PUB - Publikationen an der Universität Bielefeld

Females should adjust costly nursing to their own and to offspring condition in order to allow optimal offspring development at minimal fitness costs to themselves. They may assess offspring condition by monitoring offspring appearance and solicitation intensity. Young should be selected to influence maternal effort to maximize their own fitness, leading to parent-offspring conflict. Experimental studies on parent-offspring interactions in mammals have mainly been carried out in altricial species and models on the effects of offspring demand on parental supply and of supply on demand refer to altricial birds. However, in highly precocial mammals where young can forage independently from early on while still being nursed the situation may be different from that in altricials. I investigated the influence of pup demand on nursing performance and the timing of weaning in the precocial guinea pig (Cavia aperea f. porcellus) by cross-fostering different aged pups. As cross-fostered younger pups were weaned early and older pups late compared to normal conditions, the results clearly indicate a conflict in which mothers wield the power. In contrast to findings in altricials, females hardly adjusted the timing of weaning to pup age. I tested if the models on the effects of supply and demand could be applied to precocial mammals by cross-fostering guinea pig pups with same aged cavy pups (Cavia aperea). Females nursing the much larger guinea pig pups confronted higher demand than females nursing cavy pups. Pups raised by guinea pigs found a higher milk supply than pups raised by cavies. In confirmation with current models, high demand pups showed more solicitation and mothers reacted to this by nursing more frequently. However, the assumptions for the effects of supply were not met: when confronted with a high supply, pups increased solicitation. The results of these two experiments support the idea that the early ability to forage independently may have lead to different maternal strategies for the optimization of supply and the offspring decision to initiate nursing bouts. Maternal state may also affect nursing performance. In altricials lactation has been found to be reduced in concurrently pregnant and lactating mothers, maybe because energetic peaks of the phases overlap. In pregnant-lactating precocials these peaks are well separated. However, I found that pregnant guinea pigs also shortened lactation, indicating that reductions in nursing performance may not exclusively be caused by energetic constraints.