INTRODUCTION
When studying interspecific interactions, we often ignore the potential
effects of intraspecific variation. But in the context of the
interactions between a plant and its associated arthropod community, the
individual-plant traits can have a profound impact on the arthropod
community because of the multiple ways in which a plant affects its
resident arthropods (Mooney et al. 2012, Abdala-Roberts et al. 2016,
Nell et al. 2018, Moreira et al. 2019). For example, for herbivore
arthropods, a plant not only constitutes a nutrient resource, but it
also provides shelter by modifying microenvironmental conditions like
temperature and humidity (Obeso 2002). Because a single plant commonly
interacts with more than one individual arthropod, it also influences
the arthropod community assemblage; thus, determining the
arthropod-arthropod interactions that individual arthropod residents
experience (Strong et al. 1984, Schoonhoven et al. 2005).
Because sexual dimorphism in plants is expected to provide consistent
variation among groups of individuals of the same species (i.e., males
vs females), researchers have often studied the effect that this type of
intraspecific variation has on arthropods. Differences between male and
female plants have been well documented on vegetative (Nell et al.
2018), reproductive (Delph 1999, Eckhart 1999, Barret and Hough 2013),
and defensive traits (Agren et al. 1999, Cornelissen and Stiling 2005,
Sargent and McKeough 2022). The effects of these differences on
arthropod communities have been explored, primarily through the study of
plant-herbivore interactions, like foraging preferences and densities
(Danell et al. 1985, Agren 1988, Elmqvist and Gardfjell 1988, Boecklen
et al.1990, Hjaltén et al. 1993), or herbivory bias. For a long time,
studies pointed to a male-biased herbivory preference as the rule (Agren
1988, Agren et al. 1999, Cornelissen and Stiling 2005), but recently
Sargent and McKeough (2022) challenged that view through a meta-analysis
that revealed no consistent differences on chemical defenses and
herbivory between male and female plants. Even if this study suggests
that the effect of sexual dimorphism is not consistent across sexes or
plant-lineages, most studies still find an effect on herbivores due to
sexual dimorphism which may be given by the differences on the resource
allocation to reproduction in each sex (Cornelissen and Stiling 2005).
Why the effects of sexual dimorphism are not consistent across plant
groups might be due to sexual dimorphism being only one of the axes of
plant-phenotypic variation. One of the most drastic and consistent
changes that plants, particularly deciduous ones, experience are
phenological changes (Bawa and Opler 1975), and these have the potential
to interact and conflate the effects of sexual dimorphism on the
arthropod communities. Furthermore, most of the work regarding the
effect of sexual dimorphism on arthropod-plant interaction has focused
on understanding how differences in plant resource allocation affect
pairwise interactions (i.e., plant herbivore interactions). But by
affecting the herbivore populations, plant-sex might indirectly affect
arthropod carnivores through bottom-up forces (Oksanen1988, Chen and
Wise 1999, Gruner 2004; Han et al. 2022), so a community approach might
help to unravel patterns on the effect of plant sexual dimorphism in
arthropods. So far, very few studies have explored the effect of dioecy
on a multitrophic approach (Nell et al. 2018, Tsuji and Fukami 2018).
Nell et al. (2018) found that, in Baccharis salicifolia(Asteraceae), plant sex influenced plant traits like flower number,
relative growth of the plant, predator density, and arthropod community
composition. Tsuji and Fukami (2018) evaluated the effects of dioecy in
the shrubs Eurya emarginata and E. japonica on the
microbiome community associated with plant nectar. They found that the
microbes and fungi that colonize nectar were more abundant in male
flowers compared to female flowers; also they found that the composition
of microbial species was different between sexes.
The objective of this study was to use a community and year-long
(phenological) approach to evaluate the effects of plant sex in the
shrub Buddleja cordata Kunth (Scrophulariacae), 1) on several
plant traits, 2) on the arthropod community associated to this plant
species and 3) on the guild of herbivores and carnivores that inhabit
these plants.