Claudio C. Ramírez

Bio: Claudio C. Ramírez is an academic researcher from University of Talca. The author has contributed to research in topics: Aphid & Aphididae. The author has an hindex of 18, co-authored 66 publications receiving 1090 citations. Previous affiliations of Claudio C. Ramírez include University of Chile & University of Oxford.

Cross-species amplification of microsatellite loci in aphids: assessment and application

Abstract: Despite the relative ease of isolating microsatellites, their development still requires substantial inputs of time, money and expertise For this reason there is considerable interest in using existing microsatellites on species from which markers were not cloned We tested cross-species amplification of 48 existing aphid loci in species of the following genera: Aphidinae: Aphidini: Aphis and Rhopalosiphum ; Aphidinae: Macrosiphini: Acyrthosiphum , Brevicoryne , Diuraphis , Illinoia , Macrosiphoniella , Macrosiphum , Metopeurum , Metapolophium , Myzus , Phorodon , Sitobion and Uroleucon and Neuquenaphidinae: Neuquenaphis Our results show cross-species application of known microsatellite loci is a highly promising source of codominant markers for population genetic and evolutionary studies in aphids

Host range expansion of an introduced insect pest through multiple colonizations of specialized clones

Abstract: Asexuality confers demographic advantages to invasive taxa, but generally limits adaptive potential for colonizing of new habitats. Therefore, pre-existing adaptations and habitat tolerance are essential in the success of asexual invaders. We investigated these key factors of invasiveness by assessing reproductive modes and host-plant adaptations in the pea aphid, Acyrthosiphon pisum, a pest recently introduced into Chile. The pea aphid encompasses lineages differing in their reproductive mode, ranging from obligatory cyclical parthenogenesis to fully asexual reproduction. This species also shows variation in host use, with distinct biotypes specialized on different species of legumes as well as more polyphagous populations. In central Chile, microsatellite genotyping of pea aphids sampled on five crops and wild legumes revealed three main clonal genotypes, which showed striking associations with particular host plants rather than sampling locations. Phenotypic analyses confirmed their strong host specialization and demonstrated parthenogenesis as their sole reproductive mode. The genetic relatedness of these clonal genotypes with corresponding host-specialized populations from the Old World indicated that each clone descended from a particular Eurasian biotype, which involved at least three successful introduction events followed by spread on different crops. This study illustrates that multiple introductions of highly specialized clones, rather than local evolution in resource use and/or selection of generalist genotypes, can explain the demographic success of a strictly asexual invader.

The invasion route for an insect pest species: the tobacco aphid in the New World.

Abstract: Biological invasions are rapid evolutionary events in which populations are usually subject to a founder event during introduction followed by rapid adaptation to the new environment. Molecular tools and Bayesian approaches have shown their utility in exploring different evolutionary scenarios regarding the invasion routes of introduced species. We examined the situation for the tobacco aphid, Myzus persicae nicotianae, a recently introduced aphid species in Chile. Using seven microsatellite loci and approximate Bayesian computation, we studied populations of the tobacco aphid sampled from several American and European countries, identifying the most likely source populations and tracking the route of introduction to Chile. Our population genetic data are consistent with available historical information, pointing to an introduction route of the tobacco aphid from Europe and/or from other putative populations (e.g. Asia) with subsequent introduction through North America to South America. Evidence of multiple introductions to North America from different genetic pools, with successive loss of genetic diversity from Europe towards North America and a strong bottleneck during the southward introduction to South America, was also found. Additionally, we examined the special case of a widespread multilocus genotype that was found in all American countries examined. This case provides further evidence for the existence of highly successful genotypes or ‘superclones' in asexually reproducing organisms.

Population Genetic Structure of Codling Moth (Lepidoptera: Tortricidae) from Apple Orchards in Central Chile

Abstract: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is the main pest of pome fruits worldwide. Despite its economic importance, little is known about the genetic structure and patterns of dispersal at the local and regional scale, which are important aspects for establishing a control strategy for this pest. An analysis of genetic variability using microsatellites was performed for 11 codling moth populations in the two major apple (Malus domestica Borkh) cropping regions in central Chile. Despite the geographical distances between some populations (185 km), there was low genetic differentiation among populations (FST 0.002176), with only slight isolation by distance. Only 0.2% of the genetic variability was found among the populations. Geographically structured genetic variation was independent of apple orchard management (production or abandoned). These results suggest a high genetic exchange of codling moth between orchards, possibly mediated by human activities related to fruit production.

Genetic Data Analysis

Abstract: LEARNING The objectives of BIOS 781 are to present: OBJECTIVES: 1. basic population and quantitative genetic principles, including classical genetics, chromosomal theory of inheritance, and meiotic recombination 2. an exposure to QTL mapping methods of complex quantitative traits and linkage methods to detect co-segregation with disease 3. methods for assessing marker-disease linkage disequilibrium, including case-control approaches 4. methods for genome-wide association and stratification control.

Natural selection in action during speciation

Abstract: The role of natural selection in speciation, first described by Darwin, has finally been widely accepted. Yet, the nature and time course of the genetic changes that result in speciation remain mysterious. To date, genetic analyses of speciation have focused almost exclusively on retrospective analyses of reproductive isolation between species or subspecies and on hybrid sterility or inviability rather than on ecologically based barriers to gene flow. However, if we are to fully understand the origin of species, we must analyze the process from additional vantage points. By studying the genetic causes of partial reproductive isolation between specialized ecological races, early barriers to gene flow can be identified before they become confounded with other species differences. This population-level approach can reveal patterns that become invisible over time, such as the mosaic nature of the genome early in speciation. Under divergent selection in sympatry, the genomes of incipient species become temporary genetic mosaics in which ecologically important genomic regions resist gene exchange, even as gene flow continues over most of the genome. Analysis of such mosaic genomes suggests that surprisingly large genomic regions around divergently selected quantitative trait loci can be protected from interrace recombination by "divergence hitchhiking." Here, I describe the formation of the genetic mosaic during early ecological speciation, consider the establishment, effects, and transitory nature of divergence hitchhiking around key ecologically important genes, and describe a 2-stage model for genetic divergence during ecological speciation with gene flow.

A continuum of genetic divergence from sympatric host races to species in the pea aphid complex

Abstract: Sympatric populations of insects adapted to different host plants, i.e., host races, are good models to investigate how natural selection can promote speciation in the face of ongoing gene flow. However, host races are documented in very few model systems and their gradual evolution into good species, as assumed under a Darwinian view of species formation, lacks strong empirical support. We aim at resolving this uncertainty by investigating host specialization and gene flow among populations of the pea aphid complex, Acyrthosiphon pisum. Genetic markers and tests of host plant specificity indicate the existence of at least 11 well-distinguished sympatric populations associated with different host plants in Western Europe. Population assignment tests show variable migration and hybridization rates among sympatric populations, delineating 8 host races and 3 possible species. Notably, hybridization correlates negatively with genetic differentiation, forming a continuum of population divergence toward virtually complete speciation. The pea aphid complex thus illustrates how ecological divergence can be sustained among many hybridizing populations and how insect host races blend into species by gradual reduction of gene flow.