Annual Reproductive Success = Fertilization Success X Offspring Survival MaleFemale Previous difficulty in assigning paternity

Previous work on mammalian male reproductive success Large mammals Pronounced sexual dimorphism (size and weaponry) Harem polygyny Variation in Reproductive Success: Lifetime: 0-24 calves (n=13) Annual: 50% of males sire 0 calves; 4

Exclusive territories Minimal sexual dimorphism (Male/Female mass ratio ~ ) Asynchronous estrus Harem defense Pronounced sexual dimorphism (Male/Female mass ratio ~ 1.70)

Hypothesis Reproductive success in male red squirrels will be unrelated to size. Rather it will be driven by: Age Mobility Resource Availability Inbreeding Avoidance

The Players 74 Males and 57 Reproductive Females on 2 plots (KLOO and SUL) Seasonal OSR = 1.3

Methodology Radio-collared females Behavioural monitoring of mating chases –Time –Male/female behaviour –Male ID (attending and copulating) Morphological measurements Data set –Age –Relatedness

Squirrel Mating at Kluane 2003 February 19 - May 2 49 (usable) mating chases observed 0-3 Estrus bouts/day Number of males/chase = 10.4 ± 2.4 (N = 19; Range = 6-14)

Mating Success Male – KLOO: 3.2 ± 2.3 copulations/male –SUL: 4.5 ± 2.6 copulations/male Female –KLOO: 5.9 ± 3.2 copulations/female –SUL: 8.5 ± 2.3 copulations/female Proportion of males in chase receiving a copulation = 0.77 ± 0.19 (N = 41)

Variation in copulatory success

Variation in chase attendance

R 2 = 0.7; P <.001

Hypothesis Reproductive success in male red squirrels will be unrelated to size. Rather it will be driven by: Age Mobility Resource Availability Inbreeding Avoidance

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Hypothesis Reproductive success in male red squirrels will be unrelated to size. Rather it will be driven by: Age Mobility Resource Availability Inbreeding Avoidance

Hypothesis: Age will affect male reproductive success Prediction: Older males will have a higher reproductive success than younger males Have more experience Selected for by females Higher quality genome Confounding issues Independent Variable: Age Dependent Variable: Mating Success

Linear IncreaseSenescencePlateau

Age Distribution Mean Age = 3.8 ± 2.0 (N=44 ;Range 1-8)

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Tentative Conclusions Mating success largely unrelated to age or mass Driven by reproductive effort Factors affecting chase attendance –Sex ratio of neighbours –Inbreeding avoidance –Energetics –Behavioural attributes (e.g exploration forays) Factors affecting fertilization success –Sperm competition –Behavioural attributes (e.g. mate guarding)

Future Directions Paternity (Coltman/Gunn) –Actual Reproductive Success –Relatedness (Inbreeding) –Sperm Competition Energetics (Humphries) –Costs of reproduction for males –Effect of resources Endocrinology (Boonstra) –Condition –Immunocompetence