Abstract
Die calanoiden CopepodenEurytemora affinis (Poppe) undE. herdmani Thompson &Scott wurden über zahlreiche Generationen im Laboratorium gezüchtet. Mit einem Überschuß an Algennahrung vermehrt sichE. affinis in Salzgehalten zwischen 5 und 33 ‰ und bei Temperaturen zwischen 2° und 23,5° C.E. herdmani pflanzt sich in Salzgehalten unter 15 ‰ und bei 21,5° C und höheren Temperaturen nicht fort. Diese Ergebnisse stimmen überein mit Untersuchungen im natürlichen Lebensraum und zeigen, daßE. herdmani an kälteres und salzhaltigeres Wasser gebunden ist als die weiter verbreiteteE. affinis. An den Jungtieren, die von einzelnen Weibchen erhalten worden waren, wurden die Entwicklungszeitspannen vom Ei bis zum ersten Nauplius, ersten Copepoditen, Adultus und eiertragenden Weibchen ermittelt. In 20 ‰ Salzgehalt variiert die Generationszeit beiE. affinis von etwa 105 Tagen bei 2° C bis 9 Tagen bei 23,5° C. Die entsprechenden Generationszeiten fürE. herdmani betragen 73 Tage bei 2° C und 19 Tage bei 15° C. Die Körperlänge beider Arten nimmt bei niedrigeren Temperaturen zu. Die Errechnung des Zahlenverhältnisses der Geschlechter der Jungtiere einzelner Weibchen legt die Vermutung nahe, daß die Temperatur das Geschlechtsverhältnis beeinflußt. Überlebenszeiten wurden ermittelt für Weibchen, welche unter verschiedenen Temperatur- und Salzgehaltsbedingungen gehalten worden waren. Die Lebensspannen von Weibchen beider Arten übertreffen 100 Tage bei 2° C und nehmen bei höheren Temperaturen ab. Weibchen beider Arten vermögen noch lange nach der Kopulation fertile Eier zu produzieren. Diese Beobachtungen sprechen dafür, daß kleine Lokalpopulationen möglicherweise im Herbst kopulieren, dann überwintern und daß die Weibchen im Frühjahr ohne erneute Kopulation Junge produzieren.
Summary
1. The calanoid copepodsEurytemora affinis (Poppe) andE. herdmani Thompson &Scott were cultured for numerous generations in the laboratory.
2. With excess algal food,Eurytemora affinis reproduced at salinities between 5 ‰ and 33 ‰ and at temperatures between 2° and 23.5° C. Reproduction ofE. herdmani failed at salinities below 15 ‰ and at temperatures of 19.5° C and higher.
3. Using the progeny from individual females, generation times were calculated as the time required for development from eggs to ovigerous females. At 20 ‰ salinity, generation times forEurytemora affinis ranged from about 105 days at 2° C to 9 days at 23.5° C. Corresponding generation times forE. herdmani ranged from 73 days at 2° C to 19 days at 15° C.
4. The body length of culturedEurytemora affinis was within the normal range for wild specimens. CulturedE. herdmani individuals were always smaller than wild specimens, suggesting that the culture conditions for this species were not optimal. Body lengths of both species were greater at 2° C than at 21.5° C with the exception ofE. herdmani females.
5. Low developmental temperatures increased the proportion of femaleEurytemora affinis and increased the proportion of maleE. herdmani in cultures. Possible adaptive advantages of these variations are discussed.
6. Females of both species lived longer than 100 days at 2° C, and survival time decreased at higher temperatures. Females of both species could produce fertile eggs long after mating. These results suggest the possibility that females could mate in autumn, then overwinter and produce larvae in spring without a further mating.
7. Better reproduction and faster development ofEurytemora herdmani at low temperature helps explain its more northerly distribution. The ability ofE. affinis to reproduce at temperatures approaching 25° C correlates with distribution as far south as the Gulf of Mexico. The tolerance ofE. affinis to a wide range of temperatures and salinities helps explain its great ability to colonize upper estuarine regions and even fresh water lakes.
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Katona, S.K. Growth characteristics of the copepodsEurytemora affinis andE. herdmani in laboratory cultures. Helgolander Wiss. Meeresunters 20, 373–384 (1970). https://doi.org/10.1007/BF01609914
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DOI: https://doi.org/10.1007/BF01609914