Evaluation of reproductive costs for Weddell seals in Erebus Bay, Antarctica

Abstract

Summary1. Organisms balance current reproduction against future survival and reproduction, which results in life-history trade-offs. These trade-offs are also known as reproductive costs and may represent significant factors shaping life-history strategy for many species. 2. Using multistate mark-resight models and 26 years of mark-resight data , we estimated the costs of reproduction to survival and reproductive probabilities for Weddell seals in Erebus Bay, Antarctica and evaluated whether this species either conformed to the 'prudent parent' reproductive strategy predicted by life-history theory for long-lived mammals or alternatively, incurred costs to survival in order to reproduce in a variable environment (flexible-strategy hypothesis). 3. Results strongly supported the presence of reproductive costs to survival (mean annual survival probability was 0·91 for breeders vs. 0·94 for nonbreeders), a notable difference for a long-lived mammal, demonstrating that investment in reproduction does result in a cost to survival for Weddell seals, contrary to the prudent parent hypothesis. 4. Reproductive costs to subsequent reproductive probabilities were also present for first-time breeders (mean probability of breeding the next year was 31·3% lower for first-time breeders than for experienced breeders), thus supporting our prediction of the influence of breeding experience. 5. We detected substantial annual variation in survival and breeding probabilities. Breeding probabilities were negatively influenced by summer sea-ice extent, whereas weak evidence suggested that survival probabilities were affected more by winter sea-ice extent, and the direction of this effect was negative. However, a model with annual variation unrelated to any of our climate or sea-ice covariates performed best, indicating that further study will be needed to determine the appropriate mechanism or combination of mechanisms underlying this annual variation.

Annual reproductive rates of Weddell seals in eastern Antarctica from 1973 to 2000

“…Those signals did occur following a strong El Niño event in equatorial regions (Fig. 4).In contrast, low reproductive rates were experienced by Weddell seals throughout the 1990s at the Vestfold Hills but not at McMurdo Sound (Hadley et al 2007). If the Vestfold Hills signal was in response to El Niño forcing, then the geographical scale of forcing was not to the extent of the entire Southern Ocean.…”

“…Lake (2007) and Hadley et al (2007) Multi-strata models can pertain to costs of reproduction; costs of reproduction are the energetic trade-off of producing a pup and may include lower probability of surviving and/or reproducing the following year (Stearns 1992). Hadley et al (2007) found evidence of 3% lower survival the year after reproduction and inferred Weddell seal life history on that basis. We use the independent data set from the Vestfold Hills to validate their conclusions.…”

Environmental extremes versus ecological extremes: impact of a massive iceberg on the population dynamics of a high-level Antarctic marine predator

“…Recruitment was defined as the transition from state P to F (c PF ) and reproduction as transition from state F, E or S to state E (c FE , c EE , c SE ). Several combinations of age and year effects were considered for each reproductive status [36,37,44] and evaluated with the Akaike information criterion (AIC) corrected for sample size (AICc) and overdispersion (QAICc). The estimates that were subsequently used in the analysis come from the most supported of these models.…”

Individual quality and age but not environmental or social conditions modulate costs of reproduction in a capital breeder

“…The difference between previously reproducing and nonreproducing females suggests that the cost of reproduction depends on a female's age, with prime‐aged females bearing higher costs of reproduction. Age‐dependent cost of reproduction was reported in several species, with higher costs of reproduction found in younger (i.e., first breeding) and/or older individuals (red deer, Cervus elaphus [Clutton‐Brock, 1984]; lesser snow geese, Anas caerulescens caerulescens [Viallefont, Cooke, & Lebreton, 1995]; greater flamingos, Phoenicopterus ruber roseus [Tavecchia, Pradel, Boy, Johnson, & Cezilly, 2001]; Soay sheep, Ovis aries [Tavecchia et al., 2005]; Weddell seals, Leptonychotes weddellii [Hadley, Rotella, & Garrott, 2007]; and wolverines [Rauset et al., 2015]). The probability of giving birth after a nonbreeding event is low in older animals (more than 10 years old; Figure 2a), and this decrease in fecundity and reproductive success in older individuals (i.e., senescence) is commonly observed in iteroparous species (Clutton‐Brock, 1984).…”

“…Moreover, reproductive costs on future reproduction were found to vary with population density in red deer (Clutton‐Brock, 1984) and mountain goats (Hamel, Cote et al., 2010). However, our results are similar to a study in female Weddell seals ( Leptonychotes weddellii ), where even in a highly variable environment, reproductive costs on future reproduction did not appear to vary substantially from year to year nor according to summer sea‐ice conditions (Hadley et al., 2007). …”