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HarlequinHistrionicus histrionicus |
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Birds of America by John James Audubon The Harlequin Duck : recent discoveries http://www.qc.ec.gc.ca/faune/sauvagine/html/information_hd.html Harlequin Duck Satellite tracking Activity Budgets of molting Harlequin Ducks
Histrionicus histrionicus at the Gannet Islands, Labrador. Within-Season Moulting And Wintering Site Philopatry In
Harlequin Ducks. Winter Philopatry In Harlequin Ducks: Implications For
Their Conservation In The Strait Of Georgia,
BC. The timing of pair formation in Harlequin Ducks
Robertson, Modeling The Population Demography Of Harlequin Ducks
Population demography models are valuable tools in detecting population trends and identifying crucial components in the life history of a species. They are also useful in determining critical research needs to estimate needed parameters. A matrix-based p opulation model was expanded for Harlequin Ducks (Histrionicus histrionicus) originally developed by Goudie et al. (1994, Trans. North Am. Wildl. Nat. Resour. Conf. 59:27- 49.). A population growth rate of 16% (lambda=1.16) and a stable age distribution of 32.5% juveniles per year was calculated using parameters extracted from the literature. Both of these two values are much higher than seen in the Pacific Northwest populations (lambda ~= 1.00 and the proportion of juveniles ~= 10-15%). The population growth rate was most sensitive to survival of older age classes, however adult survival probably varies little on an annual basis. Juvenile survival (post-fledging to the following spring) and adult breeding propensity ha d a lesser effect on the population growth rate than adult survival, however, these two parameters are both, hard to estimate accurately, and, vary considerably between years. Lowering adult survival rates did not lower the proportion of juveniles in the projected population, unlike lowering juvenile survival and breeding propensity. Thus, the estimates of breeding propensity (0.6) and/or juvenile survival (0.5) must be higher than the actual field value. I decomposed the projection matrix into two matri ces, a breeding ground matrix and a non-breeding matrix to examine the effects of these periods separately. A substantial proportion of the sensitivity in the population growth rate occurs during the non-breeding period. Simulations using two different b reeding sites varying in quality revealed that movements of adults between sites had a greater impact on the population growth rate than juvenile movements. Better estimates for adult survival (breeding and non-breeding), juvenile survival and breeding pr opensity are currently being gathered and will be incorporated into future modeling efforts. Timing Of Pairing And Molt Chronology Of Harlequin
Ducks. Winter pair formation is one of the more unique aspects of waterfowl biology. Besides the dabbling ducks, relatively little is known about the chronology of pair formation and factors, such as molt chronology, which cause the between individual variation in the timing of pair formation. A small (60 - 100 birds) molting and wintering population of Harlequin ducks (Histrionicus histrionicus) was studied from June to November 1995 to assess the molting and pairing chronology of this population. Males returned from the breeding grounds in June and July, and immediately began the pre-basic molt. Most males were in the basic plumage and flightless by late July through August. The pre- alternate molt began in September and most males were back in full alternate plumage by the beginning of October. Courtship and pairing began immediately after the finish of the pre-alternate molt. At the time some males were in alternate plumage and others were still molting, males in alternate plumage exhibited courtship behavio r more frequently. Through August and September, the sexes tended to segregate into same sex groupings and males were clumped into large groups, possibly interacting and establishing a dominance hierarchy. In October, mixed sex groups were more prevalent and all the ducks were much more dispersed. Pair formation peaked at two different periods during the non-breeding season. Adult females re-established previous pair bonds with males in the fall and young females, presumably pairing for the first time, p aired in the spring. As males are molting immediately after arrival on the molting grounds and begin to court females immediately after they have finished their molt, it is very likely that there is strong sexual selection for early pairing in Harlequin Ducks, and probably most other sea ducks. Molt Speed Predicts Pairing Success in Male Harlequin
Ducks. Moult Chronology And The Timing Of Pairing In Harlequin Ducks. *Gregory J. Robertson, F. Cooke, R. I. Goudie and W.S. Boyd. Department of Biological Sciences, Simon Fraser University, Burnaby, B.C., V5A 1S6, CANADA & Pacific Wildlife Research Centre, Canadian Wildlife Service, 5421 Robertson Rd., Delta, B.C. V4K 3N2, CANADA. Unlike most other birds, waterfowl pair on their wintering grounds, not the breeding grounds. Across waterfowl species, larger dabbling ducks pair the earliest (starting in November), smaller dabblers and diving ducks pair closer to the spring. Very little is known about the pairing chronology of sea ducks. A small (60 -100 birds) moulting and wintering population of Harlequin ducks was studied from June to November 1995 to assess the moulting and pairing chronology of this population. Males returned from the breeding grounds in June and July, and immediately began the pre-basic moult. Most males were in the basic plumage and flightless by late July through August. The pre- alternate moult began in September and most males were back in full atternate plumage by October 1. Courtship and pairing began immediately after the finish of the pre- alternate moult. Through August and September the sexes tended to segregate into same sex groupings. Additionally through this period males clumped into progressively larger and larger groupings, possibly interacting to determine a dominance hierarchy. In October mixed sex groups were more prevelent and all the ducks were much more dispersed. As males are moulting immediately after arrival on the moulting grounds and begin to pair immediately after they have finished their moult, it is very likely that there is strong sexual selection for early pairing in Harlequin, and probably other, sea ducks. Molt and the basic plumage of male Harlequin Ducks Sex-biased winter philopatry in Harlequin Ducks: are
waterfowl really an exception to the rule? Many birds species exhibit a resource based mating system where males defend breeding territories. This mating system is thought to have lead to male-biased philopatry as male birds are better able to defend familiar territories. In contrast, female waterfowl are more likely than males to return to their breeding grounds. Waterfowl are the exception because males cannot economically defend breeding territories and a mate-defense system has evolved. However, waterfowl pair in the winter. If male waterfowl can defend winter territories a resource defense mating system may evolve and, consequently, male-biased philopatry to the wintering grounds. Since August 1994 I have studied a small population of wintering Harlequin Ducks (Histrionicus histrionicus) in coastal southwestern British Columbia. Locally, a total of 122 individuals have been caught during the wing molt and marked with individually identifiable tarsal leg bands. Weekly surveys were conducted to assess population size, sex ratio, age structure and as many bands as possible were read. The local population size and sex ratio fluctuated considerably over the two winter seasons. An influx of young males and unpaired males occurred in April of each year, before departure to the breeding grounds. Males moved around the study site more than females. Unpaired males moved around the study site more than paired males. Return rates from one season to the next were high (males: 72%, females: 66%) and did not differ between the sexes. Pairing occurred early in the winter (November) and pair re- formation occurred in 4 pairs where both members returned to the study area. Harlequin Ducks appear to have a mate-defense mating system and male- biased winter philopatry would not be expected. Movements and temporary emigration of moulting and wintering Harlequin Ducks. Gregory J ROBERTSON, Fred COOKE CWS/ NSERC Wildlife Ecology Research Chair, Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada R Ian GOUDIE and W Sean BOYD Pacific Wildlife Research Centre, 5421 Robertson Rd., Delta, BC V4K 3Y3, Canada Over 2500 Harlequin Ducks (Histrionicus histrionicus) have been marked with individually identifiable tarsal leg bands in the Pacific Northwest of North America. Two of these populations have been intensively studied near Vancouver, British Columbia over three winters (1994-1996). Intensive marking and surveys were done at these two sites (White Rock and Point Roberts, WA) to assess movement patterns and emigration of Harlequin Ducks. Because the population size and the number of birds assessed for bands was known on all surveys, independent estimates of p* could be obtained, allowing temporary emigration to be estimated. Some proportion of the marked population of both sexes temporally emigrated from the White Rock study site in the mid-winter and in the spring. Independent assessments of p* also provided the ability for us to estimate the probability that an individual bird was not present at the study sites for a given period of time. Some birds were not sighted for long periods of time (i.e. months) while other birds were sighted as often as expected based on our estimates of p*. The estimated number of banded and unbanded birds also varied significantly over the year at White Rock. Some unmarked birds moved into the White Rock study area after the moult while some marked birds departed. Only one male changed moulting grounds (1 of 50, WR to PR), no females exchanged moulting sites (0 of 71). After the wing moult some WR females (9 of 47 (19.1%) in 1995) were sighted at PR , however a reciprocal movement of PR females to WR was not detected (0 of 24 birds). Similar movements of males were not seen. On the scale of months our p value approaches 1.0, therefore individual which stay longer than a month after moving should be detected. Smaller intensive studies (either through intense re-sightings effort or radio tracking a small portion of the population) can provide valuable insights when designing and analyzing a large scale CMR data set to eliminate potential sources of bias due to temporary emigration. For example, we found low levels of exchange during the moult, yet afterwards significant numbers of females moved to other sites. Therefore, a re- sighting effort done after the moult would result in fewer local females being resighted, thereby underestimating female survival as compared to the males. Movements And Survival Of Molting And Wintering
Harlequin Ducks Movement or emigration can significantly effect estimates of survival obtained from capture-mark-recapture (CMR) studies. We estimate both movement and survival of a molting and wintering population of Harlequin Ducks (Histrionicus histrionicus) in coastal southwestern British Columbia. Over 150 individuals from two populations 15 km apart were marked with individually identifiable colored tarsal bands. Surveys were conducted at both sites throughout the entire non-breeding period. At the main study site of White Rock, complete population counts were taken and the number of unmarked birds in the population was also assessed. Significant movements of individuals were detected all throughout the non-breeding period. A number of males and females departed from the study area after the molt in the fall, only to be replaced by an influx of birds from other molting sites. The timing of this movement differed between the sexes as the females molt approximately six weeks later than the males. An additional influx of birds, mostly unpaired males, occurred in the spring before departure for the breeding grounds. Exchanges between the two sites appeared to biased in one direction. More birds moved from the inland site to the more coastal site than vice versa. Furthermore, more females (9 of 47) than males (1 of 50) made this move. Young (second and third year) females were more likely to move out of the study sites or exchange study sites than adult females. Annual return rates were similar in the first year of the study (65% of females and 74% males) however fewer females, (54% of females and 80% of males) returned in the second season. We documented only one mortality (a male) during the non-breeding period. The lower apparent survival of females may be due to a truly lower survival rate or a function of the greater propensity of females to move between areas of suitable habitat. Harlequin Duck Participant in LIA study: "When I used to go hunting, different species of birds were getting scarcer, like the harlequin ducks, they were declining fast. I used to see them in all the bays in the 1970s to the 1980s." (Williamson 1997:36) The harlequin duck is a relatively uncommon seaduck considered unique among North American waterfowl because of its discontinuous distribution and its habit of breeding along swiftly flowing streams (Bellrose 1976; Todd 1963; Dzinbal 1982; Williamson 1997: 36). COSEWIC has designated the eastern North American population as endangered. The breeding distribution (Figure 18.1) of this population includes southern Baffin Island, Ungava Bay, northern Labrador, the Gaspé Peninsula, Hudson Bay, James Bay, and western Newfoundland (Montevecchi et al. 1995). Goudie (1989) estimated the former (during first European contact) size of this population at 5,000-10,000. Vickery (1988) examined the winter distribution of this population during the 1980s and estimated less than 1,000 known individuals within coastal Newfoundland, the Maritimes, and New England (Figure 18.1). Goudie (1989) suggests hunting as the dominant factor for the decline. Species of Special Conservation Status Figure 18.1 Distribution of Harlequin Ducks in Eastern North America Recent surveys by the Canadian Wildlife Service within the breeding area of the eastern North American population (Montevecchi et al. 1995), the Department of National Defence (LFA 1992; JWEL 1992; JWEL 1994; JWEL 1995; JWEL 1996; JWEL 1997a), Hydro-Quebec (Morneau and Decarie 1993), and VBNC (JWEL 1997b) suggest that the current population is likely larger than that suggested by Vickery (1988). This is consistent with increasing trends in numbers at traditional wintering sites since the late 1980s and early 1990s. Canadian Wildlife Service Hinterland Who's Who Harlequin http://www.cws-scf.ec.gc.ca/hww-fap/harlduck/harlequin.html ADFG Wildlife Notebook Series - Harlequin http://www.state.ak.us/local/akpages/FISH.GAME/notebook/bird/harlequn.htm Anderson, M.G., R.D. Sayler and A.D. Afton. 1980. A decoy trap for diving ducks. J. Wildl. Manage. 44:217-219 Harlequin Duck Recovery From The Exxon Valdez Oil Spill: A Population
Genetics Perspective Methods. –We compared genetic characteristics of four aggregations of molting birds (referred to as populations) captured within each of two regions (PWS and APKA, Fig. 1). Because band resightings and radio telemetry data indicate Harlequin Ducks almost always winter at or near their molting sites (Robertson 1997, D. Esler unpubl. data), we considered these molting aggregates to represent discrete winter populations. Sampling sites within PWS region included Bay of Isles, the Green Island area, the Foul Bay area and Montague Island, whereas sampling sites within APKA region included Uganik and Uyak bays and Afognak Island of the Kodiak Archipelago, and southern portions of the Alaska Peninsula. Molting Harlequin Ducks were captured at each of the eight sampling sites during July to Sept of 1995, 1996 and 1997 by herding the flightless birds into pens (after Clarkson and Goudie 1994). The sex of each duck was determined by plumage characteristics and aged by bursal probing (Mather and Esler in press). Blood was extracted from the jugular or tarsal vein and preserved with lysis buffer (Longmire et al. 1988). DNA was extracted using Puregene DNA extraction kits (Gentra Systems, Inc., Minneapolis, MN) and standard proteinase-K, phenol-chlorophorm methods (Sambrook et al. 1991). Thirty-three microsatellite loci (Fields and Scribner 1997, Cathy et al. 1998, Buchholtz et al. 1998; Scribner, unpubl. data) were examined for variation by screening two individuals each from four populations on the west coast of North America. Of these, four bi-parentally inherited loci (Sfi?4, Hhi?2, Hhi?5, and Bca?10) and two sex- linked loci (Sfi?1, Bca?4) were variable. The sex-linked (Z-specific) loci provide an estimate of male-mediated gene flow from the preceding generation if sampling is conducting using females. Microsatellite loci were assayed using the polymerase chain reaction, employing end-labeled (32P-?ATP) primers. Specific conditions for each locus are available from R. Lanctot. Products were visualized on 6% denaturing polyacrylamide sequencing gel after autoradiography. A M13 sequencing reaction (Amersham Life Sciences Sequenase Kit, Arlington Heights, IL) and individual standards of known genotypes were run adjacent to the samples to provide an absolute-size marker for determining the size of microsatellite alleles. Mitochondrial DNA (mtDNA) specific primers were designed so that mtDNA sequences, and not nuclear DNA sequences originating from transposed mtDNA (numt, Sorenson and Fleischer 1996), would be amplified. This was verified by sequencing mitochondrial rich heart and mitochondrial poor blood DNA extracts from the same individual as described in Sorenson and Quinn (1998). Using the mtDNA specific primers, we amplified a ?385 base-pair fragment of the 5' end of the control region which is comparable to the hypervariable region 1 of the mammalian mtDNA control region (Vigilant 1990, Wakely 1993). Mitochondrial DNA specific primers included HADUM1L (L16744, ref. Chicken, Desjardins and Morais 1990): 5' TGC CCG AGA CCT ACG GCT C 3'; HADUM2L (L12, ref. Chicken, Desjardins and Morais 1990): 5' TCT AAA ATG ACT CAA CAG TGC C 3'; and HADUMITH (H737, ref. Chicken, Desjardins and Morais 1990): 5' TGA GTA ATG GTG TAG ATA TCG 3'. Nuclear specific primers included HADUN1L (L16744, ref. Chicken, Desjardins and Morais 1990): 5' TAC CCG AGA CCT ACA GCT T 3' and HADUNUCH (H737, ref. Chicken, Desjardins and Morais 1990): 5' TGA GTT ATG GTG TAG ATA CTA 3'. MtDNA sequences (Genbank accession numbers AF101372-81) were obtained by matching either the HADUM1L and HADUM2L primers with the HADUMITH primer. Mitochondrial DNA was PCR-amplified, purified and sequenced using Sequitherm's EXCEL DNA Sequencing Kits (Epicentre Technologies, Madison, WI) and 1.5 mM of HADUMITH primer (contact S. Talbot for specific information). Sequences were visualized using autoradiography, manually scored and aligned. Genetic analyses were restricted to birds ?1 year of age. Data from males and females were used for the bi-parentally inherited loci, but were restricted to females for the maternally inherited mtDNA and sex-linked microsatellite loci. For each population, all bi-parentally inherited loci were tested for linkage (all two-locus comparisons) and Hardy-Weinberg disequilibrium using the Fisher's Exact Test in the Genetics Data Analysis (GDA) program (Lewis and Zaykin 1998). P-values were adjusted for the number of statistical tests. Mean number of alleles per locus were calculated using BIOSYS (Swofford and Selander 1989). We estimated observed (Ho) and expected (He) heterozygosity under Hardy-Weinberg assumptions for each locus (BIOSYS) and for each population and locus (GDA). These estimates of Ho and He were used to generate inbreeding coefficients (F = 1-[Ho/He]) combined across loci for each population (Wright 1951) and tested for significance as described in Li and Horivitz (1953). Statistical analyses of spatial heterogeneity in gene frequency between and within regions for each locus were assessed using hierarchical F-statistics (Weir 1996) in the GDA program at three levels: (1) among individuals within populations, (2) among populations within regions, and (3) between regions. We also calculated RST, an analogue of FST (Michalakis and Excoffier 1996) using the Analysis of Molecular Variance (AMOVA) program (Excoffier et al. 1992). Significance of FST values was based on 95% confidence intervals determined by bootstrapping across loci. Confidence intervals that overlap zero were considered non-significant. We used allele frequencies to calculate Cavalli-Sforza and Edwards (1967) chord distances among the populations and constructed boot-strapped population trees using subroutines within the PHYLIP program (Version 3.572c, Felsenstein 1993). This distance metric has been described as producing robust tree topologies for groups separated evolutionarily over time periods comparable to these populations (Takezaki and Nei 1996). We used birds sampled at Shemya, on the outer Aleutian Islands of Alaska, as an outgroup in this analysis. For the Sfi?1 and Bca?4 sex-linked loci, we calculated allele frequencies and a measure of genetic diversity (D, equation 8.3, Nei 1987). Estimates of variance among individuals within populations (?SC), among populations within regions (?CT), and between regions (?ST) were derived using the AMOVA program. Mitochondrial DNA sequence haplotypes were assigned based on at least a single base-pair substitution or insertion/deletion across the 163 base-pair segment. Pairwise haplotype distances were calculated by the MEGA program (Kumar et al. 1991) and used to estimate haplotype (h) and nucleotide diversity (?) indices for nonselfing populations (equations 8.1 and 10.4, respectively of Nei 1987) using the REAP program (McElroy et al. 1991). We tested heterogeneity of genotype distribution among samples using Monte- Carlo resampling and the chi-square test of Roff and Bentzen (1989). This approach is suitable for genetic data matrices in which many or most elements are very small (<5) or zero. Estimates of regional, population and individual variance (F-statistics) in haplotype frequency were assessed using the AMOVA program as discussed by Excoffier et al. (1992). We considered haplotype frequencies alone and by weighting the number of base-pair substitutions among haplotypes. Evolutionary relationships among haplotypes were estimated using distances generated under the Tamura-Nei model of sequence evolution (Tamura-Nei 1992). The neighbor-joining method of Saitou and Nei (1987) was used to generate the evolutionary tree. We next determined relationships among populations by constructing neighbor-joining phylogeographic trees using coancestry coefficient distances (Reynolds et al. 1983) generated using the AMOVA and PHYLIP programs. Harlequin ducks (n=16) sampled in Shemya, Alaska, were used as an outgroup for this tree. Results. – Each population of Harlequin Ducks had three to eight alleles at each bi- parentally inherited locus (Table 1). Mean number of alleles per locus, and observed and expected heterozygosities were moderately high and concordant across all populations (Table 2). The bi-parental loci did not deviate significantly from Hardy-Weinberg equilibrium (i.e. there was no heterozygote deficit) and no evidence of linkage was observed in any population. This lack of heterozygote deficiency corresponds with the low and non-significant values of f (alleles within individuals variation) present for each locus and across all loci (Table 1). Inbreeding coefficients (F) were low when averaged across loci (Table 2) but were more variable when analyzed for each population and locus combination (range: –0.266 to 0.262; mean = 0.008; data not shown). These values were not significant in all cases except for the Katmai population for one locus (Sfi?4, P < 0.05). Estimates of spatial variation for the four bi-parental microsatellite loci were low (Table 1). No locus showed a significant difference in allele frequencies among populations within regions or between regions (all P>0.05). When averaged across all loci, allele frequencies also did not differ significantly among populations within regions or between regions (Table 1). Estimates of RST did not differ appreciably from FST spatial variation values, and also showed no significant difference in allele frequencies among populations within regions or between regions (data not shown). The lack of spatial variation among populations was further evident based on the low levels of bootstrap support for most nodes of the consensus neighbor-joining tree using the bi-parental loci (Fig. 2). Only three nodes within the microsatellite tree received >50% bootstrap support. The fact that clusters were composed of populations from both regions, coupled with the lack of consistent clustering at most tree nodes, suggests weak population structuring. However, our ability to place accurate and precise bootstrap values on the various nodes of the tree may be compromised by the relatively small number of bi- parental loci used (Takezaki and Nei 1996). Genetic diversity was high for the Bca?4 sex-linked locus where the number of alleles in any one population frequently exceeded ten (Table 2). The Sfi?1 locus had much lower genetic diversity scores. Like the bi-parentally inherited loci, there were no significant differences in allele frequencies for sex-linked loci among populations within regions or between regions (Table 1). The absence of population structure using the Bca?4 locus was potentially misleading, however, given the large number of rare alleles and the relatively low sample sizes for each population. Allele frequencies were generally very similar among populations for the Sfi?1 locus. One hundred twenty seven Harlequin Ducks from the PWS (n = 63) and APKA (n = 64) regions (Table 1) were sequenced to test for variation in the mtDNA control region. Six of the 163 base-pair sites were variable across all individuals; only two were present in more than one haplotypes, and all occurred as transition substitutions (data not shown). There were 53 nucleotide substitution differences between the numt and the mtDNA haplotypes. Forty-nine sites occurred as transition substitutions and the remainder were inversion/deletions (data not shown). This variation resulted in a total of seven unique haplotypes. Six of the seven haplotypes were found in both the PWS and APKA regions, and only one haplotype ("F" in Table 1) was detected in a single individual whereas the most common haplotype ("G" in Table 1) accounted for 52% of the samples. Haplotype diversities ranged from 0.427 to 0.745 (Table 2), with the highest diversity located in the Montague Island and Afognak populations. Haplotype diversity was not significantly lower in PWS (0.574) than in the APKA (0.702) region (Monte Carlo simulation, P = 0.08). Haplotype diversity values were highly concordant across populations, and were not significant among populations or regions based on Monte Carlo simulations (all P > 0.05). Nucleotide diversity corresponded closely to haplotype diversity. Neighbor- joining phylogenetic trees based on distances between haplotypes failed to support phylogeographic relationships (i.e., particular haplotypes were not restricted to specific sampling sites). Indeed, phylogenetic relationships (tree not shown) determined by the neighbor-joining analysis were only weakly supported by the bootstrapping analyses. Hierarchical analyses conducted without information on haplotype evolutionary relationships (i.e. number of nucleotide substitutions) revealed no significant differences in mtDNA haplotype frequencies (Table 1). When haplotype evolutionary information was included, similar results were produced, however a marginally significant difference in frequency of the two most common haplotypes ("A" and "G") was found among regions (P=0.049, see Table 1). Haplotypes differed in sequence by 1-2 base-pair substitutions (data not shown). The lack of structuring among populations was also evident when we constructed a neighbor-joining tree using the mtDNA haplotype frequency information (Fig. 3 – maybe combined with 2). Branch lengths were extremely short and it was not unusual for populations from the PWS and APKA to be clustered together. A comparison of the population consensus tree generated from the four bi-parental microsatellite loci (Fig. 2) and the branch length tree generated with mtDNA sequence information (Fig. 3 - maybe combined with 2) revealed several similarities. First, the Bay of Isles and Katmai populations, and the Uyak and Uganik populations clustered together in both trees. The Afognak population also clustered near the Uyak and Uganik populations in both trees, although this cluster differed in its relative position within each of the trees. Discussion – Our analyses show that Harlequin Ducks molting and wintering within PWS and APKA share population genetic characteristics consistent with those expected for organisms belonging to one panmictic population (i.e. there is little or no spatial population structuring). Indeed, within regions, all three classes of molecular genetic markers indicated no significant differences in allele and haplotype frequencies among populations. Further, the topologies of neighbor-joining consensus trees and the short lengths of tree branches revealed few consistent population groupings. There was, however, a significant difference between PWS and APKA regions with the mtDNA marker (Table 1). Given the lack of information on evolutionary rates on microsatellite loci relative to the mtDNA, it is difficult to interpret these findings. Nevertheless, this regional difference was found only when the frequencies of mtDNA haplotypes were compared, i.e. there was a notable paucity of private alleles within populations. Consequently, we interpret these results as a general lack of historic structuring within and across regions. Our finding that Harlequin Ducks have little to no population structuring within PWS and APKA was surprising given that life history characteristics suggest that discrete, reproductively isolated populations exist. Indeed, males and females are highly philopatric to molting and wintering areas (Robertson 1997, D. Esler unpubl. data) and pair formation occurs on the wintering grounds during early to mid-winter (Gowans et al. 1997, Robertson et al. 1998). This disparity may be explained in four ways. First, Harlequin Ducks in PWS and APKA may represent a recent range expansion from a refugial population (Wenink et al. 1994). Second, barriers to gene flow may have only recently become established and insufficient time has elapsed for genetic differences to have evolved. Third, habitat alterations (e.g. Katmai Eruption, Rigg 1914; Great Alaskan Earthquake of 1964, Jacob 1986) may result in episodic dispersal and possible gene flow among populations which are otherwise presently reproductively isolated. And finally, low levels of adult or juvenile movement may occur between populations and regions. Recent band-resighting data within APKA and PWS regions support the idea that individuals occasionally move between populations (although apparently not between regions; D. Esler and D. Zwiefelhofer unpubl. data). If these emigrants mate with local individuals, they may provide sufficient gene flow to homogenize gene frequencies (Wright 1931). Indeed, subadults and juveniles are the most likely avenue for gene flow because they may remain in the marine coastal environment for several years during maturation (xxxxxxx). Lack of natal philopatry to molt and/or wintering sites may, in essence, nullify the effects of high adult fidelity to these same sites. Although the specific reason for the absence of genetic structuring among these populations is not known, our results indicate genetic variation was not lost as a result of the Exxon Valdez Oil Spill. This assumes, of course, that our genetic markers are representative of the overall genetic characteristics of the populations. The poor recovery of Harlequin Ducks in oiled areas does not appear to be related to Harlequin Duck population genetic characteristics, but may instead be associated with unfavorable local environmental conditions. Further, our inability to determine whether or not there is currently gene flow among regions or populations, makes it impossible to know if immigration will bolster population numbers in damaged areas within the spill zone. Even though genetic characteristics of the populations appear to be similar, translocations of Harlequin Ducks to augment populations which have not recovered seems unwise given the paucity of information on adult movements, breeding philopatry, mating strategies, and other basic natural history data on this species. Nevertheless, these genetic data do serve as an important baseline from which to assess the impact of future environment perturbations on genetic characteristics. Acknowledgments – Funding for this project was provided by the Exxon Valdez Oil Spill Trustee Council (project no. 96161), the Alaska Biological Science Center of the U. S. Geological Survey, Biological Resources Division, Kodiak National Wildlife Refuge, Katmai National Park and Preserve, and the U.S. Fish and Wildlife Service Ecological Services Lafayette Field Office. Support during the final stages of data analysis and writing were provided by the Belgium Fund for Scientific Research, the Michigan Department of Natural Resources, and the Department of Fisheries and Wildlife at Michigan State University through the Partnership for Research and Management (PERM) program. J. Pearce helped test microsatellites for amplification and variability. J. Piatt provided unpublished information on Harlequin Duck mortality resulting from the Exxon Valdez oil spill. Office and field assistance was provided by G. Johnson, H. Brokate, B. Hobbins, T. Arensburg, B. Rice, C. Berg, L. Bennett, R. Leatherman, and A. Goatcher (APKA); and B. Baetsle, R. Ballas, B. Benter, T. Bowman, K. Burek, J. DeGroot, B. Jarvis, D. Mather, D. Monson, J. Morse, D. Mulcahy, D. Ruthrauff, D. Schaeffer, and K. Trust (PWS). J. Pearce, B. Greene, G. Mittelhauser, J. Rhymer, and G. Shields provided useful comments on analyses or earlier drafts of this paper. |
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