Seasonal fluctuations in offspring body size in the wolf spider, Pardosa astrigera (Araneae: Lycosidae)

Seasonal fluctuations in body sizes of mother spiders, spiderlings, and clutch size in the wolf spider, Pardosa astrigera (L. Koch) (Araneae: Lycosidae), were investigated. Cephalothorax and abdomen widths were measured in females with egg sacs collected in Tsu, Mie Prefecture, from May 2009 to October 2013. Spiderlings that emerged from the egg sacs were counted and those widths measured. In addition, abdomen–cephalothorax size ratio, which could be correlated with seasonal adaptation of spiderlings, was calculated. Means for cephalothorax size of mothers and offspring tended to decrease from March to October. Mean cephalothorax and abdomen sizes of the spiderlings in March, April, May, and October were significantly larger than in July and August. Abdomen–cephalothorax size ratios in March, April, May, and June were significantly larger than in July and August. Environmental temperature in Tsu increases steadily from March to August and drops toward October. Significant negative correlations were detected between temperature and cephalothorax and abdomen widths of spiderlings. These results suggest that body size and abdomen–cephalothorax size ratio of spiderlings change seasonally, and environmental temperature would affect body size. Furthermore, considering that body size would put a limit on the available prey, food conditions could also be an influence.