One critical life-history trait for organisms is how energy is allocated among the individual offspring they produce. One way of examining the expected trade-off between number of offspring and offspring size is by examining how females respond to different amounts of resources. It has been predicted that females with increased energy uptake should allocate these resources to extra eggs if this does not decrease the size of the other offspring from an optimal value. However, the trade-off of egg size and number is more problematic when considering species that have small clutches (and very large eggs), because changing clutch size requires a large investment per additional egg (the fractional egg size hypothesis). Thus, species with large eggs and small clutches may be more likely to apportion additional energy into increasing offspring size than to increasing clutch size. This prediction has been tested rarely in reptiles. In this study, we placed females of the diadem snake, Spalerosophis diadema (a species that produces very large eggs in small numbers), on either high- or low-energy diets and then recorded reproductive traits after oviposition. As predicted, there was a negative correlation between clutch size and mean egg mass. Females on high-energy diets did not modify clutch size but produced larger eggs relative to those on low-energy diets. However, there was no difference in variance in egg size between diets. Our data therefore support one of the predictions from the fractional egg size hypothesis (larger eggs rather than larger clutch sizes) but not the second prediction that egg size should be more variable in smaller clutches.
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Vol. 66 • No. 4