Life Cycle Development
75
The open question is whether - as is the case in arthropods of deciduous
forests (e.g. Luxton 1981a,b; McQueen and Steel 1980) - external signals operate as indicators stimulating the timing of development. Existing evidence is
controversial. Photoperiod in conjunction with temperature seems to trigger
oogenesis in the oniscids of xeric Mediterranean formations (Warburg 1994).
Baker (1979a) also reported that the activity of the diplopod O. moreletii in
southern Australia is stimulated by rainfall and increasing temperature. In
contrast, Bercovitz and Warburg (1988) studied the reproductive patterns of
the diplopod A. t. judaicus in Israel and reported that egg laying occurs at
temperatures between 16 and 32°C, but the onset of egg deposition does not
take place on a definite date. Moreover, they did not find any effect of the
length of daylight on the onset of egg laying. Asikidis and Stamou (1992) reasoned that external triggering might be associated with the uncertainty
emerging in cases where outstanding environmental hazards mask the functioning of predictable variables. In Mediterranean regions, the preponderance of the predictable components of the climate over accidental hazards is
well documented (e.g. Sgardelis 1988). Hence, signals that trigger the timing
of life cycle development are needless in Mediterranean environments.
Instead, the existence of critical climatic thresholds - either allowing biological activity or not - may force development to occur during short periods,
thereby ensuring synchronisation with seasonally varying environments.
75
The open question is whether - as is the case in arthropods of deciduous
forests (e.g. Luxton 1981a,b; McQueen and Steel 1980) - external signals operate as indicators stimulating the timing of development. Existing evidence is
controversial. Photoperiod in conjunction with temperature seems to trigger
oogenesis in the oniscids of xeric Mediterranean formations (Warburg 1994).
Baker (1979a) also reported that the activity of the diplopod O. moreletii in
southern Australia is stimulated by rainfall and increasing temperature. In
contrast, Bercovitz and Warburg (1988) studied the reproductive patterns of
the diplopod A. t. judaicus in Israel and reported that egg laying occurs at
temperatures between 16 and 32°C, but the onset of egg deposition does not
take place on a definite date. Moreover, they did not find any effect of the
length of daylight on the onset of egg laying. Asikidis and Stamou (1992) reasoned that external triggering might be associated with the uncertainty
emerging in cases where outstanding environmental hazards mask the functioning of predictable variables. In Mediterranean regions, the preponderance of the predictable components of the climate over accidental hazards is
well documented (e.g. Sgardelis 1988). Hence, signals that trigger the timing
of life cycle development are needless in Mediterranean environments.
Instead, the existence of critical climatic thresholds - either allowing biological activity or not - may force development to occur during short periods,
thereby ensuring synchronisation with seasonally varying environments.