Complex environmental effects on the expression of alternative reproductive phenotypes in the bulb mite

Abstract

Understanding the evolution and maintenance of within-sex reproductive morphs, or alternative reproductive phenotypes (ARPs), requires in depth understanding of the proximate mechanisms that determine ARP expression. Most species express ARPs in complex ecological environments, yet little is know about how different environmental variables collectively affect ARP expression. Here, I investigated the influence of maternal and developmental nutrition and sire phenotype on ARP expression in bulb mites (Rhizoglyphus robini), where males are either fighters, able to kill other mites, or benign scramblers. In a factorial experiment, females were raised on a rich or a poor diet, and after maturation they were paired to a fighter or a scrambler. Their offspring were put on the rich or poor diet. Females on the rich diet increased investment into eggs when mated to a fighter, but suffered reduced longevity. Females indirectly affected offspring ARP expression as larger eggs developed into larger final instars, which were more likely to develop into a fighter. Final instar size, which also strongly depended on offspring nutrition, was the main cue for morph development: a switch point, or size threshold, existed where development switched from one phenotype to the other. Sire phenotype affected offspring phenotype, but only if offspring were on the poor diet, indicating a gene by environment interaction. Overall, the results revealed that complex environmental effects can underlie ARP expression, with differential maternal investment potentially amplifying genetic effects on offspring morphology. These effects can therefore play an important role in understanding how selection affects ARP expression and, like quantitative genetics models for continuous traits, should be incorporated into models of threshold traits.Keywords Differential allocation hypothesis Á Environmentally cued threshold model Á Liability Á Life-history trade-offs Á Male attractiveness Á Reaction norm between age and size at maturity Electronic supplementary material The online version of this article (

Paternal Effects on the Expression of a Male Polyphenism

“…However, Smallegange's (2011) results might align with ours, as the maternal effects detected by Smallegange (2011) would probably be detected as paternal effects in a diallel approach such as the one we used. The reason being that Smallegange's (2011) study also found a sire effect on the size of eggs produced by females.…”

“…However, Smallegange's (2011) results might align with ours, as the maternal effects detected by Smallegange (2011) would probably be detected as paternal effects in a diallel approach such as the one we used. The reason being that Smallegange's (2011) study also found a sire effect on the size of eggs produced by females. If a female's mate influences the size of her eggs, paternal effects could actually be the ultimate determining factor of egg size, as sires would actually be driving the differential allocation of resources into eggs by dams (Burley 1986).…”

“…Our approach disentangles the paternal effects of sire morph from other paternal effects (such as body size, for instance) that are environmentally or genetically transmitted through the sire line. In a previous study on the closely related species R. robini (Smallegange 2011), such effects would have been confounded with sire morph effects, given that no sire traits (such as body size, for instance) were measured in that study. Therefore, any sire trait that correlates with sire morph would have been detected as a sire morph effect by Smallegange (2011).…”

“…In a previous study on the closely related species R. robini (Smallegange 2011), such effects would have been confounded with sire morph effects, given that no sire traits (such as body size, for instance) were measured in that study. Therefore, any sire trait that correlates with sire morph would have been detected as a sire morph effect by Smallegange (2011). Even in the present study, if we analyze the offspring of all crosses together regardless of parental line, a t-test on arcsine square-root transformed proportions in the offspring indicates that the proportion of fighters was significantly lower in offspring sired by scramblers than in offspring sired by fighters (analysis not shown).…”

Why Are Childhood Family Factors Associated With Timing of Maturation? A Role for Internal Prediction

“…In many species, individuals develop profoundly different behavioral 269 repertoires or subsequent physical characteristics depending on aspects of state (e.g., 270 size) at a critical point in development (Emlen & Nijhout, 1999;Gross, 1985; 271 likelihood that they will develop into 'fighters' (Smallegange, 2011). This example is 288 based upon two extreme morphs whose divergence far outstrips anything seen in any 289 mammal, let alone humans.…”