Quantifying the benefits and costs of parental care in assassin bugs

Abstract

1. Which sex should care for offspring depends on the cost and benefits of the behaviour for each sex. Understanding these differences between the sexes is a fundamental step to explain the evolution of animal societies, but it is often difficult to quantify them empirically. A possible approach is to investigate two closely related species that perform a very similar type of care but in which the caring sex differs.2. Using field and laboratory data, we estimated the benefits and costs of parental care in two species of assassin bugs with very similar ecologies: Rhinocoris tristis, which has exclusive paternal care, and Rhinocoris carmelita, which has exclusive maternal care.3. In both species, the main benefit of care was a reduction in parasitism and predation of eggs. Guarding R. tristis males consumed eggs (filial cannibalism), and thus managed not to lose weight, but R. carmelita females paid the full energetic cost of care. Guarding male R. tristis incurred survival costs relative to non-guarding male and female conspecifics.4. Very high population density and female preference for males already guarding eggs (a preference previously recorded in fish) minimised the promiscuity cost of paternal care in R. tristis, explaining the difference in care pattern between the two species.

Investimento parental e papéis sexuais em opiliões com cuidado paternal exclusivo

“…Experimental evidence supporting this suggestion has already been reported for several fishes [e.g., [23][24][25][26] and at least two arthropod species [9,27].…”

“…Therefore, maternal care is energetically costly for females, especially in the case of iteroparous species [4], since it reduces the available energy to produce additional eggs, negatively affecting females' future reproduction and fecundity [e.g., [5][6][7][8][9]. Among species exhibiting exclusive paternal care, the available data do not seem consensual.…”

“…Instead of cannibalizing eggs, a rare behavior that we have observed only twice during more than 3,000 h of field observations, Iporangaia caring males may temporarily abandon the offspring to search for food [28]. However, given that body volume and mass of caring males clearly decreases over the course of the caring period, it seems that Iporangaia's foraging behavior is not as efficient in maintaining caring males' body condition as the strategies reported for sea spiders [13] and assassin bugs [9] ─ probably because foraging is limited to a small area on the vegetation around the eggbatch where dead arthropods, an unpredictable food source, are likely to be scarce. Our results suggest, therefore, that the energetic costs of male care in this harvestman species are probably higher than the ones paid by the other two arthropod species in which the costs of paternal care have been measured.…”

“…For the assassin bug R. tristis, on the other hand, the apparent survival probability of caring males was lower than that of non-guarding males [9]. Apparently, suppression of escape behavior in caring males, rather than their conspicuousness on the host plant, accounts for their lower survival.…”

“…Studies with giant water bugs (Belostomatinae), whose males carry egg pads attached to their backs, demonstrated that paternal behavior incurs energetic costs to parental individuals by both decreasing their foraging efficiency and food intake [10], and by increasing their muscular activity while promoting water flow and oxygen diffusion through the eggs membrane [11][12]. On the other hand, studies with the sea spider Achelia simplissima [13] and the assassin bug Rhinocoris tristis [9] showed that, besides differences in movement and activity patterns between caring and non-caring individuals, paternal care does not negatively affect foraging efficiency or weight loss, respectively.…”