Maternal investment in a spider with suicidal maternal care, Stegodyphus lineatus (Araneae, Eresidae) Mor Salomon, Jutta Schneider and Yael Lubin Salomon, M., Schneider, J. and Lubin, Y. 2005. Maternal investment in a spider with suicidal maternal care, Stegodyphus lineatus (Araneae, Eresidae).  / Oikos 109: 614  /622. Providing parental care is costly for the parent, but generally beneficial for the young whose survival, growth and reproductive value can be increased. Selection should strongly favour an optimal distribution of parental resources, depending on the relationship between the costs and benefits for parents and their offspring. Parental care is characterized by trade offs in investment, for example between egg size and number of young or providing resources at the egg stage versus the post-hatching stage. Females of the spider Stegodyphus lineatus (Eresidae) produce a single small brood with small eggs and provide the young with regurgitated fluid and later, with their body contents via matriphagy. We askedwhether females adjust the investment of resources differentially into eggs, regurgitation feeding and matriphagy, and how maternal investment affects the size of the young at dispersal. We followed the growth of young of broods in the lab and in the field and manipulated brood size in order to determine the pattern of resource allocation. We found that brood size was positively correlated with body mass: larger females had larger broods. Females provided 95%of their body mass to the young, allocating more resources to regurgitation than to matriphagy. Females provided regurgitated food to the young according to the brood size, providing less food when the brood was reduced. Maternal resources had a large influence on offspring mass at dispersal, which is likely to affect their future fitness. The study shows the importance of the female’s body mass and her resource allocation decisions for her reproductive outcome. M. Salomon, Life Sciences Dept, Ben-Gurion Univ. of the Negev, Israel (mors@ bgumail. bgu.ac.il).  / Y. Lubin, Mitrani Dept of Desert Ecology, Blaustein Institute for Desert Research, Ben-Gurion Univ., Sede Boqer Campus, Israel.  / J. Schneider, Inst. of Evolutionary Biology and Ecology, Univ. of Bonn, Germany. Providing parental care is costly for the parent because it limits investment in future reproduction, but it is generally beneficial for the individual young whose survival, growth and reproductive value can be increased (Clutton-Brock 1991, Fox and Czesak 2000). Selection should strongly favour an optimal distribution of parental resources, depending on the relation between costs and benefits for parents and their offspring. Reproductive resources can be allocated to the young in different ways, and parents will be selected to distribute their resources optimally between their off- spring and between different reproductive stages. When oviparous females provide post-hatching care, maternal resources can be provided both at the egg stage and to the young directly. Assuming a fixed amount of resources assigned to reproduction, there is a trade off between the number and size of the progeny (Fox and Czesak 2000): increased investment into larger eggs will be followed by a reduction in egg number. Furthermore, while allocating resources mainly to the egg stage will produce large, yolk-rich eggs, retention of resources for post-hatching care may prolong the development of the Accepted 12 November 2004 Copyright # OIKOS 2005 ISSN 0030-1299 OIKOS 109: 614 /622, 2005 614 OIKOS 109:3 (2005)