Molecular Ecology and Evolution
Fonnemann, Brandon J. , Mason-Gamer, Roberta .
Molecular phylogenetic analysis of Coreopsis nuecensoides and C. nuecensis: a putative progenitor-derivative species pair.
The classical model of speciation frames populations within the context of allopatry in which gene flow is significantly reduced or effectively eliminated. However, other modes of speciation may be more common than originally thought, yet remain difficult to detect in comparison to species originating from gradual divergence. Locally isolated, peripheral populations of a species can rapidly diverge due to radical genotypic and phenotypic changes associated with genetic drift and a heightened intensity of selection. This mode of speciation differs from allopatric speciation in that changes associated with speciation are more evident in the derivative, while the progenitor remains relatively unaffected. Coreopsis nuecensoides and C. nuecensis are narrowly distributed endemics of southeastern Texas with overlapping ranges but no observed incidences of co-occurrence. They are distinguished from one another by minor morphological and life history traits. Coreopsis nuecensoides has a chromosomal count of n=9 or 10 and C. nuecensis has n=6 or 7, while the remaining species in Coreopsis sect. Coreopsis have n=13. Hybridization between the two species results in sterile hybrids. Coreopsis nuecensis is nearly endemic to a narrow strip (ca. 10 x 450 miles) of fine, porous sandy soil known as the Carrizo Sands formation, whose composition directly correlates to its water retention properties. This formation spans from northeast to southcentral Texas and has been described as an edaphic island generating considerable diversification. Coreopsis nuecensoides is found in southeastern Texas including areas adjacent to the Carrizo Sands. Past studies examining distribution, cytogenetics, allozyme data, cpDNA restriction sites, and life history traits of C. nuecensoides and C. nuecensis were consistent with a progenitor-derivative relationship between them. In contrast, preliminary data from a sample of 7-8 individuals/species, based on three nuclear markers - A25 (putative peroxisomal membrane protein, 400bp), A39 (putativeglucose-6-phosphate/phosphate-translocator, 500bp), and A31 (unknown function,500bp) - revealed considerable variation in C.nuecensis inconsistent with predicted bottlenecking associated with karyotype change in small populations suggesting a single phylogenetic species. Five populations (5 individuals/population) were subsequently sampled from each species to further elucidate the phylogenetic relationship. Three nuclear markers, along with cpDNA sequence data were utilized to see if the presumed derivative showed a genetic signal consistent with rapid adaptation and speciation onto the Carrizo Sands formation.
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1 - University of Illinois at Chicago, Department of Biological Sciences, 845 West Taylor St., MC 066, Chicago, IL, 60607-7060, USA
2 - University Of Illinois Chicago, DEPT. OF BIOLOGICAL SCIENCES (M/C 066), 845 W. TAYLOR ST., CHICAGO, IL, 60607, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Union B/Hyatt
Date: Monday, July 9th, 2012
Time: 3:00 PM