William S. Moore’s research while affiliated with Wayne State University and other places

Dispersal resulting in gene flow strongly affects the evolution of genetic structure in populations. This report describes statistical estimators of dispersal parameters based on USFWS banding recovery records. Finite-area studies of avian species yield estimates of root-mean-square (RMS) dispersal along a transect of about 1 km per generation. In contrast, estimates of RMS dispersal for the Red-winged Blackbird (Agelaius phoeniceus) and Common Grackle (Quiscalus quiscula), based on USFWS banding recovery records, are 94.6 and 111.4 km per generation, respectively. Distributions for both species are extremely leptokurtic, and confidence intervals based on jackknife statistics are large because the estimators are sensitive to outlying values. Dispersal rates can also be estimated from gene frequency data. Although all three kinds of data are not available for any one avian species, genetic-based estimates for several species are consistent with our estimates for Red-winged Black-birds and Common Grackles in inferring that gene flow is generally high in North American birds--probably closer to 100 km than 1 km per generation. High gene flow also implies that where geographic variation is observed, such as plumage patterns across hybrid zones, selection plays a role in maintaining the pattern of geographic variation.

The Yellow-shafted Flicker (Colaptes auratus auratus) and Red-shafted Flicker (C. a. cafer) form a stable, narrow hybrid zone on the western Great Plains of North America. Allozyme data were obtained from 31 structural gene loci for 33 samples representing 246 Northern Flickers from throughout the Great Plains. Flickers were approximately equivalent to other birds in terms of proportion of polymorphic loci (P̄ = 0.207) and average heterozygosity (H̄ = 0.056). There was no concordant variation between plumage characters and allelic frequencies. Gene-diversity analysis indicated that 92.5% of the genic variation occurred as within-deme heterozygosity(GD= 0.925),a pproximately 7% occurred among individual demes( GST= 0.07), and only 0.9% occurred among major river drainages (GST = 0.009). Even less diversity was found amongp arentala nd hybrid groups( GST= 0.002).T here is substantiaal llozymics tructuring of the Northern Flicker speciesp opulation, but the structuringis not associated with the hybrid zone, and there is, at most, very weak structuring into riparian zones of habitat. The electrophoretic data support the inference that gene flow among Northern Flicker populationsis high (Nm = 1.9-4.4/generation).I f the high gene-flowe stimatesa recorrect, then geographicasl electiong radientsw ould be the most likely mechanismm aintaining the narrow hybrid zone of plumage and morphometric traits.

The Red-shafted and Yellow-shafted Flickers hybridize in a narrow zone on the western Great Plains of North America. The two subspecies are markedly different in six plumage traits. Plumage phenotypes were scored for the male and female of 125 mated pairs from the hybrid zone. Correlation analyses revealed no tendency towards pairing of similar phenotypes. A binomial test was performed to determine whether flickers that have parental phenotypes and are presumably immigrants rather than hybrids tend to choose mates similar to themselves. This test again indicated random mating in the hybrid zone. These data complement earlier reports in providing an additional test of alternative hybrid zone theories. Random mating along with evidence of high reproductive success in hybrids suggests that reinforcement of premating reproductive isolation is not occurring and that speciation will not result from the dynamics of the hybrid zone. At least some of the plumage traits seem to be important in the integrated courtship and territorial behaviors of flickers. Since these plumage differences have no significance in mate choice, it is inferred that they evolved in an intrasexual selection context rather than in intersexual or species-recognition contexts. Selection gradients appear to be important in restricting hybridization to a narrow zone. The gradients could result from ecological selection or from sexual selection.

The Red-shafted and Yellow-shafted Flickers hybridize in a narrow zone on the western Great Plains of North America. The two subspecies are markedly different in six plumage traits. Plumage phenotypes were scored for the male and female of 125 mated pairs from the hybrid zone. Correlation analyses revealed no tendency towards pairing of similar phenotypes. A binomial test was performed to determine whether flickers that have parental phenotypes and are presumably immigrants rather than hybrids tend to choose mates similar to themselves. This test again indicated random mating in the hybrid zone. These data complement earlier reports in providing an additional test of alternative hybrid zone theories. Random mating along with evidence of high reproductive success in hybrids suggests that reinforcement of premating reproductive isolation is not occurring and that speciation will not result from the dynamics of the hybrid zone. At least some of the plumage traits seem to be important in the integrated courtship and territorial behaviors of flickers. Since these plumage differences have no significance in mate choice, it is inferred that they evolved in an intrasexual selection context rather than in intersexual or species-recognition contexts. Selection gradients appear to be important in restricting hybridization to a narrow zone. The gradients could result from ecological selection or from sexual selection.

Red-shafted and yellow-shafted subspecies of the northern flicker do not show statistically significant genetic differentiation. Genetic distance between hybridizing flicker subspecies is lower than average interspecific avian values (as expected), and is small relative to genetic distance values between 'pure' samples from other bird hybrid zones.

Starch gel electrophoresis of the common shiner, Notropis cornutus, was used to determine if this species exhibits genotypic structuring. Specimens were collected from seven widespread localities representing three branches of a single river drainage. χ2 tests revealed no significant heterogeneity of Est-A electromorphs within or between localities except where physical barriers prevent contact. Therefore, schooling behavior of N. cornutus is not associated with significant genotypic structuring of this species.

Alternative hypotheses of hybrid zones make specific predictions about reproductive components of fitness in the hybrids. The dynamic-equilibrium and reinforcement hypotheses are premised on reduced hybrid fitness, which should be apparent as reduced clutch or brood size or as increased embryonic mortality. The hybrid-superiority and introgression hypotheses predict normal clutch and brood size and embryonic mortality. Reproductive success was measured at four study sites on a transect across the hybrid zone between the Yellow- (Colaptes auratus auratus) and Red-shafted (C. a. cafer) subspecies of the Northern Flicker. Two additional clutch size samples representing pure Yellow- and Red-shafted flickers were obtained from museum egg collections. Mean clutch size did not differ significantly among the six samples. Factorial ANOVAs showed that early clutches and broods are larger than late clutches and broods, but no significant difference was detected between hybrid and parental study sites. Analyses of the effect of phenotype (yellow-shafted, red-shafted, hybrid) also suggest that neither clutch size nor brood size is affected, with the exception that hybrid males sired significantly smaller broods. Finally, there were no significant effects of type of cross (red-shafted male × hybrid female, etc.) on the ratio brood-size/clutch-size. The only evidence for reduced hybrid fitness was in the test where males with hybrid phenotypes appear to have sired small broods. This may indicate that abnormal behavior of hybrid males affects female fecundity, but it is also plausible that this marginally significant result is a type I statistical error. The overall lack of evidence for reduced hybrid fitness is inconsistent with either the dynamic-equilibrium or reinforcement models. Of the two remaining alternatives, the bounded hybrid-superiority model appears the more likely explanation of the Northern Flicker hybrid zone because earlier work (Moore and Buchanan 1985) showed that the hybrid zone is not becoming broader, as predicted by the introgression model.

Horizontal starch gel electrophoresis was used to estimate the amount of genetic divergence between Notropis cornutus and N. chrysocephalus. Measures of genetic identity (1) and distance (D) were 0.881 and 0.127 ± 0.055 (s.e.), respectively. These estimates correspond more closely to the sibling species status of these taxa than other previously reported estimates. Notropis cornutus was found to be significantly more variable than N. chrysocephalus electrophoretically and morphologically. Assuming the existence of an electrophoretic clock, the time of divergence was calculated to be roughly 1.9–2.5 million years. This estimate corresponds very closely to a previously hypothesized late Pliocene divergence.

The hybrid zone between the Red- and Yellow-shafted Flickers has been stable on the United States Great Plains in historical times. This conclusion is based on multivariate comparisons of historical and contemporary collections from 18 locales. Adaptive speciation theory predicts that the hybrid zone should either become broader or narrower as a result of introgressive hybridization or reinforcement of premating isolating mechanisms. Neither of these predictions was borne out. Despite 10,000-13,000 years of hybridization, mating between subspecies remains indiscriminate. The data are also inconsistent with a dynamicequilibrium hypothesis wherein narrow hybrid zones are maintained by hybrid unfitness. According to this hypothesis, the hybrid zone would probably "flow" unless it was trapped by a population density trough. The hybrid zone does not appear to be associated with such a feature. The data are consistent with a bounded hybrid superiority theory of a hybrid zone, but this is more a question of survival in a process of elimination than a resounding corroboration.