Small Number Of Founders Research Articles

Relative importance of colonist quantity, quality, and arrival frequency to the extinction of two zooplankton species.

Colonist quantity, quality, and arrival frequency can all individually drive the dynamics and extinction of new populations. However, we do not understand which has the strongest influence, nor the circumstances under which their relative importance may change. We conducted a field mesocosm experiment that manipulated colonist quantity, quality, and arrival frequency in two zooplankton species (Daphnia pulicaria and Skistodiaptomus oregonensis). Individuals of each species were cultured under either high or low food concentrations to produce, respectively, 'good' and 'poor' quality colonists. Each species was then introduced at either small (2 individuals) or large introduction quantities (8 individuals) divided over single or multiple introduction events. We found that the extinction of Daphnia pulicaria was not particularly affected by any of our treatments. Introductions of just two individuals performed as well as larger or more frequent introductions, regardless of quality. Conversely, Skistodiaptomus oregonensis extinction was strongly driven by arrival frequency. Populations that arrived in a single event exhibited high rates of extinction (75-83%), with this probability declining dramatically when colonists were introduced over multiple events (33% extinction). Our results show that other less studied aspects of the colonist pool, such as arrival frequency, could be as important to population persistence as the initial quantity of arriving colonists. Additionally, there are potentially numerous species that are well suited to succeeding with a small number of founders, and whose success is therefore not necessarily dependent upon colonist quantity, quality, or arrival frequency.

The origin and genetic diversity of the yellow-legged hornet, Vespa velutina introduced in Japan

Biological invasions have severe economic and ecological impacts. The yellow-legged hornet, Vespa velutina was originally distributed throughout most of the Oriental region, but it has invasive populations in South Korea, Europe, and most recently, Japan. This species is a predator of honeybees, raising concerns about costs to beekeeping. A previous study concluded that South Korean and European populations originated from China. In this study, we investigate the genetic structure of V. velutina to infer the origin of Japanese populations. A maximum likelihood tree based on three mitochondrial genes (COI, Cytb, and 16S rRNA) revealed that V. velutina consists of an Indonesian–Malaysian clade and an Asian Continent clade, although some Indonesian samples are included in the latter clade. Sequences from individuals in the Japanese and South Korean populations were identical, suggesting that V. velutina in Japan came from South Korea. The single haplotype found in these introduced populations suggests that they originated from a very small number of founders from the natural distributional area. Nevertheless, their distribution continues to expand in introduced areas. Special attention should be paid to diapausing queens of the hornet, as they are likely responsible for these introductions.

Founder contribution in the endangered Czech draught horse breeds

There are many horse breeds included in conservation programs around the world. The current populations of these breeds have often been derived from a small number of founders. The genetic structure of two endangered horse breeds – Silesian Noriker and Czech-Moravian Belgian was studied based on founder contribution analysis. Silesian Norikers are descended from 1235 founders and Czech-Moravian Belgians are descended from 2583 founders. The effective numbers of founders and ancestors contributing to the current genetic pool were 69.42 and 22.32 for the Silesian Noriker breed and 43.33 and 23.32 for the Czech-Moravian Belgian breed respectively. Approximately 50 % of total genetic variation was explained by 31 founders with the greatest influence for the Silesian Noriker and 47 most influential founders for the Czech-Moravian Belgian, with a maximum individual contribution of 8 % for Silesian Noriker and 14 % for Czech-Moravian Belgian. These results suggest that the genetic variability has decreased and without changes in breeding strategy, the genetic variability might continue to decline. The further expected loss of genetic variability in the populations can be minimized by increasing the number of descendants of low-represented founders.

Koalas (Phascolarctos cinereus) From Queensland Are Genetically Distinct From 2 Populations in Victoria.

The koala (Phascolarctos cinereus) suffered population declines and local extirpation due to hunting in the early 20th century, especially in southern Australia. Koalas were subsequently reintroduced to the Brisbane Ranges (BR) and Stony Rises (SR) by translocating individuals from a population on French Island descended from a small number of founders. To examine genetic diversity and north-south differentiation, we genotyped 13 microsatellite markers in 46 wild koalas from the BR and SR, and 27 Queensland koalas kept at the US zoos. The Queensland koalas displayed much higher heterozygosity (H O = 0.73) than the 2 southern Australian koala populations examined: H O = 0.49 in the BR, whereas H O = 0.41 in the SR. This is consistent with the historical accounts of bottlenecks and founder events affecting the southern populations and contrasts with reports of high genetic diversity in some southern populations. The 2 southern Australian koala populations were genetically similar (F ST = 0.018, P = 0.052). By contrast, northern and southern Australian koalas were highly differentiated (F ST = 0.27, P < 0.001), thereby suggesting that geographic structuring should be considered in the conservation management of koalas. Sequencing of 648bp of the mtDNA control region in Queensland koalas found 8 distinct haplotypes, one of which had not been previously detected among koalas. Queensland koalas displayed high mitochondrial haplotype diversity (H = 0.753) and nucleotide diversity (π = 0.0072), indicating along with the microsatellite data that North American zoos have maintained high levels of genetic diversity among their Queensland koalas.

Multiple geographic origins and high genetic differentiation of the Alpine marmots reintroduced in the Pyrenees

Reintroductions inherently involve a small number of founders leading reintroduced populations to be prone to genetic drift and, consequently, to inbreeding depression. Assessing the origins as the genetic diversity and structure of reintroduced populations compared to native populations are thus crucial to foresee their future. Here, we aim to clarify the origins of the Alpine marmots reintroduced in the Pyrenees and to evaluate the genetic consequences of this reintroduction after almost 30 years without monitoring. We search for the origins and compare the genetic structure and the genetic variability of three reintroduced Pyrenean and eight native Alpine populations using pairwise genetic distances, Bayesian clustering method and multivariate analyses. Our results reveal that the Alpine marmots reintroduced in the Pyrenees originated both from the Northern and the Southern Alps, and that, despite these multiple origins, none of the current Pyrenean marmots are admixed. The reintroduction led to a strong genetic differentiation and to a decrease in genetic diversity. This pattern likely results from the small number of founders and the low dispersal capacities of Alpine marmots and thus, highlight the necessity to consider both genetic characteristics and natural history when reintroducing a species.

A search for genetic diversity among Italian Greyhounds from Continental Europe and the USA and the effect of inbreeding on susceptibility to autoimmune disease.

BackgroundPrevious studies documented the problem of inbreeding among Italian Greyhounds (IG) from the USA and its possible role in a multiple autoimmune disease syndrome. The present study is an extension of these earlier experiments and had two objectives: 1) to identify pockets of additional genetic diversity that might still exist among IG from the USA and Continental Europe, and 2) to determine how loss of genetic diversity within the genome and in the dog leukocyte antigen (DLA) complex relates to the problem of autoimmune disease in IG from the USA. Genetic testing was conducted using 33 short tandem repeat (STR) loci across 25 chromosomes and 7 STR loci that associated with specific dog leukocyte antigen (DLA) class I and II haplotypes. Standard genetic assessment tests based on allele frequencies and internal relatedness (IR) were used as measures of breed-wide and individual heterozygosity.ResultsThe results of these tests demonstrated that IG from the USA and Continental Europe belonged to a single breed but were genetically distinguishable by genomic allele frequencies, DLA class I and II haplotypes, and principal coordinate analysis (PCoA). In the second part of the study, 85 IG from the USA that had suffered various autoimmune disorders (case) and 104 healthy dogs (control) of comparable age were studied for genetic associations with disease. Case dogs were found to be significantly more homozygous in the DLA regions than control dogs. Principal coordinate analysis did not differentiate case from control populations. No specific STR-associated DLA-class I or II haplotype was associated with increased autoimmune disease risks. Reasons for the loss of genetic diversity and increased homozygosity among IG from the USA were studied using registration data and deep pedigrees. The breed in the USA started from a small number of founders from Europe and has remained relatively isolated and small in numbers, limiting breeding choices especially in the period before modern transportation and artificial insemination. An additional cause of lost diversity and increased homozygosity has been the influence of famous sires and their show-winning progeny. The most influential of these sires was Ch. Dasa’s King of the Mountain (King) born in 1978. Virtually all contemporary IG from the USA have King at least once in 10 generation pedigrees and 18 % of the genome of contemporary IG from the USA is shared with King.ConclusionsIt was concluded that artificial genetic bottlenecks have concentrated numerous genetic polymorphisms responsible for autoimmune disease and that these risk factors did not originate in a specific individual or bloodline of the breed. Rather, they were of ancestral origin in both purebred and random bred dogs and inherited by descent. Italian Greyhound breeders in the USA have several options to improve breed health: 1) breed against homozygosity within the genome and in the DLA region, 2) avoid breeding dogs that have suffered an autoimmune disorder, 3) increase diversity by incorporating the genetic differences that exist in IG from Continental Europe, or 4) outcross to other small sighthound breeds. The latter two approaches must be undertaken with care to avoid introduction of new deleterious traits and to maximize retention and dissemination of new genetic diversity.

'Mutiny on the Bounty': the genetic history of Norfolk Island reveals extreme gender-biased admixture.

BackgroundThe Pacific Oceania region was one of the last regions of the world to be settled via human migration. Here we outline a settlement of this region that has given rise to a uniquely admixed population. The current Norfolk Island population has arisen from a small number of founders with mixed Caucasian and Polynesian ancestry, descendants of a famous historical event. The ‘Mutiny on the Bounty’ has been told in history books, songs and the big screen, but recently this story can be portrayed through comprehensive molecular genetics. Written history details betrayal and murder leading to the founding of Pitcairn Island by European mutineers and the Polynesian women who left Tahiti with them. Investigation of detailed genealogical records supports historical accounts.FindingsUsing genetics, we show distinct maternal Polynesian mitochondrial lineages in the present day population, as well as a European centric Y-chromosome phylogeny. These results comprehensively characterise the unique gender-biased admixture of this genetic isolate and further support the historical records relating to Norfolk Island.ConclusionsOur results significantly refine previous population genetic studies investigating Polynesian versus Caucasian diversity in the Norfolk Island population and add information that is beneficial to future disease and gene mapping studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13323-015-0028-9) contains supplementary material, which is available to authorized users.

Historical Invasion Records Can Be Misleading: Genetic Evidence for Multiple Introductions of Invasive Raccoons (Procyon lotor) in Germany.

Biological invasions provide excellent study systems to understand evolutionary, genetic and ecological processes during range expansions. There is strong evidence for positive effects of high propagule pressure and the associated higher genetic diversity on invasion success, but some species have become invasive despite small founder numbers. The raccoon (Procyon lotor) is often considered as a typical example for such a successful invasion resulting from a small number of founders. The species’ largest non-native population in Germany is commonly assumed to stem from a small number of founders and two separate founding events in the 1930s and 1940s. In the present study we analyzed 407 raccoons at 20 microsatellite loci sampled from the invasive range in Western Europe to test if these assumptions are correct. Contrary to the expectations, different genetic clustering methods detected evidence for at least four independent introduction events that gave rise to genetically differentiated subpopulations. Further smaller clusters were either artifacts or resulted from founder events at the range margin and recent release of captive individuals. We also found genetic evidence for on-going introductions of individuals. Furthermore a novel randomization process was used to determine the potential range of founder population size that would suffice to capture all the alleles present in a cluster. Our results falsify the assumption that this species has become widespread and abundant despite being genetically depauperate and show that historical records of species introductions may be misleading.

Experimental island invasion of house mice

AbstractThe ability of invasive species to recurrently establish populations from small numbers of founders, while threatened species struggle at the same low population sizes, is a paradox in conservation biology. Little is known about the mechanisms contributing to the post‐arrival success of low density invasive populations as most invasive species research focuses on established, high density populations. Experimental studies are powerful, but generally limited to laboratory or invertebrate experiments. Here, we experimentally demonstrate that vertebrate mammal invasion from a very small (n = 2) number of founders follows relatively simple deterministic predictions. An intentional island invasion of introduced house mice (Mus musculus Linnaeus) from one founding pair closely tracked the density dependent logistic growth curve and reached the seasonal carrying capacity of a previously extant population in only 5 months. Carrying capacity reflected both density dependent and independent processes. In contrast to the previously incumbent population, the invading population retained a marked genetic signal of its recent founder event, but the populations were otherwise demographically indistinguishable. Stochastic events such as individual variability, supplemental immigration and ecological release, but not Allee effects, played important roles during colonisation, but following establishment dynamics rapidly became deterministic, with little demographic impact of reduced genetic diversity. The small population paradigm appears to have little influence on the population dynamics of highly successful invasive species.

Genetic Considerations in the Restoration of Small Forest Populations: Perspectives From Fish and Wildlife Genetics

The evolutionary forces that drive recent population genetic changes include migration, mating strategy, genetic drift, and selection. However, the strength of these forces varies depending on population size. The purpose of this article is to review genetic issues associated with small forest populations and to provide perspectives from fish and wildlife genetics through case studies. Small populations are often fragmented, potentially preventing migration. In forest trees, long-distance pollen dispersal and highly mobile, generalist pollinators can help maintain connectivity. A landscape and community approach to understanding connectivity is critical (case study: mussels). Outbreeding depression can also be a concern in forest restoration. This becomes a greater risk when mixing populations that are highly diverged and when the species is polyploid. Management units should be designated that mimic natural gene flow (case study: lake sturgeon). At the other extreme, inbreeding depression can result in reduced fitness. When inbreeding depression is a concern, genetic rescue may be necessary (case study: Florida panther). Loss of diversity through genetic drift can occur with small effective population sizes (Ne) and a small number of founders (case study: salmonids). Selection is most likely to occur through adaptation to captivity or introduction of resistant/tolerant strains (case study: amphibians).

Modelling nesting site suitability in a population of reintroduced Eurasian black vultures Aegypius monachus in the Grands Causses, France

AbstractDefining habitat selection features and predicting the distribution of species are important for conservation management, and habitat suitability models can provide the statistical framework linking environmental variables to occurrence locations. However, the reliability of such models is restricted for datasets that have limited presence data, which is problematic when population size is low and population dynamics are transient, such as in reintroductions. We characterized and projected nest-site suitability for a black vulture Aegypius monachus population reintroduced in the Grands Causses, France. We performed temporal validations with subsample datasets based on chronological establishment, to assess whether first nests are able to predict subsequent nests. We compared these results to a spatial validation to ensure robustness. Predictions were reliable even with only 10 nest locations. The black vultures reintroduced in the Grands Causses selected pine trees and steep slopes, similar to natural populations elsewhere in Europe. Although our projections were made from only a small number of founders, they are conservative and indicate that a large area in this region is available for nesting and thus availability of breeding habitat is not currently a limiting factor for the species. Our findings will aid the modelling of habitat suitability for further reintroductions. We propose conservation management strategies for this region that integrate socio-economic constraints with the prediction of sites suitable for nesting. Where habitat is the most suitable for black vultures, logging and human activities need to be reduced during the critical breeding stages.

Mystery Case: An unexpected complication of IV thrombolysis for acute ischemic stroke

<h3>ABSTRACT</h3> Most populations of giraffes have declined in recent decades, leading to the recent decision to upgrade the species to vulnerable status, and some subspecies to endangered. Translocations have been used as a conservation tool to re-introduce giraffes to previously occupied areas or establish new populations, but guidelines for founding populations are lacking. To provide general guidelines for translocation projects regarding feasibility, we simulated various scenarios of translocated giraffe populations to identify viable age and sex distributions of founding populations using Population Viability Analysis (PVA) implemented in Vortex software. We explored the parameter space for demography (population growth rates: λ = 1.001, 1.010, 1.024), and the genetic load (number of lethal equivalents: LE = 2.5, 6.29, 12.6), examining how variation in founding numbers (N = 5 to 80 females) and sex ratios (M:F = 0.1 to 0.5) affected 100-year probability of extinction and genetic diversity. We found that even very small numbers of founders (N ≤10 females) can appear to be successful in the first decades due to transient positive population growth, but with moderate population growth rate and moderate genetic load, long-term population viability (probability of extinction &lt;0.01) was only achieved with ≥30 females and ≥3 males released. To maintain &gt;95% genetic diversity of the source population in an isolated population, 50 females and 5 males are recommended to comprise the founding population. Sensitivity analyses revealed first-year survival and reproductive rate were the simulation parameters with the greatest proportional influence on probability of extinction and genetic diversity. These simulations highlight important considerations for translocation success, and data gaps including true genetic load in wild giraffe populations.

Demographic variation, reintroduction, and persistence of an island duck (Anas laysanensis )

Population variation in life history can be important for predicting successful establishment and persistence of reintroduced populations of endangered species. The Laysan duck (Anas laysanensis) is an endangered bird native to the Hawaiian Archipelago that was extirpated from most islands after the introduction of mammalian predators. Laysan ducks were restricted to a single remote island, Laysan Island (4.1 km2), for nearly 150 years. Since the species is not known to disperse between distant Hawaiian Islands today, 42 wild birds from Laysan Island were translocated to another mammalian predator-free low-lying atoll (Midway Atoll; 6.0 km2) to reduce extinction risk. We explored how variation in demography influences establishment and longer-term retention of genetic diversity (rare alleles) for reintroductions of this species. We observed dramatic differences in population growth between the source (λ = 1.18) and reintroduced (λ = 3.28) population. The number of eggs hatched at Midway Atoll was greater than at Laysan Island, however, we found no difference in hatching success (proportion of clutch hatched) between populations. Adult females produced 3 times as many fledglings per breeding year on Midway Atoll compared to Laysan Island. We estimated population abundance of both populations until 2010 and applied a Gompertz model with a Bayesian approach to infer density dependence, process variation, observation error, and carrying capacity for the Laysan Island and Midway Atoll populations. The carrying capacity from the Gompertz model for Midway Atoll (K = 883 ± 210 SD) was estimated to be greater than that of Laysan Island (K = 598 ± 76 SD). Translocations with small numbers of founders and no immigration can create population bottlenecks, leading to loss of genetic variation over time, and potentially reducing the reintroduced population's viability or its potential to serve as a source for future translocations. Therefore, we also assessed the probability of retaining rare alleles in an isolated reintroduced Laysan duck population using life history parameters observed from the Laysan Island and Midway Atoll populations; we concluded that additional founders are needed under scenarios using demographic estimates from both Laysan Island and Midway Atoll to retain either 90% or 95% of source population genetic diversity. © 2013 The Wildlife Society.

No correlation between neonatal fitness and heterozygosity in a reintroduced population of Père David’s deer

Abstract Considering the severe impacts of genetic bottlenecks and small numbers of founders in populations of reintroduced animals, it is necessary to study inbreeding and its effect on fitness in species of conservation concern. Père David’s deer is one of few large mammal species extinct in the wild but safely preserved in captivity. Its specific background gives us the opportunity to study the relationships between heterozygosity and neonatal fitness in relocated populations. We employed five microsatellite loci to explore heterozygosity-fitness correlations in a population of Père David’s deer at the Beijing Milu Ecological Research Center. We observed associations between microsatellite-based variables sMLH, IR, MD2 and HL, and two components of fitness expressed early in life (birth weight and the neonatal mortality of 123 Père David’s deer calves born over six consecutive years). We found that neonatal mortality was 19.1% ± 7.6%, not higher than the 19% or 18% reported in other ungulates. The heterozygosity of calves was not associated with neonatal mortality, nor birth weight. Our study implies that low genetic variability of microsatellite loci has no overt effect on birth weight and neonatal mortality in reintroduced populations of Père David’s deer.

Genetic drift and the population history of the Irish travellers

The Irish Travellers are an itinerant group in Ireland that has been socially isolated. Two hypotheses have been proposed concerning the genetic origin of the Travellers: (1) they are genetically related to Roma populations in Europe that share a nomadic lifestyle or (2) they are of Irish origin, and genetic differences from the rest of Ireland reflect genetic drift. These hypotheses were tested using data on 33 alleles from 12 red blood cell polymorphism loci. Comparison with other European, Roma, and Indian populations shows that the Travellers are genetically distinct from the Roma and Indian populations and most genetically similar to Ireland, in agreement with earlier genetic analyses of the Travellers. However, the Travellers are still genetically distinct from other Irish populations, which could reflect some external gene flow and/or the action of genetic drift in a small group that was descended from a small number of founders. In order to test the drift hypothesis, we analyzed genetic distances comparing the Travellers to four geographic regions in Ireland. These distances were then compared with adjusted distances that account for differential genetic drift using a method developed by Relethford (Hum Biol 68 (1996) 29-44). The unadjusted distances show the genetic distinctiveness of the Travellers. After adjustment for the expected effects of genetic drift, the Travellers are equidistant from the other Irish samples, showing their Irish origins and population history. The observed genetic differences are thus a reflection of genetic drift, and there is no evidence of any external gene flow.

Genetic variability and French breeding programs of three goat breeds under selection

Pedigree analyses have been widely used to assess the genetic variability of livestock species, however, limited number of examples can be found for the goat species. France is one of the only countries in the world where collective goat selection is well implemented with successful breeding programs. This paper will briefly describe the French dairy goat and fiber goat selection schemes. It will present the results of a pedigree analysis, by using the PEDIG software, of two dairy goat breeds, the Alpine and Saanen, and a fiber goat breed, the Angora, in order to assess their genetic variability. The populations under study are large for the Saanen and Alpine (125,797 and 183,611 goats, respectively) and small (1271) for the Angora. The pedigree depth can be considered to be good (from 5.5 equivalent generations for the Angora to 7.8 for the Alpine). The effective number of ancestors is equal to 34, 46 and 51 for the Angora, Alpine and Saanen breeds respectively, while the effective population size varies between 76, 129 and 149 for the Angora, Saanen and Alpine breeds respectively. In the light of these results, in the case of the dairy breeds, there are reasons to believe that despite the fact that genetic variability has narrowed as an effect of 30 years of efficient selection, the specific management program implemented 10 years ago to maintain genetic diversity was successful. Meanwhile, for the Angora breed, the narrower genetic basis of the breed appears to be caused by its thin population basis as well as the small number of founders used at the start of the selection scheme. These results give us a good insight on the genetic variability of intensively selected populations as well as a direction on the programs that are efficient to keep a sustainable level of genetic variability.

Temporal genetic samples indicate small effective population size of the endangered yellow-eyed penguin

There is an increasing awareness that the long-term viability of endemic island populations is negatively affected by genetic factors associated with population bottlenecks and/or persistence at small population size. Here we use contemporary samples and historic museum specimens (collected 1888–1938) to estimate the effective population size (Ne) for the endangered yellow-eyed penguin (Megadyptes antipodes) in South Island, New Zealand, and evaluate the genetic concern for this iconic species. The South Island population of M. antipodes—constituting almost half of the species’ census size—is thought to be descended from a small number of founders that reached New Zealand just a few hundred years ago. Despite intensive conservation measures, this population has shown dramatic fluctuations in size over recent decades. We compare estimates of the harmonic mean Ne for this population, obtained using one moment and three likelihood based-temporal methods, including one method that simultaneously estimates migration rate. Evaluation of the Ne estimates reveals a harmonic mean Ne in the low hundreds. Additionally, the inferred low immigration rates (m = 0.003) agree well with contemporary migration rate estimates between the South Island and subantarctic populations of M. antipodes. The low Ne of South Island M. antipodes is likely affected by strong fluctuations in population size, and high variance in reproductive success. These results show that genetic concerns for this population are valid and that the long-term viability of this species may be compromised by reduced adaptive potential.

Nucleotide sequence polymorphism at the apical membrane antigen-1 locus reveals population history of Plasmodium vivax in Thailand

Apical membrane antigen-1 is a candidate for inclusion in a vaccine for the human malaria parasite Plasmodium vivax. We collected 231 complete sequences of the gene encoding this antigen ( pvama-1) from three regions of Thailand, the most extensive collection to date of sequences at this locus. The domain II loop (previously mentioned as a potential vaccine component) was almost completely conserved, with a single amino acid variant (I313R) observed in a single sequence. The 3′ portion of the gene (domain II through the stop codon) showed significantly lower nucleotide diversity than the 5′ portion (start codon through domain I); and a given domain I sequence might be found in a haplotype with more than one domain II sequence. These results imply a hotspot of recombination between domains I and II. We found significant geographic subdivision among the three regions of Thailand (NW, East, and South) in which collections were made in 2007. Numbers of P. vivax infections have experienced overall declines since 1990 in all three regions; but the decline has been most recent in the NW, and there has been a rebound in numbers of infections in the South since 2000. Consistent with population history, amino acid sequence diversity was greatest in the NW. The South, which had by far the lowest sequence diversity of the three regions, showed signs of a population that has expanded from a small number of founders after a bottleneck.

Bottlenecks, population differentiation and apparent selection at microsatellite loci in Australian Drosophila buzzatii

Species colonizing new areas disjunct from their original habitat may be subject to novel selection pressures, and exhibit adaptive genetic changes. However, if colonization occurs through a small number of founders, the genetic composition of the colonized population may differ from that of the original population simply due to genetic drift. Disentangling the effects of founder drift and selection after colonization is crucial to understanding the adaptive process. Drosophila buzzatii colonized Australia some 600-700 generations ago, and spread rapidly over a wide geographical range. Genetic variation for 15 microsatellite loci in each of nine populations in eastern Australia was used to estimate the size of the bottleneck, and to determine if any of these microsatellites marked genomic regions subject to recent selection. We estimate that on its introduction to Australia, D. buzzatii went through a moderate bottleneck (approximately 30-40 founders). Linkage disequilibrium was common, both intrachromosomal and between loci on different chromosomes. Of the 15 loci, 2 showed evidence of selection, one exhibiting local adaptation in different populations and the other balancing selection. We conclude that linkage disequilibria may be far more common in natural populations than is generally assumed, and the loci apparently affected by selection may well be marking selection in large genome regions including many loci that are not necessarily closely linked.

ADHD in the Northern Finnish Birth Cohort

The Northern Finnish Birth Cohort (NFBC) study of Attention Deficit Hyperactivity Disorder (ADHD) was initiated in 2001 to identify risk genes and gene–by–environmental interactions underlying ADHD in a population-based cohort of adolescents who have been followed prospectively since their birth in 1986. The cohort is drawn from northern Finland (pop. 630,000), where the population consists primarily of two groups—an early settlement and a late settlement. The late settlement descended from a small number of families (or founders) who migrated there in the 17th century and expanded locally. The small number of founders in a region that is fairly geographically isolated has resulted in a “population isolate” that is invaluable to genetic studies of single gene (i.e., monogenic) disorders as well as disorders which are thought to be due to several genes (i.e., polygenic). The first set of five papers on the NFBC study of ADHD was recently published in the December 2007 issue of the Journal of the American Academy of Child and Adolescent Psychiatry, and this article will summarize those detailed papers to present the main conclusions drawn about ADHD, based on one of the largest population-based studies of ADHD. Readers are directed to that journal for the methods, detailed results, and a more extensive discussion of the conclusions. The NFBC provides a unique opportunity to examine the developmental trajectory of ADHD in a social setting where medication is not the primary approach to treating ADHD. In fact, very few of the almost 457 (ADHD = 188, Controls = 269) adolescents assessed during the study had ever received any pharmacological treatment. Despite striking differences in treatment approaches between northern Finland and the United States, the clinical characteristics, psychiatric comorbidity, and cognitive deficits associated with ADHD are very much alike. Thus, one of the first major conclusions from this set of studies is that, despite the controversy regarding the validity of the ADHD diagnosis, ADHD is a clearly recognizable condition with a relatively stable prevalence worldwide. Using DSM–IV diagnostic criteria in a population-based cohort of adolescents (ages 16–18) in northern Finland, the prevalence is 8.5%. The clinical characteristics of ADHD in this population are strikingly similar to other ADHD samples drawn around the world with more boys than girls being affected, similar rates of psychiatric comorbidity, and similar rates of persistence of ADHD from childhood into adolescence (~2/3). Description of the ascertainment method and clinical characteristics of the sample were described in the paper by Smalley and colleagues (Smalley et al., 2007). One goal of the study was to examine ADHD symptoms within a large popu-