Biology subjects

Hilker, M.

Publications and source records attributed to Hilker, M..

3 recordsLinked to original sources

bioRxiv2024

Butterfly eggs prime anti-herbivore defense in an annual but not perennial Arabidopsis species

While plant anti-herbivore defenses of the annual plant species Arabidopsis thaliana were shown to be primable by Pieris brassicae eggs, the primability of the phylogenetically closely related perennial Arabidopsis lyrata has not yet been investigated. Previous studies revealed that closely related wild Brassicaceae plant species, the annual Brassica nigra and the perennial Brassica oleracea, exhibit an egg-primable defense trait, even though they have different life spans. Here, we tested whether P. brassicae eggs prime anti-herbivore defenses of the perennial A. lyrata. We exposed A. lyrata to P. brassicae eggs and larval feeding and assessed their primability by i) determining the biomass of P. brassicae larvae after feeding on plants with and without prior P. brassicae egg deposition and ii) investigating the plant transcriptomic response after egg deposition and/or larval feeding. For comparison, these studies were also conducted with A. thaliana. Consistent with previous findings, A. thalianas response to prior P. brassicae egg deposition negatively affected conspecific larvae feeding upon A. thaliana. However, this was not observed in A. lyrata. Arabidopsis thaliana responded to P. brassicae eggs with strong transcriptional reprogramming, whereas A. lyrata responses to eggs were negligible. In response to larval feeding, A. lyrata exhibited a greater transcriptome change compared to A. thaliana. Among the strongly feeding-induced A. lyrata genes were those that are egg-primed in feeding-induced A. thaliana, i.e., CAX3, PR1, PR5 and PDF1.4. These results suggest that A. lyrata compensates for its lack of egg-mediated primability by a stronger response to larval feeding.

plant biology↗

bioRxiv2023

Microbial Associates of the Elm Leaf Beetle: Uncovering the Absence of Resident Bacteria and the Influence of Fungi on Insect Performance

Microbial symbionts play crucial roles in the biology of many insects. While bacteria have been the primary focus of research on insect-microbe symbiosis, recent studies suggest that fungal symbionts may be just as important. The elm leaf beetle (ELB, Xanthogaleruca luteola) is a serious pest species of elm (Ulmus minor). Using culture-dependent and independent methods, we investigated the abundance and species richness of bacteria and fungi throughout various ELB life stages and generations, while concurrently analysing microbial communities on elm leaves. No persistent bacterial community was found to be associated with the ELB or elm leaves. By contrast, fungi were persistently present in the beetles feeding life stages and on elm leaves. Fungal community sequencing revealed a predominance of the genera Penicillium and Aspergillus in insects and on leaves. Culture-dependent surveys showed a high prevalence of two fungal colony morphotypes closely related to Penicillium lanosocoeruleum and Aspergillus flavus. Among these, the Penicillium morphotype was significantly more abundant on feeding-damaged compared to intact leaves, suggesting that the fungus thrives in the presence of the ELB. We assessed whether the detected prevalent fungal morphotypes influenced ELBs performance by rearing insects on i) surface-sterilised leaves, ii) leaves inoculated with Penicillium spores, and iii) leaves inoculated with Aspergillus spores. Insects feeding on Penicillium-inoculated leaves gained more biomass and tended to lay larger egg clutches than those consuming surface-sterilised leaves or Aspergillus-inoculated leaves. Our results demonstrate that the ELB does not harbour resident bacteria and that it might benefit from associating with Penicillium fungi. ImportanceOur study provides insights into the still understudied role of microbial symbionts in the biology of the ELB, a major pest of elms. Contrary to expectations, we found no persistent bacterial symbionts associated with the ELB or elm leaves. Our research thus contributes to the growing body of knowledge that not all insects rely on bacterial symbionts. While no persistent bacterial symbionts were detectable in the ELB and elm leaf samples, our analyses revealed the persistent presence of fungi, particularly Penicillium and Aspergillus on both elm leaves and in the feeding ELB stages. Moreover, when ELB were fed with fungus-treated elm leaves, we detected a potentially beneficial effect of Penicillium on the ELBs development and fecundity. Our results highlight the significance of fungal symbionts in the biology of this insect.

ecology↗

bioRxiv2019

Plant responses to butterfly oviposition partly explain preference-performance relationships on different brassicaceous species

According to the preference-performance hypothesis (PPH), also known as mother-knows-best hypothesis, herbivorous insects prefer those plants for oviposition, which yield the best offspring performance. Yet, most studies testing the PPH neglect the possibility that plant responses to insect eggs may affect both egg survival and larval performance. Here, we tested the PPH by studying responses of seven Brassicaceae plant species to oviposition by two cabbage white species. When including the egg phase, our study supports the mother-knows-best hypothesis: larvae of Pieris rapae (solitary) or P. brassicae (gregarious) gained most weight on those plant species which had received most eggs (B. nigra or B. montana, respectively). However, our experiments did not reveal any relationship between oviposition preference and egg survival. Brassicaceous species are known to respond to these butterfly eggs with a hypersensitive response (HR)-like necrosis, which can lower egg survival. Pieris eggs frequently induced necrosis in five of the tested plant species. Survival of clustered P. brassicae eggs was unaffected by HR-like in four of the five species. Therefore, our experiments did not reveal any relationship between P. brassicae egg survival and oviposition preference. Females of P. rapae preferred oviposition on plant species which most frequently showed HR-like necrosis. Remarkably, although egg survival was lower on HR-like plants, larval biomass was higher compared to plants without a necrosis. We conclude that egg survival does not seem to be a deciding factor for oviposition choices. However, egg-mediated plant responses might be important to explain the PPH of the two Pieris species.\n\nLay summaryEgg-laying preferences of herbivorous insects can often be linked to offspring performance. Commonly, the fate of insect eggs and the plant responses to the eggs have been ignored when studying the link between preference and performance. By including the egg phase, our study supports the mother-knows-best hypothesis, explained by butterfly oviposition and associated egg and larval performances on different plant species. We especially found that egg-mediated responses seem a deciding factor for butterfly oviposition choices.

ecology↗