Some ARTs are plastic by nature, driven by seemingly pure environmental effects (e.g., dung beetles, Onthophagus acuminatus ), whereas others are fixed, determined exclusively by genetic underpinnings (e.g. Although taxonomically widespread and studied in various organisms, the proximate mechanisms responsible for ART trait evolution, or the processes that maintain ARTs within single populations, are not always well understood. Referred to as alternative reproductive tactics (ARTs), strategies such as these encompass trade-offs between increased reproductive potential versus the costs incurred to produce traits under selection, often leading to the development of a less energetically demanding tactic, such as sneakers (versus guards) or satellites (versus callers). These strategies can ultimately lead to diversity within populations, comprising of characteristics such as behaviour, physiology, or morphology. In numerous species, it is common for individuals (usually males) to adopt different strategies to increase their reproductive success when intrasexual competition is intense. Ultimately, understanding the genetic context that maintains thresholds, even for conditionally-dependent ARTs, will enhance our understanding of within population variation and our ability to predict responses to selection. This cryptic genetic variation also conceivably facilitates stable population persistence even in the face of spatially or temporally unstable environmental challenges. Asymmetric reproductive output, coupled with the purging of highly inbred individuals during environmental oscillations, also facilitates genetic variation within populations, despite evidence for strong directional selection. Our study provides new insights into the origin of ARTs in the bulb mite, highlighting the importance of GEIs: genetic correlations, epistatic interactions, and sex-specific inbreeding depression across environmental stressors. AMOVA analyses further corroborated significant genetic differentiation across subpopulations, between morphs and sexes, and among subpopulations within each environment. In fact within the poor environment, scrambler males and females showed no significant difference in genetic differentiation (Fst) compared to all other comparisons, and although fighters were highly divergent from the rest of the population in both poor or rich environments (e.g., Fst, STRUCTURE), fighters demonstrated approximately three times less genetic divergence from the population in poor environments. Using never-before-published individual genetic profiling, we found all individuals across populations are highly inbred with the exception of scrambler males in stressed environments. Our study aims to investigate the origins and maintenance of ARTs within environmentally disparate populations of the microscopic bulb mite, Rhizoglyphus robini, that express ‘fighter’ and ‘scrambler’ male morphs mediated by a complex combination of environmental and genetic factors. Even for conditionally-dependent traits, consensus postulates most ARTs involve both genetic and environmental interactions (GEIs), but to date, quantifying genetic variation underlying the threshold disposing an individual to switch phenotypes in response to an environmental cue has been a difficult undertaking. Alternative reproductive tactics (ARTs) are taxonomically pervasive strategies adopted by individuals to maximize reproductive success within populations.
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