�ber Die Geschlechtsbeeinflussende Wirkung Von Farballelen Bei Gammarus Pulex SSP. Subterraneus (Schneider)

Helgolander Wiss. Meeresunters

1978

Sex determination in Gamrnarus duebeni duebeni was analyzed by breeding experiments conducted with individuals obtained from various populations. Sex ratio of progeny depends on genetic factors and photoperiod. Generally, a preponderance of males was noted when offspring were raised under long-day photoperiods, whereas females prevailed under short-day photoperiods (Bulnheim, 1967(Bulnheim, , 1969. Based on these previous studies the critical daylength, the transition point at which the photoperiodic response switches, was estimated in specimens from a population of the Elbe estuary as ranging between 13 and 14 hours of light per day at 15 ~ C. The susceptibility to photoperiod is assumed to depend on the balance between a system of male and female determining genetic factors that act on a polygenie basis. From various coastal brackish-water populations thelygenie (all-female) strains could be selected. This maternally inherited sex-ratio condition is caused by the transovarially transferred microsporidians Octosporea efferninans and Thelohania herediteria which, independently of each other, exert a feminizing influence on the host's offspring. Either perfectly or imperfectly thelygenic females may occur. The latter produce eggs that are not all infected; hence their progeny are bisexual. As a consequence of the sex-determining influence of the microsporidians males are generally not parasitized. However, some males associated with O. effeminans were found in a strain derived from a population at Bornholm (Baltic Sea).Also, males infested with one or both of the two parasite species occur in some populations of G. d. eelticus, indicating that in these sex determination is not governed by the microsporidians concerned. The feminizing influence of the parasites may be affected by environmental factors. An increase of the ambient salinity level to 25-30 %o results in a disappearance of O. efferninans in the eggs released by infected G.d. duebeni femaies. Thus, the normally acting switch mechanism of sex determination is re-established. In addition, long exposures to low temperatures (~ 4 ~ C) may have an adverse effect on the vegetative stages of both microsporidians. Owing to this, infected females may produce eggs which are not all parasitized. Consequently, mixed progeny may arise. Studies on the incidence rates of the two microsporidians comprising 18 populations indicate that the parasites are widespread in their geographical range. Most populations studied in the Baltic Sea area and brackish-water habitats of the German North Sea coast are associated with either one or both of the two microsporidian parasites. Observations on the sex ratio of a population from the Elbe estuary, performed over several years, revealed considerable seasonal fluctuations. The percentages of infected females, however, remained at a fairly constant level during the study period. The results obtained are discussed with reference to the mechanisms of sex determination and differentiation as revealed in other amphipod speci...

Section: Monogeny and Effects Of Environmental Factorsmentioning

confidence: 99%

Section: Monogeny and Effects Of Environmental Factorsmentioning

confidence: 99%

Interaction between genetic, external and parasitic factors in sex determination of the crustacean amphipodGammarus duebeni

Helgolander Wiss. Meeresunters

1978

“…Das hierbei zutage tretende Geschlechtsverh~iltnis wird zudem von der w~ih-rend der Postembryonalentwicklung herrschenden Photoperiode beeinfluBt, wobei Langtagbedingungen eine m~nnliche Entwicklung begfinstigen. Durch erhShte Salzgehalte l~Bt sich eine Normalisierung des Mechanismus der Geschlechtsbestimmung erzielen, wodurch bewiesen ist, dab die geschlechtsbeeinflussende Wirkung der Mikrosporidien dem System von genetischen und photoperiodischen Faktoren, welche prim~ir die Geschlechtsreahsation kontrollieren, sekund~r fiberlagert ist (Bulnheim, 1978a (Anders, 1957).…”

Section: Okophysiologieunclassified

Zur Ökophysiologie, Sexualität und Populationsgenetik litoraler Gammaridea — ein Überblick

Helgolander Meeresunters

1991

On ecophysiology, sexuality and population genetics of littoral Gammaridea -a survey. Comparative investigations on the physiological capacities in the euryhahne amphipods Gammarus locusta, G. oceanicus, G. sallnus, G. zaddacln and G. duebeni were reviewed. In order to assess the adaptations of these species to the abiotic conditions of their environment, the following criteria were examined: oxygen consumption in relation to ambient salinity and temperature levels, respiratory responses following osmotic stress, resistance capacities to oxygen deficiency, resistance to aerial exposure and the simultaneous presence of hydrogen sulphide. Covering the range from marine to typically brackish-water inhabitants, the 5 species show adaptive responses in the abovementioned order. Respiration is less intensely modified by external factors, and oxygen consumption decreases. Accompanied by faster rates of acclimation to new steady states of performance, resistance capacities increase. The significance of the findings obtained is discussed in relation to the environmental requirements of the amphipods considered: Based on breeding experiments, the sex-determining systems reported thus far in Gammarus species are outlined. As demonstrated in G. duebeni, a more or less pronounced influence of external factors such as photoperiod may become effective. A preponderance of males was noted when offspring were raised under long-day photoperiods, whereas females prevailed under short-day conditions. In terms of the critical daylength, the light per day was estimated as being between 13 and 14 h (Elbe estuary population}.Feminizing microsporidians (Octosporea effeminans, Thelohania herediteria), which are transovarially transmitted, can interfere with the system of sex determination and sex differentiation of the host. As reflected in various G. duebeni populations, they cause a maternally transferred sex-ratio condition by the production of all-female broods, thereby mimicking extrachromosomal inheritance. An increase of the salinity level to 25-30 %0 results in a disappearance of O. effeminans. In both microsporidians, long exposure to low temperatures (-<4~ produces eggs which are not all parasitized. Furthermore, intersexuality can be induced by changing environmental factors. Microsporidian species have no influence on sex differentiation in G. duebeni celticus, G. salinus, G. locusta and G. pulex. Patterns of relative electrophoretic mobilities of proteins and the distribution of allele frequencies at polymorphic gene loci can be utilized for species diagnosis and for the evaluation of the relationships between different taxa, particularly at and below the species level. As exemplified by studies on several gammarids from marine, brackish and freshwater environments, inter-and infraspecific gone-enzyme variation is described. Electrophoretic investigations on natural populations of the euryhaline amphipods G. zaddachi, G. salinus, G, tigrinus and others from different geographic areas provided evidence of considera...

“…Durch die Entdeckung der androgenen Driise bei Orchestia gammarella und den Nachweis ihres allgemeinen Vorkommens bei den Malakostraken erfuhr die Erforschung der endokrinen Vorg~inge, welche die Geschlechtsauspr~igung steuern, einen wesentlichen Impuls. CHARNIAvx-CoTTON (1956, 1957 konnte experimentell belegen, daf~ die Ausbildung der prim~iren und sekund~iren m~innlichen Geschlechtsmerkmale von einem in den androgenen Driisen gebildeten Sexualhormon abh~ingig ist. W~ihrend die Hoden keine nachweisbare endokrine Funktion ausiiben, unterliegt die Auspr~igung der sekund~iren weiblichen Sexualcharaktere hingegen einer hormonalen Steuerung durch die Ovarien.…”

Section: E I N L E I T U N Gunclassified

“…Genetische Aspekte der Geschlechtsdetermination sind bei Amphipoden insbesondere an Gammarus pulex subterraneus (ANDERS 1957) und Gammarus duebeni (TRAuT 1962) bearbeitet worden. Die Ergebnisse dieser Untersuchungen haben zur Annahme einer polyfaktoriellen Bestimmung des Geschlechts gefiihrt, das heit~t geschlechtsdeterminierend wirkt ein polymeres System iiber das gesamte Genom verteilter und frei kombinierbarer Gene.…”

Section: E I N L E I T U N Gunclassified

On the influence of the photoperiod on sex realization inGammarus duebeni

Helgolander Wiss. Meeresunters

1967

On the influence of the photoperiod on sex realization in Gamraarusduebeni. 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.