Toward an understanding of the chemical ecology of alternative reproductive tactics in the bulb mite (Rhizoglyphus robini)

Background Under strong sexual selection, certain species evolve distinct intrasexual, alternative reproductive tactics (ARTs). In many cases, ARTs can be viewed as environmentally-cued threshold traits, such that ARTs coexist if their relative fitness alternates over the environmental cue gradient. Surprisingly, the chemical ecology of ARTs has been underexplored in this context. To our knowledge, no prior study has directly quantified pheromone production for ARTs in a male-polymorphic species. Here, we used the bulb mite—in which males are either armed fighters that kill conspecifics, or unarmed scramblers (which have occasionally been observed to induce mating behavior in other males)—as a model system to gain insight into the role of pheromones in the evolutionary maintenance of ARTs. Given that scramblers forgo investment into weaponry, we tested whether scramblers produce higher quantities of the putative female sex-pheromone α-acaridial than fighters, which would improve the fitness of the scrambler phenotype through female mimicry by allowing avoidance of aggression from competitors. To this end, we sampled mites from a rich and a poor nutritional environment and quantified their production of α-acaridial through gas chromatography analysis. Results We found a positive relationship between pheromone production and body size, but males exhibited a steeper slope in pheromone production with increasing size than females. Females exhibited a higher average pheromone production than males. We found no significant difference in slope of pheromone production over body size between fighters and scramblers. However, scramblers reached larger body sizes and higher pheromone production than fighters, providing some evidence for a potential female mimic strategy adopted by large scramblers. Pheromone production was significantly higher in mites from the rich nutritional environment than the poor environment. Conclusion Further elucidation of pheromone functionality in bulb mites, and additional inter- and intrasexual comparisons of pheromone profiles are needed to determine if the observed intersexual and intrasexual differences in pheromone production are adaptive, if they are a by-product of allometric scaling, or diet-mediated pheromone production under weak selection. We argue chemical ecology offers a novel perspective for research on ARTs and other complex life-history traits.

Toward an understanding of the chemical ecology of alternative reproductive tactics in the bulb mite (Rhizoglyphus robini)

BackgroundUnder strong sexual selection, certain species evolve distinct intrasexual, alternative reproductive tactics (ARTs). In many cases, ARTs can be viewed as environmentally-cued threshold traits, such that ARTs coexist if their relative fitness alternates over the environmental cue gradient. Surprisingly, the chemical ecology of ARTs has been underexplored in this context. To our knowledge, no prior study has directly quantified pheromone production for ARTs in a male-polymorphic species. Here, we used the bulb mite—in which males are either armed fighters that kill conspecifics, or unarmed scramblers—as a model system to gain insight into the role of pheromones in the evolutionary maintenance of ARTs. Given that scramblers forgo investment into weaponry, we tested whether scramblers produce higher pheromone quantities than fighters, which would improve the fitness of the scrambler phenotype, e.g. through female mimicry to avoid aggression from competitors. To this end, we sampled mites from a rich and a poor nutritional environment and quantified their production of the female sex pheromone α-acaridial through gas chromatography analysis. ResultsWe found a positive relationship between pheromone production and body size, but males exhibited a steeper slope in pheromone production with increasing size than females. Females exhibited a higher average pheromone production than males. We found no significant difference in slope of pheromone production over body size between fighters and scramblers. However, scramblers reached larger body sizes and higher pheromone production than fighters, providing some evidence for a potential female mimic strategy adopted by large scramblers. Pheromone production was significantly higher in mites from the rich nutritional environment than the poor environment. ConclusionFurther elucidation of pheromone functionality in bulb mites, and additional inter- and intrasexual comparisons of pheromone profiles are needed to determine if the observed intersexual and intrasexual differences in pheromone production are adaptive, if they are a by-product of allometric scaling, or diet-mediated pheromone production under weak selection. We argue chemical ecology offers a novel perspective for research on ARTs and other complex life-history traits.

Toward an understanding of the chemical ecology of alternative reproductive tactics in the bulb mite (Rhizoglyphus robini)

Background Under strong sexual selection, certain species evolve distinct intrasexual, alternative reproductive tactics (ARTs). In many cases, ARTs can be viewed as environmentally cued threshold traits, such that ARTs coexist if their relative fitness alternates over the environmental cue gradient. Surprisingly, the chemical ecology of ARTs has been underexplored in this context. To our knowledge, no prior study has directly quantified pheromone production for ARTs in a male polymorphic species. Here, we used the bulb mite — in which males are either armed fighters that kill conspecifics, or unarmed scramblers — as a model system to gain insight into the role of pheromones in the evolutionary maintenance of ARTs. Given that scramblers forgo investment into weaponry, we tested whether scramblers produce higher pheromone quantities than fighters, which would improve the fitness of the scrambler phenotype, e.g. through female mimicry to avoid aggression from competitors. To this end, we sampled mites from a rich and a poor nutritional environment and quantified their production of the female sex pheromone α acaridial through gas chromatography analysis. Results We found a positive relationship between pheromone production and body size, but males exhibited a steeper slope in pheromone production with increasing size than females. Females exhibited a higher average pheromone production than males. We found no significant difference in slope of pheromone production over body size between fighters and scramblers. However, scramblers reached larger body sizes and higher pheromone production than fighters, providing some evidence for a potential female mimic strategy adopted by large scramblers. Pheromone production was significantly higher in mites from the rich nutritional environment than the poor environment. Conclusion Further elucidation of pheromone functionality in bulb mites, and additional inter and intrasexual comparisons of pheromone profiles are needed to determine if the observed intersexual and intrasexual differences in pheromone production are adaptive, if they are a byproduct of allometric scaling, or diet mediated pheromone production under weak selection. We argue chemical ecology offers a novel perspective for research on ARTs and other complex life-history traits.

Alternative Reproductive Tactics

Alternative reproductive tactics (ARTs) describe variation among individuals of a single sex in the tactics used to obtain mating opportunities. In crustaceans, ARTs have been observed in multiple taxa and take a variety of forms. ARTs are most commonly observed in males and are generally associated with intense competition among males to monopolize access to breeding females. ARTs frequently involve a guard tactic that competes with other males to monopolize access to females, while a second usurper tactic foregos competition with other males and instead obtains mating opportunities through sneaking behavior. Guard and usurper tactics may be expressed conditionally based on a male’s ability to guard a female (e.g. his body size, the abundance of competitors), or may be expressed as discrete phenotypes that can also include morphological differentiation. For example, in Jassa amphipods the guard tactic is associated with large body size and an enlarged “thumb” on the claw that is used in aggressive interactions with other males, while the usurper tactic is associated with small body size and a reduced thumb. The usurper tactic can take two forms in a marine isopod: small males (gamma) use sneaking behavior to avoid competition with large males (alpha), whereas intermediate-sized males (beta) use female mimicry to avoid competition. Overall, ARTs are well-represented in crustaceans, with many opportunities for continued study to better characterize these unique adaptations.

Alternative mating tactics and tactical deception: Is the common cuttlefish (Sepia officinalis) nothing but a common cheat?

Alternative mating tactics (AMTs) are common in the animal kingdom, yet much work remains before their evolution and role in driving sexual selection is fully understood. Utilizing features of citizen science, we present compelling evidence that a third species in the cuttlefish genusSepia(Cephalopoda) possess males who use sneaky mating and female mimicry as alternative strategies to conspicuous signalling and fighting. We also present new evidence of large aggregations (n~30) in this species that possibly drive alternative mating strategies. Lastly, we provide footage of an opportunistic sneaky copulation in this species. We believe that alternative mating tactics may be more common in this genus than previously recorded (based on observations presented here and a search of the literature for similar life history, environmental and behavioural factors found in other species within theSepiagenus), and as much of their captive husbandry is well known, they could an ideal system for studying the evolution of alternative reproductive strategies.