Life-history consequences of bidirectional selection for male morph in a male-dimorphic bulb mite

Abstract

Intralocus sexual conflict (IASC) arises when males and females have different trait optima. Some males pursue different alternative reproductive tactics (ARTs) with different trait optima, resulting in different strengths of IASC. Consequently, for instance daughter fitness is differentially affected by her sire’s morph. We tested if—and which—other life-history traits correlatively change in bidirectional, artificial selection experiments for ARTs. We used the male-dimorphic bulb mite Rhizoglyphus robini, the males of which are high-fitness ‘fighters’ or low-fitness ‘scramblers’. Twice in each of the five generations of selection, we assessed clutch composition (number of mites of the various life stages present) and size (total number of offspring). Furthermore, we tracked offspring from egg to adulthood in the first and final generation to detect differences between selection lines in the size and duration of stages, and in maturation time. We found that selection for male morph increased the frequency of that morph. Furthermore, compared to fighter lines, scrambler lines produced more females, which laid larger eggs (in the final generations), and maintained a higher egg-laying rate for longer. Otherwise, our results showed no consistent differences between the selection lines in clutch size and composition, life stage size or duration, or maturation time. Though we found few correlated life-history trait changes in response to selection on male morph, the differences in egg laying rate and egg size suggest that IASC between fighters is costlier to females than IASC with scramblers. We hypothesize that these differences in reproductive traits allow fighter-offspring to perform better in small, declining populations but scrambler-offspring to perform better in large, growing populations.Electronic supplementary materialThe online version of this article (10.1007/s10493-018-0320-5) contains supplementary material, which is available to authorized users.

Costs of weaponry: Unarmed males sire more offspring than armed males in a male‐dimorphic mite

“…In other words: the level of intralocus sexual conflict may be lower between females and scramblers than between females and fighters (Bonduriansky & Chenoweth, ). Other studies support the possibility of a lower intralocus sexual conflict between females and scramblers as bidirectional selection for male morph expression yields higher fitness daughters in scrambler lines than in fighter lines (Plesnar‐Bielak, Skwierzyńska, Miler, & Radwan, ; Van den Beuken & Smallegange, ). Alternatively, scramblers transfer an oviposition‐stimulating compound to females to increase the males’ reproductive output.…”

The role of genetic diversity in the evolution and maintenance of environmentally-cued, male alternative reproductive tactics

“…Previous empirical evidence in bulb mites not only demonstrates that scrambler morphs live longer [78], but importantly, that scrambler-selected lines produce more females that lay larger and more eggs over a longer period of time [79], and are generally more fecund than fighter-selected lines [60]. These morph-specific patterns may help to elucidate why we observed the genetic architecture of scramblers and females to be more similar to each other in contrast to fighters, patterns corroborated in gene expression profiles [52].…”