Influence of photoperiod and temperature on oocyte growth in the semelparous polychaete Nereis (Neanthes) virens

Abstract

Environmental factors influencing the rate of oogenesis in the seasonal cycle of the semelparous polychaete Nereis (Neanthes) virens Sars have been investigated in specimens reared under commercial conditions (concrete tanks under natural light supplied with a mixture of power station heated and ambient sea water to maintain ca 18°C all year round). The rate of oocyte growth is strongly influenced by the external photoperiod and the responses to static 24 h LD (light-dark) cycles have been investigated. Oocyte growth is more rapid when specimens are exposed to a 24 h LD cycle in which the photophase is below a critical value between 1 2 and 13 h The critical photopenod transition in natural environments is therefore at the autumn equinox hr. rJirens are able to respond to transfer between LD 16:8 h and LD 8 16 h at all times of the year, which suggests the operation of a continuously consulted system of photoperiod~c control. The rate of oocyte growth in co~llpetent specimens is a 11near function of the number of LD 8-16 h cycles experienced. The critical photopt!riod divides the solar year into 2 nearly equal periods, with the short day period (winter) favouring oocyte growth. There is a synergism between the effects of photoperiod and seasonally reducing temperature. During the cdlendar winter transition to LD 8:16 h or other LD cycles below the critical value initiates rapid oocyte growth whatever the temperature but in the calendar summer this only occurs if the external temperature is also reduced to 12OC or below. The response to photoperiod and temperature is moderated by internal factors and under commercial production systems elevated rates of oocyte growth can only be achieved in females that are about 1 yr old. The oocyte growth induced by exposure to LD 8:16 h light cycles and low temperature is similar to, but slightly less than, that induced by hormone depnvatlon, i.e. supra-oesophageal ganglion ablation. The results are discussed in relation to the control of seasonal cycles in Nereidae, the role of the endocrine system and ~n the context of the life history theory for long lived semelparous organisms with variable age at maturity

Tidal, Daily, and Lunar‐Day Activity Cycles in the Marine PolychaeteNereis virens

“…One of the largest intertidal polychaetes, Nereis virens Sars, has been the focus of extensive work over the years with regard to its reproductive biology (Olive, 1984(Olive, , 1985Olive et al, 1986Olive et al, , 2000 and photoperiodism (Last, 2000;Olive et al, 1998), with evidence of long-term circannual cycling in reproductive development (Olive, 1995) or at least the operation of long-period interval timing capability . described a photoperiodic response curve in N. virens with a critical photoperiod (LD crit ,11: .…”

Pre-emptive competition as a selective pressure for early reproduction in the polychaete Nereis virens

“…data). It has been demonstrated that a key event is the response to a critical photoperiodic threshold in the autumn (Olive et al 1998, Rees & Olive 1999 though the time of breeding may also be modified by the environmental conditions experienced after the time of this key transition (Rees & Olive 2000).…”

An actographic study of diel activity in the semelparous polychaeteNereis(Neanthes)virensSars in relation to the annual cycle of growth and reproduction

“…The period after the autumn equinox is characterized by an increase in the rate of gamete maturation of those individuals that will breed and die during the following breeding season (April to May). In sexually competent females this is manifested as an increase in the rate of oocyte growth (Fischer et a!, 1991;Fischer and Hoeger, 1993;Olive et al, 1998b;Rees and Olive, in submission). This increased rate of oocyte growth normally occurs shortly after the autumn equinox but can be induced by an artificial switch from ambient summer photoperiodic conditions (LD 16:8, photophase 16 h: scotophase 8 h) to winter conditions (LD 8: 16).…”

“…This increased rate of oocyte growth normally occurs shortly after the autumn equinox but can be induced by an artificial switch from ambient summer photoperiodic conditions (LD 16:8, photophase 16 h: scotophase 8 h) to winter conditions (LD 8: 16). This response can be induced at least from June onwards and further analysis suggests that the threshold photophase for this response in a 24 h LD cycle is around LD 12:12 (Olive et al, 1998b). The seasonal onset of rapid oocyte growth is thus an overt indication of the response to the changing natural photoperiod.…”

“…The transition from photo-development (Olive et al, 1998a;Olive et al, 1998b). ' Nereis (Neanthes) virens is a semelparous animal with a variable age at maturity (Bass and Brafield, 1972;Brafield and Chapman, 1967;Creaser and Clifford, 1982;Desrosiers et al, 1994;Olive et al, 1998a;Snow and Marsden, 1974;Yokouchi, 1985); consequently natural populations may be composed of a number of age classes.…”