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

Abstract

Reproduction in the semelparous polychaete Nereis virens occurs at a time of year when seawater temperatures are lower than the optimum temperatures for fertilization and larval development and at a time when seawater temperatures are rising. This study assesses the possible role of intra-specific competitive interactions between settling N. virens post-larvae as a selective pressure for 'early' reproduction. A series of laboratory competition experiments were conducted between 2 cohorts of N. virens post-larvae, under a range of environmental conditions. Significant pre-emptive competition between settling post-larvae was recorded at 15°C, whereby a survival advantage was gained via prior residence with early larval settlers out-competing later arrivals. This competitive interaction was reduced at lower temperatures and no significant effect was measured at 5°C. An increase in age difference between the 2 cohorts of post-larvae increased the competitive effect, whilst photoperiod regime and food availability had no significant effect on the outcome of these experiments. Intra-specific competition was greatest at the temperatures at which maximum fertilization and development are known to occur, but was reduced at the temperature range at which spawning occurs in the field. It is suggested, therefore, that pre-emptive competition between settling post-larvae forms a strong selective pressure for breeding early at a time of year when temperatures are below the optimum for fertilization and development. KEY WORDS: Polychaeta · Pre-emptive competition · Nereis virens · Seasonal reproductionResale or republication not permitted without written consent of the publisher

Effects of copper and other metals on fertilization, embryo development, larval survival and settlement of the polychaeteNereis (Neanthes) virens

“…Lewis et al (2003) found this protocol to have no impact on survivorship. Sediment was passed though the 100 µm sieve and the settled larvae were recorded as dead or alive as described above.…”

“…After 10 min, 7 ml of the overlying solution was replaced three times with 7 ml of pasteurized seawater to reduce the chances of polyspermy. Petri dishes were then covered and maintained at 10EC (LD12:12) for 24 h. The contents of each dish were then fixed with 4% formalin solution in seawater and developmental success was assessed in 50 oocytes as described by Lewis et al (2003).…”

Dancing to the rhythms of geological time: the biorhythm capabilities of Polychaeta in a geological context

“…Typically, the reproductive strategy of the large-bodied phyllodocid and eunicid polychaetes involves highly synchronised epidemic spawning and there appears to have been strong selection for reproductive precision (Lewis et al, 2002(Lewis et al, , 2003Olive et al, 2001;Watson et al, 2000). Such worms liberate a large mass of gametes that are matured simultaneously to the external environment where fertilisation takes place.…”

Impact of pH on oocyte fertilisation and the overrun of meiotic checkpoints leading to parthenogenetic development inNereis virens

“…An analysis of foraging behaviour, however, indicated that all individuals in a population subjected to this environmental cue exhibit a suppression of foraging behaviour (Last and Olive, 1999) in the autumn and must therefore have responded to this environmental cue. Lewis et al (2003) argue that this universal response may be adaptive as it reduces risk. Individuals are less likely to emerge from their burrows after the photoperiodic transition.…”