Predatory mites discriminate eggs laid by other females, but protect these eggs against predators.

Parental care is costly to parents because it consumes energy and reduces the available time for future reproduction. Hence, in theory, parents should not care for the eggs or offspring of unrelated individuals. However, parental care for unrelated offspring has been demonstrated for some animal species, although it has been unclear whether such animals distinguish their offspring from unrelated individuals. Here, we examined protection of non-offspring eggs by adult females of the predatory mite Gynaeseius liturivorus, which discriminate eggs laid by other females, against the predatory mite Neoseiulus californicus. Adult female G. liturivorus protect their eggs against predators. Several adult females of this species are sometimes found with clustered eggs in field; hence, G. liturivorus mothers may protect non-offspring eggs. When G. liturivorus eggs were kept with N. californicus in the presence of conspecific adult females that were not mothers of the eggs, their survival was higher than in the absence of conspecific females. Although adult female G. liturivorus oviposited during experiments, the addition of eggs did not increase the survival of non-offspring eggs. Adult females did not cannibalise newly hatched non-offspring larvae in the presence of food, suggesting that the presence of adult females did not affect larval survival. Furthermore, adult females protected their own eggs laid during experiments, suggesting that protection of non-offspring eggs was not costly to the females. Our results also suggest that adult female G. liturivorus may protect conspecific eggs when abundant food is available. Significance statement: Parental care is observed in a wide range of taxa and commonly provided for offspring and/or kin individuals. However, some animal species take care of unrelated individuals. This might be because such species do not discriminate between their own offspring and those of conspecifics. In this study, we experimentally demonstrated that non-offspring eggs were protected from predators by adult females of the predatory mite, Gynaeseius liturivorus, which distinguish their own eggs from conspecific eggs. Newly hatched non-offspring larvae were not cannibalised by adult female mites in the presence of food. Adult females also protected their own eggs irrespective of the presence of conspecific eggs. Our results suggest that adult female predatory mites protect non-offspring when food availability is high. [ABSTRACT FROM AUTHOR]