A Comparison of Hybridization between Mottled Ducks (<Emphasis Type="Italic">Anas fulvigula</Emphasis>)and Mallards (<Emphasis Type="Italic">A. platyrhynchos</Emphasis>) in Florida and South Carolina using Microsatellite DNA Analysis

Interspecific hybridization has been implicated in population declines for some waterfowl species within the mallard complex, and hybridization with mallards (Anas platyrhynchos) is currently considered the largest threat to mottled ducks (A. fulvigula), one North American member of that complex. We assessed genetic variation among 225 mottled ducks and mallards using five microsatellite loci, and detected significant overall differences between these species within two geographic areas. We characterized hybridization in Florida, where mottled ducks are endemic and mallards are beginning to appear on the breeding grounds, and in South Carolina, where mottled ducks were introduced outside their native range. We used Bayesian genetic mixture analysis in an attempt to distinguish between these closely related species. In Florida, we detected two distinct genetic groups, and 10.9% of our samples from Florida mottled ducks were inferred to have been hybrids. In contrast only 3.4% of Florida mallards were inferred to have been hybrids, suggesting asymmetric hybridization. Populations from different geographic areas within Florida exhibited hybridization rates ranging from 0% to 24%. These data indicate a genetic component would be appropriate in actively managing interspecific hybridization in Florida mottled ducks. In contrast, South Carolina mottled ducks and mallards cannot be differentiated.     

Mottled ducks,feral mallards,and their hybrids in Florida

The nonmigratory and endemic Florida mottled duck (Anas fulvigula fulvigula) is facing conservation threats from the combined effects of urbanization and introgressive hybridization with feral mallards (Anas platyrhynchos) and mallard x mottled duck hybrids. In the past, the status of the Florida mottled duck population was assessed during annual aerial surveys and most brown ducks (mottled ducks, mallards, and hybrids of them) detected during the survey would have been mottled ducks. But the release of domesticated mallards for aesthetic purposes has led to increases in the prevalence of mallards-hybrids (mallards or mallard x mottled duck hybrids) throughout peninsular Florida, USA, and because it is impossible to differentiate among mottled ducks, female mallards, and hybrids during aerial surveys, helicopter surveys were halted in 2009 until state researchers could conduct a range-wide study to determine what proportion of brown ducks are mottled ducks versus mallards-hybrids. We used plumage keys and high-resolution photography to categorize brown ducks from 557 wetland grid points as either mottled ducks or mallards-hybrids. Of the 5,179 brown ducks categorized, 40.1% were mottled ducks and 59.9% were mallards-hybrids. We used logistic regression analysis to model the interactive effect of a site's latitude and level of urbanization (urban gradient value within a 2-km buffer) to generate a predictive raster surface (1-km resolution) of the study area with values corresponding to the probability that a brown duck observed within a cell is a pure mottled duck. Predicted values will be used as correction factors when estimating final mottled duck population abundance from brown-duck survey data. Additionally, the predictive raster surface will be used to identify wetlands where mottled ducks remain predominant so that these sites can be targeted for preservation. Overall, mallards-hybrids outnumbered mottled ducks throughout most of peninsular Florida, especially in more urbanized regions, and their current prevalence rate presents a serious conservation threat, via hybridization, to extant mottled duck populations.     

Breeding Ecology of Mottled Ducks: A Review

Mottled ducks (Anas fulvigula) are endemic to the Gulf Coast of North America, and their range stretches from Alabama to the Laguna Madre of Mexico, with a distinct population in peninsular Florida and an introduced population in South Carolina. As one of the few non-migratory ducks in North America, mottled ducks depend on a variety of locally available habitat throughout the annual cycle, and threats to these landscapes may affect mottled ducks more acutely than migratory species. Annual population monitoring has revealed declines in mottled duck populations in Texas and Louisiana since 2008, and the genetic integrity of the Florida population has been muddled by the presence of large numbers of feral mallards (Anas platyrhynchos) resulting in hybridization. Similar to other closely related dabbling ducks, mottled duck populations are influenced by recruitment and breeding season survival, so changes in these factors may contribute to population decline. Accordingly, researchers have attempted to address various aspects of mottled duck breeding season ecology and population dynamics since the 1950s. We conducted a literature review on this topic by searching a combination of key terms using Google Scholar, including mottled duck, nesting ecology, habitat use, breeding incidence, nest success, brood, and breeding season survival, and followed citation trees to eventually aggregate information from nearly 50 publications on mottled duck breeding ecology. Our review concluded that mottled ducks use brackish and intermediate coastal marsh, including managed impoundments, and agricultural land during the breeding season. Their nests can be found in pastures, levees, dry cordgrass marsh, cutgrass marsh, spoil banks, and small islands. Nesting propensity and nest success estimates are often lower than other waterfowl species that are characterized by stable or increasing populations. Broods use wetlands composed of a mix of open water with submerged and emergent vegetation. Breeding season survival is higher for the Florida population than the western Gulf Coast population, but adult survival in both geographies is comparable to (or higher than) that of other dabbling duck species. Breeding habitat use, breeding season survival, and nest-site selection and success have been studied extensively in mottled ducks, whereas information on nesting propensity, renesting intensity, and post-hatch ecology is lacking. © 2021 The Wildlife Society.     

Interspecific hybridization contributes to high genetic diversity and apparent effective population size in an endemic population of mottled ducks (Anas fulvigula maculosa)

Under drift-mutation equilibrium, genetic diversity is expected to be correlated with effective population size (N _e ). Changes in population size and gene flow are two important processes that can cause populations to deviate from this expected relationship. In this study, we used DNA sequences from six independent loci to examine the influence of these processes on standing genetic diversity in endemic mottled ducks (Anas fulvigula) and geographically widespread mallards (A. platyrhynchos), two species known to hybridize. Mottled ducks have an estimated census size that is about two orders-of-magnitude smaller than that of mallards, yet these two species have similar levels of genetic diversity, especially at nuclear DNA. Coalescent analyses suggest that a population expansion in the mallard at least partly explains this discrepancy, but the mottled duck harbors higher genetic diversity and apparent N _e than expected for its census size even after accounting for a population decline. Incorporating gene flow into the model, however, reduced the estimated N _e of mottled ducks to 33 % of the equilibrium N _e and yielded an estimated N _e consistent with census size. We also examined the utility of these loci to distinguish among mallards, mottled ducks, and their hybrids. Most putatively pure individuals were correctly assigned to species, but the power for detecting hybrids was low. Although hybridization with mallards potentially poses a conservation threat to mottled ducks by creating a risk of extinction by hybridization, introgression of mallard alleles has helped maintain high genetic diversity in mottled ducks and might be important for the adaptability and survival of this species.     

Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula)

The mottled duck (Anas fulvigula) is a year-round endemicresident of the Gulf Coast and one of two non-migratory dabbling ducksthat inhabit North America. To investigate population genetic structureof allopatric mottled duck populations, we collected 5' control regionsequences (bp 78–774) from the mitochondria of 219 mottled duckssampled at 11 widely spaced geographic localities in Texas, Louisiana,and Florida and compared them to each other and to homologous sequencesfrom 4 Mexican ducks (A. diazi), 13 American black ducks(A. rubripes), and 10 mallards (A. platyrhynchos). Weidentified 57 unique haplotypes composed of 665 or 666 nucleotides inthe 246 control region sequences. Of the 665 homologous positions,8.3% (n = 55) vary among haplotypes, and98.2% (n = 54) of these occur within the first351 nucleotides from the 5' end of the outgroup sequence.Neighbor-joining analysis shows a large distal clade (52.5% ofmottled ducks sampled in our study) composed of two reciprocallymonophyletic clades of mottled duck haplotypes, one of which is endemicto Texas and Louisiana and the other endemic to Florida. No mottledducks sampled in Florida occur in the clade composed of mottled ducksfrom Texas and Louisiana or vice versa, suggesting that (1) an enduringgeographic split has existed for many years between east and west, and(2) gene flow currently is non-existent (or at least undetectable)across the central Gulf Coast. The remaining 47.5% of mottledducks sampled in our study branch basally from this derived clade, showsubstantially less hierarchical structure, and fall into various lineagegroups of mixed species composition with no geographic orspecies-specific pattern. Pairwise F _ST valuescorroborate the pattern of strong differentiation observed betweenTexas/Louisiana and Florida. Our findings are consistent with apattern of partial lineage sorting from a polymorphic ancestral genepool reshuffled by hybridizing mallards. Control region data andpatterns of divergence in mallard-like species worldwide, furthermore,suggest that mottled ducks are close relatives of Mexican ducks, and inturn nested within black ducks. Genetic similarities to nominatemallards are less likely to be the product of common ancestry, but theresult of past hybridization with a dichromatic mallard ancestor thatinvaded North America from Asia many generations ago. Our findings haveseveral important consequences for the conservation biology of mottledducks across the Gulf Coast and our understanding of the phylogeographyof mallard-like species worldwide.     

Mallard–Black Duck Hybridization and Population Genetic Structure in North Carolina

North Carolina, USA, represents the southern extent of the American black duck's (Anas rubripes) breeding range. Mallards (A. platyrhynchos) are present on the breeding grounds of the American black duck and hybridization is observed between these species; therefore, we assessed the genetic integrity, hybridization rates, and population structure of this local breeding population. We extracted genomic and mitochondrial DNA from chorioallantoic membranes and contour feathers from monitored black duck nests. We then prepared the extracted DNA for analysis using high-throughput DNA sequencing methods (ddRAD-seq). First, we assessed nuclear and mitochondrial population structure, genetic diversity, and differentiation across samples from North Carolina, and compared them against 199 genetically vetted mallards, black ducks, and mallard × black duck hybrids that served as genetic references. Next, we tested for parentage and sibling relationship and overall relatedness of black ducks in North Carolina. We recovered strong population structure and high co-ancestry across genetic markers due to interrelatedness among sampled nests in North Carolina and concluded that black ducks have been locally breeding in this area for a prolonged period of time. Despite a high level of interrelatedness among our samples, nucleotide diversity was similar to the reference continental black duck population, suggesting little effect of genetic drift, including inbreeding. Additionally, we conclude that molecular diversity of black ducks in North Carolina is maintained at reference population levels through the influx of genetic material from unrelated, migrating male black ducks. Finally, we report a hybridization level of 47.5%, covering 3 filial generations. Of identified hybrids, 54.7% and 53% were the direct result of interbreeding between black ducks and captive-reared or wild mallards, respectively. We conclude that because of high rates of interspecific hybridization and successive backcrossing events, introgression from wild and feral mallards is occurring into this population of breeding black ducks and requires careful consideration in future management efforts. © 2021 The Wildlife Society.     

Variation in Survival and Harvest Rates in Florida Mottled Duck

The Florida mottled duck (Anas fulvigula fulvigula) inhabits a relatively small range of approximately 90,000 km² within peninsular Florida, USA, and is threatened by habitat loss and genetic introgression with feral mallards (Anas platyrhynchos). Moreover, the Florida mottled duck population status has not been assessed for more than a decade. We used band-recovery and recapture data from 2000–2013 to examine geographic and demographic factors that influence the survival of Florida mottled ducks and to determine whether survival and harvest probabilities have changed over time. Mean survival probabilities were higher for birds banded in the southern portion of their Florida range than for those banded in the northern portion and higher for adult males than for adult females in both areas. Harvest probabilities increased in the northern extent of its range in Florida for adults and juveniles and remained relatively constant in the southern portion of its range during the study period. Mean harvest probabilities for adult males in both areas were higher than for adult females. Mean harvest probability for juvenile females was higher than that for juvenile males in the north but was similar between the sexes in the south. Our results suggest that mortality rates are generally greater in the northern portion of the Florida mottled duck range because of regional differences in habitat distribution and permanence and in how mottled ducks and humans use wetlands in these areas. We suggest increasing conservation efforts in the north portion of the Florida mottled duck range and improving inferences from leg banding by incorporating live recapture data. © 2020 The Wildlife Society.     

Assessing changes in genomic divergence following a century of human‐mediated secondary contact among wild and captive‐bred ducks

Along with manipulating habitat, the direct release of domesticated individuals into the wild is a practice used worldwide to augment wildlife populations. We test between possible outcomes of human‐mediated secondary contact using genomic techniques at both historical and contemporary timescales for two iconic duck species. First, we sequence several thousand ddRAD‐seq loci for contemporary mallards (Anas platyrhynchos) throughout North America and two domestic mallard types (i.e., known game‐farm mallards and feral Khaki Campbell's). We show that North American mallards may well be becoming a hybrid swarm due to interbreeding with domesticated game‐farm mallards released for hunting. Next, to attain a historical perspective, we applied a bait‐capture array targeting thousands of loci in century‐old (1842–1915) and contemporary (2009–2010) mallard and American black duck (Anas rubripes) specimens. We conclude that American black ducks and mallards have always been closely related, with a divergence time of ~600,000 years before present, and likely evolved through prolonged isolation followed by limited bouts of gene flow (i.e., secondary contact). They continue to maintain genetic separation, a finding that overturns decades of prior research and speculation suggesting the genetic extinction of the American black duck due to contemporary interbreeding with mallards. Thus, despite having high rates of hybridization, actual gene flow is limited between mallards and American black ducks. Conversely, our historical and contemporary data confirm that the intensive stocking of game‐farm mallards during the last ~100 years has fundamentally changed the genetic integrity of North America's wild mallard population, especially in the east. It thus becomes of great interest to ask whether the iconic North American mallard is declining in the wild due to introgression of maladaptive traits from domesticated forms. Moreover, we hypothesize that differential gene flow from domestic game‐farm mallards into the wild mallard population may explain the overall temporal increase in differentiation between wild black ducks and mallards, as well as the uncoupling of genetic diversity and effective population size estimates across time in our results. Finally, our findings highlight how genomic methods can recover complex population histories by capturing DNA preserved in traditional museum specimens.     

Temporal variation and landcover influence survival in adult female mottled ducks

Adult survival is a key driver of waterfowl population growth and is subject to temporal and spatial variation. Mottled ducks (Anas fulvigula) are native to the Gulf Coast and peninsular Florida, USA, and have suffered population declines over the past decade, especially in Texas and Louisiana, USA. Although the cause of this decline is not well understood, previous research concluded variation in survival contributed to nearly a third of variation in the species' population growth rate. We used global positioning system-groupe spécial mobile (GPS-GSM) transmitters to study temporal and spatial variation in survival of adult female western Gulf Coast mottled ducks in southwestern Louisiana, 2017–2020. We evaluated weekly survival models parameterized with combinations of hunted and non-hunted periods, biological seasons, and landcover types that were used by mottled ducks. There were 3 competitive survival models, and all contained 4 parameters that parsed the annual cycle into the non-hunted period, first part of the general waterfowl season, and second part of the waterfowl season, and included the proportion of GPS locations in agricultural lands. Weekly survival was 0.979 during the first part of the general waterfowl hunting season, and 0.996 during the second part of the general waterfowl season. Daily survival rate increased with an increasing proportion of locations logged in agricultural lands. Annual survival rates were similar to other waterfowl that are not experiencing population declines, which suggests survival is not limiting population growth of mottled ducks along the western Gulf Coast. Managers should ensure the availability of refuge areas where hunting is prohibited during the first part of the general waterfowl season, when mottled ducks are at an increased risk of mortality, in addition to the targeted conservation of agricultural lands that provide cover and forage.     

Inheritance patterns of enzymes and serum proteins of mallard-black duck hybrids

From 1974 to 1976, a breeding program was used to produce hybrids of black ducks and mallards for the evaluation of inheritance patterns of serum proteins and serum, liver and muscle enzymes. In addition to the crosses designed to produce hybrids, a series of matings in 1975 and 1976 were designed to evaluate inheritance patterns of a hybrid with either a black duck or mallard. At the F₁ level, hybrids were easily distinguished using serum proteins. However, once a hybrid was crossed back to either a mallard or black duck, only 12–23% of the progeny were distinguishable from black ducks or mallards using serum proteins and 23–39% using esterases. Muscle, serum and liver enzymes were similar between the two species.     

Identifying hybrids & the genomics of hybridization: Mallards & American black ducks of Eastern North America

Resolving evolutionary relationships and establishing population structure depends on molecular diagnosability that is often limited for closely related taxa. Here, we use 3,200 ddRAD‐seq loci across 290 mallards, American black ducks, and putative hybrids to establish population structure and estimate hybridization rates. We test between traditional assignment probability and accumulated recombination events based analyses to assign hybrids to generational classes. For hybrid identification, we report the distribution of recombination events complements ADMIXTURE simulation by extending resolution past F4 hybrid status; however, caution against hybrid assignment based on accumulated recombination events due to an inability to resolve F1 hybrids. Nevertheless, both analyses suggest that there are relatively few backcrossed stages before a lineage's hybrid ancestry is lost and the offspring are effectively parental again. We conclude that despite high rates of observed interspecific hybridization between mallards and black ducks in the middle part of the 20th century, our results do not support the predicted hybrid swarm. Conversely, we report that mallard samples genetically assigned to western and non‐western clusters. We indicate that these non‐western mallards likely originated from game‐farm stock, suggesting landscape level gene flow between domestic and wild conspecifics.     

Identification of endangered Hawaiian ducks (Anas wyvilliana), introduced North American mallards (A. platyrhynchos) and their hybrids using multilocus genotypes

Hawaiian ducks (Anas wyvilliana), or koloa, are endemic to the Hawaiian Islands and are listed as a federal and state endangered species. Hybridization between koloa and introduced mallards (A. platyrhynchos) is believed to be a primary threat to the recovery of koloa. We evaluated the utility of two sets of nuclear markers (microsatellite loci and amplified fragment length polymorphisms) and a variable portion of the mitochondrial DNA control region to distinguish among koloa, mallards, and hybrids. We show that microsatellite and AFLP markers can be used to distinguish between koloa and mallard-koloa hybrids with a high degree of confidence. For all but one of the putative koloa in our sample, the posterior probability of belonging to the koloa category was >0.90. Similarly all but one of the mallard-koloa hybrids were assigned to the hybrid category with posterior probabilities >0.98. Subsets of markers led to poorer resolution among koloa, mallard and hybrid categories. Among a sample of 61 koloa, hybrids and mallards, we found 25 different mtDNA haplotypes, belonging to two groups of haplotypes (A and B) identified previously in mallards and their relatives. All putative koloa samples exhibited group B haplotypes, of which 65% comprised one haplotype, while the rest were divided among four haplotypes. All Hawai’i mallard samples exhibited haplotypes that belonged to group A. Hybrids and California mallards exhibited haplotypes belonging to both groups, but a majority were of group A, suggesting that hybridization may more commonly involve mating between Hawai’i mallard females and koloa males.     

Mottled Duck introductions to South Carolina: The ugly,the bad,and the good?

Translocations or other movements of wildlife sometimes accomplish their intended objectives, but unforeseen consequences may arise and disrupt locally adapted ecological communities, restructure or dilute genetic integrity of populations or subspecies of the moved organism, and otherwise negatively influences a species’ long‐term fitness. Two historical populations of Mottled Ducks (Anas fulvigula) exist and are endemic to (1) Mexico and the West‐Gulf Coast (A. f. maculosa) regions of the United States and (2) Florida (A. f. fulvigula). From 1975 to 1983, 1285 Mottled Ducks from Florida, Louisiana, and Texas were released to coastal South Carolina, primarily to ultimately establish a legally harvestable population. This movement stirred mixed reactions amid the conservation community. Contemporary information suggests an increasing Mottled Duck population in South Carolina and possibly dispersing into Georgia. Herein, I objectively discuss the potential consequences of this new population per the birds’ evolution, ecology, and management. Ultimately, I suggest that this translocation is a long‐term benefit to the species.     

Persistence of an endangered native duck,feral mallards,and multiple hybrid swarms across the main Hawaiian Islands

Interspecific hybridization is recognized as an important process in the evolutionary dynamics of both speciation and the reversal of speciation. However, our understanding of the spatial and temporal patterns of hybridization that erode versus promote species boundaries is incomplete. The endangered, endemic koloa maoli (or Hawaiian duck, Anas wyvilliana) is thought to be threatened with genetic extinction through ongoing hybridization with an introduced congener, the feral mallard (A. platyrhynchos). We investigated spatial and temporal variation in hybrid prevalence in populations throughout the main Hawaiian Islands, using genomic data to characterize population structure of koloa, quantify the extent of hybridization, and compare hybrid proportions over time. To accomplish this, we genotyped 3,308 double‐digest restriction‐site‐associated DNA (ddRAD) loci in 425 putative koloa, mallards, and hybrids from populations across the main Hawaiian Islands. We found that despite a population decline in the last century, koloa genetic diversity is high. There were few hybrids on the island of Kaua?i, home to the largest population of koloa. By contrast, we report that sampled populations outside of Kaua?i can now be characterized as hybrid swarms, in that all individuals sampled were of mixed koloa × mallard ancestry. Further, there is some evidence that these swarms are stable over time. These findings demonstrate spatial variation in the extent and consequences of interspecific hybridization, and highlight how islands or island‐like systems with small population sizes may be especially prone to genetic extinction when met with a congener that is not reproductively isolated.     

Genetic admixture supports an ancient hybrid origin of the endangered Hawaiian duck

Speciation is regarded primarily as a bifurcation from an ancestral species into two distinct taxonomic units, but gene flow can create complex signals of phylogenetic relationships, especially among different loci. We evaluated several hypotheses that could account for phylogenetic discord between mitochondrial DNA (mtDNA) and nuclear DNA (nuDNA) within Hawaiian duck (Anas wyvilliana), including stochastic lineage sorting, mtDNA capture and widespread genomic introgression. Our results best support the hypothesis that the contemporary Hawaiian duck is descended from an ancient hybridization event between the mallard (Anas platyrhynchos) and Laysan duck (Anas laysanensis). Whereas mtDNA clearly shows a sister relationship between Hawaiian duck and mallard, nuDNA is consistent with a genetic mosaic with nearly equal contributions from Laysan duck and mallard. In addition, coalescent analyses suggest that gene flow from either mallard or Laysan duck, depending on the predefined tree topology, is necessary to explain contemporary genetic diversity in Hawaiian ducks, and these estimates are more consistent with ancient, rather than contemporary, hybridization. Time since divergence estimates suggest that the genetic admixture event occurred around the Pleistocene–Holocene boundary, which is further supported by circumstantial evidence from the Hawaiian subfossil record. Although the extent of reproductive isolation from either putative parental taxon is not currently known, these species are phenotypically, genetically and ecologically different, and they meet primary criteria used in avian taxonomy for species designation. Thus, the available data are consistent with an admixed origin and support the hypothesis that the Hawaiian duck may represent a young hybrid species.     

Genetic structure of Eurasian and North American mallard ducks based on mtDNA data

To elucidate the origin and genetic structure of the domesticated duck in Eurasia and North America, we sequenced 114 duck D-loop sequences and retrieved 489 D-loop sequences from GenBank. In total, 603 ducks including 50 duck breeds/populations from eight countries (China, France, Russia, India, Kazakhstan, Mongolia, Thailand and USA) were used in this study. One hundred and thirty-four haplotypes and 81 variable sites were detected. H49 was the predominant haplotype, which was considered to be the same dominant haplotype found in the previous studies, and was found in 309 birds. The smallest values for both genetic differentiation index (F(ST), 0.04156) and the number of the net nucleotide substitutions between two populations (D(A), 0.00018) were observed between Eurasian domestic ducks and Eurasian mallards. No geography, breed or population clusters were observed in the Eurasian domestic ducks and mallards. Five haplotypes were shared by USA mallards and Eurasian domestic duck/Eurasian mallards. Only one haplotype (H49) was shared by Eurasian domestic ducks and China spot-billed ducks. By combining phylogenetic analyses, haplotype network profile, genetic distances and shared haplotypes, we can draw two major conclusions: (i) Eurasian and North American mallards show a clear geographic distribution pattern; (ii) Eurasian domestic ducks are derived from the Eurasian mallards, not from the spot-billed ducks.     

Phylogeography of the New Zealand blue duck (<Emphasis Type="Italic">Hymenolaimus malacorhynchos</Emphasis>): implications for translocation and species recovery

Translocation of individuals among extant populations is an important tool in species conservation that allows managers to supplement dwindling populations and potentially alleviate the deleterious effects of inbreeding. Ideal translocation strategy should consider historical relationships among existing populations to avoid potential disruption of population subdivision and local adaptation. Here, we examine mitochondrial sequence variation in the endangered blue duck Hymenolaimus malacorhynchos, a New Zealand endemic riverine specialist, to facilitate informed decision making in future translocations. Behavioural observations suggest that blue duck dispersal is limited and may result in genetic structure within and between regional populations. We analysed 894 base pairs of mitochondrial control region in 78 adult blue ducks sampled from 11 river catchments across the species’ range (representing four regions in the North Island and three regions in the South Island) and found strong and significant genetic structure both within and among islands. These results, combined with a 2.0% sequence divergence between islands, indicates that North Island and South Island blue ducks should be treated as separate management units. The relationship between genetic differentiation and geographic distance for blue ducks on the South Island conformed to an “isolation by distance” pattern. Overall, we recommend that translocations of blue ducks should not be made between the North and the South Islands and those within each island should be restricted to neighbouring catchments.     

Correlation Between Nest and Duckling Survival of Mallards Breeding in Saskatchewan

Abstract: Few studies have estimated reproductive and survival parameters of breeding ducks simultaneously, although such efforts can reveal relationships among vital rates. We estimated survival of mallard (Anas platyrhynchos) nests and duckling on 8 study sites in south-central Saskatchewan during spring and summer 2000 and 2001. We observed a strong positive correlation between these parameters (r = 0.914) and through analysis of residual values found 14% of the relationship was explained by a predator-removal treatment, 26% by year effects, 44% by spatial variation, and 16% unexplained. Potential mechanisms include similar environmental factors influencing both parameters (e.g., predators) and positive density dependence. Information regarding covariation among vital rates is important in construction and interpretation of population growth models describing population dynamics of mallards and other upland-nesting ducks.     

Hybridization between white-headed ducks and introduced ruddy ducks in Spain

The ruddy duck, Oxyura jamaicensis, was introduced to Great Britain in the mid-20th century and has recently spread to other Western European countries. In Spain, ruddy ducks hybridize with the globally endangered white-headed duck, Oxyura leucocephala. We assessed the effects of hybridization on the Spanish white-headed ducks, which constitute 25% of the global population of this species, using a panel of eight nuclear intron markers, 10 microsatellite loci, and mtDNA control region sequences. These data allowed parental individuals, F(1) hybrids, and the progeny of backcrossing to be reliably distinguished. We show that hybrids between the two species are fertile and produce viable offspring in backcrosses with both parental species. To date, however, we found no extensive introgression of ruddy duck genes into the Spanish white-headed duck population, probably due to the early implementation of an effective ruddy duck and hybrid control programme. We also show that genetic diversity in the expanding European ruddy duck population, which was founded by just seven individuals, exceeds that of the native Spanish white-headed duck population, which recently recovered from a severe bottleneck. Unless effective control of ruddy ducks is continued, genetic introgression will compromise the unique behavioural and ecological adaptations of white-headed ducks and consequently their survival as a genetically and evolutionary distinct species.     

A Century of Hybridization: Decreasing Genetic Distance Between American Black Ducks and Mallards

American black ducks (Anas rubripes) and mallards (A. platyrhynchos) are morphologically and behaviorally similar species that were primarily allopatric prior to European colonization of North America. Subsequent sympatry has resulted in hybridization, and recent molecular analyses of mallards and black ducks failed to identify two distinct taxa, either due to horizontal gene flow, homoplasy, or shared ancestry. We analyzed microsatellite markers in modern and museum specimens to determine if the inter-relatedness of mallards and black ducks was an ancestral or recent character. Gst, a measure of genetic differentiation, decreased from 0.146 for mallards and black ducks living before 1940, to 0.008 for birds taken in 1998. This is a significant reduction in genetic differentiation, and represents a breakdown in species integrity most likely due to hybridization. Using modern specimens, we observed that despite a lower incidence of sympatry, northern black ducks are now no more distinct from mallards than their southern conspecifics.