Abstract
Female investment in large eggs increases the demand for fatty acids, which are allocated for yolk production. Since the biosynthetic pathway leading to fatty acids uses the same precursors used in the formation of polyketides, allocation trade-offs are expected to emerge. Therefore, egg production should constrain the investment in chemical defenses based on polyketides, such as benzoquinones. We tested this hypothesis using the harvestman Acutiosoma longipes, which produces large eggs and releases benzoquinones as chemical defense. We predicted that the amount of secretion released by ovigerous females (OFs) would be smaller than that of non-ovigerous females (NOF). We also conducted a series of bioassays in the field and in the laboratory to test whether egg production renders OFs more vulnerable to predation. OFs produce less secretion than NOFs, which is congruent with the hypothesis that egg production constrains the investment in chemical defenses. Results of the bioassays show that the secretion released by OFs is less effective in deterring potential predators (ants and spiders) than the secretion released by NOFs. In conclusion, females allocate resources to chemical defenses in a way that preserves a primary biological function related to reproduction. However, the trade-off between egg and secretion production makes OFs vulnerable to predators. We suggest that egg production is a critical moment in the life of harvestman females, representing perhaps the highest cost of reproduction in the group.
Highlights
The production of large and heavily yolked eggs is perhaps the most widespread form of parental care among animals [1]
We found that females of the harvestman A. longipes bearing mature eggs produce less defensive secretion than females in other reproductive phases, including non-ovigerous and eggguarding females
We found no difference in the concentration of total benzoquinones released by ovigerous females (OFs) and non-ovigerous females (NOF), indicating that there is no compensation related to increased concentration of defensive compounds during egg production
Summary
The production of large and heavily yolked eggs is perhaps the most widespread form of parental care among animals [1]. Despite the benefits to the offspring, the production of large eggs may impose costs to females because reproduction and self-maintenance are two processes that require great investment of energy and resources (review in [6]). A negative correlation between survival and female investment in current reproduction is one of the most ubiquitous life-history trade-offs. Reported in the literature [7,8] This pattern may emerge as a consequence of several different processes, but the allocation trade-off between reproduction and immune function has received the most attention in recent years [9,10]. Experimental evidence of insects, lizards, and birds has consistently shown that increases in the reproductive effort lead to decreases in the immune function and vice-versa (e.g., [11,12,13,14,15])
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