Water exchange in reptile eggs: mechanism for transportation, driving forces behind movement, and the effects on hatchling size

摘要

The mechanism for water transport in reptile eggs is examined with particular interest in the phase water is in while being exchanged. Eggs were examined at various times during the incubation. A non-volatile dye was used as an indicator of liquid water movement. Presence of the dye after 48 hours of exposure may be indicative of liquid water movement. If the egg changes mass and no dye is present the water was considered to be exchanged in the vapor phase. Eggs exposed to the dye early during incubation took up the dye, while eggs exposed after day ten have dye levels very close to zero. It is therefore concluded that the majority of incubation is dominated by vapor water transport as the transport mechanism for water in reptile eggs;The role of water exchange in determining hatchling size was also assessed. Eggs were incubated under constant water potential conditions that would lead to differing amounts of water exchange. Hatchling size was then assessed using length and mass measurements and generating a size index using principle components. The hatchlings from eggs held on the substrate that yielded the highest water uptake were not the largest. The remaining treatments yielded hatchlings that were successively smaller on substrates that had increasingly limited water uptake. In addition to looking at constant water potentials, some eggs were exposed to shifted conditions during three periods of incubation. The hatchlings from eggs encountering successively higher periods of unfavorable conditions were smaller. Eggs exposed to unfavorable conditions during the first period of incubation produced hatchlings that were smaller than hatchlings from eggs under more favorable conditions. The first period was the most important in determining hatchling size, independent of the conditions encountered in the second or third period, even though the water exchange was most greatly affected by the third period. If a female can select nest sites dependent upon moisture then a female can provide an advantage to her hatchlings by laying in a favorable site even if later during incubation the conditions of the nest become unfavorable.