Effects of plant sex and heterogeneous habitat light conditions in populations of dioecious Mercurialis perennis L. on differential herbivory

U ovom istraživanju ispitivano je prisustvo polno-specifične i diferencijalne herbivorije u odnosu na svetlosne uslove staništa kod dvodome vrste Mercurialis perennis L. (Euphorbiaceae). Testirani su efekti pola, svetlosnih uslova staništa i ontogenetskog stadijuma na osobine veličine biljaka (visinu, ukupnu površinu listova) i listova (dužinu drške i centralnog nerva, širinu i površinu lisne ploče), nutritivne (sadržaj vode, ukupnih solubilnih proteina i nestrukturnih ugljenih hidrata) i defanzivne osobine listova (sadržaj fenola i kondenzovanih tanina), specifičnu lisnu površinu i razvojnu nestabilnost (procenjenu preko indeksa fluktuirajuće asimetrije – FA). Ispitivano je koje od analiziranih osobina biljaka imaju ulogu u interakcijama M. perennis sa herbivorima u zavisnosti od svetlosnih uslova staništa i ontogenetskog stadijuma. Analizom korelacionih odnosa istraživana je povezanost između stepena herbivorije, razvojne nestabilnosti i ispitivanih osobina biljaka u odnosu na pol i svetlosne uslove staništa. Mercurialis perennis ili šumski prosinac je višegodišnja, zeljasta, dvodoma biljka koja je najčešće član biljnih zajednica prizemnog sprata nenarušenih šumskih ekosistema. Ređe se može naći na staništima sa otvorenim vegetacijskim sklopom. Kod dvodomih vrsta polovi se mogu razlikovati kako u vegetativnim osobinama tako i u stepenu oštećenja listova izazvanih aktivnošću herbivora. Iz navedenih razloga M. perennis predstavlja izuzetno pogodan model sistem za istovremeno proučavanje uticaja pola i svetlosnih uslova staništa na stepen herbivorije, osobine biljaka i razvojnu nestabilnost. U ovo istraživanje uključene su populacije M. perennis sa lokaliteta Bele stene (Kopaonik) i Beograd. Na lokalitetu Bele stene biljke su uzorkovane tokom dve uzastopne godine sa dva susedna staniša. Jedno stanište je bilo izloženo punoj dnevnoj svetlosti u sastavu rudine, dok se drugo nalazilo pod vegetacijskom senkom unutar četinarske šume. Razlike u svetlosnim uslovima na staništu kvantifikovane su merenjem razlika u pokrovnosti staništa korišćenjem hemisfernih fotografija...This study investigated the presence of sex – biased and light differential herbivory in dioecious Mercurialis perennis L. (Euphorbiaceae). It was tested if plant sex, light conditions and the ontogenetic stage had significant effect on plant size (height, total leaf area) and leaf size (petiole and midvein length, width and leaf blade surface), leaf nutritional (water, total soluble protein and nonstructural carbohydrate content) and defensive traits (total phenolic and condensed tannin content), specific leaf area and developmental instability (estimated as fluctuating asymmetry). It was examined which of the analyzed plant traits mediated interactions between M. perennis and herbivores depending on habitat light conditions and plant ontogenetic stage. By using correlation analyses the connection between herbivory, developmental instability and analyzed plant traits was investigated in relation to habitat light conditions. Mercurialis perennis or dogs' mercury is a perennial, dioecious herb that is a common member of the ground level communities of undisturbed forests. Rarely this species can be found in completely open field. In dioecious plants, the sexes can differ in vegetative traits as well as in herbivory rates. Therefore, M. perennis represents a suitable model system for exploring simultaneously the effects of plant sex and habitat light conditions on herbivory, plant traits and developmental instability. This research included populations of M. perennis from two sites: Bele stene (Kopaonik) and Belgrade. At Bele stene site the plants were sampled during two consecutive years from two neighboring habitats. One habitat was exposed to full sunlight in an open field, while the other was inside of an evergreen forest. Differences in light conditions between the habitats (canopy openness) were quantified by means of hemispherical photography. The sample from 2015. was used to test the effects of plant sex and habitat light conditions on herbivory and analyzed plant traits, while the sample from 2016. apart from already stated, was also used to test the mentioned effects on leaf size traits and fluctuating asymmetry as an indicator of developmental instability. Four fluctuating asymmetry indices were quantified for leaf petiole length, midvein length, leaf blade width and leaf blade surface area..

Patterns of herbivore damage, developmental stability, morphological and biochemical traits in female and male Mercurialis perennis in contrasting light habitats

Light environments can influence variation in plant morphology, development and susceptibility to herbivores. Our research interest was to investigate the patterns of herbivore damage and developmental stability in dioecious understory forb Mercurialis perennis in contrasting light habitats, located at 1700 m a.s.l. on Mt. Kopaonik. Male and female plants from two light habitats, open (a sun-exposed field) and shaded (a spruce forest) were examined with respect to: herbivore damage (percentage of leaf area loss), fluctuating asymetry (FA) as a measurement of developmental stability, plant morphological and, specifically, leaf size traits, as well as biochemical traits relating to nutritional quality and defence, taking into account the possible presence of intersexual differences. Our results show that herbivore damage was significantly higher in open habitat, as well as one out of four univariate FA indices and the multivariate index. Morphological and biochemical traits, apart from defensive compounds, had higher values in the shade, pointing to sun-exposed habitat being more stressful for this species. Intersexual differences were observed for foliar damage, defensive compounds (phenolics and tannins), all leaf size traits, total leaf area, and protein content. Contrasting light habitats affected most of the analysed traits. Both foliar damage and FA were higher in a more stressful habitat; within habitats, no positive correlations were found. Herbivore damage was significantly male biased in open habitat. The analysis of intersexual differences in developmental stability measured by leaf asymmetry levels provided no evidence that female plants were more sensitive to environmental stress.This is a post-peer-review, pre-copyedit version of an article published in Alpine Botany. The final authenticated version is available online at: [http://dx.doi.org/10.1007/s00035-018-0203-8

Ontogenetic stage, plant vigor and sex mediate herbivory loads in a dioecious understory herb

Plant-herbivore interactions can be mediated by plant apparency, defensive and nutritional quality traits that change through plant ontogeny, resulting in age-specific herbivory. In dioecious species, opposing allocation patterns in defense may lead to sex-biased herbivory. Here, we examine how onto stage and plant sex determine levels of herbivore damage in understory herb Mercurialis perennis under field conditions. We analyzed variation in plant size (height, total leaf area), physical (specific leaf area) and chemical (total phenolic and condensed tannins contents) defense, and nutritional quality (total water, soluble protein and nonstructural carbohydrate contents) during the shift from reproductive to post-reproductive stage. Furthermore, we explored correlations between the analyzed traits and levels of foliar damage. Post-reproductive plants had lower levels of chemical defense, and larger leaf area removed, in spite of having lower nutritive quality. Opposing patterns of intersexual differences were detected in protein and phenolic contents during reproductive stage, while in post-reproductive stage total leaf area was sexually dimorphic. Female-biased herbivory was apparent only after reproduction. Plant size parameters combined with condensed tannins content determined levels of foliar damage during post reproductive stage, while the only trait covarying with herbivory in reproductive stage was total nonstructural carbohydrate content. Our results support claims of optimal defense theory - sensitive stage of reproduction was better defended. We conclude that different combinations of plant traits mediated interactions with herbivores in mature stages. Differences in reproductive allocation between the sexes may not immediately translate into different levels of damage, stressing the need for considering different ontogenetic stages when exploring sex bias in herbivory

Light and sex interplay: differential herbivore damage in sun and shade in dioecious Mercurialis perennis

Interactions between plants and herbivorous insects can be shaped by light environment, resulting in differential herbivory in sun and shade. In dioecious species, the combination of plant sex and light-induced changes in defense traits and nutritive value can alter the patterns of foliar damage. We explored the combined effects of light environment and plant sex on natural herbivore damage and plant traits in the dioecious understory forb Mercurialis perennis on Mt. Kopaonik (Serbia). The role of plant traits in predicting the extent of damage was examined as well. Male and female plants from contrasting light environments (shade vs. sun) were analyzed with respect to leaf damage, as well as plant morphological and biochemical traits (size, specific leaf area, carbon-based defensive compounds and nutritional quality). We found prominent differences in herbivore damage between sun and shade conditions, but not between the sexes. Plants from the sun-exposed site had a significantly larger leaf area removed. The specific leaf area co-varied with herbivore damage in an inverse fashion, while leaf nutritional value had a moderate effect. Contrasting light conditions influenced the patterns of intersexual differences in the contents of condensed tannins and soluble proteins, with females exhibiting higher trait values. We found that factors defining risk of consumption were related to plant morphological traits and nutritive value rather than to chemical defenses