1984] 
Wise — Phenology of filmy dome spider 
285 
Perhaps adult N. radiata cannot adapt physiologically to cold. 
Thus winter mortality of adults might be one selective factor that 
has favored maturation well in advance of winter. Another possible 
selective factor might be the lower rate of survival over winter of 
smaller juvenile N. radiata (Martyniuk 1983; Wise, unpubl. data). 
The peak of egg-laying by the second generation occurs early 
enough for most hatchlings to emerge and complete one or more 
molts before the end of the growing season. Their chances of surviv- 
ing the winter are greater than if they had emerged from egg sacs 
laid at the end of the season. Since egg size and hatchling size are 
positively correlated, the fact that summer females lay larger eggs 
than spring females also suggests the increased importance of size to 
juvenile survival later in the season. 
Those spiderlings that postpone maturation tend to mature at a 
larger size, which leads to higher female fecundity. Increased size 
may also improve the mating success of males, since they compete 
aggressively for females (pers. obs.). These and other aspects of N. 
radiata ’s life history suggest that slower development is not unadap- 
tive within the constraints seasonality imposes upon the timing of 
reproduction, and as part of a phenotype that also can develop more 
rapidly if environmental conditions are favorable. The hypothesis 
that the developmental plasticity of the filmy dome spider involves a 
developmental switch in the middle of the summer is tenable, but 
requires further testing. In particular, what are the proximate cues 
involved in the switch? Research on developmental rates of other 
spiders suggests that changing photoperiod may be important 
(Schaefer 1976, 1977). How do seasonal cues interact with the cur- 
rent physiological state and developmental history of the individual? 
What is the non-genetic maternal contribution to the developmental 
fate of hatchlings? 
In addition to answering questions such as these, it would be 
fruitful to determine whether or not the type of developmental flex- 
ibility exhibited by N. radiata has evolved in other spiders. Such a 
life history pattern may be more widespread among temperate spi- 
ders than is now realized. 
Summary 
A polymorphic phenology, apparently characterized by rapid and 
slow developers among the progeny of spring-maturing adults, was 
found in two Maryland populations of the filmy dome spider, N. 
