Most Proteaceae and some Fabaceae species produce specialised cluster roots (CRs), and are abundant in severely phosphorus (P)-impoverished soils in southwest Australia. Two types of CRs, compound and simple, have been identified. However, the difference in their P-mining strategies remains unclear. Therefore, we conducted glasshouse and field experiments to compare the P-acquisition strategies among 18 CR-producing species in Proteaceae and Fabaceae. Proteaceae produced a significantly larger mass of CRs than Fabaceae. Particularly, Banksia species produced the largest mass of compound CRs and exhibited the greatest net plant-absorbed P in pots and consistently higher mature leaf manganese concentration in the field. In contrast, Hakea and Grevillea species produced less mass of simple CRs but three times as much soil adhered to their CRs per CR dry weight, resulting in greater absorbed P per CR weight. All plants depleted similar P compounds from soil and accessed c. 52% of P that was not extracted by a NaOH-EDTA solution, suggesting that both CRs shared a common physiological function for mining scarcely available P. This study highlights two divergent P-acquisition strategies: greater biomass investment in compound CRs versus greater P-acquisition efficiency in simple CRs.

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Plants have evolved multiple defensive traits in response to herbivory; in turn, herbivore specialists evolved adaptive behaviours to avoid or tolerate such defences. Here, we employ milkweeds (Asclepias spp.) to test two defences, latex and trichomes, for their independent and interactive effects on behaviour and performance of monarch caterpillars (Danaus plexippus). Latex exuded upon damage and the density of leaf trichomes positively correlate across milkweed species, suggesting they may have evolved together as synergistic defences. Nonetheless, the complementary roles of these two traits have been little‐studied. We focus on two behaviours: shaving, or the removal of trichomes, and chewing, which encompasses both deactivation of latex and leaf consumption. In an experiment with seven milkweed species, with and without manipulated latex flow, we found latex to be the primary determinant of reducing chewing, while both defences positively predicted shaving behaviour in the first instar. Next, we conducted a factorial experiment throughout the first three instars, manipulating latex and trichomes on a high‐latex, high‐trichome species, the woolly milkweed Asclepias vestita. On plants with latex and trichomes intact, caterpillars spent the most time shaving and least time chewing of all treatment groups, suggesting a possible synergism. These defence‐driven behavioural effects decreased later in larval development. Latex and trichomes both impacted monarch performance, additively increasing mortality and reducing growth of survivors. Thus, latex and trichomes represent two important plant defences with effects on specialist herbivore behaviour and implications for insect fitness.

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Latex-bearing plants have been in the research spotlight for the past couple of decades. Since ancient times their extracts have been used in folk medicine to treat various illnesses. Currently they serve as promising candidates for cancer treatment. Up to date there have been several in vitro and in vivo studies related to the topic of cytotoxicity and anticancer activity of extracts from latex-bearing plants towards various cell types. The number of clinical studies still remains scarce, however, over the years the number is systematically increasing. To the best of our knowledge, the scientific community is still lacking in a recent review summarizing the research on the topic of cytotoxicity and anticancer activity of latex-bearing plant extracts. Therefore, the aim of this paper is to review the current knowledge on in vitro and in vivo studies, which focus on the cytotoxicity and anticancer activities of latex-bearing plants. The vast majority of the studies are in vitro , however, the interest in this topic has resulted in the substantial growth of the number of in vivo studies, leading to a promising number of plant species whose latex can potentially be tested in clinical trials. The paper is divided into sections, each of them focuses on specific latex-bearing plant family representatives and their potential anticancer activity, which in some instances is comparable to that induced by commonly used therapeutics currently available on the market. The cytotoxic effect of the plant's crude latex, its fractions or isolated compounds, is analyzed, along with a study of cell apoptosis, chromatin condensation, DNA damage, changes in gene regulation and morphology changes, which can be observed in cell post plant extract addition. The in vivo studies go beyond the molecular level by showing significant reduction of the tumor growth and volume in animal models. Additionally, we present data regarding plant-mediated biosynthesis of nanoparticles, which is regarded as a new branch in plant latex research. It is solely based on the green-synthesis approach, which presents an interesting alternative to chemical-based nanoparticle synthesis. We have analyzed the cytotoxic effect of these particles on cells. Data regarding the cytotoxicity of such particles raises their potential to be involved in the design of novel cancer therapies, which further underlines the significance of latex-bearing plants in biotechnology. Throughout the course of this review, we concluded that plant latex is a rich source of many compounds, which can be further investigated and applied in the design of anticancer pharmaceuticals. The molecules, to which this cytotoxic effect can be attributed, include alkaloids, flavonoids, tannins, terpenoids, proteases, nucleases and many novel compounds, which still remain to be characterized. They have been studied extensively in both in vitro and in vivo studies, which provide an excellent starting point for their rapid transfer to clinical studies in the near future. The comprehensive study of molecules from latex-bearing plants can result in finding a promising alternative to several pharmaceuticals on the market and help unravel the molecular mode of action of latex-based preparations.

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The preference-performance hypothesis explains host specificity in phytophagous insects, positing that host plants chosen by adults confer the greatest larval fitness. However, adults sometimes oviposit on plants supporting low larval success because the components of host specificity (adult preference, plant palatability, and larval survival) are non-binary and not necessarily correlated. Palatability (willingness to eat) is governed by chemical cues and physical barriers such as trichomes, while survival (ability to complete development) depends upon nutrition and toxicity. Absence of a correlation between the components of host specificity results in low-performance hosts supporting limited larval development. Most studies of specificity focus on oviposition behavior leaving the importance and basis of palatability and survival under-explored. We conducted a comprehensive review of 127 plant species that have been claimed or tested to be hosts for the monarch butterfly Danaus plexippus to classify them as non-hosts, low performance, or high performance. We performed a meta-analysis to test if performance status could be explained by properties of neurotoxic cardenolides or trichome density. We also conducted a no-choice larval feeding experiment to identify causes of low performance. We identified 34 high performance, 42 low performance, 33 non-hosts, and 18 species with unsubstantiated claims. Mean cardenolide concentration was greater in high- than low-performance hosts and a significant predictor of host status, suggesting possible evolutionary trade-offs in monarch specialization. Other cardenolide properties and trichome density were not significant predictors of host status. In the experiment, we found, of the 62% of larvae that attempted to eat low-performance hosts, only 3.5% survived to adult compared to 85% of those on the high-performance host, demonstrating that multiple factors affect larval host plant specificity. Our study is the first to classify all known host plants for monarchs and has conservation implications for this threatened species.

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The purpose of this study was to assess the ecological knowledge surrounding the western queen butterfly, Danaus gilippus thersippus (H. Bates). Specifically, our objectives were to synthesize existing data and knowledge on the ecology of the queen and use results of this assessment to inform the direction of future research on this understudied species. We identified six core areas for assessment: distribution, the biodiversity of plant resources, western queen and their host plant phenology, chemical ecology, and four key life history traits. We mapped the distribution of D. g. thersippus from museum specimen records, citizen science (e.g., iNaturalist) and image sharing app-based observations, along with other observational data enumerating all current known plant resources and long-range movements. We assembled 14 larval food plants, six pyrrolizidine alkaloids plants and six nectar plants distributed in the western Mojave and Sonoran Desert regions of the United States and Baja California. We report on its phenology and its long-range movement. Butterfly species have declined across the western US, and western monarch populations have declined by 97%. Danaus g. thersippus has received little research attention compared with its famous congener D. plexippus L . Danaus g. thersippus' desert distribution may be at its temperature limits for the species distribution and for its rare host plant Asclepias nyctaginifolia.

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