|On sex-determining factors in some euryhaline Gammarus species|
Bulnheim, H.-P. (1972). On sex-determining factors in some euryhaline Gammarus species, in: Battaglia, B. (Ed.) Fifth European Marine Biology Symposium. pp. 115-130
In: Battaglia, B. (Ed.) (1972). Fifth European Marine Biology Symposium. Piccin Editore: Padova. 348 pp., more
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VLIZ: Proceedings 
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Comparative investigations on sex determination in the euryhaline amphipods Gammarus duebeni Lillj., G. zaddachi Sexton and G. locusta (L) revealed that rather different factors are involved in this mechanism. In G. duebeni, determination of sex is controlled by genetic and non-genetic factors: (1) a polyfactorial system of sex genes: (2) photoperiodic factors which may bring about a shift in the sex ratio during post-embryonic development; and (3) influences of certain microsporidians which - by transmission to the offspring through the eggs - cause the production of all female broods. Microsporidian infections could not be found in G. zaddachi; however, breeding experiments provided some evidence that different photoperiods may also induce changes in the sex ratio of the offspring. In G. locusta, no significant deviation from the 1:1 sex ratio was recorded and no photoperiodic response could be ascertained. Furthermore, the infection by a microsphoridian, which is also transovarially transmitted, was shown to exert no sex-determining influence in this species. The results obtained indicate a combined influcence of polygenic and environmental factors in G. duebeni and G. zaddachi. In G. locusta, it is assumed that sex is determined by a homo-heterogamety mechanism. Some aspects and perspectives with regard to modes of sex determination in gammarids are discussed.