ABSTRACT
Highly variable environmental conditions can put the survival of inhabitants of temporary pools at high risk, as they may not complete their life cycle. Different evolutionary responses can prevent the extinction of the inhabitants of ephemeral wetland habitats. One specific mode of response to environmental changes is bet-hedging as risk-spreading strategy and long-term fluctuating selection. The fairy shrimp Branchinecta orientalis G.O. Sars, 1901 is a broadly distributed species in Europe and Asia. We investigated the hatching pattern of B. orientalis resting eggs as a result of various factors, alone or interacting: 1) brood order, 2) food supplied to the parental generation, and 3) various pre-inundation conditions. Results were recorded for cumulative hatching over 10 d, hatching at the first day, and the first day of hatching. The factors with significant effects on hatching percentage were 1) brood order, 2) type of food, 3) pre-inundation conditions, 4) interaction between brood order and type of food, and 5) interaction between type of food and pre-inundation conditions (P < 0.05). Within the first 24 h, 44% of total hatching occurred. Resting eggs from the first brood showed the highest cumulative hatching. The lowest mean resting egg size was found when parents were fed fish pond effluents supplemented with Haematococcus sp. (Chlorophyta); this group of resting eggs also had the highest cumulative hatching percentage. Eggs that had stayed for one week in the parental medium showed significantly higher cumulative hatching percentage, than eggs that had stayed in the medium for two weeks, or that had not stayed in the medium at all (P < 0.05). Overall, hatching showed an irregular pattern, affected by the mode of response of the resting eggs to our experimental factors. The irregular hatching pattern may result in fairy shrimps better adapted to environmental instability.
