BIOTIC Species Information for Hediste diversicolor
|Researched by||Georgina Budd||Data supplied by||MarLIN|
|Refereed by||Mike Kendall|
|Reproductive Season||Spring - summer||Reproductive Location||Adult burrow|
|Reproductive frequency||Semelparous||Regeneration potential||No|
|Life span||1 year||Age at reproductive maturity||<1 year|
|Generation time||1-2 years||Fecundity||Insufficient information|
|Egg/propagule size||Insufficient information||Fertilization type||External|
|Reproduction Preferences Additional Information||
Nereidae are monotelic, that is, they reproduce only once in their lifetime and then die (Olive & Garwood, 1981). Hediste diversicolor is gonochoristic (dioecious) and remains atokous throughout its life (Scaps, 2002).
In summer and autumn the sexes are externally indistinguishable being both reddish brown in colour. In any one population females are predominant, although to varying extent between localities (Dales, 1950; Clay, 1967 (c) and references therein). This observation led early workers to suggest parthenogenetic reproduction and hermaphroditism within Hediste diversicolor (Dales, 1950) but it is now acknowledged that these reproductive mechanisms are not found in Hediste diversicolor. Hediste diversicolor does not display epitoky or swarming behaviour associated with sexual reproduction like other nereid polychaetes, such as Nereis succinea and Nereis virens. The sex ratio in populations of Hediste diversicolor is heavily biased towards females. Olive & Garwood (1981) reported a ratio of females to males of approximately 4.6 : 1 in northeastern England.
Maturation & spawning
Colour differences between the sexes become more apparent upon maturation. Maturation and spawning are induced by a temperature rise in early spring to between 6°C and 11°C following a period of low winter temperatures. The male becomes bright green in colour. In contrast, the female appears darker green in colour which may be lacking on the ventral side. Reddish brown pigments may also still be visible in the female.
Bartels-Hardege & Zeeck (1990) induced spawning in the laboratory, in specimens of Hediste diversicolor from tidal flats of the Jadebusen (North Sea), outside the normal spawning period of early spring. Temperatures were not lowered to simulate winter conditions but maintained at 16°C. Mature specimens appeared after four weeks and released gametes after a further four weeks according to a semilunar cycle. Reproduction was sustained for a period of four months. Such an extended spawning was witnessed on the Jadebusen following an unusually warm winter. Spawning occurred from February until May and was less synchronized. In contrast, the same population spawned within two months (February - March) following lower winter temperatures in another year. They concluded that not only a threshold temperature was important for synchronized spawning but the timing of the rise in temperature following winter was also a significant factor (Bartels-Hardege & Zeeck, 1990).
Age at maturity
Generally Hediste diversicolor is reported to reach maturity between one and three years of age. Populations appear to show local characteristics in terms of spawning periods. Spawning may be limited to a short period in spring or extend over the summer. In the Thames Estuary, Dales (1950) reported specimens growing to maturity within one year, spawning in February, with some individuals surviving up to 18 months. Mettam et al. (1982), reported that Hediste diversicolor from the Severn Estuary matured rapidly in the spring and spawned at two years old. Olive & Garwood (1981), found that females in the Blyth Estuary, Northumberland, were in their second year before eggs began to appear, so most probably spawned in their third year. However, these authors also reported that spermatogenesis was only found to take about six months in the Blyth. They therefore suggested that there is a variable age at maturity and that this could have arisen either because the population were polymorphic in terms of their genetically determined age at maturity or if the age at maturity was variable and influenced by the environmental conditions (Olive & Garwood, 1981). Golding & Yuwono (1994) showed that, although full maturation of the gametes occurred, spawning was blocked by implanting cerebral ganglia from immature donors into the body cavity of adult hosts.
In the Ythan Estuary, Scotland, Chambers & Milne (1975) witnessed two spawning peaks in the population of Hediste diversicolor, the first occurring between January and March, and another between June and August.
|Reproduction References||Barnes, 1994, Clay, 1967 (c.), Chambers & Milne, 1975, Dales, 1950, Mettam et al., 1982, Olive & Garwood, 1981, Bachelet, 1987, Bentley & Pacey, 1992, Bartels-Hardege & Zeeck, 1990, Chambers & Garwood, 1992, Scaps, 2002, Golding & Yuwono, 1994,|