65 research outputs found
Genetic differentiation among host-associated Alebra leafhoppers (Hemiptera: Cicadellidae)
The limited importance ascribed to sympatric speciation pro cesses via host race formation is partially due to the few
cases of host races that have been reported among host
populations. This work sheds light on the taxonomy of Alebra
leafhoppers and examines the possible existence of host
races among host-associated populations. The species of
this genus show varying degrees of host association with
deciduous trees and shrubs and, frequently, host popu lations of uncertain taxonomic status coexist and occasion ally become pests. Allozyme electrophoresis of 21 Greek
populations including sympatric, local and geographically
distant samples collected on 13 different plant species, show
that they represent at least five species: A. albostriella
Falle´n, A. viridis (Rey) (sensu Gillham), A. wahlbergi Bo Keywords: host races; leafhoppers; sympatric speciation; sibling species; allozymes; Alebra
Introduction
Sympatric speciation is a controversial subject in evol utionary biology (see Mayr, 1963; Futuyma and Mayer,
1980; Paterson, 1981; Via, 2001). One of the reasons for
this controversy is that sympatric speciation seems to be
an extremely rare phenomenon occurring only in very
few groups of taxa, represented chiefly by phytophagous
insects (Tauber and Tauber, 1977; Menken, 1981; Wood,
1993; Emelianov et al, 1995; Via, 1999; Finchak et al, 2000;
Craig et al, 2001). The limited number of reported cases
among organisms with sexual reproduction can be at
least partially attributed to the fact that taxa undergoing
sympatric speciation events must fulfill very restrictive
biological and ecological requirements.
Most sympatric speciation models demand that there is
intraspecific genetic variation in traits that differentially
affect the fitness of individuals that colonise new habitats
or hosts (Dieckman and Doebeli, 1999; Hawthorne and
Via, 2001 but see Higashi et al, 1999 and Takimoto et al,
2000). They assume that selection acting on these traits
can prevent genetic exchange between populations
(Bush, 1975; Tauber and Tauber, 1977; Diehl and Bush,
1989). In phytophagous insects, this means that host pref erences must be genetically determined and mating
should occur on the host (Bush, 1975; Diehl and Bush,
Correspondence: D Aguin-Pombo, Department of Biology, University of
Madeira, Campus Universitario da Penteada, 9000 Funchal, Madeira,
Portugal. E-mail: aguin uma.pt
Received 12 December 2000; accepted 13 December 2001
heman and two new species. Of these, one is associated
to Quercus frainetto and other is specific to Crataegus spp.
Significant genetic differences among sympatric and local
host populations were found only in A. albostriella, between
populations on Turkey oak, beech and common alder. It is
suggested that the last two of these host populations may
represent different host races. The results show that both
the host plant and geographical distance affect the patterns
of differentiation in the genus. The formation of some spec ies seems to have been the result of allopatric speciation
events while, for others, their origin can be equally explained
either by sympatric or allopatric speciation.info:eu-repo/semantics/publishedVersio
Exploring Species Limits in Two Closely Related Chinese Oaks
Background. The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches. [br/]
Methodology/Principal Findings. Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.[br/]
Main Conclusions/Significance. All results based on SSRs and AFLPs reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors
A set of primers for the amplification of chloroplast microsatellites in Quercus
International audienceThe increase in demand for the certification of oak seed lots, as well as control of the geographical origin of oak wood, has led us to develop powerful genetic markers permitting us to discriminate among provenance regions. With the aim of detecting new chloroplast variants, we have identified 17 potential cpSSRs motifs from available oak sequences and tested their variability among French oak populations. Six loci were polymorphic at the intraspecific level in Quercus petraea and Q. robur . Moreover, conservation of the primer pairs was checked on a set of 21 forest tree species and they were all shown to work well on several Quercus species, and even within Fagacaea
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