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Pleistocene glacial cycles influenced the diversification of high-latitude wildlife species through recurrent periods of range contraction, isolation, divergence, and expansion from refugia and subsequent admixture of refugial populations. We investigate population size changes and the introgressive history of caribou (Rangifer tarandus) in western Canada using 33 whole genome sequences coupled with larger-scale mitochondrial data. We found that a major population expansion of caribou occurred starting around 110,000 years ago (kya), the start of the last glacial period. Additionally, we found effective population sizes of some caribou reaching ~700,000 to 1,000,000 individuals, one of the highest recorded historical effective population sizes for any mammal species thus far. Mitochondrial analyses dated introgression events prior to the LGM dating to 20-30 kya and even more ancient at 60 kya, coinciding with colder periods with extensive ice coverage, further demonstrating the importance of glacial cycles and events prior to the LGM in shaping demographic history. Reconstructing the origins and differential introgressive history has implications for predictions on species responses under climate change. Our results have implications for other whole genome analyses using pairwise sequentially Markovian coalescent (PSMC) analyses, as well as highlighting the need to investigate pre-LGM demographic patterns to fully reconstruct the origin of species diversity, especially for high-latitude species.

The evolutionary origins and hybridization patterns of Canis species in North America have been hotly debated for the past 30 years. Disentangling ancestry and timing of hybridization in Great Lakes wolves, eastern Canadian wolves, red wolves, and eastern coyotes are most often partitioned into a 2‐species model that assigns all ancestry to gray wolves and/or coyotes, and a 3‐species model that includes a third, North American evolved eastern wolf genome. The proposed models address recent or sometimes late Holocene hybridization events but have largely ignored potential Pleistocene era progenitors and opportunities for hybridization that may have impacted the current mixed genomes in eastern Canada and the United States. Here, we re‐analyze contemporary and ancient mitochondrial DNA genomes with Bayesian phylogenetic analyses to more accurately estimate divergence dates among lineages. We combine that with a review of the literature on Late Pleistocene Canis distributions to: (a) identify potential Pleistocene progenitors to southern North American gray wolves and eastern wolves; and (b) illuminate opportunities for ancient hybridization events. Specifically, we propose that Beringian gray wolves (C. lupus) and extinct large wolf‐like coyotes (C. latrans orcutti) are likely progenitors to Mexican and Plains gray wolves and eastern wolves, respectively, and may represent a potentially unrecognized source of introgressed genomic variation within contemporary Canis genomes. These events speak to the potential origins of contemporary genomes and provide a new perspective on Canis ancestry, but do not negate current conservation priorities of dwindling wolf populations with unique genomic signatures and key ecologically critical roles.

In social species, reproductive success and rates of dispersal vary among individuals resulting in spatially structured populations. Network analyses of familial relationships may provide insights on how these parameters influence population‐level demographic patterns. These methods, however, have rarely been applied to genetically derived pedigree data from wild populations.Here, we use parent–offspring relationships to construct familial networks from polygamous boreal woodland caribou (Rangifer tarandus caribou) in Saskatchewan, Canada, to inform recovery efforts. We collected samples from 933 individuals at 15 variable microsatellite loci along with caribou‐specific primers for sex identification. Using network measures, we assess the contribution of individual caribou to the population with several centrality measures and then determine which measures are best suited to inform on the population demographic structure. We investigate the centrality of individuals from eighteen different local areas, along with the entire population.We found substantial differences in centrality of individuals in different local areas, that in turn contributed differently to the full network, highlighting the importance of analyzing networks at different scales. The full network revealed that boreal caribou in Saskatchewan form a complex, interconnected familial network, as the removal of edges with high betweenness did not result in distinct subgroups. Alpha, betweenness, and eccentricity centrality were the most informative measures to characterize the population demographic structure and for spatially identifying areas of highest fitness levels and family cohesion across the range. We found varied levels of dispersal, fitness, and cohesion in family groups. Synthesis and applications: Our results demonstrate the value of different network measures in assessing genetically derived familial networks. The spatial application of the familial networks identified individuals presenting different fitness levels, short‐ and long‐distance dispersing ability across the range in support of population monitoring and recovery efforts., Network analyses of familial relationships may provide insights on how fitness influences population‐level demographic patterns in socially structured populations. Here, we use networks to reconstruct parent‐offspring relationships and create a familial network from polygamous boreal woodland caribou (Rangifer tarandus caribou), assessing the contribution of individual caribou to the population with several centrality metrics and determine which metrics are best suited to inform on population demographic structure. The familial network revealed that boreal caribou in Saskatchewan form a complex, interconnected social network, and identified areas of higher fitness levels and social cohesion across the range in support of population monitoring and recovery efforts.

Clock genes exhibit substantial control over gene expression and ultimately life-histories using external cues such as photoperiod, and are thus likely to be critical for adaptation to shifting seasonal conditions and novel environments as species redistribute their ranges under climate change. Coding trinucleotide repeats (cTNRs) are found within several clock genes, and may be interesting targets of selection due to their containment within exonic regions and elevated mutation rates. Here, we conduct inter-specific characterization of the NR1D1 cTNR between Canada lynx and bobcat, and intra-specific spatial and environmental association analyses of neutral microsatellites and our functional cTNR marker, to investigate the role of selection on this locus in Canada lynx. We report signatures of divergent selection between lynx and bobcat, with the potential for hybrid-mediated gene flow in the area of range overlap. We also provide evidence that this locus is under selection across Canada lynx in eastern Canada, with both spatial and environmental variables significantly contributing to the explained variation, after controlling for neutral population structure. These results suggest that cTNRs may play an important role in the generation of functional diversity within some mammal species, and allow for contemporary rates of adaptation in wild populations in response to environmental change. We encourage continued investment into the study of cTNR markers to better understand their broader relevance to the evolution and adaptation of mammals.

Accurately estimating abundance is a critical component of monitoring and recovery of rare and elusive species. Spatial capture–recapture (SCR) models are an increasingly popular method for robust estimation of ecological parameters. We provide an analytical framework to assess results from empirical studies to inform SCR sampling design, using both simulated and empirical data from noninvasive genetic sampling of seven boreal caribou populations (Rangifer tarandus caribou), which varied in range size and estimated population density. We use simulated population data with varying levels of clustered distributions to quantify the impact of nonindependence of detections on density estimates, and empirical datasets to explore the influence of varied sampling intensity on the relative bias and precision of density estimates. Simulations revealed that clustered distributions of detections did not significantly impact relative bias or precision of density estimates. The genotyping success rate of our empirical dataset (n = 7,210 samples) was 95.1%, and 1,755 unique individuals were identified. Analysis of the empirical data indicated that reduced sampling intensity had a greater impact on density estimates in smaller ranges. The number of captures and spatial recaptures was strongly correlated with precision, but not absolute relative bias. The best sampling designs did not differ with estimated population density but differed between large and small ranges. We provide an efficient framework implemented in R to estimate the detection parameters required when designing SCR studies. The framework can be used when designing a monitoring program to minimize effort and cost while maximizing effectiveness, which is critical for informing wildlife management and conservation., We provide an analytical framework to assess results from empirical studies to inform spatial capture–recapture sampling design, using both simulated and empirical data from noninvasive genetic sampling of seven boreal caribou populations (Rangifer tarandus caribou). Simulations revealed that clustered distributions of detections did not significantly impact relative bias or precision of density estimates, and analysis of the empirical data indicated that reduced sampling intensity had a greater impact on density estimates in smaller ranges. The framework can be used when designing a monitoring program to minimize effort and cost while maximizing effectiveness, which is critical for informing wildlife management and conservation.

The release of domestic organisms to the wild threatens biodiversity because the introduction of domestic genes through interbreeding can negatively impact wild conspecifics via outbreeding depression. In North America, farmed American mink (Neovison vison) frequently escape captivity, yet the impact of these events on functional genetic diversity of wild mink populations is unclear. We characterized domestic and wild mink in Ontario at 17 trinucleotide microsatellites located in functional genes thought to be associated with traits affected by domestication. We found low functional genetic diversity in both mink types, as only four of 17 genes were variable, yet allele frequencies varied widely between captive and wild populations. To determine whether allele frequencies of wild populations were affected by geographic location, we performed redundancy analysis and spatial analysis of principal components on three polymorphic loci (AR, ATN1 and IGF‐1). We found evidence to suggest domestic release events are affecting the functional genetic diversity of wild mink, as sPCA showed clear distinctions between wild individuals near mink farms and those located in areas without mink farms. This is further substantiated through RDA, where spatial location was associated with genetic variation of AR, ATN1 and IGF1.

The Great Lakes and the St. Lawrence River are imposing barriers for wildlife, and the additive effect of urban and agricultural development that dominates the lower Great Lakes region likely further reduces functional connectivity for many terrestrial species. As the climate warms, species will need to track climate across these barriers. It is important therefore to investigate land cover and bioclimatic hypotheses that may explain the northward expansion of species through the Great Lakes. We investigated the functional connectivity of a vagile generalist, the bobcat, as a representative generalist forest species common to the region. We genotyped tissue samples collected across the region at 14 microsatellite loci and compared different landscape hypotheses that might explain the observed gene flow or functional connectivity. We found that the Great Lakes and the additive influence of forest stands with either low or high canopy cover and deep lake‐effect snow have disrupted gene flow, whereas intermediate forest cover has facilitated gene flow. Functional connectivity in southern Ontario is relatively low and was limited in part by the low amount of forest cover. Pathways across the Great Lakes were through the Niagara region and through the Lower Peninsula of Michigan over the Straits of Mackinac and the St. Marys River. These pathways are important routes for bobcat range expansion north of the Great Lakes and are also likely pathways that many other mobile habitat generalists must navigate to track the changing climate. The extent to which species can navigate these routes will be important for determining the future biodiversity of areas north of the Great Lakes., The range of the bobcat has expanded northward in the Great Lakes region in North America. We compared expectations from different models of expansion with genetic observations and then mapped observed pathways north through the Great Lakes region. We found that many of the routes used by this vagile generalist crossed large water bodies and highly modified areas that are not likely to be navigable by less mobile species while they track the changing climate.

Population monitoring can take many different forms, and monitoring elusive and endangered species frequently involves a variety of sparse data from different sources. Small populations are often hard to sample precisely and without bias, so when estimates of vital rates like survival or recruitment point to conflicting population trends, it can be hard to determine which is more correct. Furthermore, data can be extremely hard to collect on small populations and it can be helpful to find a way to use all available hard‐won data. To address these issues, we developed an integrated population model (IPM) using all available data to estimate vital rates and abundance for a case study of an endangered woodland caribou (Rangifer tarandus caribou) population. This IPM allowed us to incorporate data from juvenile recruitment surveys, telemetry‐based survival, aerial population counts and mark–resight data, and non‐invasive capture–recapture DNA data to better understand population status and trend. We estimated survival, abundance, and recruitment of four age classes of male and female caribou: young, juveniles, subadults, and adults. The four‐age class structure of the IPM allowed us to estimate recruitment from reproductive‐aged female caribou alone, even though it can be difficult to distinguish age classes—and even sexes—in the field. As part of our IPM, we developed a novel mixture model to break apart data from different age classes when age is unobservable, as it typically is from non‐invasive DNA samples. This helped us decrease bias in juvenile and adult survival estimates from scat data, which was important to our understanding of the population dynamics. Overall, our integrated model provided more precise estimates of population trends than any one method (e.g., telemetry or non‐invasive DNA) alone. This IPM provides a useful, flexible tool for biologists to monitor populations and provides a valuable example of the benefits of integrated population modeling approaches for endangered species management and recovery.

RATIONALE To detect the small changes in past pH, the boron isotope ratio of coral carbonates, expressed as the δ11 B value, needs to be both precise and accurate (2sd <

Aim The presence of refugia in the Canadian High Arctic has been subject to debate for decades. We investigated the potential existence of Arctic refugia during the Pleistocene for a large mammal species in the Canadian Archipelago because if these refugia were present, reconsideration of the evolutionary histories of North American fauna and flora beyond the major refugia of Beringia and south of the Laurentide and Cordilleran Ice Sheets would be required. Peary caribou (Rangifer tarandus pearyi), identified as a subspecies based on morphological characteristics, inhabits the Canadian Arctic Islands and Boothia Peninsula. Previous studies demonstrated incomplete lineage sorting of mitochondrial DNA interpreted as a Beringian origin but were based on small sample sizes. Location Canadian Arctic. Major taxa studied Mammals: caribou (Rangifer tarandus). Methods We used two molecular markers (microsatellites and mitochondrial DNA) and approximate Bayesian computations (ABC) testing the hypotheses of colonization out of Beringia into the Arctic Islands following the Last Glacial Maximum (LGM) or a divergence from Beringia significantly before the end of the LGM within a different refugium. Results The coalescent-based analyses rejected a recent Beringian origin with subsequent colonization, instead supporting a divergence of Peary caribou from Beringia ~100,000 years ago linking it to the last interglacial/early Wisconsin Glacial Stage (125,000–75,000 years ago). Admixture on Banks Island with Beringian-derived barren-ground caribou is indicative of post-Pleistocene secondary contact; further supporting a divergent history of Peary caribou within a separated Arctic refugium. Main conclusions Our results offer support for the existence of an Arctic refugium for large mammal species and add to the increasing evidence of such refugia in North America. This has significant implications on understanding the evolution and conservation of Arctic species, particularly in light of sensitivities and adaptive potential to a rapidly changing climate.

Climate change is predicted to affect the reproductive ecology of wildlife; however, we have yet to understand if and how species can adapt to the rapid pace of change. Clock genes are functional genes likely critical for adaptation to shifting seasonal conditions through shifts in timing cues. Many of these genes contain coding trinucleotide repeats, which offer the potential for higher rates of change than single nucleotide polymorphisms (SNPs) at coding sites, and, thus, may translate to faster rates of adaptation in changing environments. We characterized repeats in 22 clock genes across all annotated mammal species and evaluated the potential for selection on repeat motifs in three clock genes (NR1D1, CLOCK, and PER1) in three congeneric species pairs with different latitudinal range limits: Canada lynx and bobcat (Lynx canadensis and L. rufus), northern and southern flying squirrels (Glaucomys sabrinus and G. volans), and white‐footed and deer mouse (Peromyscus leucopus and P. maniculatus). Signatures of positive selection were found in both the interspecific comparison of Canada lynx and bobcat, and intraspecific analyses in Canada lynx. Northern and southern flying squirrels showed differing frequencies at common CLOCK alleles and a signature of balancing selection. Regional excess homozygosity was found in the deer mouse at PER1 suggesting disruptive selection, and further analyses suggested balancing selection in the white‐footed mouse. These preliminary signatures of selection and the presence of trinucleotide repeats within many clock genes warrant further consideration of the importance of candidate gene motifs for adaptation to climate change.

Summary Continued consolidation of the US banking industry and a general increase in the size of banks have prompted some policymakers to consider policies that discourage banks from getting larger, including explicit caps on bank size. However, limits on the size of banks could entail economic costs if they prevent banks from achieving economies of scale. This paper presents new estimates of returns to scale for US banks based on nonparametric, local-linear estimation of bank cost, revenue, and profit functions. We report estimates for both 2006 and 2015 to compare returns to scale some 7 years after the financial crisis and 5 years after enactment of the Dodd–Frank Act with returns to scale before the crisis. We find that a high percentage of banks faced increasing returns to scale in cost in both years, including most of the 10 largest bank holding companies. Also, while returns to scale in revenue and profit vary more across banks, we find evidence that the largest four banks operate under increasing returns to scale.

Sex-specific genetic structure is a commonly observed pattern among vertebrate species. Facing differential selective pressures, individuals may adopt sex-specific life history traits that ultimately shape genetic variation among populations. Although differential dispersal dynamics are commonly detected in the literature, few studies have used genetic structure to investigate sex-specific functional connectivity. The recent use of graph theoretic approaches in landscape genetics has demonstrated network capacities to describe complex system behaviours where network topology represents genetic interaction among subunits. Here, we partition the overall genetic structure into sex-specific graphs, revealing different male and female dispersal dynamics of a fisher (Pekania [Martes] pennanti) metapopulation in southern Ontario. Our analyses based on network topologies supported the hypothesis of male-biased dispersal. Furthermore, we demonstrated that the effect of the landscape, identified at the population level, could be partitioned among sex-specific strata. We found that female connectivity was negatively correlated with snow depth, whereas connectivity among males was not. Our findings underscore the potential of conducting sex-specific analysis by identifying landscape elements or configuration that differentially promotes or impedes functional connectivity between sexes, revealing processes that may otherwise remain cryptic. We propose that the sex-specific graph approach would be applicable to other vagile species where differential sex-specific processes are expected to occur.

Aim Glacial-interglacial cycles influenced the contemporary genetic structure of many North American species. While phylogeographical lineage divergence among Pleistocene refugia has been proposed as a significant driver of subspecific and ecotypic differentiation, emerging evidence highlights the role of diversification within refugia in producing post-glacial variation. Caribou (Rangifer tarandus) exhibit significant morphological, ecological and behavioural phenotypic variation and occurred within Beringian and sub-Laurentide refugia. More specifically, the boreal ecotype of woodland caribou ranges from the southern regions of Canada to the Northwest Territories (NWT). Woodland caribou are generally accepted to have evolved south of the glacial extent, but the boreal ecotype in the northern part of their range co-occurs with caribou that have a Beringian origin. This proximity provides an opportunity to test whether woodland caribou colonized boreal habitats from a single southern refugial source or if independent evolution to a common ecotype resulted from diversification within refugia. Location Northwestern Canada. Methods We used approximate Bayesian computation to discriminate between alternate evolutionary histories of caribou belonging to boreal, northern mountain and barren-ground ecotypes using microsatellite and mtDNA markers. Results Our analysis indicates that unlike the southern-evolved boreal ecotype, the boreal ecotype of central NWT has Beringian origins and arose from a common lineage with barren-ground and mountain caribou. Importantly, the divergence of the lineage resulting in the boreal ecotype of central NWT significantly pre-dates the Last Glacial Maximum. Main conclusions We demonstrate that independent evolutionary trajectories can converge on a similar phenotype and for the first time show that the boreal ecotype of caribou in North America contains two phylogeographical assemblages. The ancient divergence suggests that diversification within Beringia could have resulted in ecological specialization. An eco-evolutionary focus will be essential to designing biodiversity conservation strategies for caribou that maximize genetic diversity and preserve adaptive potential in this intraspecifically diverse species.

A rich theory of production and analysis of productive eciency has developed since pioneering work by Koopmans (1951) and Debreu (1951). Farrell (1957) is the earliest published empirical study, and appeared in a statistical journal (JRSS), even though Farrell provided no statistical theory. The literature in econometrics, management sciences, operations research and mathematical statistics has since been enriched by hundreds of papers trying to develop or implement new tools for analyzing productivity and efficiency of firms. Both parametric and nonparametric approaches have been proposed. The mathematical challenge is to derive estimators of production, cost, revenue,or profit frontiers which represent, in the case of production frontiers, the optimal loci of combinations of inputs (like labor, energy, capital, etc.) and outputs (the products or services produced by the firms). Optimality is defined in terms of various economic considerations. Then the efficiency of a particular unit is measured by its distance to the estimated frontier. The statistical problem can be viewed as the problem of estimating the support of a multivariate random variable, subject to some shape constraints, in multiple dimensions. These techniques are applied in thousands of papers in the economic and business literature. This "Guided Tour" reviews the development of various nonparametric approaches since the early work of Farrell. Remaining challenges and open issues in this challenging arena are also described.

Summary Determining the causes of cyclic fluctuations in population size is a central tenet in population ecology and provides insights into population regulatory mechanisms. We have a firm understanding of how direct and delayed density dependence affects population stability and cyclic dynamics, but there remains considerable uncertainty in the specific processes contributing to demographic variability and consequent change in cyclic propensity. Spatiotemporal variability in cyclic propensity, including recent attenuation or loss of cyclicity among several temperate populations and the implications of habitat fragmentation and climate change on this pattern, highlights the heightened need to understand processes underlying cyclic variation. Because these stressors can differentially impact survival and productivity and thereby impose variable time delays in density dependence, there is a specific need to elucidate how demographic vital rates interact with the type and action of density dependence to contribute to population stability and cyclic variation. Here, we address this knowledge gap by comparing the stability of time series derived from general and species-specific (Canada lynx: Lynx canadensis; small rodents: Microtus, Lemmus and Clethrionomys spp.) matrix population models, which vary in their demographic rates and the direct action of density dependence. Our results reveal that density dependence acting exclusively on survival as opposed to productivity is destabilizing, suggesting that a shift in the action of population regulation toward reproductive output may decrease cyclic propensity and cycle amplitude. This result was the same whether delayed density dependence was pulsatile and acted on a single time period (e.g. t−1, t−2 or t−3) vs. more constant by affecting a successive range of years (e.g. t−1,…, t−3). Consistent with our general models, reductions in reproductive potential in both the lynx and small rodent systems led to notably large drops in cyclic propensity and amplitude, suggesting that changes in this vital rate may contribute to the spatial or temporal variability observed in the cyclic dynamics of both systems. Collectively, our results reveal that the type of density dependence and its effect on different demographic parameters can profoundly influence numeric stability and cyclic propensity and therefore may shift populations across the cyclic-to-noncyclic boundary.

Shifts in species distributions due to environmental change may aff ect the spatial pattern of genetic structure within a species ’ range, including possible changes to the adaptive potential of populations. We investigated spatial patterns of neutral genetic diversity and diff erentiation at the southern edge of the Canada lynx Lynx canadensis distribution in Ontario, Canada. We analyzed provincial fur harvest records (1972 – 2010) and collected and genotyped lynx pelt samples (2007 – 2009) from 702 lynx at 14 microsatellite loci. We show that the southern range boundary of lynx in central Canada has contracted northward by � 175 km since the 1970s, and that high winter temperature, low snow depth, and low proportion of suitable habitat are strongly correlated with low neutral genetic diversity and high genetic diff erentiation at the trailing range edge. Our work tests fundamental ideas about species range limits and demonstrates that environmental conditions can have a marked infl uence on neutral genetic structure. Our results suggest that changes in environmental conditions will result in further loss of genetic diversity and possibly reduce adaptive potential in southern peripheral lynx populations.

Landscape genetic analyses are typically conducted at one spatial scale. Considering multiple scales may be essential for identifying landscape features influencing gene flow. We examined landscape connectivity for woodland caribou (Rangifer tarandus caribou) at multiple spatial scales using a new approach based on landscape graphs that creates a Voronoi tessellation of the landscape. To illustrate the potential of the method, we generated five resistance surfaces to explain how landscape pattern may influence gene flow across the range of this population. We tested each resistance surface using a raster at the spatial grain of available landscape data (200 m grid squares). We then used our method to produce up to 127 additional grains for each resistance surface. We applied a causal modelling framework with partial Mantel tests, where evidence of landscape resistance is tested against an alternative hypothesis of isolation-by-distance, and found statistically significant support for landscape resistance to gene flow in 89 of the 507 spatial grains examined. We found evidence that major roads as well as the cumulative effects of natural and anthropogenic disturbance may be contributing to the genetic structure. Using only the original grid surface yielded no evidence for landscape resistance to gene flow. Our results show that using multiple spatial grains can reveal landscape influences on genetic structure that may be overlooked with a single grain, and suggest that coarsening the grain of landcover data may be appropriate for highly mobile species. We discuss how grains of connectivity and related analyses have potential landscape genetic applications in a broad range of systems.

Aleutian mink disease (AMD) is a prominent infectious disease in mink farms. The AMD virus (AMDV) has been well characterized in Europe where American mink (Neovison vison) are an introduced species; however, in North America, where American mink are native and the disease is thought to have originated, the virus’ molecular epidemiology is unknown. As such, we characterized viral isolates from Ontario free-ranging mink of domestic, hybrid, and wild origin at two proteins: NS1, a nonstructural protein, and VP2, a capsid protein. AMDV DNA was detected in 25% of free-ranging mink (45 of 183), indicating prevalent active infection. Median-joining networks showed that Ontario AMDV isolates formed two subgroups in the NS1 region and three in the VP2 region, which were somewhat separate from, but closely related to, AMDVs circulating in domestic mink worldwide. Molecular analyses showed evidence of AMDV crossing from domestic to wild mink. Our results suggest that AMDV isolate grouping is linked to both wild endogenous reservoirs and the long-term global trade in domestic mink, and that AMD spills back and forth between domestic and wild mink. As such, biosecurity on mink farms is warranted to prevent transmission of the disease between mink farms and the wild.

This paper presents new, fully nonparametric estimates of ray-scale and expansion-path scale economies for U.S. banks based on a model of bank costs. Unlike prior studies that use models with restrictive parametric assumptions or limited samples, our methodology uses local polynomial estimators and data on all U.S. banks over the period 1984–2006. Our estimates indicate that as recently as 2006, most U.S. banks faced increasing returns to scale, suggesting that scale economies are a plausible (but not necessarily only) reason for the growth in average bank size and that the tendency toward increasing scale is likely to continue unless checked by government intervention.

Climate is an important factor limiting species distributions. Historic climate-change related range movements have modified the genetic diversity of species by the merging and splitting of gene pools and by the effects associated with recurrent founder events. These effects are often inferred, either from retrospective analyses of current genetic patterns or from simulations. Rarely has it been possible for the population genetic effects of range expansion to be examined with contemporaneous demographic data. We characterized the genetic signature of rapid range expansion by southern flying squirrels (Glaucomys volans) and compared these results to a stationary population of the closely related northern flying squirrel (Glaucomys sabrinus) in Ontario, Canada. Samples were taken during an approximately 200 km range expansion by G. volans (1994–2003) and genotyped at 6 (G. sabrinus) and 8 (G. volans) microsatellite loci. For G. volans, but not G. sabrinus, we found evidence of a latitudinal gradient in allele frequencies and a decrease in allelic richness along the axis of expansion. We found no evidence of isolation-by-distance in either species or of genetic bottlenecks in the area of G. volans expansion. These results suggest that serial founder events can cause an immediate reduction in genetic diversity following rapid range expansion with high levels of gene flow giving rise to heterogeneity within what would classically be termed panmixia. Given the pace of anthropogenic climate change, and the increasing incidence of range movements in response, this may be an important, immediate consequence of climate change.

Systemic infectious complications following adenotonsillectomy are exceedingly rare. We describe an otherwise healthy 2-year-old patient who developed group A beta-hemolytic Streptococcus sepsis and presumptive scarlet fever 3 days after an uncomplicated adenotonsillectomy. After resolution of fever, rash, and discharge home on antibiotics, the patient returned on postoperative day 10 with an abdominal wall abscess. This is the first reported case of an abdominal wall abscess as a complication of adenotonsillectomy. This case demonstrates that an awareness of unexpected infectious complications of adenotonsillectomy should be a part of postsurgical management. Laryngoscope, 125:1230-1232, 2015.

Chronic kidney disease and associated co-morbidities (diabetes, cardiovascular diseases) manifest with an accelerated ageing phenotype, leading ultimately to organ failure and renal replacement therapy. This process can be modulated by epigenetic and environmental factors and promote loss of physiological function and resilience to stress earlier, linking biological age with adverse outcomes post-transplantation including Delayed Graft Function (DGF). \ud The molecular features underpinning this have yet to be fully elucidated. We have determined a molecular signature for loss of resilience and impaired physiological function, via a synchronous genome, transcriptome and proteome snapshot, using human renal allografts as a source of healthy tissue for in vivo model of ageing in humans. \ud This comprises 42 specific transcripts, related through IFNγ signalling, which in allografts displaying clinically impaired physiological function (DGF) exhibited a greater magnitude of change in transcriptional amplitude and elevated expression of non-coding RNAs and pseudogenes, consistent with increased allostatic load. This was accompanied by increased DNA methylation within the promoter and intragenic regions of the DGF panel in pre-perfusion allografts with Immediate Graft Function (IGF) \ud Pathway analysis indicated that an inability to sufficiently resolve inflammatory responses was enabled by decreased resilience to stress and resulted in impaired physiological function in biologically older allografts. Cross-comparison with publically available data sets for renal pathologies identified significant transcriptional commonality for over 20 DGF transcripts. Our data are clinically relevant and important, as they provide a clear molecular signature for the burden of ‘wear and tear’ within the kidney and thus age related physiological capability and resilience.

There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels (Glaucomys volans) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel (Glaucomys sabrinus). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans .T here was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.

Fishers (Martes pennanti) were extirpated from much of southern Ontario, Canada, prior to the 1950s. We hypothesised that the recent recolonization of this area originated from an expansion of the population in Algonquin Provincial Park, which historically served as a refuge for fishers. To test this hypothesis, we created a sampling lattice to encompass Algonquin and the surrounding area, and we collected contemporaneous DNA samples. We sampled fishers from each of 35 sites and genotyped them at 16 microsatellite loci. Using a Bayesian assignment approach, with no a priori geographic information, we inferred 5 discrete genetic populations and used genetic population assignment as a means to cluster sites together. We concluded that the Algonquin Park fisher population has not been a substantial source for recolonization and expansion, which has instead occurred from a number of remnant populations within Ontario, Quebec, and most recently from the Adirondacks in New York, USA. The genetic struct...

Previous studies using rodent cells indicate that a deficiency in XRCC1 results in reduced single-strand break repair, increased sensitivity to DNA-damaging agents, and elevated levels of sister chromatid exchange (SCE). Epidemiological studies have suggested an association of certain human XRCC1 polymorphisms with genetic instability and cancer susceptibility. However, investigations on the molecular functions of XRCC1 in human cells are limited. To determine the contributions of this nonenzymatic scaffold protein, we suppressed XRCC1 levels in several human cell lines using small interfering RNA (siRNA) technology. We report that XRCC1 down-regulation in HeLa cells leads to a concomitant decrease in the DNA ligase 3 protein level and an impaired nick ligation capacity. In addition, depletion of XRCC1 resulted in a significantly increased sensitivity to the alkylating agent methyl methanesulfonate and the thymidine base analog 5-hydroxymethyl-2'-deoxyuridine, a slightly increased sensitivity to ethyl methanesulfonate and 1,3-bis(2-chloroethyl)-1-nitrosourea, and no change in the response to camptothecin. We also discovered that a 70-80% reduction in XRCC1 protein leads to an elevated level of SCE in both HeLa cells and normal human fibroblasts, but does not affect chromosome aberrations in the diploid fibroblasts. Last, XRCC1 siRNA transfection led to an approximately 40% decrease in the survival of BRCA2-deficient cells, supporting a model whereby the accumulation of unrepaired SSBs leads to the accumulation of cytotoxic DNA double strand breaks following replication fork collapse in cells defective in homologous recombination.

Recent research shows that density dependence should result in predictable movements between habitats of different suitability, depending on whether population densities are increasing or decreasing. When population densities are increasing, habitats become filled in order of their suitability, resulting in a net flow from high suitability to low suitability. When populations decrease in density, the reverse can happen. These patterns suggest that genetic information can be used to infer habitat suitability since individual-based genetic assignment tests permit high resolution assessments of migration. We used replicated landscapes to study fishers (Martes pennanti) during a population increase and predicted that there should be a net flow of individuals from areas of shallow to deep snow, since snow depth has previously been linked to fisher fitness. A total of 769 fishers were sampled from 35 different landscapes and profiled at 16 microsatellite loci. From assignment tests, we inferred five genetic populations. By assigning each of the 35 landscapes to one of these five populations, we were able to determine the proportion of immigrants to each. Consistent with our prediction, there was a positive relationship between the proportion of immigrants and snow depth. The best model of fisher habitat suitability was one with both snow depth and the proportion of coniferous forest in landscapes. Our findings suggest that where population trend is known, genetic information can be used to measure habitat suitability.

Social scientists, including numerous economists, have explored the incidence and importance of social capital embedded networks as a governance mechanism in business operations. The buyer-seller dyads represented by 12 large-scale dairies and 7 feed suppliers were studied to contribute to our understanding of network capital in business-to-business (B2B) transactions. A high incidence of institutional and personal trust was found in these buyer-seller networks. Trust facilitates economic exchange through uncertainty management, information sharing, and time savings. [L140, Q120]. © 2007 Wiley Periodicals, Inc. Agribusiness 23: 435–448, 2007.

Background: There is some evidence that surgical plume may pose a risk to health professionals, but the risks posed by volatile organic compounds have not been thoroughly investigated. Methods: The composition of volatile organic compounds in diathermy plume produced during surgery was analysed by selected ion flow tube mass spectrometry. Results: Hydrogen cyanide (3–51 parts per million), acetylene (2–8 parts per million), and 1,3-butadiene (0.15–0.69 parts per million) were identified in the plume. Conclusion: Although there is no evidence of adverse health effects from the volatile organic compound in diathermy plume, the evidence that it is safe to breathe this plume is lacking. Therefore, we would recommend the use of smoke evacuators where practical.

Selected ion flow tube mass spectrometry (SIFT-MS) is a technique that is well suited to the realtime analysis of head-space. SIFT-MS gives a non-discriminatory snapshot of the volatiles present and their amounts, and is considered to display less bias than chromatographic techniques as neither sample pre-treatment nor separation are necessary in most cases. The technique has been used for analysis of virgin olive oil head-space on more than 100 different oils. Twenty of these are reported. The results obtained using this technique differ from those normally reported from chromatographic analyses in that the dominant species in the head-space of all oils tested were methanol and ethanol. These volatiles were present in the head-space in the concentration ranges of 2.8‐ 11.3ppm (methanol) and 0.4‐4.9ppm (ethanol). (E)-2-Hexenal, normally reported as the dominant olive oil volatile, is found in significantly lower concentrations and is in the range of 0.02‐1.6ppm. Copyright # 2005 John Wiley & Sons, Ltd. The consumption of olive oil is deeply entrenched in the culture of all countries surrounding the Mediterranean basin. Olives are thought to have been first cultivated around 5000 years ago, mostly for their oil. 1 Only recently, however, has high-quality olive oil become a sought-after product, attaining high prices in markets the world over. The most sought-after oils are those displaying an attractive aroma and flavour, no noticeable oxidation and no fermentation. Unfavourable conditions at any stage immediately begin altering the oil, so it is desirable to analyse oil at various stages in its life to discover if it has been affected by poor storage conditions. Because of the industry’s high value, research into the composition of olive oil has become widespread. One important area of research has been the correlation of volatile organic compounds (VOCs) found in olive oil with the perceived aroma and flavour. The proportion of VOCs in olive oil is very small, less than 0.2%, 2 but they are solely responsible for the aroma, and largely responsible for the taste, of olive oil. The current test used to monitor the VOCs of olive oil is the organoleptic taste panel, which is regulated by the International Olive Oil Council (IOOC). 3 This test is performed by a panel of 8–12 trained and accredited judges who score olive oils based on a defined scale. Their results are then combined to minimise the inevitable differences in perception from person to person. 4 Tasting panels generally

Two groups of children, one able-bodied and the other with physical disabilities, explored a symmetrical three-tiered virtual building that contained six distinctive target objects, two on each storey. In a subsequent test, the target objects were removed and participants were asked to make judgments of the directions to the former target locations from each floor in turn. At each test site, judgments were required for targets that were formerly on the same floor and for those on higher and lower floors. Relative tilt error scores suggested a bias for both groups, in that targets that were higher than the test location were judged as consistently lower than their actual position, whereas targets that were lower than the test location were judged as higher than their actual position. Absolute tilt errors revealed an asymmetry in both groups, with more accurate tilt errors for judgments directed to lower than higher floors. The relevance of these results for the source of the asymmetry is discussed.

This paper presents new estimates of scale economies for US hospitals. We show that the common translog specification of hospital costs is a misspecification, and employ nonparametric, local linear estimation with both continuous and discrete covariates. A bootstrap method is used to provide inferences regarding ray scale economies and expansion path scale economies for a large sample of hospitals covering 1984–1996. We find evidence of changes in the structure of hospital costs over the sample period, as well as evidence of locally optimal hospital sizes. Copyright © 2004 John Wiley & Sons, Ltd.

In Experiment 1, participants explored two desktop, virtual environments (VEs), each comprising three city streets connected at right angles; for each participant one VE was open and one was enclosed. Following the first VE exploration, orientation estimates to remembered test locations were most accurate when participants imagined themselves aligned, rather than 90 degrees misaligned or 180 degrees or contra-aligned, with the first part of the route. In the second VE, the effect was attenuated and the data pattern conformed to that anticipated from an orientation-free memory. Experiment 2 followed the procedure of Experiment 1, but omitted the alignment tests after the first VE; following the second VE exploration, orientation estimates presented a similar pattern to those in first test of Experiment 1. These data are discussed in terms of cognitive load.

A new technique is presented for the rapid, high-resolution identification and quantification of multiple trace gases above soils, at concentrations down to 0.01 microL L(-1) (10 ppb). The technique, selected ion flow tube mass spectrometry (SIFT-MS), utilizes chemical ionization reagent ions that react with trace gases but not with the major air components (N2, O2, Ar, CO2). This allows the real-time measurement of multiple trace gases without the need for preconcentration, trapping, or chromatographic separation. The technique is demonstrated by monitoring the emission of ammonia and nitric oxide, and the search for volatile organics, above containerized soil samples treated with synthetic cattle urine. In this model system, NH3 emissions peaked after 24 h at 2000 nmol m(-2) s(-1) and integrated to approximately 7% of the urea N applied, while NO emissions peaked about 25 d after urine addition at approximately 140 nmol m(-2) s(-1) and integrated to approximately 10% of the applied urea N. The monitoring of organics along with NH3 and NO was demonstrated in soils treated with synthetic urine, pyridine, and dimethylamine. No emission of volatile nitrogen organics from the urine treatments was observed at levels >0.01% of the applied nitrogen. The SIFT method allows the simultaneous in situ measurement of multiple gas components with a high spatial resolution of < 10 cm and time resolution

The signaling mechanisms that specify, guide and coordinate cell behavior during embryonic morphogenesis are poorly understood. We report that a Xenopus homolog of the Drosophila planar cell polarity gene strabismus (stbm) participates in the regulation of convergent extension, a critical morphogenetic process required for the elongation of dorsal structures in vertebrate embryos. Overexpression of Xstbm, which is expressed broadly in early development and subsequently in the nervous system, causes severely shortened trunk structures; a similar phenotype results from inhibiting Xstbm translation using a morpholino antisense oligo. Experiments with Keller explants further demonstrate that Xstbm can regulate convergent extension in both dorsal mesoderm and neural tissue. The specification of dorsal tissues is not affected. The Xstbm phenotype resembles those obtained with several other molecules with roles in planar polarity signaling, including Dishevelled and Frizzled-7 and -8. Unlike these proteins, however, Stbm has little effect on conventional Wnt/beta-catenin signaling in either frog or fly assays. Thus our results strongly support the emerging hypothesis that a vertebrate analog of the planar polarity pathway governs convergent extension movements.

We report measurements of residual vapour levels of xylenes and trimethylbenzenes, present following a floor re-surfacing procedure, using the technique of selected ion flow tube mass spectrometry (SIFT-MS). A subject exposed to controlled amounts of xylene and mesitylene was monitored by direct breath exhalation over a 4-hour period after exposure to the volatile organic compounds (VOCs) had stopped. The headspace gases above 5 mL blood samples taken over this period were also monitored. The decays of the solvent levels with time were fitted to a two-compartment model with residence times for xylene and mesitylene of 0.37 h and 0.38 h, respectively (compartment one) and 2.5 h and 2.8 h, respectively (compartment two).

The electronic structures of dicarboxylate-bridged complexes containing dimolybdenum and ditungsten quadruple bonds have been investigated using density function theory (gradient corrected and time-dependent), which reveals the consequences of strong mixing of M 2 δ and oxalate π orbitals within extended chains and cyclic structures. Where the bridge is oxalate, acetylene dicarboxylate, and perfluoroterephthalate (PFT), the M 2 centers are in all cases strongly coupled through M 2 δ to bridge π-conjugation. In the case of the chain compounds, this is strongly mediated by torsion angles along the chain. For the squares, only when the bridge is PFT is there a dependence on the orientation of the phenyl ring.

Primer sets for five different ungulate loci were used to obtain individual microsatellite DNA profiles for 29 Mashona cattle from a herd in Zimbabwe. There were 3-13 alleles for each locus and, using the entire suite of five loci, each animal within the herd, including closely related individuals, could be unequivocally distinguished. Wild-caught Glossina pallidipes Austen (Diptera: Glossinidae) were fed on specific cattle and the bloodmeal was profiled 0.5-72 h after feeding. The individual specific sources of the bloodmeals, including mixe meals produced by allowing tsetse to feed on two different cattle, were reliabl identified up to 24 h after feeding. The technique was used in field studies of hos selection by G. pallidipes and G. morsitans morsitans Westwood (Diptera Glossinidae) attracted to pairs of cattle. When the pair comprised an adult and a calf, 100% of meals were from the adult. For some pairs of adult cattle, tsetse were biased significantly towards feeding on one animal, whereas for other pairs there was no such bias. In general, feeding was greater on the animal known to have lower rate of host defensive behaviour. Results suggest that relatively slight differences in the inherent defensive behaviour of cattle produce large difference in host-specific feeding rates when the hosts are adjacent. For flies attracted to pair of cattle, < 2% contained blood from both hosts. The DNA profiling technique will be useful in studying the epidemiology of vector-borne diseases of livestock.

In this paper we compare the amounts of ethanol in breath and in blood after ingestion of whisky using analysis by selected ion flow tube mass spectrometry (SIFT-MS). Blood ethanol concentrations were also obtained using standard hospital forensic procedures for blood alcohol analyses. We demonstrate the quantitative nature of SIFT-MS analysis by correlating the observed alcohol content of the headspace above 5-mL amounts of venous blood and aqueous solution to which known trace amounts of alcohol have been added. This procedure provides a Henry's Law coefficient for ethanol in aqueous solution at 298 +/- 3 K of 209 +/- 7 mol/kg*bar. We also demonstrate that measurement of the ethanol concentration in the alveolar portion of a single breath using the SIFT-MS technique gives an accurate measure of blood alcohol and could obviate the need for blood samples in forensic processing. The storage performance of breath samples in Mylar bags with a volume greater than 1 L has been shown to maintain the mixture integrity for ethanol but not for some other species.

The control region of the mitochondrial DNA haplotype frequencies were significantly different among the two separate lagoon populations of Oreochromis alcalicus grahami in Lake Magadi and of O. a. alcalicus from lake Natron, and DNA fingerprint similarity indices were significantly higher for intra-population comparisons of the two Magadi lagoon populations and the Lake Natron population than the inter-population similarity indices among these populations. A modified Fst measure indicated population sub-division and the phylogeographic partitioning of the VNTR fragments observed were unique to specific populations further indicating substantial genetic differentiation. The lagoon populations within Lake Magadi demonstrated the same degree of genetic differentiation as either of these populations did to the outgroup (the Lake Natron population). There appears to be limited gene flow between Lake Magadi tilapia populations and this population structure has important implications for protecting locally adapted populations within this unique ecosystem.

The catalytic mechanism for the enzyme, IMP cyclohydrolase, may involve a reaction intermediate with negative charge in the 2-position of the purine ring (Szabados, E., Hindmarsh, E., Phillips, L., Duggleby, R.G.Christopherson, R.I. (1994) Biochemistry 33, 14237-14245). Three analogues of IMP have been synthesised where fluorine, chlorine or bromine has been substituted in the 2-position on the purine ring. These analogues with an electronegative substituent may resemble a reaction intermediate for IMP cyclohydrolase; 2-fluoro IMP is a potent inhibitor of the enzyme with a Ki value of 0.19 microM, while 2-chloro IMP has a Ki of 1.9 microM and 2-bromo IMP is not inhibitory. However, IMP cyclohydrolase is not inhibited in human CCRF-CEM leukaemia cells exposed to 2-fluoro inosine although it is toxic to these cells with an IC50 value of 4.9 microM.

This study was prompted by international concern over the expanding global trade in wildlife parts and derivatives. Pinniped (seals, sea lions, fur seals, and walrus) penises purchased in traditional Chinese medicine shops in Asia and North America were examined using molecular genetic techniques. A 261 base pair region of the cytochrome b gene was sequenced for 21 unknown samples, 3 harp seal ( Phoca groenlandica) reference samples, and 2 hooded seal ( Cystophora cristata) reference samples. These sequences were compared against published sequences for pinniped species. Eleven samples from Shanghai and 1 from Bangkok were identified as harp seals and 1 Vancouver sample was derived from a hooded seal. One sample ( from Hong Kong) was most closely associated with an Australian fur seal ( Arctocephalus pusillus doriferus), though the possibility of it originating from a Cape fur seal ( A. p. pusillus) could not be discounted due to the unavailability of a reference sequence. Seven samples were not derived from pinnipeds: 1 from Bangkok was identified as originating from domestic cattle ( Bos taurus) and the remaining 6 were not identifiable to species due to a lack of relevant published sequences. Of these 6 samples, 2 from Canada were most similar to African wild dog ( Lycaon pictus), 3 (2 from Toronto and 1 from Bangkok) were most similar to domestic cattle followed by water buffalo ( Bubalis bubalis), and 1 from San Francisco was most similar to water buffalo. Our results confirm that penises from different pinnipeds are in international trade. The detection of unidentifiable species and, possibly, the Australian fur seal—a species that is not legally hunted—suggests that legal trade in seal products is serving as a cover for illegal trade. These findings are consistent with other recent evidence that the lucrative market for pinniped penises may be encouraging the unregulated hunting of seals, including protected species, and the harvesting of other unidentified mammalian species. Venta de Penes de Pinipedos: Una Investigacion Genetico-Molecular Este estudio fue impulsado por una preocupacion internacional sobre la expansion global de la venta de partes de vida silvestre y sus derivados. Los penes de Pinipedos ( focas, leones marinos y morsas) vendidos en tiendas de medicina tradicional China en Asia y Norteamerica fueron examinados usando tecnicas de genetica molecular. Una region del gen citocromo b de 261 pares de bases fue secuenciada para 21 muestras desconocidas, 3 muestras de referencia de Phoca groenlandica y 2 de Cystophora cristata. Estas secuencias fueron comparadas contra secuencias publicadas de especies de pinipedos. Once muestras de Shangai y una de Bangkok fueron identificadas como Phoca groenlandica y una muetsra de Vancouver se derivo de Cystophora cristata. Una muestra (procedente de Hong Kong) estuvo cercanamente asociada con la foca Australiana ( Arctocephalus pusillus doriferus) aunque la posibilidad de que provenga de una foca del Cabo ( A. p. pusillus) no puede ser descartada debido a la carencia de una secuencia de referencia. Siete muestras no provenian de pinipedos: Una proveniente de Bangkok se identifico como originaria del toro domestico ( Bos taurus) y las seis restantes no fueron identificadas debido a la carencia de secuencias relevantes publicadas. De estas 6 muestras, 2 provenientes de Canada fueron muy similares a las secuencias del perro salvaje africano ( Lycaon pictus), 3 (2 de Toronto y 1 de Bangkok) fueron muy similares al ganado domestico seguido del Bufalo del agua ( Bubalis bubalis), una muestra de San Francisco fue muy similar al Bufalo del agua. Nuestros resultados confirman que los penes de diferentes pinipedos son vendidos en el mercado internacional. La deteccion de especies no identificables y posiblemente la presencia de la foca Australiana—una especie cazada ilegalmente—sugiere que la venta legal de poductos de focas esta sirviendo como cobertura para la venta ilegal. Estos resultados son consistentes con otras evidencias recientes que muestran que el lucrativo mercado de penes de pinipedos podria estar formentando la caza no regulada de focas, incluyendo a especies protegidas, ademas de la captura de otras especies de mamiferos no identificados. X82292X72209X82294L39209U12851X82297X82293U12831X82302X82304X82298X72005X82301D34635

Primary data collected from grower-shippers of fresh tomatoes in California, Florida, and Mexico reveal considerable heterogeneity among firms. Many firms which are extending their shipping seasons outside traditional seasons must have access to land in diverse geographic areas through ownership and contracts. Besides attempting to be low-cost producers, some firms compete by differentiating their products. The extended shelf life tomato from Mexico is one such differentiated product which has garnered higher FOB prices relative to Florida tomatoes. The implications of heterogeneous firms for trade disputes have not been considered in recent deliberations concerning Florida- and Mexico-based tomato growers. © 1997 John Wiley & Sons, Inc.

In this study we report the first documentation of mating between harp (Phoca groenlandica) and hooded seals (Cystophora cristata). The production of this hybrid was quite unusual, being the result of a cross between parents of different genera which are morphologically dissimilar and have quite different mating behavior and dramatically different body sizes. The molecular techniques (mtDNA and macrosatellite nuclear DNA banding patterns) used in this study will undoubtedly be applied widely to many different taxa in the near future, allowing us to re-examine many suspected cases of hybridization among marine mammals and, in a larger context, the meaning of the species concept.