Summary
Maternal investment and sex-allocation were measured in a large, sexually dimorphic mammal, the Galapagos fur seal (Arctocephalus galapagoensis). The sex ratio at birth was 1.06. Males were always heavier than females and, at least initially, grew faster. Growth was variable from year to year suggesting energetic constraints on maternal investment. Sucking time conrrelated with milk intake. Mothers suckled yearling and 2-year-old sons more than daughters of the same age. Age at weaning appeared to be the same in both sexes or even slightly greater in males. No sex differences was found in mortality prior to weaning or in post-weaning dispersal. Birth rates of females with yearlings or 2-year-olds were significantly lower than those of females with no dependent young. Mothers invested more in sons than in daughters until weaning. It is unlikely that higher post-weaning investment in daughters balances the higher pre-weaning investment in sons. Data on sex ratio at birth, different growth rates, and weaning age of the sexes are typical of otariid seals as a group. The results of this study fit Maynard Smith's (1980) model of the evolution of sex allocation better than Fisher's (1930).
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References
Alexander RD, Hoogland JL, Howard RD, Noonan KM, Sherman PD (1979) Sexual dimorphism and breeding systems in pinnipeds, ungulates, primates, and humans. In: Chagnon NA and Irons W (eds) Evolutionary biology and human social behavior. An anthropological perspective. Duxbury, North Scituate, pp 402–435
Altmann J (1974) Observational study of behavior: sampling methods. Behaviour 49:227–267
Altmann J, Altmann SA, Hausfater G (1978) Primate infant's effects on mother's future reproduction. Science 201:1028–1030
Barber RT, Chavez FP (1983) Biological consequences of E1 Niño. Science 222:1203–1210
Bartholomew GA (1970) A model for the evolution of pinniped polygyny. Evolution 24:546–559
Bryant DM (1979) Reproductive costs in the house martin (Delichon urbica). J Anim Ecol 48:655–675
Cane MA (1983) Oceanographic events during El Niño. Science 222:1189–1195
Charnov EL (1982) The theory of sex allocation. Princeton University Press, Princeton NJ
Clark A (1978) Sex ratio and local resource competition in a prosimian primate. Science 201:163–165
Clutton-Brock TH, Albon SD (1982) Parental investment in male and female offspring in mammals. In: King's College Sociobiology Group (eds) Current problems in sociobiology. Cambridge University Press, Cambridge, pp 223–247
Clutton-Brock TH, Albon SD, Guinness FE (1981) Parental investment in male and female offspring in polygynous mammals. Nature 289:487–489
Clutton-Brock TH, Albon SD, Guinness FE (1985) Parental investment and sex differences in juvenile mortality in birds and mammals. Nature 313:131–133
Clutton-Brock TH, Guinness FE, Albon SD (1983) The costs of reproduction to red deer hinds. J Anim Ecol 52:367–383
Croxall JP, Gentry RL (eds) (in press) Proceedings of the first international symposium on the biology of fur seals. Nat Mar Fish Ser Spec Sci Rep-Fish, Washington, DC
David JHM (in press) Species summary for the Cape fur seal, Arctocephalus pusillus pusillus. In: Croxall JP, Gentry RL (eds) Proceedings of the first international symposium on the biology of fur seals. Nat Mar Fish Ser Spec Sci Rep-Fish, Washington, DC
Dittus WP (1979) The evolution of behaviors regulating density and age-specific sex ratios in a primate population. Behaviour 69:265–302
Drent RH, Daan S (1980) The prudent parent: energetic adjustments in avian breeding. Ardea 68:225–252
Feldman GC, Clark D, Halpern D (1984) Satellite color observations of the phytoplankton distribution in the eastern equatorial Pacific during the 1982–1983 El Niño. Science 226:1069–1071
Fisher RA (1930) The genetical theory of natural selection. Oxford University Press, Oxford
Kooyman GL, Trillmich F (in press) Diving behavior of the Galapagos fur seal. In: Gentry RL, Kooyman GL (eds) Fur seals: Maternal strategies on land and at sea. Princeton University Press, Princeton NJ
Le Boeuf BJ (1974) Male-male competition and reproductive success in elephant seals. Am Zool 14:163–176
Hirschfield MF, Tinkle DW (1975) Natural selection and the evolution of reproductive effort. Proc Nat Acad Sci USA 72:2227–2231
Maxwell DC (1974) Marine primary productivity of the Galapagos archipelago. Ph D Thesis, Ohio State University, Columbus
Maynard Smith J (1980) A new theory of sexual investment. Behav Ecol Sociobiol 7:247–251
Ortiz CL, Le Boeuf BJ, Costa DP (1984) Milk intake of elephant seal pups: an index of parental investment. Am Nat 124:416–422
Payne MR (1979) Growth in the Antarctic fur seal Arctocephalus gazella. J Zool Lond 187:1–20
Ralls K, Brownell RL, Ballou J (1980) Differential mortality by sex and age in mammals, with specific reference to the Sperm whale. Rep Int Whal Comm Spec Issue 2:223–243
Rand RW (1956) The Cape fur seal Arctocephalus pusillus (Schreber). Its general characteristics and moult. Investl Rep Div Fish S Afr 21:1–52
Reyer HU (1984) Investment and relatedness: a cost-benefit analysis of breeding and helping in the Pied Kingfisher (Ceryle rudis). Anim Behav 32:1163–1178
Reiter J, Stinson NL, Le Boeuf BJ (1978) Northern elephant seal development: the transition from weaning to nutritional independence. Behav Ecol Sociobiol 3:337–367
Shaughnessy PD (in press) Population estimates of the Cape fur seal Arctocephalus pusillus II. From tagging and recapturing. Investl Rep Sea Fish Inst S Afr
Sokal RR, Rohlf FJ (1981) Biometry. Freeman, San Francisco
Trillmich F (1981) Mutual mother-pup recognition in Galapagos fur seals and sea lions: cues used and functional significance. Behaviour 78:21–42
Trillmich F (1984) Natural history of the Galapagos fur seal (Arctocephalus galapagoensis, Heller) In: Perry R (ed) Key environments — Galapagos. Pergamon Press, Oxford, pp 215–223
Trillmich F (in press a) Attendance behavior of Galapagos fur seal females. In: Gentry RL, Kooyman GL (eds) Fur seals: maternal strategies on land and at sea. Princeton University Press, Princeton NJ
Trillmich F (in press b) Attendance behavior of Galapagos sea lion females. In: Gentry RL, Kooyman GL (eds) Fur seals: maternal strategies on land and at sea. Princeton University Press, Princeton NJ
Trillmich F, Limberger D (1985) Drastic effects of El Niño on Galapagos pinnipeds. Oecologia 67:19–22
Trillmich F, Mohren W (1981) Effects of the lunar cycle on the Galapagos fur seal, Arctocephalus galapagoensis. Oecologia 48:85–92
Trivers RL (1972) Parental investment and sexual selection. In: Campbell B (ed) Sexual selection and the descent of man. Heinemann, London, pp 136–179
Widdowson EM (1976) The response of the sexes to nutritional stress. Proc Nutr Soc 35:175–180
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Trillmich, F. Maternal investment and sex-allocation in the Galapagos fur seal, Arctocephalus galapagoensis . Behav Ecol Sociobiol 19, 157–164 (1986). https://doi.org/10.1007/BF00300855
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DOI: https://doi.org/10.1007/BF00300855