Annual Reproductive Success = Fertilization Success X Offspring Survival

Male Female

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; <5% sire >4

• Exclusive territories• Minimal sexual dimorphism

(Male/Female mass ratio ~ 1.05-1.11)

• 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

024681012141618

0 1 2 3 4 5 6 7 8 9 10 11 12

Number of Copulations

Num

ber o

f Mal

es

Variation in chase attendance

024681012141618

0 1 2 3 4 5 6 7 8 9 10 11 12

Number of Copulations

Num

ber

of M

ales

CopulationChase

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Chases Attended

Cop

ulat

ions

Atta

ined

R2 = 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

0

2

4

6

8

10

12

200 250 300

February Mass (g)

Num

ber

of C

opul

atio

ns

n/s

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 Increase Senescence Plateau

Age Distribution

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

02468101214161820

1 2 3 4 5 6 7 8

Age (yr)

Num

ber

of M

ales

02468

101214

0 1 2 3 4 5 6 7 8

Age (yr)

Num

ber

of C

opul

atio

ns

n/s

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