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1-1-1992 Further analysis of allozyme variation in the Northern Flicker, in comparison with mitochondrial DNA variation Stephen D. Fletcher Wayne State University

William S. Moore Wayne State University, [email protected]

Recommended Citation Fletcher, S. D. and Moore, W. S. 1992. Further analysis of allozyme variation in the Northern Flicker, in comparison with mitochondrial DNA variation. The ondorC 94:988-991. Available at: http://digitalcommons.wayne.edu/biosci_frp/10

This Article is brought to you for free and open access by the Biological Sciences at DigitalCommons@WayneState. It has been accepted for inclusion in Biological Sciences Faculty Research Publications by an authorized administrator of DigitalCommons@WayneState. 988 SHORT COMMUNICATIONS

The Condor 94:988-991 © The Cooper Ornithological Society 1992

FURTHER ANALYSIS OF ALLOZYME VARIATION IN THE NORTHERN FLICKER, IN COMPARISON WITH MITOCHONDRIAL DNA VARIATION'

STEPHEN D. FLETCHER AND WILLIAMS. MOORE2 Department of Biology, Wayne State University, Detroit, MI 48202

Key words: Allozyme; Colaptes auratus; geographic et a!. I 991) indicated that there is a significant geo­ variation; Northern Flicker. graphic structure in mtDNA, not associated with the hybrid zone, that involves divergence of populations The Northern Flicker (Colaptes auratus) is a common in the southwest from northern and eastern popula­ woodpecker whose range includes nearly all of the con­ tions. tinental United States, and extends into Canada, Mex­ The allozyme surveys did not include samples from ico, Central America, and the West Indies. Short (I 965) the western and southwestern U.S. where divergence recognized I 5 subspecies which he divided into five in mtDNA haplotype frequencies was most apparent. subspecies "groups": C. a. auratus (theYell ow-shafted Consequently, the objective of this study is to inves­ Flicker of eastern North America), C. a. cafer (the Red­ tigate the geographic distribution of nuclear genes in shafted Flicker of western North America), C. a. chry­ the southwest for comparison with the mtDNA data; soides (the Gilded Flicker of the southwestern deserts), the comparison bears on questions concerning the dif­ C. a. chrysocaulosus (Cuba and Grand Cayman), and ferential evolution of mitochondrial and nuclear ge­ C. a. mexicanoides (highland southern Mexico to Nic­ nomes in flickers (see Discussion). aragua; Short I 965, I 982). Although presently consid­ We electrophoretically surveyed three loci, Lactate ered subspecies groups (American Ornithologists' Union Dehydrogenase (LDH-2, E.C. no. 1.1.1.27), Phospho­ I 983), the Red-shafted, Yellow-shafted, and Gilded glucomutase (PGM, E. C. no. 5.4.2.2), and Alpha-glyc­ Flickers are so distinct in plumage and size that they erophosphate Dehydrogenase (AGP, E. C. no. I. I. I .8), were formerly considered species (American Orni­ in 2 I 5 Northern Flickers. These loci are among those thologists' Union I 957). previously identified as polymorphic in this species A hybrid zone between the Red- and Yellow-shafted (Grudzien and Moore I 986, Grudzien eta!. I 987), and groups occurs where the ranges of the two come into based on the limited geographic range of samples, were contact (Short I 965, Moore and Buchanan I 985). The most suggestive of divergence in southwestern popu­ hybrid zone existed when explorers of European an­ lations. The sample surveyed includes individuals from cestry reached the Great Plains (see June, 1843 entry both Red-shafted and Yellow-shafted subspecies groups, in the journal of Edward Harris, McDermott 1951), hybrids between the two, and I 9 Gilded Flickers from and it has been historically stable (Moore and Bu­ Arizona. chanan I 985). The origin of the hybrid zone is not fully resolved, and it may be that segments of it arose at MATERIALS AND METHODS different times under different circumstances (see Short Specimens were collected in I 985, I 986, and I 988. I 965; Moore and Buchanan I 985; and Moore and Price, Collecting sites were in I I states and represent major in press, for discussion). It is probable that major por­ regions ofthe continental United States (Table I). Birds tions of the present hybrid zone formed at the end of were shot and partially dissected in the field, where the Wisconsin Glacial Advance or during the Holocene skeletal muscle, heart, and liver were immediately Altithermal, at the latest. The hybrid zone extends the placed on frozen CO, for transport. Samples were length of the western Great Plains, from northwestern maintained in the laboratory at -8o•c. Texas to southern Alaska (Short I 965; Moore and Bu­ The majority of Red- and Yellow-shafted Flicker chanan I 985; Moore and Price, in press). No evidence samples was surveyed for LDH and PGM using the of assortative mating between the subspecies groups horizontal starch-gel electrophoresis techniques of has been found (Bock I 97 I, Moore I 987). Turner (1983). However, samples from 1988 and Gild­ Previous allozyme surveys (Grudzien and Moore ed Flickers were surveyed for LDH and PGM, and all I 986, Grudzien eta!. I 987) indicated that there is little samples were surveyed for AGP, using cellulose acetate if any genic population structure corresponding with gel electrophoresis and the methods of Hebert and Bea­ features of the flicker hybrid zone and that gene flow ton (unpubl. manuscript). Results were identical at all across the zone and between the subspecies groups is loci on both media, but we completed the survey using high. In contrast, a recent mitochrondrial DNA cellulose acetate because it provided greater resolution (mtDNA) survey ofthe three subspecies groups (Moore and proved less labor-intensive than use of starch-gel. Allele frequencies and hierarchical F-statistics were calculated using the computer program BIOSYS-1 (Swofford and Selander 1981 ). The significance of the ' Received I I March I 992. Accepted 7 May 1992. estimates of between-population variance (F,.) was ' Corresponding author. tested using the methods of Rolf and Bentzen (1989).

~ Vl >-1 >-1 s;:: s;:: 00 0 z z 0 :::0 ::r: () 'C) 'C) Vl c::: 0 0 91 groups. 0.125 114 AGP 0.050 0.100 (1.1.1.8) Yellow-Shafted and 100 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.950 0.875 0.900 Red- the 127 0.050 0.150 0.167 0.125 between PGM (5.4.2.2) hybrids 100 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.833 0.950 0.850 0.875 and Flicker 73 0.050 0.063 0.125 0.143 0.050 0.050 0.167 0.100 0.056 Northern LDH-2 (1.1.1.27) the 100 1.00 1.00 1.00 of 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.950 0.900 0.938 0.875 0.857 0.944 0.950 0.950 0.833 groups (n) (10) (10) (7) (7) (5) (6) (5) (9) (10) (10) (5) (10) (10) (10) (10) (10) (8) (9) (2) (8) (9) (9) (5) (6) (8) (4) (5)* year~ locale subspecies Collection 86-13 86-14 86-9 85-5 85-1 86-15 86-1 85-2 85-3 85-4 86-10 88-2 86-16 86-20 86-23 83-5 86-4 86-7 86-17 86-18 86-19(6) 86-21 86-22 86-11 88-4 88-5 86-8 86-2 three State UT MI MI KY MI MI MI MT MT MT NM NO NO NO NO NM AZ AZ AL WA MT TX TX CA CA AZ AZ AZ the ofF-statistics. for calculation for frequencies (4) Obispo Missaukee 88-4 allele County & Miguel Luis with and McCreary Benzie Potter Newaygo Valley Mason Ward Pima Hill Dawson Burleigh McKenzie Pima Pima Lincoln Oscoda Clare Quay Covington Coconino Cochise Siskiyou San San Saginaw Summit Slope Oldham sites combined was Sample I. population This • Yellow-shafted Hybrid Red-shafted TABLE Gilded

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TABLE 2. Summary ofF-statistics at all loci. in Arizona, and one in California) reveals no clear geographic trend. These results agree with previous findings (Grudzien Locus F" Fn F,T and Moore 1986, Grudzien et al. 1987) that the hybrid AGP -0.114 -0.008 0.095 zone between Red- and Yellow-shafted Flickers does LDH-2 -0.124 -0.031 0.083 not act as a barrier to nuclear gene flow. In addition, PGM -0.162 -0.019 0.123 they are consistent with the conclusion reached by Grudzien eta!. (1987) that allozymic variation in flick­ Mean -0.134 -0.023 0.098 ers is selectively neutral, whereas morphological char­ acters are apparently subject to fairly intense selection pressure, a hypothesis suggested previously for Canada The Roff-Bentzen test is analogous to a x2 test for het­ Geese (Van Wagner and Baker 1986). erogeneity of allele frequencies among populations but Widespread allozymic homogeneity in flickers is not compares the observed x2 value with a probability dis­ unexpected. Studies of other avian hybrid zones (Cor­ tribution based on computer re-sampling. This test bin et al. 1979, Barrowclough 1980a, Seutin and Simon eliminates problems inherent in x2 analysis resulting 1988) similarly uncovered neither subspecies-specific from small sample sizes. The distribution of the test alleles nor clinal variation in allele frequency. Further, 2 statistic is actually a close approximation of x • birds in general are known to display little allozymic differentiation, even between recognized species (Bar­ RESULTS rowclough 1980a, !980b; Johnson and Zink 1983, Two LDH alleles were observed in Northern Flicker Braun and Robbins 1986). The F,. values observed here tissue, with relative migration distances of 100 (com­ are comparable to those reported for other avian spe­ mon) and 73 (rare) (Table 1). Two alleles were likewise cies (Evans 1987). identified for PGM, scored as 100 (common) and 127 Perhaps most interesting is that, with the inclusion (rare) (Table 1). AGP displayed three alleles, two rare of allozyme data for collecting sites in the far west and one common, with the relative migration distances (notably Arizona and California), the Northern Flicker of 114, 91, and I 00, respectively. does not have the population structure in nuclear genes The data confirm that LDH, PGM, and AGP are that is apparent in mtDNA (Moore et al. 1991 ). This polymorphic in the Northern Flicker in several of the disparity has been noted previously in birds (Mack et populations surveyed (Table 1). However, the fre­ al. 1986, Ball et al. 1988, Moore et a!. 199 I). It also quency of the rare alleles surpasses 5% in only three bears on the two hypotheses suggested by Moore et al. major geographic regions: Michigan (PGM; five pop­ (1991) as the "most plausible" explanations for the ulations, 50 birds), New Mexico (LDH; two popula­ trend they observed in Northern Flicker mtDNA, al­ tions, 17 birds), and Washington (one population, 7 though it does not conclusively disprove either. First, birds, data not shown). they suggested the pattern could reflect past geographic The mean F,. value for all three loci indicates that isolation, citing evidence which suggests that popula­ only 9.8% of the maximum possible between-popu­ tions in the southwest are both less migratory and more lation variance in allele frequencies actually exists across isolated than populations from other parts of the con­ the area surveyed (Table 2). The F,. values reported tinental United States. Second, the mitochondrial and here for the entire United States are similar to those nuclear genomes in the flicker may experience different reported for the same enzymes by Grudzienet al. (1987) selection pressures, and the southwestern divergence for the region of the hybrid zone, including the order may be the result of selection for mitochondrial hap­ observed when the three values are ranked by mag­ Iotypes which increase fitness in hot, arid regions. nitude. If a pattern of divergence in nuclear gene frequencies The results of the Roff-Bentzen test for heterogeneity were congruent with that observed in mtDNA haplo­ ofallele frequencies indicate that significant spatial het­ type frequencies, the geographical isolation hypothesis erogeneity is present only in the case of PGM (P < would be strongly supported. This was not observed; 0.0 I). The data for this locus suggest that the rare allele thus, to that extent, the selection hypothesis is favored. is more common than expected at four locales: 85-1 However, the geographical isolation hypothesis can not and 85-5, both in Michigan; 86-13 in California, and be conclusively rejected because mtDNA evolves more 88-2 in Arizona. None of these locales represents spec­ rapidly than nuclear DNA (Brown eta!. 1979, Brown imens of Gilded Flicker, which were monomorphic for 1985) and mitochondrial haplotypes have a smaller the common allele at all three loci (Table 1). effective population size than nuclear genes. Thus, it is possible that the southwestern populations have been DISCUSSION isolated long enough to have diverged significantly with The allozyme data presented here suggest that the regard to mtDNA but not nuclear genes. Northern Flicker has very little geographic variation Finally it is interesting that no significant divergence across three subspecies groups and the entire conti­ was found in Gilded Flickers. Allozyme data do not nental United States. No fixed allelic differences or reflect the sharper morphological distinctions apparent subspecies-specific alleles were found, and the hetero­ between Gilded Flickers and the other two subspecies geneity test indicated significant spatial heterogeneity groups (Short 1965). In addition, limited mtDNA data only in the case ofPGM. However, the distribution of suggest that they are "closely related" to Red-shafted the locales at which PGM has a higher than expected Flickers ofthe southwest (Moore et al. 1991 ). However, frequency of its rare allele (two sites in Michigan, one more data are needed before taxonomic considerations

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