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Cm Spiny Penis of the Argentine Lake Duck &Lpar;<I>Oxyura Vittata</I>

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Cm Spiny Penis of the Argentine Lake Duck &Lpar;<I>Oxyura Vittata</I> 820 ShortCommunications [Auk, Vol. 117 Ecologiapermit numbers0492, 00987,and 11782.We white booby and the brown boobySula spp. at thank the Secretaria de la Marina, Sexta Zona Naval, Asension. Ibis 103b:174-234. Guaymas,for transportationand food deliveries.For DRUMMOND,H. 1987. A review of parent-offspring logisticsupport, we are indebtedto the InstitutoTec- conflict and brood reduction in Pelecaniformes. no16gicoy de EstudiosSuperiores de Monterrey- Colonial Waterbirds 10:1-15. CampusGuaymas, Rescue One, A. Robles,E. Velar- DRUMMOND, H., AND C. GARCIA CHAVELAS. 1989. de, J. Guzman, L. Gonzales, Prescott College, Baja Food shortageinfluences sibling aggressionin Expeditions,Special Expeditions, H. and V. Ballance, the Blue-footedBooby. Animal Behaviour37: and T. Pfiester. We are grateful to Eureka Tents, 806-820. OceanKayaks, S. Emlen,J. Guzman,and E. Velarde, FORBES,L. 1991. Insurance offspring and brood re- for use of researchequipment. We especiallythank duction in a variable environment: The costs and D. Able, A. Angeles,S. Ashe,X. Basurto,G. Brabata, benefitsof pessimism.Oikos 62:325-332. C. Carmona, M. Cervantes,D. Craig, G. Fernandez, KEPLER,C. B. 1969. Breedingbiology of the Blue- K. Mingo, C. Navaro, N. Nufiez, H. P•rez, and E. To- facedBooby Sula dactylatra personata on GreenIs- b6n for excellenthelp and companyin the field. We land, Kure Atoll. Publications of the Nuttall Or- are grateful to D. Anderson, H. Drummond, and nithologicalClub No. 8. BRT's graduate committee members E. Adkins-Re- MOCK, D. W., H. DRUMMOND, AND C. H. STINSON. gan, S. Emlen, T. Gavin, P. Sherman,and D. Winkler 1990. Avian siblicide. American Scientist 78:438- for their excellentreviews of the manuscript. 449. MOCK, D. W., AND L. S. FORBES. 1992. Parent-off- LITERATURE CITED spring conflict:A caseof arresteddevelopment. Trends in Ecologyand Evolution7:409-413. ALVAREZ-BORREGO,S. 1983. Gulf of California.Pages NELSON,J. B. 1978. The Sulidae: Gannets and boo- 427-449 in Estuaries and enclosed seas (B. H. bies. Oxford University Press,Oxford. Ketchum, Ed.). Elsevier, Amsterdam, The Neth- SIMMONS,R. G. 1988.Offspring quality and the evo- erlands. lution of cainism. Ibis 130:339-357. AMERSON,A. B., Jr., AND P. C. SHELTON.1976. The TERSHY, B. R. 1998. Sexual selection in the Brown naturalhistory of JohnstonAtoll, centralPacific Booby.Ph.D. thesis,Cornell University,Ithaca, Ocean. Atoll Research Bulletin No. 192. New York. ANDERSON,D. J. 1990a.Evolution of obligatesiblicide TRIVERS,R. L. 1974. Parent-offspringconflict. Amer- in boobies.1. A test of the insurance-egghy- ican Zoologist 14:249-264. pothesis.American Naturalist 135:334-350. WOODWARD,P. W. 1972.The natural history of Kure ANDERSON,D. J. 1990b.Evolution of obligatesiblici- Atoll, Northwestern Hawaiian Islands. Atoll Re- search Bulletin No.164. de in boobies.2. Food limitation and parent-off- spring conflict.Evolution 44:2069-2082. Received23 March 1998, accepted10 February2000. DORWARD,D. E 1962. Comparativebiology of the Associate Editor: T. W Arnold The Auk 117(3):820-825, 2000 The 20-cm Spiny Penis of the Argentine Lake Duck (Oxyura vittata) KEVIN G. MCCRACKEN • Schoolof Forestry,Wildlife, and Fisheries, Louisiana State University, Baton Rouge, Louisiana 70803, USA The genitalsof male birds generallyare not noted mutual juxtapositionof the protruded cloacae,and for their sizeor extravagantornamentation. For most there is relatively little contactbetween males and fe- speciesof birds, well-developedpenes or intromit- males comparedwith the processof coital penetra- tent organs are absent(e.g. King 1981, Briskie and tion in mammals,reptiles, some species of fish,and Montgomerie1997). Sperm transfer occursvia the most insects (Eckstein and Zuckerman 1956, Dowl- ing and Savage1960, Eberhard 1985). Several groups of birds, including ratites,screamers, waterfowl, and • Presentaddress: University of Alaska Museum, cracids,possess well-developed male copulatoryor- 907 Yukon Drive, Fairbanks, Alaska 99775, USA. E- gans (Forbes1882, King 1981, Lake 1981). In these mail: [email protected] groups,the penis(or male intromittentorgan) arises July2000] ShortCommunications 821 from the ventral wall of the cloacaand generallyis J. Fullagar pers. comm.;see also Marchant and Hig- believed to facilitate sperm transfer via a series of gins 1990), and unpublishedobservations of similar longitudinal grooves(internal spermducts homolo- intromittent organs in Ruddy Ducks (Oxyurajamai- gousto thosein mammalsare not presentin birds). censis;R. B. Brua pers. comm.),no recordsdetailing The penisof an Ostrich(Struthio camelus), for exam- the size, texture, or conformation of this structure ple, can measureas long as 20 cm when flaccidand within the abdomenare known to exist. Unusually is bright red in color (King 1981). The intromittent large testessize, elaborate sexual display repertoires, organs of various ducks, on the other hand, have and a putatively promiscuousmating system offer been reported to vary in length between50 and 90 opportunitiesfor speculationabout the relationship mm, sometimesexceeding that range (Liebe 1914, betweenform and functionof the unusualpenis in Hochbaum1942). this species. The presenceof a well-developedpenis in many Methods.--Sevenadult male ArgentineLake Ducks dabbling and diving ducks may derive in part from were collectedearly in the breedingseason on 22 No- their tendencyto copulatein the water (Lake 1981). vember 1998 from a small wetland (n = 2) and irri- Geese,which tend to copulateon land, typicallypos- gation canal (n = 5) adjacentto the Rfo Negro near sessmuch smaller penes,even thoughtheir overall General Conesa, Rfo Negro, Argentina (40ø04'S, body size is larger (Coker 1998).Another probable, 64ø16'W).Mass (+ 50 g) of eachbird was measured but not necessarilyexclusive, explanation is that at the time of collection.Carcasses subsequently large ornamentedpenes have evolved in responseto were placedon ice,frozen, and exportedto the Lou- sperm competitionwithin the female reproductive isiana State University Museum of Natural Science tract, such that males with larger penes achieve (LSUMNS). Carcasseswere thawed three monthslat- greater reproductive successthan others (Waage er and prepared as museumskins (n = 6) and a skel- 1979, Thornhill and Alcock 1983, Eberhard 1985). etal specimen(n = 1). Speciesthat experiencegreater sperm competition After discovering unusually large cloacal swell- are expectedto possesslarger penes that may in- ingsand correspondinglylarge penes in the first two crease the probability of successfulfertilization specimens,I dissectedand measuredthe intromit- (Birkheadand Moller 1992,Briskie and Montgomerie tent organsand testesof the five birds collectedon 1997). Thus, sperm competitionprobably also ex- the canal(LSUMNS B34019,B34025, B34034, B34036, plainsthe contrastbetween the larger penesof dab- B34037). Genitalia subsequentlywere removed and bling ducksand the smallerpenes of geese.Dabbling further dissectedto verify the extent of internal ducksshow some of the highestlevels of forcedand spine-likestructures. I madea seriesof photographs unforced extrapair copulations among waterfowl, from the secondspecimen to documentboth the po- whereasmost geeseshow low frequenciesof extra- sition and conformation within the abdomen; dissec- pair copulations(Mineau and Cooke1979, McKinney tion of the other four specimensrevealed approxi- et al. 1983; but see Dunn et al. 1999). An element of mately identical features and no need for further female choicealso might play a role if changesin photographs.Manually everting the organ in its physiologyand femalebehavior also affect the out- erect conformationproved impossible given the ab- come of subsequent sperm competition. Teasing senceof a vasculareversion mechanism (King 1981). apart the two processescan be difficult, however, In waterfowl,the eversionmechanism is lymphatic, particularly when the contestoccurs inside the fe- and the unusuallength of the structurerelative to its male.Females also might chooseamong males in yet width prohibitedpulling the entire length of the or- another manner, based on the size and appearance gan inside out. However,longitudinal dissectionand of the penis itself (Briskieand Montgomerie1997). subsequentinversion of the outer surfaceto view the I presenthere a descriptionof the penisof the Ar- inner surface revealed what is believed to be a close gentineLake Duck (Oxyuravittata). The use of the approximationof the everted,but nonethelessflaccid waterfowl penis as a means of sex and age identifi- conformation (see below). Genitalia and testessub- cationof live birds is commonplace(e.g. Hochbaum sequentlywere fixed in 10% formaldehyde,pre- 1942).What is noveland fascinatingin this speciesis servedin 70% ethanol,and depositedat the Louisi- therelative size (ca. half thebody length) and thorny, ana State University Museum of Natural Science. brush-liketexture of its penis. Dissectionand prep- Results.--Eachof the five birdsthat I dissectedap- arationof the ArgentineLake Duck'spenis reveal a pearedto be in breedingcondition, as indicated by a massivestructure (approximately equal in length to bright blue bill, black head, and ruddy breeding the Ostrich penis) with a peculiar array of dense plumage. Mean body mass was 630 + SD of 24 g spinesrunning the entirelength of the organ.At the (range 600 to 650 g). Mean testes dimensionswere baseof the penis,the spinesare hardenedand sharp. 40.8 + 3.6 x 17.8 ___1.8 mm for the left testis and 41.0 With the exceptionof a video sequenceand
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