The life-cycle of the asexual ostracod Darwinula stevensoni (Brady & Robertson, 1870) (Crustacea, Ostracoda) in a temporate pond

Abstract

Abstrac t 33 1The life-cycle of the ancie nt asexua l ostracod Darwinula stevensoni was studied during I year in a eutrophic pond in Belgium. The reprod uctive period of this species started in March and was effective ly completed by September of the same year. All changes in population structure took place during the spring and summer months and a rapid turnover of the instars was observed . The life-cycle of Darwinula stevensoni appears to take one year or less in Belgium and this is considerably shorter than the 4 years which had been reported previously from subarctic populations. The difference to the present study is most likely temperature-related. Maximal densitie s of D. stevensoni were observed in June and July and attained 10 5 indo m-2 . During winter, densities were lower with a mean of 10 4 indom-2 . Consequently, the calculated population size of each month was high throughout the year. Together with the low mutation rate, such a large populati on size could effectively counteract the stochastic loss of mutation-free genot ypes as predicted by Muller 's ratchet. D. steve nsoni is a brooder; the maximum number of embryos and j uvenile instars (up to third stage) found within a single female was II .

Differential transport and preservation of the instars of Limnocythere inopinata (Crustacea, Ostracoda) in three large brackish lakes in northern China

“…Various studies have been undertaken on the population age structure of marine (Horne, 1982;Whatley, 1983;van Harten, 1986;Whatley, 1988;Błachowiak-Samołyk & Osowiecki, 2002;Ruiz et al, 2003;Błachowiak-Samołyk & Angel, 2007) and non-marine (Mezquita et al, 2000;van Doninck et al, 2003;Castillo-Escrivà et al, 2013) ostracods. Most of these studies have been focused on living faunas (Horne, 1982;Mezquita et al, 2000;Błachowiak-Samołyk & Osowiecki, 2002;van Doninck et al, 2003;Błachowiak-Samołyk & Angel, 2007;Castillo-Escrivà et al, 2013), and little attention has been paid to the valve remains and the taphonomic processes experienced in these communities. Whatley (1983Whatley ( , 1988 and Boomer et al (2003) have presented diagnoses for thanatocoenosis (autochthonous) and taphocoenosis (allochthonous) valve assemblages, based on population age structure and other characters such as valve/carapace ratio, but these diagnoses need to be tested and refined with realistic data.…”

Similar distribution pattern of different phenotypes of Limnocythere inopinata (Baird) in a brackish-water lake in Inner Mongolia

“…A number of investigations have been made to document the relation between the feature of ostracods and the physical and chemical properties of the ambient water (Külköylüoglu, 2004;Bunbury & Gajewski, 2005;Viehberg, 2006;Mischke et al, 2010). However, owing to the diversity of ostracods (Martens et al, 2008), and regional differences that may occur in the ecology of the same species across its range, our understanding of the response of ostracods to different environmental factors can only be improved if we undertake detailed studies of the morphology and age structure of single species in different lakes (Yin et al, 1999;Van Doninck et al, 2003). It is also important to examine concurrently ostracod species assemblages in the same lakes (Martín-Rubio et al, 2005).…”

Early release of eggs and embryos in a brooding ancient asexual ostracod: brood selection or a gambling strategy to increase fecundity?

“…Brooding behaviour of P. brasiliensis differs from that of D. stevensoni (the only other species in the whole Family that had its life cycle studied so far) in that juveniles are brooded up to the second stage, while D. stevensoni releases its juveniles in the third stage (Van Doninck et al, 2003a). Besides this, we observed a maximum of six juveniles inside the brood chamber of P. brasiliensis at one time, while D. stevensoni is known to carry up to 15 juveniles.…”

“…There would be less eggs and juveniles in the brood pouch than the amount actually produced, while the aborted eggs and juveniles in the sediment would not be counted (only eggs and juveniles in the pouch are generally counted in these animals- Van Doninck et al, 2003a).…”

“…All darwinulids are brooders and the number of embryos and eggs that can be retained at the same time in the brood chamber varies among species. Darwinula stevensoni, for example, can hold up to 10 or 15 juveniles at once (McGregor, 1969;Ranta, 1979;Horne et al, 1998;Van Doninck et al, 2003a).…”