Effects of evolution on egg development time

Using a global data set on egg hatch times in zooplanktonic and nektonic ectotherms from marine waters, the combined effects of body size, temperature and life-history attributes on development times were examined. After correcting for mass and temperature the mean egg hatch times (from laying to hatching) were 20 times faster in some taxa than in others. Some of the divergence in hatch times can be accounted for by the disposition strategy of the eggs. Eggs that are protected after laying (e.g. carried by the female, or attached to a substrate or floating in clumped masses) take 3.3 times longer on average to develop to hatching than those spawned individually and freely into the pelagic environment (i.e. 'unprotected'), and this difference is independent of egg size. Given that unprotected eggs typically have higher mortality rates, it is proposed that evolution has acted to shorten this vulnerable period. Not only do hatch times appear to diverge on the basis of egg protection strategy, but also a similar degree of separation was apparent in cell cycle duration (i.e. time from 2 to 4 cell stage), These results reinforce the importance of egg disposition on development rate processes and their evolution.