Is variable egg size the proximate cause of diversified bet-hedging in the hatching dynamics of the red-crowned toadlet (Pseudophryne australis) (Anura : Myobatrachidae)?

摘要

The embryonic stage in the red-crowned toadlet (Pseudophryne australis) varies among individuals of a clutch in three important features that may be a source for selection: the length of the embryonic period (15-119 days), the stage of development at which hatching occurs (Gosner 24-36) and the size of the tadpole at hatching (21-97 mg). Previous evidence suggests that variation ill the Stage at hatching and the length of the embryonic period is not a facultative response to environmental cues. To ascertain whether the basis for this variation was differential maternal provisioning, we investigated the amount Of variability ill egg sizes, and then the relationship of egg size to the length of embryonic period, stage and mass at hatching. The mean coefficient of variation in egg sizes was 3.9% (range 2.5-8.5%), which is quite high when compared to other amphibians. Egg size was positively related to tadpole size at hatching, and this may have consequeuces for fitness. No relationship was found between egg size and stage at hatching. The relationship between egg size and length of embryonic period varied among clutches, with significant sibship effects evident. The basis for variation ill stage at hatching and length of embryonic period remains unknown, but could relate to factors such as the nutritive value of yolk independent of egg size or possibly genetic factors.