138
Discussion
In this paper, we present experimental evidence for
a food-dependent color pattern in Thamnocephalus
platyurus. The presence or absence of the synthetic pigment, trans-,8-carotene in a baker's yeast diet was the
controlling factor. It is known that baker's yeast contains little or no carotenes (Gilchrist & Green, 1960;
Bunker, 1963; Gilchrist, 1968; Hata & Hata, 1969).
Herring (1968a) declared Daphnia magna Straus free
of carotenoids after several generations reared on a
diet of yeast alone. Whereas all photosynthetic organisms and some other microorganisms can synthesize
carotenoids de novo, it has been a dogma that animals cannot synthesize carotenoids de novo, but they
may have the ability to structurally modify carotenoids
from the diet by oxidation (Goodwin, 1984; Partali et al., 1985). According to Goodwin (1984),
carotenoids exist in three forms in the Crustacea:
(1) as free pigments (carotenes and unesterifed xanthophylls), (2) as xanthophylls esterified to long-chain
fatty acids, and (3) as xanthophylls attached to proteins to form carotenoproteins. Carotenoids in Anostraca may occur as (1) granules, (2) in solution in fat
globules of phagocytic storage cells, and (3) as watersoluble carotenoproteins (Gilchrist, 1968). According
to Gilchrist (1968) the carotenoid contained in the fat
globules of phagocytic storage cells frequently stain
them bright orange. These cells mainly occur in the
labrum, thoracopods, and in the 'fat body' associated
with the ovary (Gilchrist, 1968). The major carotenoid
in anostracan eggs is canthaxanthin, probably derived
from the maternal ovary, and there exists some evidence that Anostraca synthesize canthaxanthin from
,8-carotene ingested with food (Gilchrist, 1968; Hsu
etal.,1970).
The food-dependent colors of the ovaries and eggs.
exhibited by the T. platyurus specimens in this study
were similar to those experimentally found in Artemia
by Hata & Hata (1969). They reported that the color of yeast-fed Artemia eggs was white in the ovary,
while the color of the pure ,8-carotene-fed Artemia
ovary was blue. After chemical analysis, Hata & Hata
(1969) concluded that the blue color ofthe eggs is due
to a canthaxanthin-protein complex. The color pattern
of T. platyurus specimens under treatment 1 is very
similar to that observed in most of the specimens collected from the wild (i.e. cercopods and thoracopods
orange, and ovaries blue) (pers. obs.). This suggests
that a natural source of ,8-carotene was available to
them, probably algae.
In the Crustacea,apart from the fact that some
carotenoids are an essential primary source of vit. A,
little is known of their function per se (Goodwin,
1984). Goodwin (1960) pointed out that the major
function of carotenoid and melanin pigments is to provide the external color pattern of the animals. A number of other functions of carotenoids in crustaceans
have been claimed, however (see Goodwin, 1984).
Cheesman et al. (1967) suggested that carotenoproteins in invertebrates may participate in protection,
coloration, photosensitivity, electron transport, and
enzymatic activity. Nelis et al. (1984) found ciscanthaxanthins specifically occurring in the ovaries
and eggs of Artemia females. They suggested that
some kind of relation to reproduction and/or embryonic development exists, thus suggesting a previously unrecognized function for carotenoids in the brine
shrimp and possibly in related Crustacea.
Our results show that T. platyurus is able to grow,
apparently normally, with or without synthetic trans,8- carotene in its diet. Only at the end of the third
culture period (day 9) was there a significant difference in growth between the females, with the synthetic trans-,8-carotene group growing faster. Herring
(1968b) reported that Daphnia magna is able to grow
and reproduce 'normally' in the absence of carotenoids
in its diet. Here, the absence of evidence for vit. A or
carotenoid requirements other than for visual purposes,
led to the conclusion that the natural metabolic fate and
subsequent deposition of ingested carotenoid is purely
fortuitous (Herring, 1968b). Partali et al. (1985), however, could not obtain a healthy, yet fully carotenoid
depleted D. magna.
Summarizing, we conclude that, while carotenoids
do not appear essential to animals reared under laboratory conditions, they still may have an ecological role
in natural conditions (e.g. photoprotection: Hairston,
1980). Without considering the color of the food itself
while in the intestinal tract, the color patterns of the
phyllOpod body can be explained by (1) structural
peculiarities of its tissues (e.g. iridescence: Goodwin, 1960), (2) the presence of pigments produced
de novo (e.g. haemoglobin: Gilchrist & Green, 1960),
and (3) the presence of food-dependent pigments (e.g.
carotenoids: Goodwin, 1984).
Acknowledgments
We thank Dr Denton Belk (Our Lady of the Lake University of San Antonio, Texas, USA) for supplying
Discussion
In this paper, we present experimental evidence for
a food-dependent color pattern in Thamnocephalus
platyurus. The presence or absence of the synthetic pigment, trans-,8-carotene in a baker's yeast diet was the
controlling factor. It is known that baker's yeast contains little or no carotenes (Gilchrist & Green, 1960;
Bunker, 1963; Gilchrist, 1968; Hata & Hata, 1969).
Herring (1968a) declared Daphnia magna Straus free
of carotenoids after several generations reared on a
diet of yeast alone. Whereas all photosynthetic organisms and some other microorganisms can synthesize
carotenoids de novo, it has been a dogma that animals cannot synthesize carotenoids de novo, but they
may have the ability to structurally modify carotenoids
from the diet by oxidation (Goodwin, 1984; Partali et al., 1985). According to Goodwin (1984),
carotenoids exist in three forms in the Crustacea:
(1) as free pigments (carotenes and unesterifed xanthophylls), (2) as xanthophylls esterified to long-chain
fatty acids, and (3) as xanthophylls attached to proteins to form carotenoproteins. Carotenoids in Anostraca may occur as (1) granules, (2) in solution in fat
globules of phagocytic storage cells, and (3) as watersoluble carotenoproteins (Gilchrist, 1968). According
to Gilchrist (1968) the carotenoid contained in the fat
globules of phagocytic storage cells frequently stain
them bright orange. These cells mainly occur in the
labrum, thoracopods, and in the 'fat body' associated
with the ovary (Gilchrist, 1968). The major carotenoid
in anostracan eggs is canthaxanthin, probably derived
from the maternal ovary, and there exists some evidence that Anostraca synthesize canthaxanthin from
,8-carotene ingested with food (Gilchrist, 1968; Hsu
etal.,1970).
The food-dependent colors of the ovaries and eggs.
exhibited by the T. platyurus specimens in this study
were similar to those experimentally found in Artemia
by Hata & Hata (1969). They reported that the color of yeast-fed Artemia eggs was white in the ovary,
while the color of the pure ,8-carotene-fed Artemia
ovary was blue. After chemical analysis, Hata & Hata
(1969) concluded that the blue color ofthe eggs is due
to a canthaxanthin-protein complex. The color pattern
of T. platyurus specimens under treatment 1 is very
similar to that observed in most of the specimens collected from the wild (i.e. cercopods and thoracopods
orange, and ovaries blue) (pers. obs.). This suggests
that a natural source of ,8-carotene was available to
them, probably algae.
In the Crustacea,apart from the fact that some
carotenoids are an essential primary source of vit. A,
little is known of their function per se (Goodwin,
1984). Goodwin (1960) pointed out that the major
function of carotenoid and melanin pigments is to provide the external color pattern of the animals. A number of other functions of carotenoids in crustaceans
have been claimed, however (see Goodwin, 1984).
Cheesman et al. (1967) suggested that carotenoproteins in invertebrates may participate in protection,
coloration, photosensitivity, electron transport, and
enzymatic activity. Nelis et al. (1984) found ciscanthaxanthins specifically occurring in the ovaries
and eggs of Artemia females. They suggested that
some kind of relation to reproduction and/or embryonic development exists, thus suggesting a previously unrecognized function for carotenoids in the brine
shrimp and possibly in related Crustacea.
Our results show that T. platyurus is able to grow,
apparently normally, with or without synthetic trans,8- carotene in its diet. Only at the end of the third
culture period (day 9) was there a significant difference in growth between the females, with the synthetic trans-,8-carotene group growing faster. Herring
(1968b) reported that Daphnia magna is able to grow
and reproduce 'normally' in the absence of carotenoids
in its diet. Here, the absence of evidence for vit. A or
carotenoid requirements other than for visual purposes,
led to the conclusion that the natural metabolic fate and
subsequent deposition of ingested carotenoid is purely
fortuitous (Herring, 1968b). Partali et al. (1985), however, could not obtain a healthy, yet fully carotenoid
depleted D. magna.
Summarizing, we conclude that, while carotenoids
do not appear essential to animals reared under laboratory conditions, they still may have an ecological role
in natural conditions (e.g. photoprotection: Hairston,
1980). Without considering the color of the food itself
while in the intestinal tract, the color patterns of the
phyllOpod body can be explained by (1) structural
peculiarities of its tissues (e.g. iridescence: Goodwin, 1960), (2) the presence of pigments produced
de novo (e.g. haemoglobin: Gilchrist & Green, 1960),
and (3) the presence of food-dependent pigments (e.g.
carotenoids: Goodwin, 1984).
Acknowledgments
We thank Dr Denton Belk (Our Lady of the Lake University of San Antonio, Texas, USA) for supplying