Evidence of Intergradation within the Golden-cheeked Woodpecker
2018; Volume: 49; Issue: 4 Linguagem: Inglês
10.21199/wb49.4.8
ISSN0045-3897
AutoresDesmond Sieburth, Devon A. DeRaad, James M. Maley,
ResumoThe Golden-cheeked Woodpecker (Melanerpes chrysogenys), restricted to the Pacific slope of Mexico from Sinaloa to Oaxaca, comprises two subspecies.Nominate M. c. chrysogenys, identified by its extensively red crown, ranges from Sinaloa south to San Blas, Nayarit (Winkler and Christie 2017).Ridgway (1914) stated that near San Blas there is an abrupt transition from the reddish-naped M. c. chrysogenys to the yellow-naped M. c. flavinuchus, which is distributed southward to western Oaxaca.The subspecies also differ in the amount of yellow in the face, with flavinuchus averaging less yellow; this subspecies is also generally paler overall (Ridgway 1914).The distinction between these two subspecies, however, is perhaps not widely appreciated.For example, geographic variation in the crown pattern of the Golden-cheeked Woodpecker was not mentioned by Howell and Webb (1995), who illustrated only flavinuchus.The question of intergradation between the two subspecies has not been addressed in the literature previously.Therefore, we investigated it by evaluating 172 specimens in the collection of the Moore Laboratory of Zoology (MLZ), 14 specimens in the Natural History Museum of Los Angeles County (LACM), five specimens in the Dickey Bird and Mammal Collection of the University of California, Los Angeles (UCLA), and 31 specimens in the Western Foundation of Vertebrate Zoology (WFVZ), Camarillo, California.In this species, males are larger than females in both wing chord and culmen (Table 1).The differences in both variables are significant (p << 0.001), so we analyzed differences between the subspecies in the two sexes separately.Measurements confirmed that in both sexes M. c. flavinuchus averages larger than M. c. chrysogenys in both features (Table 1).The specimens analyzed for variation in size exclude any from Nayarit, since that state contains the zone of contact.The difference in males was significant for wing chord (p = 0.008) but not for culmen length (p = 0.37).The difference in females was significant for both wing chord and culmen length (p < 0.001).Visual inspection confirmed that M. c. flavinuchus has a yellow nape while M. c. chrysogenys has a reddish-orange nape.In 25 specimens of M. c. chrysogenys from Sinaloa the length of the crown patch averages 32.9 mm (range 22.3-37.4mm, standard error 0.88), whereas in 74 of M. c. flavinuchus collected from Jalisco to Oaxaca it averages 24.5 mm (range 17.1-32.8mm).According to a t test this difference is highly significant (p << 0.01).Although Ridgway did not mention any phenotypic intermediates, we found that of the 20 specimens from Nayarit housed in the MLZ, 19 have a nape color between reddish-orange and yellow, suggesting intergradation (MLZ:Bird: 28042-28045, 28533-28535, 41948, 41957, 41973, 41978, 47952-47954, 47956, 47961, 58244-58246).These specimens with intermediate nape color, collected by Chester C. Lamb across the entire state of Nayarit between 1937 and 1950, represent an apparently wide contact zone (Figure 1).Intermediate specimens were collected as far north as near Acaponeta (22.5°N, 105.4°W), many in the San Blas area, and another series of intermediates in northwestern Jalisco near Puerto Vallarta.That San Blas is in the area of intermediacy, as well as a focus for ornithology and birding along Mexico's Pacific coast, has likely contributed to the neglect of geographic variation in the Golden-cheeked Woodpecker.These specimens of intermediate plumage from the transition zone between the subspecies chrysogenys and flavinuchus raise questions about the extent of historic and current gene flow between the two populations.The transition between the NOTES
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