REPRODUCTIVE SUCCESS IN MALE SOUTHERN ELEPHANT SEALS OF SEA LION ISLAND
(FALKLAND ISLANDS): BEHAVIOURAL ESTIMATES AND PATERNITY

Fabiani,A.1, Galimberti,F.2 and Hoelzel,A.R.1

1 Dept. of Biological Sciences, University of Durham, South Road, DH1
3LE Durham, England 2 Elephant Seal Research Group, Via Buonarroti 35,
20145 Milano, Italy

The aim of the study was: a) to estimate paternity using DNA markers; b)
to assess variance in male reproductive success and c) to evaluate the
relationship between observational and genetic measures of male success.
Samples were collected during three breeding seasons (1996 to 1998). In
total, 104 males and 192 mother/pup pairs belonging to seven harems
(23-104 females) were typed for 9 microsatellite loci; 356 copulations
were recorded and the harems observed for a total of 1,030 hours. There
were 4-10 alleles per locus, sufficient to identify paternity with a
very small probability of error. We were able to assign a genetic father
to 96.4% of the pups and the distribution of paternities indicated a
very high level of polygyny. Behavioural indices of breeding success
were very good predictors of the relative male reproductive success (r2
0.79-0.99). Even simple indices predicted genetic paternity 68-79% of
the time, with behaviours associated with first copulation and
association during oestrus being somewhat better than harem holding or
ENFI (index of fertilization success). Within each harem, the harem
holder achieved the highest proportion of paternities (mean 72%; range
48%-95%), regardless the size of the harem. Harems holders were on
average more successful than those seen either in Argentina (58%) or for
northern elephant seal at A–o Nuevo (38%). This suggests a difference
that could relate either to male or female strategy, or to environmental
factors at Sea Lion Island. Possible explanations include a general
proximity of oestrus females to the sea due to the lack of a large tidal
range (and consequently a lower female interception rate by peripheral
males during departures), more efficient female control by the harem
holders, or a more pronounced difference in resource holding potential
among males.

Talk to be presented at 14th Biennial Conference on the Biology of Marine
Mammals, 28 November to 3 December 2001, Vancouver, BC, Canada.