Sex pheromone signal and stability covary with fitness

Abstract

If sexual signals are costly, covariance between signal expression and fitness is expected. Signal–fitness covariance is important, because it can contribute to the maintenance of genetic variation in signals that are under natural or sexual selection. Chemical signals, such as female sex pheromones in moths, have traditionally been assumed to be species-recognition signals, but their relationship with fitness is unclear. Here, we test whether chemical, conspecific mate finding signals covary with fitness in the moth Heliothis subflexa . Additionally, as moth signals are synthesized de novo every night, the maintenance of the signal can be costly. Therefore, we also hypothesized that fitness covaries with signal stability (i.e. lack of temporal intra-individual variation). We measured among- and within-individual variation in pheromone characteristics as well as fecundity, fertility and lifespan in two independent groups that differed in the time in between two pheromone samples. In both groups, we found fitness to be correlated with pheromone amount, composition and stability, supporting both our hypotheses. This study is, to our knowledge, the first to report a correlation between fitness and sex pheromone composition in moths, supporting evidence of condition-dependence and highlighting how signal–fitness covariance may contribute to heritable variation in chemical signals both among and within individuals.

Mating status affects female choice when females are signalers

“…Since virgin females must reduce the risk of remaining unmated, we hypothesized virgin females to signal more or for longer than mated females, which we confirmed in this study. A higher signaling rate of virgin compared to mated females has previously been found in other Heliothine moths, such as the corn earworm Helicoverpa zea (Kingan et al, 1993 ), the subflexus straw Chloridea (Heliothis) subflexa (Blankers et al, 2021 ), and the Pyralid Indian meal moth Plodia interpunctella (Brady & Smithwick, 1968 ). These intuitive findings support the notion that virgin signaling females put more effort into mate attraction effort compared to mated females to increase their chance for mating.…”

“…In the closely related moth C . subflexa , a lower percentage of females was found calling in the night after mating, however, calling effort increased to about 50% again in subsequent nights (Blankers et al, 2021 ). The fact that mated females continue to signal emphasizes that both sexes may benefit from mating multiply (Blankers et al, 2021 ; Gao et al, 2020 ).…”

“…Even though mated females would have obtained enough sperm from the first mating to fertilize all their eggs (LaMunyon, 2000), we found that about 30% of mated females continued to signal in the night that followed a mating. In the closely related moth C. subflexa, a lower percentage of females was found calling in the night after mating, however, calling effort increased to about 50% again in subsequent nights (Blankers et al, 2021). The fact that mated females continue to signal emphasizes that both sexes may benefit from mating multiply (Blankers et al, 2021;Gao et al, 2020).…”

Experimental evolution of a pheromone signal

“…Genetic mapping studies have revealed several QTL underlying difference in sex pheromone composition in H. subflexa and even a single conversion step in the biochemical pathway, such as from Z11-16:OH to Z11-16:OAc, could be catalyzed by multiple enzymes (Groot et al, 2013). In addition, variation in pheromone composition in H. subflexa is explained by fitness variation (Blankers et al, 2021), indicating many different genetic factors likely contribute small additional fractions to the total variance. Another explanation comes from population genetics: re-orientation of genetic covariances in response to bottlenecks may free up additive genetic variance, thereby paradoxically increasing levels of genetic variance (Carson, 1990; Templeton, 2008).…”

Female sex pheromone emission is affected by body condition, but not immune system function, in the orb‐web spider Argiope bruennichi

“…Yet, sex pheromones can vary between and within populations (e.g. Bacquet et al, 2016; Groot et al, 2009; Pelozuelo et al, 2004; Vereecken et al, 2007), and even within individuals (Blankers et al, 2021), and can be equally important for mate assessment and choice (De Pasqual et al, 2021; Johansson & Jones, 2007; Steiger & Stökl, 2014).…”