Hydrobiologia 298: 87-91, 1995.
D. Belk, H. 1. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture 1J.
©1995 Kluwer Academic Publishers.
87
Evidence for sex-related differences in phototactic behaviour of
Streptocephalus proboscideus (Crustacea: Anostraca)
Brendonck Luc 1 , Luc De Meester 2 & Henri J. Dumont 2
1 Royal Belgian Institute of Natural Sciences, Freshwater Biology, Vautierstraat 29, B- I 040 Brussels, Belgium
2Laboratory of Animal Ecology, University afGhent, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium
Key words: phototaxis, vertical migration, temporary pools, Anostraca, Streptocephalus
Abstract
The phototactic behaviour of adults of the Sudanese fairy shrimp Streptocephalus proboscideus was studied under
laboratory conditions. Males were less negatively phototactic than females. This was also evident when colour
filters were used. Females only became little less negatively phototactic under yellow light, whereas males showed
a strong positively phototactic response. The response to the positioning of a yellow filter was stronger than to the
use of a red or blue filter for both sexes. The laboratory findings were compared with casual field observations on
Streptocephalus torvicornis that indicate differential vertical distribution between the sexes and a nocturnal vertical
migration. Migratory behaviour with ascent starting at dusk is also predicted for S. proboscideus. This behaviour
may reduce common stress factors in desert pools such as photodamage, visual predation pressure, and high surface
temperatures.
Introduction
In contrast to the vast amount of information on small
freshwater zooplankton and especially on Daphnia
(see Ringelberg, 1987; Haney, 1993), and to the recent
upsurge of interest in phototaxis of brine shrimps (Forward & Hettler, 1992; Forward, 1993) little is known
on the photobehaviouroffreshwater anostracans (fairy
shrimps).
Brine shrimps (Artemia spp.) which typically
inhabit hypersaline lakes and ponds, are reported to
be patchily distributed, but quite variable in their horizontal and vertical distribution (Lenz, 1980; Conte &
Conte, 1988; Conte et at., 1988). Part of the variability
may perhaps be explained by intraspecific genetic variation and differences in ploidy level between strains
(Lefcort et at., 1991). Laboratory studies (Mason,
1966; Bradley & Forward, 1984) and field observations
(Lenz, 1980) suggest a predominantly negative phototaxis in Artemia sp. corresponding to a nocturnal diel
vertical migration. Since brine shrimps are readily fed
upon by any zooplankton predator that can tolerate the
salinity of their habitat (Persoone & Sorgeloos, 1980),
this migratory behaviour may function as a predator
avoidance mechanism (Forward, 1993).
Negative and positive phototaxis should be considered in relation to light intensity and colour (Hailman
& Jaeger, 1975). Bradley & Forward (1984), for exampIe, found that Artemia sp. is negatively phototactic at
high, but positively phototactic at low light intensities.
It should also be noted that experimental designs testing the responses to illuminated versus shaded areas
almost always reveal a preference for the illuminated
zone (in Artemia sp.: Aiken & Hailman, 1978; in fairy
shrimps: Holmes, 1910; Howland, 1911; McGinnis,
1911; Pearse, 1912; Milller, 1918; Bernice, 1972; see
also Siebeck, 1980).
Fairy shrimps live in fish-free, mostly shallow
pools and a nocturnal vertical migration is thus not
readily expected. There are exceptions, however, especially in desert environments where rock pools may be
more than 5 m deep. Information on phototaxis and
migratory behaviour in fairy shrimps remains largely
anecdotal (e.g. Bernice, 1972). McGinnis (1911) and
Pearse (1912), working with Eubranchipus serratus
Forbes, found a 'normal' vertical migration in laboratory columns. Pearse (1912) furthermore spotted males
D. Belk, H. 1. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture 1J.
©1995 Kluwer Academic Publishers.
87
Evidence for sex-related differences in phototactic behaviour of
Streptocephalus proboscideus (Crustacea: Anostraca)
Brendonck Luc 1 , Luc De Meester 2 & Henri J. Dumont 2
1 Royal Belgian Institute of Natural Sciences, Freshwater Biology, Vautierstraat 29, B- I 040 Brussels, Belgium
2Laboratory of Animal Ecology, University afGhent, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium
Key words: phototaxis, vertical migration, temporary pools, Anostraca, Streptocephalus
Abstract
The phototactic behaviour of adults of the Sudanese fairy shrimp Streptocephalus proboscideus was studied under
laboratory conditions. Males were less negatively phototactic than females. This was also evident when colour
filters were used. Females only became little less negatively phototactic under yellow light, whereas males showed
a strong positively phototactic response. The response to the positioning of a yellow filter was stronger than to the
use of a red or blue filter for both sexes. The laboratory findings were compared with casual field observations on
Streptocephalus torvicornis that indicate differential vertical distribution between the sexes and a nocturnal vertical
migration. Migratory behaviour with ascent starting at dusk is also predicted for S. proboscideus. This behaviour
may reduce common stress factors in desert pools such as photodamage, visual predation pressure, and high surface
temperatures.
Introduction
In contrast to the vast amount of information on small
freshwater zooplankton and especially on Daphnia
(see Ringelberg, 1987; Haney, 1993), and to the recent
upsurge of interest in phototaxis of brine shrimps (Forward & Hettler, 1992; Forward, 1993) little is known
on the photobehaviouroffreshwater anostracans (fairy
shrimps).
Brine shrimps (Artemia spp.) which typically
inhabit hypersaline lakes and ponds, are reported to
be patchily distributed, but quite variable in their horizontal and vertical distribution (Lenz, 1980; Conte &
Conte, 1988; Conte et at., 1988). Part of the variability
may perhaps be explained by intraspecific genetic variation and differences in ploidy level between strains
(Lefcort et at., 1991). Laboratory studies (Mason,
1966; Bradley & Forward, 1984) and field observations
(Lenz, 1980) suggest a predominantly negative phototaxis in Artemia sp. corresponding to a nocturnal diel
vertical migration. Since brine shrimps are readily fed
upon by any zooplankton predator that can tolerate the
salinity of their habitat (Persoone & Sorgeloos, 1980),
this migratory behaviour may function as a predator
avoidance mechanism (Forward, 1993).
Negative and positive phototaxis should be considered in relation to light intensity and colour (Hailman
& Jaeger, 1975). Bradley & Forward (1984), for exampIe, found that Artemia sp. is negatively phototactic at
high, but positively phototactic at low light intensities.
It should also be noted that experimental designs testing the responses to illuminated versus shaded areas
almost always reveal a preference for the illuminated
zone (in Artemia sp.: Aiken & Hailman, 1978; in fairy
shrimps: Holmes, 1910; Howland, 1911; McGinnis,
1911; Pearse, 1912; Milller, 1918; Bernice, 1972; see
also Siebeck, 1980).
Fairy shrimps live in fish-free, mostly shallow
pools and a nocturnal vertical migration is thus not
readily expected. There are exceptions, however, especially in desert environments where rock pools may be
more than 5 m deep. Information on phototaxis and
migratory behaviour in fairy shrimps remains largely
anecdotal (e.g. Bernice, 1972). McGinnis (1911) and
Pearse (1912), working with Eubranchipus serratus
Forbes, found a 'normal' vertical migration in laboratory columns. Pearse (1912) furthermore spotted males