Plant Secondary Metabolite Diversity and Species Interactions

Abstract

Ever since the first plant secondary metabolites (PSMs) were isolated and identified, questions about their ecological functions and diversity have been raised. Recent advances in analytical chemistry and complex data computation, as well as progress in chemical ecology from mechanistic to functional and evolutionary questions, open a new box of hypotheses. Addressing these hypotheses includes the measurement of complex traits, such as chemodiversity, in a context-dependent manner and allows for a deeper understanding of the multifunctionality and functional redundancy of PSMs. Here we review a hypothesis framework that addresses PSM diversity on multiple ecological levels (α, β, and γ chemodiversity), its variation in space and time, and the potential agents of natural selection. We use the concept of chemical information transfer as mediator of antagonistic and mutualistic interaction to interpret functional and microevolutionary studies and create a hypothesis framework for understanding chemodiversity as a factor driving ecological processes.

The many dimensions of phytochemical diversity: linking theory to practice

“…While complete measures of functional diversity are unobtainable – they would require evaluation of all possible biological activities in the full range of plant processes and interactions – functional diversity is often inferred based on the structural diversity of compounds (but see limitations below). The proximate biosynthetic causes of structural diversity are elegantly summarised by Kessler & Kalske () and will not be reviewed in detail here. However, it is critical to consider that the phytochemical phenotype, on which selection acts, is the integrated result of a vast number of genes coding for biosynthetic and modifying enzymes that interact in complex pathways, often serve multiple functions, and may be differentially expressed temporally or across plant tissues to generate functional diversity in ecological interactions.…”

“…Although not named, this hypothesis has been inherent in the literature on plant-herbivore interactions for decades, and was referred to as the 'common sense scenario' by Berenbaum & Zangerl (1996). We use the term 'interaction diversity hypothesis' after the review by Kessler & Kalske (2018) to distinguish this hypothesis from other evolutionary processes generating phytochemical diversity.…”

“…Kursar et al ; Richards et al ; Bustos‐Segura et al ; Salazar et al ). Complementing this empirical work, several recent reviews have greatly advanced our conceptual understanding of phytochemical diversity by summarising its evolutionary causes, biochemical origins and ecological consequences (Dyer et al ; Moore et al ; Schuman et al ; Dyer et al ; Kessler & Kalske ; Lämke & Unsicker ). However, we still lack a unified definition of what exactly phytochemical diversity is and how its many dimensions can be quantified and related to biological hypotheses.…”

Information theory tests critical predictions of plant defense theory for specialized metabolism

“…Structurally diverse specialized metabolites are central players in plants’ adaptations to their environments and in particular in their defense against enemies ( 1 ). The spectacular diversification of specialized metabolism found in plants inspired several decades of intense research about its multifaceted ecological functions and nucleated a long list of plant defense theories that provided important guidance to empirical studies of the evolution and ecology of plant-insect interactions ( 2 ).…”

Introduction to a special feature issue – New insights into plant volatiles

“…Most interestingly, individual compounds can fulfil multiple functions while there can be multiple compounds produced by an individual plant seemingly with similar functions. This apparent contradiction of simultaneous multifunctionality with functional redundancy in secondary metabolites in general, and in VOCs in particular, is at the core of a long‐standing and overarching question (Kessler & Kalske, ). Why are there so many plant secondary metabolites, or specifically, VOCs?…”