Letter to the Editor

EFFECT OF VARYING DOSES OF CAFFEINE ON LIFE SPAN OF DROSOPHILA MELANOGASTER

To the Editor:

Despite a considerable interest in the effect caffeine has

on metazoan life span, the extent, as well as the direction, of
this effect is still unclear. One of the most extensively used
metazoan models in longevity studies is the fruit fly
Drosophila melanogaster (1). There are a number of studies
on the effect of caffeine on

Drosophila, most of them

conducted using natural populations. However, flies derived
from natural populations for longevity studies display
substantial variations in longevity (2), most likely brought
about by heterogeneous population-specific genetic back-
ground. In addition, the genetic instability brought about by
an unbalanced genetic background can significantly affect
the outcome of a longevity analysis.

A good scientific experiment requires fixing of all vari-

ables except for the one under investigation. A control-
experiment comparison analysis cannot be adequately
achieved in longevity analyses involving natural popu-
lations due to their inherent genetic variability and, thus,
varying genetic background of organisms involved in
the study.

In the present study, we used a co-isogenic inbred line

of

D. melanogaster derived from the Canton-S (CS) stock

to assess the effect of varying dietary doses of caffeine on
life span in an equalized genetic background. Being a labo-
ratory strain of

D. melanogaster, CS has reduced genetic

variation within the strain (1). Another feature of CS is
that it is reported by the Drosophila Stock Center to have
no potentially transpositionally active transposable elements
(TEs), such as

P or hobo, in its genome (3). Transposable

elements can introduce additional genetic heterogeneity and,
thus, additional instability in response to environmental
stress (4). Previous studies with fruit fly longevity did not
take the TE factor into account.

In our experiment, we observed a significant reduction in

life span of male flies reared on food containing 2.5 mg/ml
and 1.25 mg/ml of caffeine (Table 1, Figure 1). There was
a significant decrease in life span in the experimental group
in one out of three replicas with 0.625 mg/ml and 0.3125
mg/ml caffeine concentrations. In two out of three replicas
with 0.625 mg/ml and one out of three replicas with 0.3125
mg/ml of caffeine, flies lived longer on caffeine than on
control food, although the difference in life span was not
significant. The overall relationship between caffeine con-
centration and

Drosophila life span in our experiment is

presented in Figure 1.

A previous report on caffeine effect in

Drosophila

examined the development of resistance to caffeine in 10
generations of

Drosophila prosultans, a tropical fruit fly (5).

The results of that investigation suggest a negative dosage-
dependent effect of caffeine on longevity and other life
history parameters. However, the lack of experimental
replicas makes the results of that study difficult to put into
perspective. In addition, natural populations of

Drosophila,

particularly

D. prosultans, contain large numbers of TEs in

their genome (1,6,7,8,9).

Transposable elements are major contributors to genetic

instability in

Drosophila, which contributes greatly to

variations in life span (4). Somatic movement of TEs found
in the

D. prosultans genome has been documented to reduce

life span in other species of

Drosophila (10,11). Transposable

element activity could have modified the effect of caffeine on
life span in the Itoyama and colleagues study (5).

Data presented here show that high concentrations of

caffeine reduce the longevity of an inbred strain

D. melano-

gaster with a co-isogenic background lacking TEs. Whether

Table 1. Life Span of

Drosophila melanogaster Males Reared on

Varying Dietary Caffeine Concentrations (0.3125–2.5 Mg/Ml) in

Comparison With the Corresponding Controls

(No Caffeine in Food)

Caffeine
Concentration,
mg/ml

Mean Life Span

(6

SE) (

þ)

Caffeine

Mean Life Span

(6

SE) No

Caffeine

P,

Kolmogorov-Smirnov

Test

2.5

Replica 1

16.9 6 0.6

46.0 6 1.4

,.0001

Replica 2

18.6 6 0.5

46.7 6 1.5

,.0001

Replica 3

20.5 6 0.5

45.1 6 1.3

,.0001

1.25

Replica 1

31.1 6 1.1

35.6 6 1.2

.025

Replica 2

40.6 6 1.0

42.3 6 1.8

,.0001

Replica 3

38.0 6 1.1

43.7 6 1.2

,.0001

0.625

Replica 1

38.2 6 1.2

41.7 6 1.4

.013

Replica 2

50.4 6 1.4

47.3 6 1.6

.367

Replica 3

43.1 6 1.3

42.6 6 1.5

.281

0.3125

Replica 1

42.2 6 1.4

43.5 6 1.3

.588

Replica 2

50.0 6 1.6

48.4 6 1.7

.715

Replica 3

41.4 6 1.2

44.5 6 1.3

.001

Notes: SE

¼ Standard error of mean.

Each concentration was tested in three separate replicas, which are presented

in the table individually.

Figure 1. Mean life span of Canton-S

Drosophila melanogaster males of four

dietary concentrations of caffeine with corresponding controls.

149

Journal of Gerontology: BIOLOGICAL SCIENCES

Copyright 2008 by The Gerontological Society of America

2008, Vol. 63A, No. 2, 149–150

the observed relationship between caffeine and life span will
hold in other genetic backgrounds, whether or not they
contain TEs capable of transposition, remains the subject of
further investigation.

Alexey G. Nikitin

1

Serena Navitskas

2

Lee-Ann Nicole Gordon

2

1

Biology Department

2

Biomedical and Health Sciences Department

Grand Valley State University
Allendale, Michigan

Address correspondence to Alexey G. Nitikin, Biology Department,

Grand Valley State University, 1 Campus Dr., Allendale, MI 49401.
E-mail: [e-mail]

R

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LETTER TO THE EDITOR