Evolution, 4th Edition

278 CHAPTER 11

Costs of reproduction

Is there evidence for a cost of reproduction? This concept plays a large role in the

theory of life history evolution. Genotypes that allocate more to reproduction and

less to themselves may display decreased survival or growth. This allocation trade-off

would be manifested as a negative genetic correlation (see Chapter 6) between repro-

duction and survival. If there were also genetic variation in the amount of resources

individuals acquired from the environment, however, that variation could give rise to

a positive genetic correlation between reproduction and survival (FIGURE 11.3) [7, 59].

Both kinds of correlation were found in a seed beetle (Callosobruchus maculatus) that

develops as a larva within a bean [37]. Reproductive adults may continue to feed, but

females lay eggs even if they are deprived of food. Variation among families showed a

positive genetic correlation if females were given food (hence, variation in acquisition

of resource), but a negative genetic correlation between fecundity and survival—evi-

dence of a cost of reproduction—when females were deprived of food.

Costs of reproduction have been detected in many kinds of organisms. Genetic

correlations found in a wild population of Drosophila melanogaster showed strong

trade-offs between the number of eggs females laid when young and both their

longevity and their fecundity later in life. However, longer-lived genotypes showed

higher fecundity late in life—a rather significant observation, as we will soon see

[58]. In a study of brown anoles (Anolis sagrei), Robert Cox and Ryan Calsbeek sur-

gically removed the ovaries from wild females and then released them [14]. Even

though this species lays only one egg per clutch, these females, prevented from

allocating energy and nutrients to reproduction, showed higher growth and sur-

vival than did sham-operated females with intact ovaries (FIGURE 11.4).

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Survival A B

Resources

1 – x

x

Reproduction

Growth

Maintenance,

survival

Reproduction

(A)

(B)

Resource

acquisition locus

A

Resource

allocation locus

B

FIGURE 11.3 actors giving rise to genetic correlations between life history F

traits such as survival (or growth) and reproduction. (A) Alleles at locus A affect

the amount of energy or other resources that individuals acquire from the

environment. Alleles at locus B affect allocation of resources to functions

such as growth or survival versus reproduction, in proportions x and 1 – x.

(B) Genotypes that differ in their ability to acquire resources (for example, be-

cause of variation at locus A) are represented by blue circles. Genotypes that

differ in how resources are allocated between survival and reproduction (for

example, because of variation at locus B) are shown by red circles. The overall

genetic correlation between survival and reproduction depends on the rela-

tive magnitude of variation in resource acquisition versus resource allocation.

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Change in size (SVL in mm)

Change in mass (g)

SVL Mass

0

1.0

0.5

1.5

2.0

3.0

2.5

3.5

0

0.10

0.05

0.15

0.20

0.30

0.25

0.35

(A)

Measures of growth

Survival

2007 2008 Both

0

0.2

0.1

0.3

(B)

Year of study

SHAM

OVX

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Evolution4e_11.03.ai Date 11-20-2016

Survival A B

Resources

1 – x

x

Reproduction

Growth

Maintenance,

survival

Reproduction

(A)

(B)

Resource

acquisition locus

A

Resource

allocation locus

B

FIGURE 11.4 Evidence of the cost of

reproduction. (A) Female Anolis sagrei

from which ovaries were removed (OVX)

grew larger and gained more weight

than sham-operated (SHAM) females. SVL

is the snout-to-vent length. (B) Over the

2-year study, the proportion of females that

survived to the following year was higher

for ovariectomized females (blue columns)

than for sham-operated females (red

columns), which produced eggs. Allocation

to reproduction reduced females’ growth

and survival. (From [14].)

11_EVOL4E_CH11.indd 278 3/22/17 1:11 PM