Risk for the natural regeneration of Quercus species due to the expansion of rodent species (Microtus arvalis)

Abstract

The role played by rodents in the colonization of acorn-producing plant species has been interpreted in different ways along time. It has gone from a predation relationship, in which rodents destroy seeds by devouring them, to a mutualistic one, in which they leave part of their caches or, more recently consume part of the cotyledons but leave the embryo intact. We studied how three rodent species, Apodemus sylvaticus (wood mouse), Mus spretus (Algerian mouse), and Microtus arvalis (common vole) treat the acorns they consume. The wood mouse and the Algerian mouse have consumed acorns for a long time and participate in this mutualistic relationship by preserving the embryo. The common vole eats acorns for the first time, as it is not a part of its habitual diet. We observed that this rodent species devours the embryo, as opposed to the other two rodent species that usually eat acorns and modifies its behavior over time, suggesting that its way of eating the acorns is not genetically fixed. The common vole has only recently started to enter the distribution areas of Quercus species. Its population density is high during certain periods, reaching plague levels in crops. When its usual food source runs out during these periods, it has to find others which probably include acorns. This rodent species eliminates the embryo during consumption and can, therefore, become a serious problem for acorn-producing species by limiting their colonization process. The three rodent species under study showed the same preference for the Quercus species provided, rejecting acorns of Q. suber and preferring those of Q. ilex subsp. ballota.

Significance statement

Microtus arvalis (common vole) is considered as an expansive crop pest species in certain parts of Europe, and in comparison with Apodemus sylvaticus (wood mouse) and Mus spretus (Algerian mouse), it does not have co-evolutionary history with Quercus species. Thus, the common vole is suggested to lack a mutualistic relationship with Quercus species where trees benefit from seed-dispersing rodents who then use parts of acorns as a food source. Using laboratory breeding, we showed that two habitual acorn consumers rodent species (wood mouse and Algerian mouse) tend to preserve the acorn embryo, while the expansive common vole that does not include acorns in its diet tend to eat the embryo. We concluded that the feeding behavior of the two habitual acorn consumer benefit the mutualistic relation with Quercus, probably due to the results of natural selection, whereas the expansive species not accustomed to eating acorns would impose a high risk to the natural regeneration of Quercus species.