Host‐plant sex and phenology of Buddleja cordata Kunth interact to influence arthropod communities

TL;DR

This study shows that the sex of a plant and its seasonal changes affect the diversity of arthropods living on it, with male and female plants hosting more diverse communities at different times of the year.

Contribution

The study reveals a seasonal and alternating effect of plant sex on arthropod community diversity, emphasizing the importance of phenology in plant-insect interactions.

Findings

Male plants host more diverse arthropod communities during the flowering season, while female plants do so during the fructification season.

Differences in arthropod diversity were more pronounced in higher trophic levels, such as carnivores.

Plant sex effects on arthropod communities vary with phenology, offering a new framework to explain inconsistent patterns in plant-insect interactions.

Abstract

Intraspecific variation in plants is expected to have profound impacts on the arthropod communities associated with them. Because sexual dimorphism in plants is expected to provide consistent variation among individuals of the same species, researchers have often studied the effect it has on associated arthropods. Nevertheless, most studies have focused on the effect of sexual dimorphism in a single or a few herbivores, thus overlooking the potential effects on the whole arthropod community. Our main objective was to evaluate effects of Buddleja cordata's plant‐sex on its associated arthropod community. We surveyed 13 pairs of male and female plants every 2 months during a year (June 2010 to April 2011). Every sampling date, we measured plant traits (water content and leaf thickness), herbivory, and the arthropod community. We did not find differences in herbivory between plant sex or through time. However, we found differences in water content through time, with leaf water‐content matching the environmental seasonality. For arthropod richness, we found 68 morphospecies associated with female and 72 with male plants, from which 53 were shared by both sexes. We did not observe differences in morphospecies richness; however, we found sex‐associated differences in the diversity of all species and differences on the diversity of the most abundant species with an interesting temporal component. During peak flowering season, male plants showed higher values on both parameters, but during the peak fructification season female plants showed the higher values on both diversity parameters. Our research exemplifies the interaction between plant‐phenology and plant‐sex as drivers of arthropod communities' diversity, even when plant sexual‐dimorphism is inconspicuous, and highlighting the importance of accounting for seasonal variation. We stress the need of conducting more studies that test this time‐dependent framework in other dioecious systems, as it has the potential to reconcile previous contrasting observations reported in the literature.

We present the results of an empirical study that evaluates the effect of plant sex on its associated arthropod communities. Our results indicate that plant sex has a seasonal and alternating effect on the arthropod community diversity—male plants hosting a more diverse community of arthropods during the flowering season, while female plants do during the fructification season—and that this effect is stronger in higher trophic levels (i.e. carnivores). We discuss these results in the context of the resources and conditions that male and female plants offer. Our results highlight the fact that plant sex‐effects can vary with the phenology of the plant. This temporal axis of variation has been poorly explored when studying plant‐arthropod interactions, but we argue that given our observations it has the potential to clarify inconsistent patterns observed in the literature, for example the one regarding sex‐bias in arthropod herbivores preference.

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