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. 2006 May 22;273(1591):1239-44.
doi: 10.1098/rspb.2005.3393.

Good reindeer mothers live longer and become better in raising offspring

Robert B Weladji  1 , Jean-Michel Gaillard, Nigel G Yoccoz, Oystein Holand, Atle Mysterud, Anne Loison, Mauri Nieminen, Nils Chr Stenseth
Affiliations

Good reindeer mothers live longer and become better in raising offspring

Robert B Weladji et al. Proc Biol Sci. .

Abstract

Longevity is the main factor influencing individual fitness of long-lived, iteroparous species. Theories of life history evolution suggest this is because increased longevity allows individuals to (i) have more breeding attempts (time component), (ii) accumulate experience so as to become better able to rear offspring (experience component) or (iii) because individuals reaching old age have above-average quality (quality component). We assess empirically the relative influences of time, experience and quality on the relationship between longevity and individual fitness among female reindeer. Fitness increased with longevity due to all three processes. All females increased in success with age up to their penultimate year of life (experience component), the success of the terminal-breeding occasion was strongly dependent on longevity. Long-lived females had more successful breeding attempts during their life (time component), and had higher reproductive success at all ages, especially during the last year of life (individual quality component) than short-lived females. Our study reveals a more complex relationship between longevity and fitness in large mammals than the simple increase of the number of reproductive attempts when living longer.

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Figures

Figure 1
Figure 1
The relationship between longevity and LRS. (a) the relationship between age and LRS is nearly linear (continuous line: LRS based on estimated relationship weaning-success age, dotted line with shaded area, predicted values obtained using an additive model, points are observed values for females with complete observations). (b) The effect of experience (measured by the slope of the regression of weaning success against age) on LRS. A vertical slope (i.e. slope=0) would indicate no experience i.e. a constant weaning success after three years of age; while a positive slope will reflect the effect of experience. For example, LRS for longevity=10 will be 2.18 without experience (slope=0) and 3.090 with experience (i.e. slope=0.15); demonstrating that individual fitness increases with experience. (c) The consequence on fitness of the lower weaning success observed in the last year of life. The figure shows the difference between a fitness calculated assuming only an effect of experience (measured by the slope weaning-success age) but with no decrease during the last year, and the fitness calculated using the estimated last-year effect.
Figure 2
Figure 2
The relationship between longevity and lambda. (a) The relationship between age and Lambda is strongly nonlinear due to reproductive events occurring late in life being strongly downweighted as the estimated lambda are much larger than 1. (b) The effect of experience on lambda. (c) The consequence on fitness of the lower weaning success observed in the last year of life. (see figure 1 for further details).
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