Characterization of the cryptic interspecific hybrid Lemna×mediterranea by an integrated approach provides new insights into duckweed diversity.

Lemnaceae taxonomy is challenged by the particular morphology of these tiny free-floating angiosperms. Although molecular taxonomy has helped clarify the phylogenetic history of this family, some inconsistency with morphological data leads to frequent misclassifications in the genus Lemna. Recently, the finding that Lemna japonica is an interspecific hybrid between Lemna minor and Lemna turionifera provided a clear explanation for one such taxonomic question. Here we demonstrated that L. minor is also capable of hybridizing with Lemna gibba, generating a cryptic but widespread taxon in the Mediterranean area. The nothotaxon Lemna ×mediterranea is described and compared with clones of the putative parental species L. minor and L. gibba. Genetic analysis by nuclear and plastid markers, as well as genome size measurement, revealed that two different cytotypes, diploid and triploid, originated by at least two independent hybridization events. Despite high overall similarity, morphometrical, physiological, and biochemical analyses showed an intermediate position of L. ×mediterranea between its parental species in most qualitative and quantitative characters, and also separation of the two hybrid cytotypes by some criteria. These data provide evidence that hybridization and polyploidization, driving forces of terrestrial plant evolution, contribute to duckweed genetic diversity and may have shaped the phylogenetic history of these mainly asexual, aquatic plants.

Dye-Doped Polymeric Microplastics: Light Tools for Bioimaging in Test Organisms.

Ecosystems around the world are experiencing a major environmental impact from microplastic particles (MPs 0.1 µm-1 mm). Water, sediments, and aquatic biota show the widespread presence of this pollutant. However, MPs are rarely used in laboratory studies as they are scarcely available for purchase or expensive, especially if one wishes to trace the particle with a dye or fluorescent. Furthermore, existing preparation techniques have limited application in biological studies. In this work, we propose a new, easy, and cheap way to prepare fluorescent MPs. The protocol is based on the osmosis method in order to obtain spherical polymeric particles of P(S-co-MMA), with 0.7-9 micron diameter, made fluorescent because dye-doped with rhodamine B isothiocyanate (RITC) or fluorescein isothiocyanate (FITC). The dye loading was studied and optimized, and the MPs-dye conjugates were characterized by UV-vis FTIR and XPS spectrometry and scanning electron microscopy (SEM). Furthermore, preliminary tests on aquatic organisms demonstrated the possible use of these fluorescent MPs in bioimaging studies, showing their absorption/adsorption by duckweeds (Lemna minuta) and insect larvae (Cataclysta lemnata).

Effects of γ-Irradiation on Mating Behavior of Red Palm Weevil, Rhynchophorus ferrugineus (Olivier, 1790) (Coleoptera: Dryophthoridae).

Red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier 1790) is a highly invasive species originating from Southeast Asia and Melanesia. Over the past 30 years, this alien pest has spread extensively in the Middle East and the Mediterranean basin. Its endophagous larvae feed on various palm species, causing significant damage that leads to the death of palm trees. Controlling RPW infestations is challenging due to their gregarious nature and the lack of detectable early symptoms. Systemic insecticides are effective means of control, but their use in urban areas is prohibited and resistance can develop. Considering alternative options with minimal environmental impact, the Sterile Insect Technique (SIT) has been explored. Previous research has shown that male RPWs irradiated at 80 Gy or higher achieve full sterility. This study aimed to investigate in laboratory conditions whether RPW sterile males (irradiated at 60 and 80 Gy) could compete sexually with non-irradiate males. Laboratory bio-assays under both no-choice and choice conditions assessed sexual performance in terms of number of matings, mating duration and time elapsed until the first mating. The results confirmed that irradiation does not negatively affect the mating performance of sterile males, demonstrating their ability to compete successfully with non-irradiated males in both experimental setups.

Impact of the Invasive Alien Macrophyte Ludwigia hexapetala on Freshwater Ecosystems: Evidence from Field Data.

Biological invasions are a serious threat to biodiversity conservation, especially in freshwater ecosystems. The American macrophyte Ludwigia hexapetala, which colonizes both the aquatic and bank habitats of lakes, rivers, and canals, is invading many waterbodies in Europe, becoming an increasingly worrisome threat in several European countries, including Italy. However, only fragmentary information is available on the actual impact of its invasion in these habitats. This study aims to collect field data from various freshwater habitats in central and northern Italy, to assess the possible impact of L. hexapetala on the environmental parameters and plant biodiversity of the invaded habitats. The results show that in aquatic habitats, dense floating L. hexapetala populations reduce the light levels and oxygen available in the water, consequently limiting the growth of other aquatic plants. Indeed, L. hexapetala populations negatively affect aquatic plant diversity, as an increase in L. hexapetala cover corresponded to a decrease in Simpson's diversity index. In contrast, in bank habitats, L. hexapetala has no significant impact on plant diversity. Evidence suggests that some native species, such as Phragmites australis, which generally form compact populations along the banks, effectively counteract the invasion of L. hexapetala. This information may prove valuable for the environmental managers of those freshwater habitats where L. hexapetala invasion needs to be addressed and controlled.

Trophic transfer of microplastics from producer (Lemna minuta) to primary consumer (Cataclysta lemnata) in a freshwater food chain.

Contamination by microplastics (0.1 µm-5 mm plastic fragments) is currently one of the major threats to the conservation of aquatic and terrestrial ecosystems worldwide. Growing awareness on this issue has led to an increase in studies on the effects of microplastics on freshwater organisms, although there are still few investigations on possible transfer of this contaminant along water trophic chains from producers to primary consumers. In this study, aquatic herbivorous larvae of the moth Cataclysta lemnata were fed on microplastic-free (control) and contaminated (MPs treatment) Lemna minuta fronds. For treatments, Lemna fronds were grown in mineral water enriched with fluorescent microparticles of poly(styrene-co-methyl methacrylate) (MPs, 100 mg/L) and then fed to the larvae as a food source. Microplastics effects on larvae were tested at 0, 7, 14 and 21 days of exposure, corresponding to sensitive phases of the insect life cycle. Contaminant impact was assessed based on some parameters such as viability, larva body size/weight, feeding alterations and regularity of the insect life cycle. Using scanning electron and fluorescence microscopy, the presence of microplastics in the larvae was verified. The finding of fluorescent microplastics in both the intestinal lumen and excrement samples showed that larvae ingested contaminated Lemna fronds. In addition, larvae fed contaminated fronds were strongly affected by the presence of microplastic contaminant over time, showing high mortality (90 %) and total inability to complete the life cycle after 21 days by failing to reach the winged adult phase. In control tests, survival rates were higher than in treatments, and 50 % of the larvae managed to pupate and emerge as moths, reaching the adult phase. The results show that there was a trophic transfer of microplastics from producer to primary consumer along a freshwater food chain, generating negative effects on the life cycle of this aquatic herbivore.

Effects of Microplastic Contamination on the Aquatic Plant Lemna minuta (Least Duckweed).

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP's impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.