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Über den Einfluß der Photoperiode auf die Geschlechtsrealisation bei Gammarus duebeni
Bulnheim, H.-P. (1967). Über den Einfluß der Photoperiode auf die Geschlechtsrealisation bei Gammarus duebeni. Helgol. Wiss. Meeresunters. 15(1-4): 69-83.
In: Helgoländer Wissenschaftliche Meeresuntersuchungen. Biologische Anstalt Helgoland: Hamburg. ISSN 0017-9957, more
Also appears in:
Kinne, O.; Aurich, H. (Ed.) (1967). Vorträge und Diskussionen. Erstes Europäisches Symposion über Meeresbiologie = Papers and discussions. First European Symposium on Marine Biology = Rapports et discussions. Premier symposium européen sur biologie marine. Helgoländer Wissenschaftliche Meeresuntersuchungen, 15(1-4). Biologische Anstalt Helgoland: Hamburg. 669 pp., more
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  • Bulnheim, H.-P.

    In the euryhaline amphipod Gammarus duebeni Lillj., highly different sex ratios have been found. Rearing experiments proved the existence of amphogenic and thelygenic strains. Evidence is given for polygenic sex determination in this species; however, depending on the genetic background, environmental factors may also influence sex ratio. A modifying effect of the factors involved was assumed in animals producing offspring with considerable fluctuations of the sex ratio (allelogeny). In order to analyse the influence of the environment, animals of this type were selected and tested under different conditions of light time. Rearing experiments under two light-dark cycles, LD 8:16 and 16:8, have demonstrated the increase of the number of females in the short-day photoperiod, while males dominate in the long-day photoperiod. The photosensitive phase is restricted to the sexually indifferent life span after birth; it is more or less limited to the interval between the second and fourth moult. On the basis of research on physiological and developmental aspects in Malacostraca, an interpretation of the photoperiodic influence on sex realization is presented; it is assumed that the activity of neurosecretory cells in the brain depends on the day length and the differentiation of the androgenic glands is subjected to neurohormonal control of the CNS. The androgenic glands occupy a key position in sexual differentiation by causing a hormonal stimulation of primary and secondary male characters; if they do not differentiate, the sexual development tends towards feminity.

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