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Island ecosystems provide natural laboratories to assess the impacts of isolation on population persistence. However, most studies of persistence have focused on a single species, without comparisons to other organisms they interact with in the ecosystem. The case study of moose and gray wolves on Isle Royale allows for a direct contrast of genetic variation in isolated populations that have experienced dramatically differing population trajectories over the past decade. Whereas the Isle Royale wolf population recently declined nearly to extinction due to severe inbreeding depression, the moose population has thrived and continues to persist, despite having low genetic diversity and being isolated for ∼120 years. Here, we examine the patterns of genomic variation underlying the continued persistence of the Isle Royale moose population. We document high levels of inbreeding in the population, roughly as high as the wolf population at the time of its decline. However, inbreeding in the moose population manifests in the form of intermediate-length runs of homozygosity suggestive of historical inbreeding and purging, contrasting with the long runs of homozygosity observed in the smaller wolf population. Using simulations, we confirm that substantial purging has likely occurred in the moose population. However, we also document notable increases in genetic load, which could eventually threaten population viability over the long term. Overall, our results demonstrate a complex relationship between inbreeding, genetic diversity, and population viability that highlights the use of genomic datasets and computational simulation tools for understanding the factors enabling persistence in isolated populations. [ABSTRACT FROM AUTHOR]

Anthropogenic disturbances in tropical forests often affect the genetic diversity of a species. Dipterocarpus condorensis is an endangered species in the tropical forests of south-eastern Vietnam, both from its over-exploitation and habitat loss. Therefore, knowledge of population genetic diversity and population structure is essential for identifying the species conservation measures. In the present study, we evaluated genetic diversity and population structure using nine microsatellites for 183 individual trees from eight populations, representing the distribution range of D. condorensis in Vietnam. Two clustering approaches (Bayesian analysis and discriminant analysis of principal components) revealed that all studied individuals clustered into three genetic groups, which were related to gene flow across the range of D. condorensis in the lowland tropical forests of south-eastern Vietnam. Limited gene flow was implicated in anthropogenic disturbance. Genetic differentiation among populations was relatively low (the Weir and Cockerham index of 0.122 and the Hedrick index of 0.149) and showed significant differentiation. The genetic variability of the populations was low (H O = 0.298 and H E = 0.324), which suggested the negative effects of habitat degradation and over-exploitation. Our studies also determined that D. condorensis populations can have undergone recent bottlenecks. We recommend conservation activities for this species based on these results. [ABSTRACT FROM AUTHOR]

Inbreeding depression is a major driver of mating system evolution and has critical implications for population viability. Theoretical and empirical attention has been paid to predicting how inbreeding depression varies with population size. Lower inbreeding depression is predicted in small populations at equilibrium, primarily due to higher inbreeding rates facilitating purging and/or fixation of deleterious alleles (drift load), but predictions at demographic and genetic disequilibrium are less clear. In this study, we experimentally evaluate how lifetime inbreeding depression and drift load, estimated by heterosis, vary with census ( Nc) and effective (estimated as genetic diversity, He) population size across six populations of the biennial Sabatia angularis as well as present novel models of inbreeding depression and heterosis under varying demographic scenarios at disequilibrium (fragmentation, bottlenecks, disturbances). Our experimental study reveals high average inbreeding depression and heterosis across populations. Across our small sample, heterosis declined with He, as predicted, whereas inbreeding depression did not vary with He and actually decreased with Nc. Our theoretical results demonstrate that inbreeding depression and heterosis levels can vary widely across populations at disequilibrium despite similar He and highlight that joint demographic and genetic dynamics are key to predicting patterns of genetic load in nonequilibrium systems. [ABSTRACT FROM AUTHOR]

Island endemics are expected to have low effective population sizes (Ne), first because somemay experience population bottlenecks whenthey are founded, and secondbecause theyhave restricted ranges. Therefore,weexpect island species tohave reduced genetic diversity, inefficient selection, and reduced adaptive potential compared with theirmainland counterparts.We used both polymorphism and substitution data to address these predictions, improving on the approach of recent studies that only used substitution data. This allowed us to directly test the assumption that island species have small values of Ne. We found that island species had significantly less genetic diversity than mainland species; however, this pattern could be attributed to a subset of island species that appeared to have undergone a recent population bottleneck. When these species were excluded from the analysis, island and mainland specieshadsimilar levelsofgenetic diversity, despite islandspecies occupying considerably smaller areas thantheirmainland counterparts.We also found no overall difference between island andmainland species in terms of the effectiveness of selection or themutation rate. Our evidence suggests that island colonization has no lasting impact on molecular evolution. This surprising result highlights gaps in our knowledge of the relationship between census and effective population size. [ABSTRACT FROM AUTHOR]

The divergence between most stock assessments and studies in marine ecology is characterized by the low priority usually given to assessing the holding capacity of marine habitats. Habitats of high structural complexity are relatively uncommon in shelf waters, are contagiously distributed, and are damaged incidentally by bottom-towed gear. Structurally complex habitats are used by many demersal fish and crustaceans for predation abatement and as a site for feeding forays. Successive life-history stages typically migrate through several structurally complex habitats which recent studies show often to have fractal properties. One consequence of fractal structures as cover is a rapid reduction of protection from predators with growth in size: migration is the only response possible when further growth of the recruiting age class renders individuals in that habitat vulnerable to predation. A common feature of structurally complex habitats with high vulnerability at size is the occurrence of population bottlenecks. It is suggested that identifying and rectifying shortages of structured habitat, and eliminating habitat bottlenecks, will be effective in stock enhancement. This will require placing strict spatial constraints on the operation of bottom gear. This paper reviews new methods of estimating juvenile predation mortality, including mortality-at-age and mortality-at-life-history stage, which depend on the fractal characteristics of structurally complex habitats. [ABSTRACT FROM AUTHOR]

Successful invasive species can overcome or circumvent the potential genetic loss caused by an introduction bottleneck through a rapid population expansion and admixture from multiple introductions. We explore the genetic makeup and the timing of a species introduction to Santa Cruz Island in the Galápagos archipelago. We investigate the presence of processes that can maintain genetic diversity in populations of the broad-nosed weevil Galapaganus howdenae howdenae. Analyses of combined genotypes for 8 microsatellite loci showed evidence of past population size reductions through moment and likelihood-based estimators. No evidence of admixture through multiple introductions was found, but substantial current population sizes (N0 298, 95% credible limits 50–2300), genetic diversity comparable with long-established endemics (Mean number of alleles = 3.875), and lack of genetic structure across the introduced range (FST = 0.01359) could suggest that foundations are in place for populations to rapidly recover any loss of genetic variability. The time estimates for the introduction into Santa Cruz support an accidental transfer during the colonization period (1832–1959) predating the spurt in human population growth. Our evaluation of the genetic status of G. h. howdenae suggests potential for population growth in addition to our field observations of a concurrent expansion in range and feeding preferences towards protected areas and endemic host plants. [ABSTRACT FROM AUTHOR]

The article presents a study on the genetic structure of Yellow Rail (Coturnicops noveboracensis) in Oregon to determine its population bottleneck. It says that the study has evaluated the data gathered from the blood samples of Yellow Rails in six locations for genetic analysis using the mitochondrial DNA sequences (mtDNA) and microsatellite loci. It shows that the factors in the reduced population includes drought, wildfires, and loss of wetlands.

The rate at which a population adapts to its environment is a cornerstone of evolutionary theory, and recent experimental advances in microbial populations have renewed interest in predicting and testing this rate. Efforts to understand the adaptation rate theoretically are complicated by high mutation rates, to both beneficial and deleterious mutations, and by the fact that beneficial mutations compete with each other in asexual populations (clonal interference). Testable predictions must also include the effects of population bottlenecks, repeated reductions in population size imposed by the experimental protocol. In this contribution, we integrate previous work that addresses each of these issues, developing an overall prediction for the adaptation rate that includes: beneficial mutations with probabilistically distributed effects, deleterious mutations of arbitrary effect, population bottlenecks, and clonal interference. [ABSTRACT FROM AUTHOR]

Constraints on the availability of freshwater and land plants and animals to feed the 9.2 billion humans projected to inhabit Earth by 2050 can be overcome by enhancing the contribution the ocean makes to food production. Catches from ocean fisheries are unlikely to recover without adequate conservation measures, so the greater contribution of the oceans to feeding humanity must be derived largely from mariculture. For the effort to be successful, mariculture must close the production cycle to abandon its current dependence on fisheries catches; enhance the production of edible macroalgae and filter-feeder organisms; minimize environmental impacts; and increase integration with food production on land, transferring water-intensive components of the human diet (i.e., production of animal protein) to the ocean. Accommodating these changes will enable the oceans to become a major source of food, which we believe will constitute the next food revolution in human history. [ABSTRACT FROM AUTHOR]

Abstract Founder-flush speciation models propose that population bottlenecks can enhance evolutionary potential for reproductive isolation. To test this prediction, we subjected bottlenecked (three-pair founder-flush) and nonbottlenecked populations of the housefly to 18 generations of selection for assortative mating. After the selection regime, we analysed videotaped courtship bouts in these lines to identify correlated responses to the selection protocol. The realized heritabilities for assortative mating for both the bottlenecked and nonbottlenecked treatments were very low, but still significant. The founder-flush populations had thus responded to selection as well as the nonbottlenecked populations, although not significantly greater (i.e. total increases in assortative mating were 9.6 and 8.6%, respectively). Multivariate analyses on the courtship repertoires found that, although both bottlenecked and nonbottlenecked treatments attained similar levels of assortative mating, the treatments exhibited different evolutionary solutions in their correlated responses. Specifically, the bottlenecked lines demonstrated a significantly more diverse set of evolutionary trajectories (i.e. significant shifts along the second principal component for courtship). This suggests that the bottlenecked lines had greater potential for the evolution of novel phenotypes as predicted by founder-induced speciation models. Our results, however, cannot distinguish whether the more variable evolutionary responses resulted from increased heritabilities in courtship components, reduced potential to follow the convergent evolutionary trajectories noted for the nonbottlenecked lines, or some combination of both general processes in determining the resultant multivariate phenotype. [ABSTRACT FROM AUTHOR]

We review published records of laboratory experiments on peripatric and vicariance allopatric speciation to address the following three questions: (1) What was the true effect size of reproductive isolation? (2) Was the reproductive isolation persistent? (3) What influenced the development of isolation? Contrary to popular belief, laboratory evidence for allopatric speciation is quite weak. Assortative mating was only found among derived populations in vicariance experiments. Reproductive isolation against control populations was only intermittent, so there is reason to doubt if some cases showing significant reproductive isolation really should be attributed to speciation. The method of testing was at least as important as the speciation model. Experimental populations tested against each other were the most likely to demonstrate reproductive isolation. This study suggests that allopatric speciation experiments are more likely to yield conclusive results under divergent selection than under drift, and points to the benefits of large populations and many generations. [ABSTRACT FROM AUTHOR]

Courtship bouts of six founder-flush populations (two-pair founder-flush) and two nonbottlenecked controls of the housefly were videotaped over the course of 26 generations in order to evaluate the stability of mating behaviour. Limited-choice mate preference tests were conducted periodically to assess levels of homogamic preference. Both founder-flush and control treatments showed significant evolutionary potential in courtship, along with homogamic and heterogamic preferences. The founder-flush populations were significantly differentiated from the controls in courtship repertoire, but all of the populations pursued convergent evolutionary trajectories in adapting to the laboratory, resulting in dissolution of homogamic preferences. The phenotypic shifts in courtship and mate preferences were unrelated to evolutionary trends in overall mating vigour; therefore, the convergence in courtship could not be attributed to either a fitness meltdown due to inbreeding or the purge of deleterious alleles. Only one founder-flush population showed some independence from the selectional pressures for convergence; therefore, the single two-pair founder-flush event was generally inadequate to stimulate stable incipient speciation. This study thus demonstrates how convergent evolution can dissolve founder-flush effects. [ABSTRACT FROM AUTHOR]