No Evidence That the Phoretic Mite <i>Poecilochirus carabi</i> Influences Mate Choice or Fitness in the Host Burying Beetle <i>Nicrophorus nepalensis</i>

Mate choice is a fundamental aspect of sexual selection where the "chooser" chooses a "courter" by assessing a variety of traits that communicate potential fitness. However, the role of interspecific interactions, such as symbiosis, in shaping mate choice remains poorly understood. Here, we investigate whether phoretic mites <i>Poecilochirus carabi</i>, which can act as either mutualists or parasites, influence female mate choice or reproductive fitness in the burying beetle <i>Nicrophorus nepalensis</i>. These mites affect beetle fitness in context-dependent ways, influenced by temperature, competitor presence, and mite density-factors that could potentially impact mate selection. In an olfactory-based mate choice assay, we presented female <i>N. nepalensis</i> hosting a range of natural mite densities (0, 5, 10, or 20) with a choice between males carrying either 0 or 10 mites. Subsequently we allowed females to breed with their chosen male before evaluating the fitness effects of the varying male and female mite densities. We found no evidence that female <i>N. nepalensis</i> preferred males based on mite presence, regardless of their own mite density. Furthermore, mite density did not affect beetle fitness, as measured by brood size or average larval mass. However, mite reproductive output increased with higher total mite densities per breeding pair. Our findings suggest that, under naturally occurring conditions and in the absence of competitors, <i>P. carabi</i> mites do not influence female mate choice or beetle reproductive success in <i>N. nepalensis</i>.