Abstract
Strong ecological selection can erode genetic variation and render populations unable to deal with changes in ecological conditions. In the adaptation of the phoretic mite Poecilochirus carabi to its host, the burying beetle Nicrophorus vespilloides, the timing of reproduction is crucial. Safe mite development is only possible during the beetles’ brood care; mites that develop too slowly will have virtually zero fitness. If the strong specialisation in development time leaves no room for standing genetic variation to remain, changes in beetle brood care are disastrous. Beetle brood care depends on temperature and is thus vulnerable to changing climate. Accidental host switches to another beetle species with shorter brood care would also have negative effects on the mites. Only sufficient standing genetic variation could allow mismatched mite lines to survive and adapt. To test whether such rapid adaptation is possible in principle, we artificially selected on mite generation time. We were able to speed up, but not to slow down, mite development. We conclude that there is enough standing genetic variation in development time to allow P. carabi to quickly adapt to new host species or climate conditions, which could potentially lead to the evolution of new mite species.
Highlights
Life history traits are subject to strong selection due to their direct link to fitness, which often reduces genetic variation[1,2,3,4]
Beetle brood care usually assures that the parental beetles are still at the carcass when mite development is complete, so that the new generation of deuteronymphs can attach to the parental beetles and disperse with them[18,19,21]
If the parental beetles have already left before the deuteronymphs develop, the mites have to wait for the beetle offspring to disperse
Summary
Life history traits are subject to strong selection due to their direct link to fitness, which often reduces genetic variation[1,2,3,4]. Whenever life history traits evolve to match those of another symbiont species, deviation from the optimum can lead to symbiont mismatch and zero fitness In these cases, the viable range of the life history trait may be small and genetic variation may quickly erode. We investigate a phoretic mite species whose juvenile development is adapted to the brood care behaviour of its host beetles. Beetle brood care usually assures that the parental beetles are still at the carcass when mite development is complete, so that the new generation of deuteronymphs can attach to the parental beetles and disperse with them[18,19,21]. Are specialised on one main host species, and one crucial adaptation is that mite development time matches beetle brood care duration[8,13,22]. The generation time of P. carabi (associated with N. vespilloides) is shorter than that of P. necrophori (associated with N. vespillo)[13]
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