Ambystoma jeffersonianum Reproduction 137 



offer the most probable explanation for the differenes between years in 

 the date that breeding was initiated. Noticeably less precipitation oc- 

 curred at the study site between November 1980 and January 1981 than 

 for the same period during the previous year. Whereas the ponds filled 

 by January in 1980, they were not filled until February in 1981. 



Differences between years in local variation in the duration of the 

 breeding periods, and, hence, incubation periods can best be explained 

 if migration to the ponds is both a function of favorable weather condi- 

 tions and an individual's physiological readiness to respond to those 

 conditions. During 1980, by the time weather conditions were favora- 

 ble for migration to the ponds, a relatively large group of individuals 

 may have been ready to migrate. Thus, a more synchronous mass 

 migration to the ponds resulted, and breeding and egg deposition 

 occurred over a shorter time period. 



Synchrony of hatching is of particular interest, given the variation 

 that occurred in initiation and duration of the breeding season. Tem- 

 poral variation in oviposition was buffered and did not produce equal 

 variation in initiation and duration of the hatching period. Temperature 

 and developmental rates show positive correlation (Moore 1939; Has- 

 singer et al. 1970). Because ambient temperatures tend to progressively 

 increase during the incubation period, embryos of eggs deposited earlier 

 in the breeding season take longer to develop, and, as a result, the tem- 

 poral variation of the hatching period is much less in comparison to the 

 breeding period. 



Worthington (1968, 1969), and Douglas and Monroe (1981) pro- 

 posed that temporal staggering of breeding is adaptive because it results 

 in a partitioning of resources among larvae of different sizes. Since the 

 hatching period was much shorter than the breeding period, my study 

 suggests that the efficacy of staggered breeding in partitioning pond 

 resources may be greatly reduced. 



At a breeding pond approximately 135 km west of my study site, 

 Douglas and Monroe (1981) reported that adult A. jeffersonianum were 

 present from late November until early March. They did not note if 

 oviposition occurred over the entire period. They found a peak occur- 

 rence of adults during early January, as did Creusere (1972) for popula- 

 tions in western and central Kentucky. Seibert and Brandon (1960) 

 found eggs in southern Ohio as early as February, while Smith (1911) 

 and Bishop (1941) reported that breeding begins in late March or early 

 April in New York. Brandon (1961) and Creusere (1972) observed hatch- 

 lings in western Kentucky on dates similar to those reported here. 

 Bishop (1941) reported hatching to occur during April and May in New 



