Successful sons or superior daughters: sex-ratio variation in springbok.
Mothers would often benefit from producing more offspring of one sex than the other. Although some species show an astonishing ability to skew their sex ratio adaptively, the trends found in many studies on vertebrates have proved inconsistent. Furthermore, evidence for a mechanism by which such a bias is achieved is equivocal at best. Here, we examine sex-ratio variation over 30 years, both at an individual and a population level, in the highly polygynous, size-dimorphic springbok (Antidorcas marsupialis). Many previous studies of similar species have shown that mothers in superior condition preferentially produce sons, whereas those in poorer condition produce more daughters. We found the opposite to be true in springbok, perhaps because daughters provide mothers in superior condition with a more rapid and secure fitness return. This theory was supported by the findings that earlier-conceived offspring tended to be female and that an increased proportion of daughters were produced with increasing rainfall (which was likely to reduce nutritional stress). We also show that selective reabsorption of embryos is unlikely to be the main mechanism by which deviations from an equal sex ratio are achieved. Hence, either differential implantation occurs or females are able to influence the sex of the sperm fertilizing an egg.
Krüger
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O
Department of Zoology, University of Cambridge, Dowing Street, Cambridge CB2 3EJ, UK. ok212@cam.ac.uk
Radford
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AN
Anderson
C
C
Liversidge
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R
D000367:Age Factors; D000818:Animals; D000866:Antelopes / Q000502:physiology*; D001824:Body Constitution / Q000502:physiology*; D002980:Climate; D020964:Embryo Loss / Q000473:pathology; D004622:Embryo, Mammalian / Q000502:physiology; D005260:Female; D008137:Longitudinal Studies; D008297:Male; D011157:Population Dynamics; D011247:Pregnancy; D012744:Sex Ratio; D013019:South Africa
Biol Rev Camb Philos Soc. 1995 May;70(2):225-41
7605846
Trends Ecol Evol. 1999 Sep;14(9):343-348
10441307
Nature. 1993 Sep 2;365(6441):8
8361543
Proc Biol Sci. 2004 Aug 22;271(1549):1723-8
15306293
Trends Ecol Evol. 1999 Jun;14(6):229-234
10354625
Science. 2002 Mar 1;295(5560):1685-8
11823605
Evolution. 1989 Jan;43(1):223-225
28568501
Science. 1967 Apr 28;156(3774):477-88
6021675
Monogr Popul Biol. 1982;18:1-355
7144766
Q Rev Biol. 1986 Sep;61(3):339-74
3532167
Gen Comp Endocrinol. 1997 Jun;106(3):374-83
9204371
Am Nat. 1999 Aug;154(2):194-204
29578787
Science. 1973 Jan 5;179(4068):90-2
4682135
Nature. 1999 Jun 3;399(6735):459-61
10365956