Julie Turgeon - Academia.edu (original) (raw)

Papers by Julie Turgeon

The American Naturalist, 2005

the evolution of mate choice in generating reproductive isolation as species recolonized the land... more the evolution of mate choice in generating reproductive isolation as species recolonized the landscape following deglaciation. These analyses suggest that recent climate fluctuations resulted in radiations driven by similar combinations of speciation processes acting in different lineages.

Molecular Ecology Resources, 2009

Identifying and estimating individual and/or population admixture is a very common objective in e... more Identifying and estimating individual and/or population admixture is a very common objective in evolution and conservation biology. There are many situations where samples from one or many of the putatively hybridizing entities are not available or easily identified. Here we describe FLOCK, a new method especially designed to provide spatial and/or temporal admixture maps in the absence of one or several source samples. FLOCK is a non-Bayesian method and therefore differs substantially from previous clustering algorithms. Its working principle is repeated re-allocation of all collected specimens (total sample) to the k subsamples, each re-allocation being more effective than the previous one in attracting genetically similar individuals. This snowball effect, more formally referred to as a positive feedback mechanism, makes FLOCK an efficient and quick sorting process. The usage of FLOCK is illustrated with two empirical situations which have been thoroughly analysed previously with other approaches. A number of simulations were run to better assess the power of the FLOCK algorithm. Performance comparisons were made between the FLOCK and Structure algorithms. When non-negligible numbers of pure genotypes were present, the two performed equally well. However, FLOCK proved significantly more powerful in the absence of pure genotypes. Moreover, FLOCK showed more potential for fast processing. Run times were shown to increase linearly with size of total sample and with size of k, the number of reference samples from which admixture mapping is performed.

Molecular Ecology, 2001

The comparative molecular phylogeography of regional fish fauna has revealed the wide distributio... more The comparative molecular phylogeography of regional fish fauna has revealed the wide distribution of young clades in freshwater fishes of formerly glaciated areas as well as interspecific incongruences in their refugial origins and recolonization routes. In this study, we employed single-strand conformation polymorphism (SSCP) and sequence analyses to describe mitochondrial DNA (mtDNA) polymorphism among 27 populations of the lake cisco ( Coregonus artedi ) from its entire range of distribution in order to evaluate the hypothesis of dual glacial refuges proposed by Bernatchez & Dodson against the traditional view that this species is solely of Mississippian origin. Results indicate that this taxon is composed of two closely related groups that are widely distributed and intermixed over most of the sampled range. The estimated level of divergence (0.48%), the contrast in the geographical distribution of each group, as well as the general distribution of C. artedi in North America together support the hypothesis that one group dispersed from a Mississippian refuge via the proglacial lakes, while the other is of Atlantic origin and also took advantages of earlier dispersal routes towards eastern Hudson Bay drainages. However, the signal of past range fragmentation revealed by a nested clade analysis was weak, and did not allow to formally exclude the hypothesis of a single Mississippian origin for both lineages. Comparisons with the phylogeographic patterns of other Nearctic freshwater fishes suggest that the salinity tolerance and thermal sensitivity of lake cisco may have been determinant for its extensive postglacial dispersal. The presence or co-occurrence of sympatric or allopatric eco/morphotypes were not found to be necessarily associated with the presence of both haplotype groups.

Journal of Biogeography, 2010

Present species ranges are the result of an array of historical contingencies . During the last g... more Present species ranges are the result of an array of historical contingencies . During the last glacial-interglacial cycle, temperate and boreal taxa experienced major glacial range contraction into refugia and post-glacial expansion into present-day ranges. For a given tree species, current range boundaries correspond to the maximum Holocene ABSTRACT Aim The main objective of this study was to investigate the origin of white spruce (Picea glauca) range discontinuities in eastern North America. A first analysis aimed at uncovering the glacial origin and post-glacial migration route of white spruce in the eastern part of the range. A second analysis aimed at evaluating whether disjunct white spruce populations in central Québec result from a recent expansion or are remnant stands following a northern range contraction.

Evolutionary Applications, 2012

Adaptive evolution is currently accepted as playing a significant role in biological invasions. A... more Adaptive evolution is currently accepted as playing a significant role in biological invasions. Adaptations relevant to invasions are typically thought to occur either recently within the introduced range, as an evolutionary response to novel selection regimes, or within the native range, because of long-term adaptation to the local environment. We propose that recent adaptation within the native range, in particular adaptations to human-altered habitat, could also contribute to the evolution of invasive populations. Populations adapted to human-altered habitats in the native range are likely to increase in abundance within areas frequented by humans and associated with human transport mechanisms, thus enhancing the likelihood of transport to a novel range. Given that habitats are altered by humans in similar ways worldwide, as evidenced by global environmental homogenization, propagules from populations adapted to human-altered habitats in the native range should perform well within similarly human-altered habitats in the novel range. We label this scenario 'Anthropogenically Induced Adaptation to Invade'. We illustrate how it differs from other evolutionary processes that may occur during invasions, and how it can help explain accelerating rates of invasions.

Evolution, 2001

Classical models of the spatial structure of population genetics rely on the assumption of migrat... more Classical models of the spatial structure of population genetics rely on the assumption of migration-drift equilibrium, which is seldom met in natural populations having only recently colonized their current range (e.g., postglacial). Population structure then depicts historical events, and counfounding effects due to recent secondary contact between recently differentiated lineages can further counfound analyses of association between geographic and genetic distances. Mitochondrial polymorphisms have revealed the existence of two closely related lineages of the lake cisco, Coregonus artedi, whose significantly different but overlaping geographical distributions provided a weak signal of past range fragmentation blurred by putative subsequent extensive secondary contacts. In this study, we analyzed geographical patterns of genetic variation at seven microsatellite loci among 22 populations of lake cisco located along the axis of an area covered by proglacial lakes 12,000-8000 years ago in North America. The results clearly confirmed the existence of two genetically distinct races characterized by different sets of microsatellite alleles whose frequencies varied clinally across some 3000 km. Equilibrium and nonequilibrium analyses of isolation by distance revealed historical signal of gene flow resulting from the nearly complete admixture of these races following neutral secondary contacts in their historical habitat and indicated that the colonization process occurred by a stepwise expansion of an eastern (Atlantic) race into a previously established Mississippian race. This historical signal of equilibrium contrasted with the current migration-drift disequilibrium within major extant watersheds and was apparently maintained by high effective population sizes and low migration regimes.

Conservation Genetics, 2008

Reintroduction programs aim at reinstalling a self-sustained population into the wild via a perio... more Reintroduction programs aim at reinstalling a self-sustained population into the wild via a period of supplementation with captive-bred individuals. This procedure can rapidly generate inbreeding among offspring because of the mating scheme and this inbreeding might be further enhanced by the reintroduction scenario. First, we used simulations to assess the consequences of breeding designs on mean inbreeding index F among offspring when the genetic diversity of breeders, the number and sex ratios of breeders, and the proportion of successful crosses vary. A high number of breeders, a balanced sex ratio, a high proportion of effective crosses and a genetically diverse source population generally contribute to lower F values. However, moderately high ( ‡20) numbers of breeders combined with all but the most biased sex ratios produced mean F values near minimal values. The variability in F was negligible in all parameter combinations except for a very small number of breeders (5) and very biased sex ratios (£ 1M : 19F). We also simulated the long-term inbreeding dynamics in the introduced population under various demographic scenarios. Our main finding was that the annual number of introduced offspring is a decisive factor in establishing long-term F values in the supplemented population. Low supplementation levels (10 2 ) quickly generated an almost completely inbred population whereas high levels ( ‡ 10 4 ) produced stable F values close to that of the introduced offspring. Simulations were run based on the life history and specific demographics of the bloater (Coregonus hoyi), whose reintroduction in Lake Ontario is being considered.

Coregonine fishes are notorious taxonomic problems due to their extreme morphological and ecologi... more Coregonine fishes are notorious taxonomic problems due to their extreme morphological and ecological variation. In North America, diversity is particularly baffling among ciscoes, and both morphological and phylogenetic analyses have resulted in major polytomy among the 8 taxa of the "Coregonus artedi" species complex. Ciscoes are also a devastated group, accounting for 10% of the fish species listed by the Committee on the Status of Endangered Wildlife in Canada. Here, we complete the genetic characterization of North American ciscoes with mitochondrial and microsatellites markers previously used to analyse populations of C. artedi in order to elucidate the evolutionary history and identify appropriate conservation units. Our results revealed a complex evolutionary history marked by postglacial reticulation events coupled with recent and independent evolution of similar phenotypes (taxa). Genetic variation reflects geography rather than taxonomy, and consequently, we recommend that a single taxon, C. artedi (sensu lato) be recognized. Local genetic differentiation is often coupled with ecophenotypic diversification, and gill raker polymorphisms, depth-related habitat preference and reproductive behaviour are considered as phenotypic traits with probable adaptive value contributing to the niche expansion of ciscoes. Ecomorphotypes of each particular locale thus represent a unique expression of a diverse genetic pool still undergoing divergence and sorting. Consequently, ciscoes from lakes with distinct ecomorphotypes are recognized as ESUs, as well as each of sympatric forms when they are genetically differentiated. We recommend that an ESU strategy focusing at a very local level be adopted for continental ciscoes as a valid alternative to protect significant evolutionary processes of divergence encountered in polytypic species of newly colonized habitats.

PloS one, 2015

The North-east American Rainbow smelt (Osmerus mordax) is composed of two glacial races first ide... more The North-east American Rainbow smelt (Osmerus mordax) is composed of two glacial races first identified through the spatial distribution of two distinct mtDNA lineages. Contemporary breeding populations of smelt in the St. Lawrence estuary comprise contrasting mixtures of both lineages, suggesting that the two races came into secondary contact in this estuary. The overall objective of this study was to assess the role of intraspecific genetic admixture in the morphological diversification of the estuarine rainbow smelt population complex. The morphology of mixed-ancestry populations varied as a function of the relative contribution of the two races to estuarine populations, supporting the hypothesis of genetic admixture. Populations comprising both ancestral mtDNA races did not exhibit intermediate morphologies relative to pure populations but rather exhibited many traits that exceeded the parental trait values, consistent with the hypothesis of transgressive segregation. Evidence ...