favoured the sympatric model, later worked out by Bush. Bush proposed several steps in the formation of a new species by host switching. In his model host races are the first step towards sympatric ecological speciation and the evolution of host fidelity can finally result in reproductive isolation.
Galerucella nymphaeae, the water lily leaf beetle, offers great potential for studying sympatric ecological speciation. Populations of this leaf beetle species occupy moist habitats and feed on a wide variety of host plants. These host associated populations are genetically differentiated, although they are capable of successful reproduction.
To reconstruct the evolution of host association we studied the phylogenetic relationships between members of the nymphaeae species complex and between other Galerucella species. Phylogeographic analysis of the nymphaeae species complex gave insight in the past population genetic processes, such as glacial refugia and post glacial colonization. We furthermore analyzed current population genetics, such as population differentiation and gene flow and we are still in the process of a large scale paternity analysis to estimate the amount of assortative mating between the host associated populations. These past and current population genetics together with life history characteristics such as larval size and survival, and host associated phenotypic plasticity for several characters combined with the results obtained previously by Pappers make a strong case for sympatric ecological differentiation. It shows clear results of host adaptation and positive assortative mating. This prevents high levels of gene flow and facilitates further differentiation that may or may already have result(ed) in speciation.
Relevant publications
Pappers SM, Van der Velde G, Ouborg NJ, et al.
Genetically based polymorphisms in morphology and life history associated with putative host races of the water lily leaf beetle, Galerucella nymphaeae
EVOLUTION 56 (8): 1610-1621 AUG 2002
Pappers SM, van der Velde G, Ouborg NJ
Host preference and larval performance suggest host race formation in Galerucella nymphaeae
OECOLOGIA 130 (3): 433-440 FEB 2002
Pappers SM, van Dommelen H, van der Velde G, et al.
Differences in morphology and reproductive traits of Galerucella nymphaeae from four host plant species
ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA 99 (2): 183-191 MAY 2001
Curriculum vitae
I started my study Biology at Wageningen University in 1997, where I obtained my Bachelor’s in 1998. During my masters, I specialized in topics that interested me most, such as Population Biology, Evolutionary Ecology and Molecular Ecology. I performed two Master theses, the first on Molecular ecology at the department of Entomology at Wageningen University. Here, I studied the mitochondrial DNA of Trichogramma parasitic wasps in the research group of Richard Stouthamer. We looked at genetic differentiation and mitochondrial characters for species identification between two sibling species that are morphological similar but reproductively isolated. This work resulted in a publication in Biocontrol (Borghuis et al. 2001). I, furthermore, studied mitochondrial DNA characters to obtain indirect evidence for horizontal transmission of the endo-symbiotic bacteria Wolbachia in two other closely related Trichogramma species. Both Wolbachia and mitochondria are cytoplasmatically inherited factors and are transferred from mother to offspring (vertical transmission). An infection with Wolbachia will result in an association between a particular mitochondrial haplotype and Wolbachia. Indirect evidence for horizontal transmission can be obtained if this association is disrupted.
My other master thesis was at the faculty of Evolutionary Biology at the University of California in Riverside. Here I studied the life history strategy of a life bearing fish that has maternal provisioning (like the placenta of mammals) and superfetation (the initiation of a new brood before the first is born) in the group of David Reznick. Furthermore, I studied the phylogenetic relationships between members of the genus Poeciliidae (life bearing fishes) in the group of Mark Springer to determine whether maternal provisioning and/or superfetation have evolved multiple times in this genus.
In 2002 I obtained my Master’s degree and started as a Graduate student at Radboud University Nijmegen. My thesis is tilted: “Evolution at work: will host races ever become species? The driving mechanisms for speciation in the Galerucella nymphaeae complex” and in this seminar I will present some of my results.
