anglicky - Institute of Hydrobiology

mothers clearly come from the autumnal population, the neonates born immediately after the
isolation of the mothers (here referred to as 1 st offspring) had passed their oogenesis and
embryogenesis at low temperatures in the reservoir, the 2 nd offspring passed their oogenesis in
the reservoir and their embryogenesis in the experiment, the 3 rd offspring passed both of these
ontogenetic phases in the experiment. The results reveal that low temperature was the main
factor causing low FSN in neonates.
5 ºC
20 ºC
FSN
70
60
50
70
60
50
lake water with natural
seston
GF/C filtered lake
water - high food
GF/C filtered lake
water - low food
40
mothers
1st
offspring
2nd
offspring
3rd
offspring
40
mothers
1st
offspring
2nd
offspring
3rd
offspring
Fig. 6: Filtering setae number (FSN) of D. galeata mothers and that of their offspring in three
consecutive clutches. The mothers were isolated from Římov Reservoir on January 29 and
kept in the laboratory at two temperatures and three feeding treatments (amount of the
natural seston – 0.2 mg l –1 POC, high food and low food treatments – 2 and 0.2 mg l –1 POC
of Scenedesmus subspicatus culture, respectively).
The succession of ontogenetic phases and different temperature treatments during the
experiment suggested that the time in which low temperature may induce lower FSN is very
probably the period of embryonic development (embryogenesis). This was tested in another
experiment, in which eggs obtained from a laboratory clone of D. galeata were incubated in
vitro at three different levels of temperature. The eggs were removed several hours after being
deposited in the brood pouch of the female and divided into three groups. Each group of the
Table 6: Results of in vitro embryogenesis in D. galeata eggs incubated at three different
temperatures (figures with different superscripts are significantly different, unequal n HSD
tests, p=0.05).
Temperature during embryogenesis 19°C 10°C 6°C
Carapace length in the1st instar offspring
(µm ± 95% C.I.) 502 (±7) a 454 (±11) b 446 (±14) b
FSN in offspring
(± 95% C.I.) 72 (±1) a 69 (±1) a 65 (±1) b
same clutch was then incubated at a different temperature (19, 10, and 6°C). FSN was found
to be significantly lower in individuals incubated during embryogenesis at the lower
temperatures (Table 6). The difference in FSN is partly attributable to a difference in the
body size of the neonates because the neonates from the lower temperatures were significantly
smaller and a direct relationship between neonate size and FSN in their filtering screens was
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