Royal Netherlands Institute for Sea Research 1 Seasonal timing of reproduction in the bivalve Macoma balthica: a model study of fitness consequences NVTB 2008 Jaap van der Meer

2 Question  Timing of reproduction: Make sure the larvae can grow up under optimal food conditions  Spawn just before the spring bloom  Many species don’t do this  An why should they?  Alternative rule: Make sure the bloom occurs at the size of maximum growth

3 System  Semi-chemostat  Seasonal pattern in food concentration of inflowing water  Seasonal pattern in temperature  Standard DEB model  Macoma balthica parameters as estimated by Van der Veer et al. (2006)   R extremely small: 0.012%; background mortality  One spawning event per year

4 60 days after

5 110 days after

6 160 days after

7 Spawning date: bifurcation analysis

8 160 days after

9 Adaptive dynamics  Introduce a mutant that has no effect on the (food) environment, and see whether it can invade  In a k-year cycle of the resident, mutants are introduced during each of k succeeding years  In one run, three types of mutants were introduced: the first group spawns slightly earlier, the second group does as the residents, the last group spawns slightly later

Mutants 10

11 Invadability

days before the plankton peak

days before the plankton peak

14 60 days after the plankton peak

15 60 days after the plankton peak

16 Individual state

17 Invadability

18 Preliminary conclusion  Stable strategy: spawn exactly half a year before the food peak

19 Next steps  Present survival rule: [E]/[E m ] > L/L m  Resorption of reproductive material  Low  R  A-symmetric interference, which decreases the competitive ability of the youngsters