not-yet-known not-yet-known not-yet-known unknown Efects of florivory on the anatomy, histochemistry and resource production of lowers of Senna aversiflora (Herb.) H.S.Irwin & Barneby Edinalva Alves Vital dos Santos1; Emília Cristina Pereira de Arruda2; Ana Virgínia Leite3; Natan Messias Almeida3 1,3 Federal Rural University of Pernambuco. Department of Biology. Graduate Program in Biodiversity 2 Federal University of Pernambuco. Department of Botany. Graduate Program in Plant Biology 4 State University of Alagoas Abstract Florivory directly affects floral structures, especially petals and anthers. The physical damage to these whorls can alter the characteristics of the flowers, compromise their functions and, consequently, impact fertility and reduce the reproductive success of the species. We provide the floral anatomical description of Senna aversiflor a (Herb.) H.S.Irwin & Barneby. We measured various anatomical traits of petals and quantified the levels of chemical compounds and the pollen produced by intact and damaged flowers in order to identify characters associated with the plant-florivore interaction. We found that the epidermis (adaxial and abaxial surfaces) and mesophyll of the petals of healthy flowers was thicker when compared to damaged flowers. We infer that the smaller thickness of traits associated with the absence of characters with deterrent effect on herbivores and greater production of attractive/nutritive chemical compounds in relation to defense compounds contribute to make the species highly susceptible to florivory. Pollen production in damaged flowers did not differ between the different stages of floral development. However, florivory has a negative effect on the amount of pollen produced. Damaged flowers had less pollen than healthy flowers. We conclude that florivory in S. aversiflora exerts significant pressure on petal anatomy and resource production by flowers. Keywords: Floral structuring, biotic stress, male fitness 1 INTRODUCTION Plants interact with diverse animals in relationships that can be differentiated over two interfaces: mutual and antagonistic. Mutualistic interactions include pollinators, seed dispersers, among others. Antagonistic interactions, in turn, are established with large mammals, insects, viruses and bacteria (Rusman et al., 2019) and the attacks uttered by these individuals can cause a number of changes in plants. When the attack is aimed preferentially at flowers, the plant’s floral characteristics can be altered and its fitness negatively affected (McCall, 2008). Small portions of biomass consumed by herbivores can cause different effects on plants. The consumption of anthers, for example, can potentially decrease male fitness by reducing pollen export and receipt, and altered floral characteristics can indirectly affect pollinator visitation and reduce crossing rates, seed production, and fruit set (Krupnick & Weis, 1999). Anatomical studies on leaf herbivory show that plants usually use different structures for defense (Corrêa et al., 2008). Attacked leaves invest in increased cuticle and epidermal cell wall thickness, druse-containing idioblasts, and denser indument (Corrêa et al., 2008). Another defense strategy is the production of organic compounds. For example, in response to injuries caused by insects, plants release a variety of volatiles at the damaged site, and the profile of the emitted volatiles is markedly different from that of undamaged or mechanically damaged plants (Paré & Tumlinson, 1999). Foliar and floral herbivory have negative effects on reproduction, causing phenotypic changes in flowers in terms of size and symmetry, chemical characteristics, and pollen production (Quesada et al., 1995; Straus et al., 1996; McCall, 2008; Rusman et al., 2019). Higher levels of herbivory can lead to lower pollen grain production, implying a negative effect on male fitness (Quiroz-Pacheco et al., 2020). After an herbivore attack, in most cases, plants are capable of inducible defenses at the attack site or systemically throughout the plant (Mithöfer & Boland, 2012). Plants with higher levels of secondary compounds in their reproductive structures may be more resistant than those with lower levels of such substances (Adler et al., 2001; McCall & Irwin, 2006). Anatomical studies may reveal the presence of physical structures used in plant defense such as pubescence, sclerophyllous spinescence, and presence of minerals (silica and calcium) to avoid herbivores (Corrêa et al., 2008; Hanley et al., 2007; Lin et al., 2015). Concomitantly, histochemical studies may detect chemical compounds that promote or deter herbivory, such as attractive and nutritive substances (sugars, carbohydrates, proteins and lipids) that make tissues palatable or toxic compounds (phenolic compounds and alkaloids) that repel herbivores (Mason et al., 2019; Vázquez-González et al., 2020). The absence of structural defenses and the histochemical profile may explain the susceptibility of some species to herbivory/florivory, as is the case of several species belonging to the Cassiinae tribe (Cotarelli & Vieira, 2009; Cotarelli & Almeida, 2015; Oliveira et al., 2021), including Senna aversiflora (Herb.) H.S.Irwin & Barneby. The flowers of S. aversiflora suffer intense pressure from florivores that cause frequent injuries during floral development, from tender buds to flowers at anthesis, with the petals and anthers being the most damaged whorls (Santos et al., in press). The distribution of herbivores can be influenced by the anatomy and chemical composition of the plant organ. For example, sclerification and thickened cuticles can restrict the feeding of chewing and sucking insects (Peeters, 2002; Hanley et al., 2007; Mostafa et al., 2022; Demis, 2024), while low levels of alkaloids favor florivory (Adler et al., 2001). The stress caused by florivory at different stages of floral development can ultimately reduce pollen production (see Bertness & Shumway, 1992 and Oguro & Sakai, 2009). With this in mind, we aimed to characterize the floral anatomy of S. aversiflora in order to identify attributes correlated to antagonistic and mutualistic interactions and compare the anatomical and histochemical characteristics and amount of pollen produced between intact and damaged flowers. The following hypotheses guided the study: (i) the absence of structural characters that provide physical defense favors florivory in S. aversiflora , (ii) damaged flowers have less thick anatomical traits and lower concentration of defense compounds, and (iii) damaged flowers produce less pollen grains.