DOI: 10.5061/dryad.bcc2fqz7h
title: Data from: Trade-offs between age-related breeding improvement and survival senescence in highly polygynous elephant seals: dominant males always do better

description: Life history trade-off theory predicts that current reproduction can
 negatively affect survival and future reproduction. Few studies have
 assessed breeding costs for males of polygynous species compared to
 females, despite substantial variation in breeding success among
 individual males (e.g. subordinate cf. dominant breeders). Specifically,
 differentiating between the cost of attending breeding seasons, and the
 additional cost of successfully securing and mating females is lacking. We
 investigated whether trade-offs are present in the highly polygynous male
 southern elephant seal (Mirounga leonina) using 34-years of
 individual-level data. We compare age-specific survival, recruitment and
 future breeding success probabilities of pre-breeders (males yet to
 recruit) and breeders (subordinate and dominant social ranks) using
 multievent models. Pre-breeders and breeders of overlapping ages had
 similar survival probabilities, suggesting that there was no attendance
 cost for early recruits. In addition, the probability of recruiting as a
 dominant breeder never exceeded recruitment probability as a subordinate
 breeder of the same age. Therefore, older pre-breeders that delayed
 attendance costs generally did not improve their breeding success
 (probability of being dominant) at recruitment more than younger recruits.
 Rather, recruitment age may be a function of individual quality, with
 lower quality individuals requiring more time to socially mature. When
 comparing subordinate and dominant breeders, we found clear evidence for
 survival senescence, with subordinate breeders having a higher baseline
 mortality. In contrast, age-specific future breeding success (probability
 of being dominant at t+1) increased with age, with dominant breeders
 maintaining higher subsequent breeding success than subordinate breeders.
 The opposite trends in survival and future breeding success for both
 subordinate and dominant breeders may indicate a lifetime,
 population-level trade-off. However, we found no evidence to suggest that
 being a dominant breeder consecutively (and having a higher accumulated
 breeding cost) accelerated the rate of senescence when compared to
 individuals that were previously subordinate. Thus, males experienced
 actuarial senescence regardless of social rank, with dominant (and
 possibly high quality) breeders showing a reduced trade-off between
 survival and future breeding success. We make several novel contributions
 to understanding polygynous male life histories and southern elephant seal
 demography.
description: All elephant seal pups weaned at Marion Island from 1983 to 2009
 were uniquely marked with two plastic livestock tags applied to the hind
 flippers (<i>n </i>= 27 cohorts, 6245 male pups; Pistorius
 <i>et al.</i>,<i> </i>2011). Pups were tagged in
 the inner interdigital webbing from 1983 to 1999 and in the outer
 interdigital webbing from 2000 to 2009. From 1983 to 2016, all beaches
 where elephant seals bred were surveyed every seven days during the
 breeding season and every ten days outside of the breeding season. In
 total, 58 177 observations of marked male elephant seals were made over 34
 years. A seal year began at the start of every breeding season and ended
 before the following breeding season.   When a male elephant seal was
 resighted, one of nine events could be assigned to it: not seen (0); seen
 as a pre-breeder with two tags (1); seen as a pre-breeder with one tag
 (2); seen as a subordinate breeder with two tags (3); seen as a
 subordinate breeder with one tag (4); seen as a dominant breeder with two
 tags (5); seen as a dominant breeder with one tag (6); seen with an
 unknown breeding state and two tags (7); and seen with an unknown breeding
 state and one tag (8). Dominant breeders were identified as being
 associated with one or more females with pup(s), which they defended and
 mated (male often positioned within the harem). Subordinate breeders were
 either on the periphery of harems or on beaches not occupied by females.
 We assigned animals to events 7 and 8 when an individual was seen as both
 subordinate and dominant several times during the same breeding season. In
 such cases (<i>n</i> = 43), uncertainty existed about the true
 breeding state that the individual occupied during the breeding season. On
 only nine occasions were individuals that had previously participated in a
 breeding season not seen in a future breeding season, given that the
 individual was known to be alive through subsequent encounters. These nine
 individuals were also classified as having an unknown breeding status
 during absent years.   An
 individual could occupy one of nine possible states during each seal year
 (Pradel, 2005). The states were: pre-breeder with two tags (PB2, has not
 previously participated in a breeding season); pre-breeder with one tag
 (PB1); pre-breeder alive elsewhere with two tags (PBAE2, temporarily
 emigrated and last seen with two tags); pre-breeder alive elsewhere with
 one tag (PBAE1); subordinate breeder with two tags (SB2); subordinate
 breeder with one tag (SB1); dominant breeder with two tags (DB2); dominant
 breeder with one tag (DB1); and dead (D, an absorbing state representing
 death and permanent emigration). Pre-breeders alive elsewhere were hidden
 states constructed to account for temporary emigration from the study
 population (Schaub, Gimenez, Schmidt, & Pradel 2004).
 Goodness-of-fit tests indicated that this behaviour was prevalent among
 pre-breeders, but not breeders. Introducing an unobservable state improved
 estimates of survival and detection probabilities of
 pre-breeders.   Data were formatted
 into a multievent encounter history matrix to be analysed in E-SURGE 2.1.4
 (Choquet, Rouan, & Pradel 2009). Rows represent the encounter
 history of individuals and columns represent time steps (i.e. 34 seal
 years). The last column identifies the position of tag placement on each
 seal (IIT - inner-interdigital, OIT - outer-interdigital). The encounter
 history of each individual is numbered using event codes (see
 above).