Badge Size and Extra-Pair Fertilizations in the House Sparrow1
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The Condor 102:342-348 0 The Cooper Ornithological Socmy 2000 BADGE SIZE AND EXTRA-PAIR FERTILIZATIONS IN THE HOUSE SPARROW1 R. R. WHITEKILLER~ Department of Zoology, University of Oklahoma, Norman, OK 73019 DAVID E WESTNEAT Center for Ecology, Evolution, and Behavior, T. H. Morgan School of Biological Sciences, 101 Morgan Building, University of Kentucky, Lexington, KY 40506 l? L. SCHWAGMEYER AND DOUGLAS W. MOCK Department of Zoology, University of Oklahoma, Norman, OK 73019 Abstract. For House Sparrows, Passer domesticus, it has been proposedthat the size of a male’s throat badge correlateswith his successin avoiding cuckoldry as well as obtaining extra-pair copulations(EPCs), and that females gain indirect (genetic) benefits from EPCs with large-badged males. Alternatively, female House Sparrows may engage in EPCs as a guard against their social mate’s infertility. We used multi-locus DNA fingerprinting to examine paternity and found that among 41 broods and 136 offspring, 20% of the offspring were attributableto extra-pair fertilizations (EPFs). Forty-one percent of the 34 males were cuckolded; however, large-badged males were as likely to be cuckolded as small-badged males. Moreover, we found no evidence that large-badged males were inherently superior to small-badgedmales in terms of survivorship.We comparedthe prevalence of unhatched eggs in broods with and without extra-pair offspring to determine whether EPFs are asso- ciated with hatching failure. Although we detected no associationbetween hatch failure and EPFs, enhanced fertility remains a plausible EPC benefit to females, but experimental ap- proachesmay be required to evaluate its significance. Key words: cuckoldry, extra-pair copulation, extra-pair fertilization, fertility insurance, House Sparrow, Passerdomesticus, sexual selection. INTRODUCTION (1988) showed that males with large throat Conspicuous ornaments could be favored under badges were more likely to acquire mates than sexual selection if they provide some advantage small-badged males; large-badged males, in in male-male competition for mates and/or are turn, tended to occupy areas with better nesting attractive to females. In the latter case, two types sites. In an Oklahoma population, Voltura of benefits to females have been proposed. Fe- (1998) found that large-badged males do a great- males might gain direct (nongenetic) benefits er share of nestling feeding than small-badged (Trivers 1972, Kirkpatrick and Ryan 1991) if or- males. namented males provide more parental care, Male ornamentation additionally has been possessbetter territories, or better guard the fe- suggestedto play a role in the extra-pair mating male from predators or the harassment of con- system of House Sparrows. Although the species specifics. Alternatively, conspicuoustraits might is considered mainly monogamous, females so- indicate indirect (genetic) benefits (Fisher 1930, licit extra-pair copulations (EPCs) and are tar- Hamilton and Zuk 1982, Kirkpatrick and Ryan gets for forced extra-pair copulations (Moller 1991), thereby conferring greater fitness on the 1987). Moller (1990) reported that large-badged female’s offspring. males performed more EPCs than small-badged Research on House Sparrows (Passer domes- males, and he suggestedthat females may gain ticus) indicates that females of this speciesmay indirect benefits by choosing large-badged males gain direct benefits from pairing with highly or- as EPC Partners. namented males. In a Danish population, Moller Moller’s perspective (1990) emphasizes the potential role of badge size as a true indicator of male genetic quality; he proposed that the ’ ’ Received22 July 1999.Accepted 25 January2000. 2 Current address:Department of Biology and trait is under strong directional sexual selection Chemistry,University of Montevallo,Montevallo, AL by virtue of its importance in female mate 35115. choice and in the context of sperm competition. 13421 BADGE SIZE AND EXTRA-PAIR FERTILIZATIONS 343 In addition to finding that male badge size is nest boxes (Summers-Smith 1963); both parents related to EPC participation, Moller (1990) also participate in nest building, incubation, and found that large-badged males copulate more of- feeding of the nestlings. Incubation lasts approx- ten with their own mates than small-badged imately 11 days and most young fledge about 14 males, and that they appear to guard their mates days after hatching. more intensely than do small-badged males (Moller 1987). These behavioral observations, METHODS along with the larger testes size of large-badged STUDY SITE AND GENERAL FIELD METHODS males (Moller and Erritzoe 1988), led Mprller (1990) to predict that such males have greater We erected 100 nest boxes at two sites (North success at siring extra-pair offspring while si- Base and South Base, University of Oklahoma, multaneously avoiding cuckoldry. Norman, Oklahoma) in 1993 and 1994. One Using DNA fingerprinting techniques, Wetton hundred and nineteen additional nest boxes were and Parkin (1991a) found that 13.6% of the off- erected at four additional sites near North and spring in a British population were sired by ex- South Bases in 1995 and 1996. We censused tra-pair males. However, subsequentresearch on nest boxes at least twice weekly during the both that population as well as a Spanish pop- 1994-1997 breeding seasons to determine the ulation showed no support for Moller’s predic- date the first egg was laid, clutch size, number tion that large-badged males would be cuckold- of eggs that hatched, number of young that ed less often than small-badged males (Corder0 fledged, and inter-brood interval. When the date et al. 1999). Instead, Wetton and Parkin’s the first egg was laid was not observed, it was (1991b) results have led to an alternative hy- calculated assuming that a female lays one egg pothesisfor why female House Sparrows engage per day. in EPCs. They found a striking association be- Adults were captured in ground traps, mist tween the number of unhatched eggs in a clutch nets, or in wire corridors attachedto the nest box and the presence of extra-pair offspring in the (Mock et al. 1999). We weighed individuals on brood: the extra-pair fertilization (EPF) rate in an electronic balance (t 0.1 g) and then banded broods with at least some hatching failure was each with U.S. Fish and Wildlife aluminum roughly twice as high as in broods where all bands plus a unique combination of plastic color eggs hatched successfully. This result prompted bands for field identification. A scaled close-up them to suggest that females may use EPCs photograph of each male’s badge was taken at more as a guard against a mate’s potential in- the time of his capture using a 0.5 X 0.5-cm grid fertility, than as a means to upgrade the genetic in the background. All badge area estimates quality of their offspring. were from males captured during the breeding We examined the frequency of extra-pair off- season, which minimizes the effects of feather spring in House Sparrows using multi-locus tip abrasion on visible badge size (Griffith et al. DNA fingerprinting. We also used video image 1999b). The badge area was quantified using analysis to measure digitized photographs of video image analysis. In a separate sample, we male badges, and we used those measurements found that area estimates obtained from photo- to investigate whether variation in male badge graphs were highly correlated with estimates for size is related to loss of paternity to extra-pair the same individuals based on video-taped im- matings, as Moller (1990) predicted, or to male ages of their badge sizes (Whitekiller, unpubl. survival. By comparing the prevalence of un- data). Badge sizes were scoredindependently by hatched eggs among broods with and without R. R. Whitekiller and K. Voltura. Badge size for extra-pair offspring, we also testedthe generality each male was scored “blind” as to his identity. of Wetton and Parkin’s (1991b) finding that fe- The areas obtained by the two scorers were male production of offspring sired by EPFs is highly correlated (1. = 0.99, IZ = 65, P < 0.001). associatedwith hatching failure. Corder0 et al. (1999) reported a similar tech- House Sparrows are semi-colonial passerines nique for measuring badge size and found that that begin breeding in central Oklahoma in it produced similar measures as that of Moller March and continue through early August, pro- (1990). Mean values for the two sets of scores ducing two to three clutches of approximately are used in all analyses. four to five eggs each. This speciesreadily uses To examine the relationship between badge 344 R. R. WHITEKILLER ET AL size and adult male survival, we compared the FINGERPRINT SCORING AND PARENTAGE badge size of males banded as adults in 1994 or ANALYSES 1995 that were resighted within the next two Scoring followed the methods outlined in West- years with the badge size of males that failed to neat (1990, 1993). Bands on the autoradiographs return. Individuals were considered to have sur- were marked on acetate sheet overlays with per- vived if they were resighted at any nest boxes, manent markers. We compared banding patterns during ground trapping, or at any other location. between two individuals (putative parent and offspring) using the statistic D = 2N,,/(N, + BLOOD COLLECTION AND MULTI-LOCUS DNA Na) where N, and N, are the number of frag- FINGERPRINTING ments in individual A (putative parent) and in- A 70-100 pl blood sample was collected (from dividual B (offspring), and N,, is the number of putative parents and offspring) from the brachial bands shared by both (Wetton et al. 1987). Pu- vein into heparinized capillary tubes, placed on tative parents were run in lanes directly adjacent ice in the field, and transported back to the lab- to offspring for scoring accuracy. For each off- oratory. We expelled the sample into microcen- spring, we also determined the number of novel trifuge tubes filled with 500 p,l of lysis buffer bands present.