Saturday, 14 December 2013

The ostracods eat their spinach

The three ostracods featured in the last blog are typical of their kind; widespread in small ponds and pools, especially those prone to drying, relying on tough eggs to resist drought. During the good times when ponds flood again they use asexual reproduction to churn out young through parthenogenesis, the process in which unfertilised eggs develop and mature. Despite the adults tough bivalve carapaces many predators catch these small prey. Dragonfly larvae and water boatmen have been shown to reduce populations significantly. The Ostracods respond by changing behaviour migrating to safer parts of the pond. Heterocyrpis incongruens reacts to chemical cues in the water, shifting to more open water and being less active. Moving about less is potentially tricky for male ostracods in search of a mate, although experiments to compare predation on sexual versus asexual individuals of Eucypris virens showed no marked difference in vulnerability. Male ostracods are unknown for some species, but it seems unlikely that being eaten is the cause of this absence. Asexual reproduction could have advantages faced with intense predation, because one female can potentially found a population.  Ostracods themselves seem to be rather generalist feeders but with some preferences. Eucypris virens has a liking for spinach when offered a variety of foods and also Tolypothrix tenuis a type of cyanobacterium, a combination humans are unlikely to encounter outside of an extreme sushi bar. Animal prey can be on the menu too, especially sickly or injured larger creatures, who can be overwhelmed by the sheer number of ostracods ganging up on them. ... perhaps, like Popeye,  it’s is the beneficial effects of all that spinach.
Schmit, O. et al (2012) Vulnerability of sexual and asexual Eucypris virens (Crustacea: Ostracoda) to predation: an experimental approach with dragonfly naiads. Fundamental and Applied Limnology, Vol 181, 207-214.
Schmit, O. et al (2007) Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions. Hydrobiologia, Vol 585, 135-140.

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