Isozyme diversity in large and isolated populations of Luma apiculata (Myrtaceae) in north-western Patagonia, Argentina

2005 ◽  
Vol 53 (8) ◽  
pp. 781 ◽  
Author(s):  
Mayra S. Caldiz ◽  
Andrea C. Premoli
Keyword(s):  
Genetic Variation ◽  
Isolated Populations ◽  
Isozyme Electrophoresis ◽  
Wahlund Effect ◽  
Rivers And Lakes ◽  
Large Populations ◽  
Vegetative Spread ◽  
Number Of Individuals ◽  
North Western ◽  
Isozyme Diversity

We evaluated the amount and distribution of genetic variation in large and small isolated populations of Luma apiculata (DC.) Burret (Myrtaceae) in north-western Patagonia. The hypothesis tested was that isolated smaller populations were more affected by drift and isolation than large stands. Higher genetic diversity was predicted in the latter. Fresh leaf material for isozyme electrophoresis was collected from 30 individuals in four isolated and two large and continuous stands (Quetrihue Peninsula and Punta Norte, Isla Victoria). Five subpopulations were sampled in both large stands, and in addition, three regeneration gaps in Punta Norte. Eleven loci were resolved; 91% were polymorphic in at least one population. Isolated and large populations had similar levels of genetic variation. Reduced observed heterozygosity and elevated inbreeding were measured in subpopulations and regeneration gaps within dense stands. Although small populations consist of a reduced number of individuals they are mostly coastal populations nearby rivers and lakes that may maintain considerable gene flow with other faraway populations counteracting the effects of drift. In addition to potential selfing, increased inbreeding within large populations and regeneration gaps may be due to an intra-population Wahlund effect from local seedling establishment and vegetative spread, resulting in clustered cohorts of similar genotypes.

Genetic and Ecological Variation in Atherosperma moschatum and the Implications for Conservation of Its Biodiversity

1994 ◽  
Vol 42 (6) ◽  
pp. 663 ◽  
Author(s):  
A Shapcott
Keyword(s):  
Genetic Diversity ◽  
Genetic Variation ◽  
New South ◽  
Genetic Distances ◽  
Isolated Populations ◽  
Canopy Tree ◽  
South Wales ◽  
Genetic Substructure ◽  
Temperate Rainforests ◽  
Vegetative Spread

Population genetics and ecology of Atherosperma moschatum Labill. (sassafras), a major canopy tree of Australian temperate rainforests, were examined and used to identify priorities and strategies for conservation of its genetic diversity. The genetic diversity among populations was fairly low, but higher than average for long-lived late successional or wind dispersed species (Hamrick and Godt 1989). Genetic distances between populations were correlated with geographic distances and climatic differences. The major genetic differentiation was between the mainland populations and those in Tasmania, with the New South Wales populations being quite genetically distinct. Most genetic variation was found within populations, however, most populations were inbred. This is likely to be due to selfing and spatial genetic substructure resulting from vegetative spread and local dispersal. There was evidence of regeneration in all populations, however no consistent regeneration patterns emerged. Population density was inexplicably correlated with genetic distance. There was as much diversity in all variables (ecological and genetic) measured in small isolated populations as there was in stands within larger assemblages; therefore, population size does not appear to be a major factor affecting viability. Genetic variation was spread throughout the distribution of A. moschatum. Therefore, populations from throughout its range would need to be conserved to retain the genetic diversity within this species.

scholarly journals Evolutionary rescue and the limits of adaptation

2013 ◽  
Vol 368 (1610) ◽  
pp. 20120080 ◽  
Author(s):  
Graham Bell
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Relative Fitness ◽  
Population Declines ◽  
Genetic Constraints ◽  
Evolutionary Rescue ◽  
Large Populations ◽  
Effective Selection ◽  
The Cost ◽  
Number Of Individuals

Populations subject to severe stress may be rescued by natural selection, but its operation is restricted by ecological and genetic constraints. The cost of natural selection expresses the limited capacity of a population to sustain the load of mortality or sterility required for effective selection. Genostasis expresses the lack of variation that prevents many populations from adapting to stress. While the role of relative fitness in adaptation is well understood, evolutionary rescue emphasizes the need to recognize explicitly the importance of absolute fitness. Permanent adaptation requires a range of genetic variation in absolute fitness that is broad enough to provide a few extreme types capable of sustained growth under a stress that would cause extinction if they were not present. This principle implies that population size is an important determinant of rescue. The overall number of individuals exposed to selection will be greater when the population declines gradually under a constant stress, or is progressively challenged by gradually increasing stress. In gradually deteriorating environments, survival at lethal stress may be procured by prior adaptation to sublethal stress through genetic correlation. Neither the standing genetic variation of small populations nor the mutation supply of large populations, however, may be sufficient to provide evolutionary rescue for most populations.

Genetic variation in westslope cutthroat trout reveals that widespread genetic rescue is warranted

2021 ◽  
Author(s):  
Ryan P. Kovach ◽  
Robb F. Leary ◽  
Donovan Bell ◽  
Sally Painter ◽  
Angela Lodmell ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Cutthroat Trout ◽  
Freshwater Species ◽  
Genetic Rescue ◽  
Westslope Cutthroat Trout ◽  
Isolated Populations ◽  
Freshwater Habitats ◽  
Potential Benefits ◽  
Major Region ◽  
Number Of Individuals

Although human fragmentation of freshwater habitats is ubiquitous, the genetic consequences of isolation and a roadmap to address them are poorly documented for most fishes. This is unfortunate, because translocation for genetic rescue could help mitigate problems. We used genetic data (32 SNPs) from 203 populations of westslope cutthroat trout to (1) document the effect of fragmentation on genetic variation and population structure, (2) identify candidate populations for genetic rescue, and (3) quantify the potential benefits of strategic translocation efforts. Human-isolated populations had substantially lower genetic variation and elevated genetic differentiation, indicating that many populations are strongly influenced by random genetic drift. Based on simple criteria, 23 populations were candidates for genetic rescue, which represented a majority (51%) of suitable populations in one major region (Missouri drainage). Population genetic theory suggests that translocation of a small number of individuals (~5 adults) from nearby populations could dramatically increase heterozygosity by up to 58% (average across populations). This effort provides a clear template for future conservation of westslope cutthroat trout, while simultaneously highlighting the potential need for similar efforts in many freshwater species.

Genetic variation in central and disjunct populations of Lilium parryi

1994 ◽  
Vol 72 (1) ◽  
pp. 79-85 ◽  
Author(s):  
Yan B. Linhart ◽  
Andrea C. Premoli
Keyword(s):  
Population Structure ◽  
Genetic Variation ◽  
Genetic Variability ◽  
The Other ◽  
Significant Genetic Differentiation ◽  
Isolated Populations ◽  
Disjunct Populations ◽  
Large Populations ◽  
Low Levels ◽  
Hawkmoth Pollination

We compared levels of genetic variability in small, isolated populations of Lilium parryi in Arizona with those found in large populations in California. Arizona populations were presumably derived from California populations; they were significantly less variable and showed evidence of much higher levels of inbreeding. One California locality whose population structure is similar to those found in Arizona also had relatively low levels of genetic variability. However, the other California populations were highly variable and showed lower levels of inbreeding than Arizona populations. There was significant genetic differentiation among all populations. In Arizona, there was no relationship between current population size and genetic variability. Arizona populations may be vulnerable to extinction, given the magnitude of environmental modifications in their habitats, their small sizes, and their low levels of variability. Key words: genetic structure, rare species, hawkmoth pollination, Lilium, disjunct populations.

Outbreeding depression is uncommon and predictable

2017 ◽  
Author(s):  
Richard Frankham ◽  
Jonathan D. Ballou ◽  
Katherine Ralls ◽  
Mark D. B. Eldridge ◽  
Michele R. Dudash ◽  
...  
Keyword(s):  
Natural Selection ◽  
Genetic Differences ◽  
Outbreeding Depression ◽  
Isolated Populations ◽  
Large Populations

Crosses between populations within species sometimes result in reduced fitness, especially in F2 and later generations (outbreeding depression). The primary mechanisms causing outbreeding depression in crosses between populations are fixed chromosomal differences and adaptive genetic differences, especially for long-isolated populations. Outbreeding depression is usually observed after crossing populations with ploidy differences or fixed differences for translocations, inversions or centric fusions: the magnitudes are usually ploidy > translocations and monobrachial centric fusions > inversions and simple centric fusions. Populations adapted to different environments (but with the same karyotype) often exhibit outbreeding depression when crossed, especially in the F2 and later generations. Even if outbreeding depression occurs, it is often only temporary, as natural selection acts to remove it, especially in large populations.

Comparative Study of Genetic Variation at 15 STR Loci in Three Isolated Populations of the Bosnian Mountain Area

Human Biology ◽  
2004 ◽  
Vol 76 (1) ◽  
pp. 15-31 ◽  
Author(s):  
D Marjanovic ◽  
L Kapur ◽  
K Drobnic ◽  
Bruce Budowle ◽  
N Pojskic ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Comparative Study ◽  
Isolated Populations ◽  
Mountain Area ◽  
Str Loci

scholarly journals Population size, habitat fragmentation, and the nature of adaptive variation in a stream fish

2014 ◽  
Vol 281 (1790) ◽  
pp. 20140370 ◽  
Author(s):  
Dylan J. Fraser ◽  
Paul V. Debes ◽  
Louis Bernatchez ◽  
Jeffrey A. Hutchings
Keyword(s):  
Genetic Variation ◽  
Habitat Fragmentation ◽  
Population Size ◽  
Brook Trout ◽  
Small Populations ◽  
Adaptive Genetic Variation ◽  
Genetic Population ◽  
Fragmented Populations ◽  
Large Populations ◽  
Adaptive Differentiation

Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to increase variability within and among habitats as population size decreases. Such variability might instead favour the maintenance of adaptive polymorphisms and/or generate more variability in adaptive differentiation at smaller population size. We investigated these alternative hypotheses by analysing coding-gene, single-nucleotide polymorphisms associated with different biological functions in fragmented brook trout populations of variable sizes. Putative adaptive differentiation was greater between small and large populations or among small populations than among large populations. These trends were stronger for genetic population size measures than demographic ones and were present despite pronounced drift in small populations. Our results suggest that fragmentation affects natural selection and that the changes elicited in the adaptive genetic composition and differentiation of fragmented populations vary with population size. By generating more variable evolutionary responses, the alteration of selective pressures during habitat fragmentation may affect future population persistence independently of, and perhaps long before, the effects of demographic and genetic stochasticity are manifest.

The effect of infection of hard ticks Ixodes ricinus (L.) and Ixodes persulcatus Sch. (Acari: Ixodinae) with the causative agent of Lyme borreliosis (Borrelia burgdorferi s.l.) on their host search activity (using attractants)

2019 ◽  
Vol 24 (10) ◽  
pp. 2358-2368
Author(s):  
L. A. GRIGORYEVA ◽  
O. A. MITEVA ◽  
V. A. MYASNIKOV ◽  
A. S. GOGOLEVSKY ◽  
L. F. SHITOVA
Keyword(s):  
Borrelia Burgdorferi ◽  
Ixodes Ricinus ◽  
Causative Agent ◽  
Methyl Salicylate ◽  
Search Activity ◽  
Potential Host ◽  
Lab Experiments ◽  
Positive Specimen ◽  
Number Of Individuals ◽  
North Western

A series of lab experiments with ticks (collected by flagging in the natural biotopes in North-Western Russia) was carried out in order to study tick reaction to attractants imitating the smell of a potential host. All the ticks that showed either positive or negative reactions to attractants in the experiment were individually PCR-tested for B. burgdorferi s.l DNA.The percent of Borrelia - positive specimen among hungry active adult I. ricinus and I. persulcatus ticks was higher than that among hungry passive ones. The discovered infection of I. persulcatus females by B. burgdorferi s. l. was 56% from which 67% were active and 36% were passive ticks. Total infection of adult ticks was 45% (61% active, 24% passive ticks). Infection of I. ricinus females was 60%, 69% in active individuals and 48% in passive, total infection of adult ticks was 56% (70% in active, 43% in passive). Synthetic kyromonas (attractant) composed of 1-octen-3-ol and a mixture of ethyl myristate-methyl salicylate (1:1), simulated the odour of the host in the experiment, attracted up to 70% of adults of I. ricinus and up to 80% of I. persulcatus. It can be assumed that this percent of adult ticks reflect an overall number of individuals searching for a hosts during the season of activity in natural biotopes.

Inbreeding and Inbreeding Depression

2020 ◽  
Author(s):  
Donald M. Waller ◽  
Lukas F. Keller
Keyword(s):  
Genetic Variation ◽  
Inbreeding Depression ◽  
Charles Darwin ◽  
Extinction Risk ◽  
Random Mating ◽  
Genetic Material ◽  
Great Length ◽  
Genetic Rescue ◽  
Isolated Populations ◽  
Genetic Transmission

Inbreeding (also referred to as “consanguinity”) occurs when mates are related to each other due to incest, assortative mating, small population size, or population sub-structuring. Inbreeding results in an excess of homozygotes and hence a deficiency of heterozygotes. This, in turn, exposes recessive genetic variation otherwise hidden by heterozygosity with dominant alleles relative to random mating. Interest in inbreeding arose from its use in animal and plant breeding programs to expose such variation and to fix variants in genetically homogenous lines. Starting with Gregor Mendel’s experiments with peas, geneticists have widely exploited inbreeding as a research tool, leading R. C. Lewontin to conclude that “Every discovery in classical and population genetics has depended on some sort of inbreeding experiment” (see Lewontin’s 1965 article “The Theory of Inbreeding.” Science 150:1800–1801). Charles Darwin wrote an entire book on the effects of inbreeding as measured in fifty-two taxa of plants. He and others noted that most plants and animals go to great length to avoid inbreeding, suggesting that inbreeding has high costs that often outweigh the benefits of inbreeding. Benefits of inbreeding include increased genetic transmission while the costs of inbreeding manifest as inbreeding depression when deleterious, mostly recessive alleles otherwise hidden as heterozygotes emerge in homozygote form upon inbreeding. Inbreeding also reduces fitness when heterozygotes are more fit than both homozygotes, but such overdominance is rare. Recurrent mutation continuously generates deleterious recessive alleles that create a genetic “load” of deleterious mutations mostly hidden within heterozygotes in outcrossing populations. Upon inbreeding, the load is expressed when deleterious alleles segregate as homozygotes, causing often substantial inbreeding depression. Although inbreeding alone does not change allele frequencies, it does redistribute genetic variation, reducing it within families or populations while increasing it among families or populations. Inbreeding also increases selection by exposing deleterious recessive mutations, a process called purging that can deplete genetic variation. For all these reasons, inbreeding is a central concept in evolutionary biology. Inbreeding is also central to conservation biology as small and isolated populations become prone to inbreeding and thus suffer inbreeding depression. Inbreeding can reduce population viability and increase extinction risk by reducing individual survival and/or reproduction. Such effects can often be reversed, however, by introducing new genetic material that re-establishes heterozygosity (“genetic rescue”). The current availability of DNA sequence and expression data is now allowing more detailed analyses of the causes and evolutionary consequences of inbreeding.

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