Biology subjects

Bernal, J. S.

Publications and source records attributed to Bernal, J. S..

4 recordsLinked to original sources

bioRxiv2024

Unraveling genetic load dynamics during biological invasion: insights from two invasive insect species

Many invasive species undergo a significant reduction in genetic diversity, i.e. a genetic bottleneck, in the early stages of invasion. However, this reduction does not necessarily prevent them from achieving considerable ecological success and becoming highly efficient colonizers. Here we investigated the purge hypothesis, which suggests that demographic bottlenecks may facilitate conditions (e.g., increased homozygosity and inbreeding) under which natural selection can purge deleterious mutations, thereby reducing genetic load. We used a transcriptome-based exome capture protocol to identify thousands of SNPs in coding regions of native and invasive populations of two highly successful invasive insect species, the western corn rootworm (Chrysomelidae: Diabrotica virgifera virgifera) and the harlequin ladybird (Coccinelidae: Harmonia axyridis). We categorized and polarized SNPs to investigate changes in genetic load between invasive populations and their sources. Our results differed between species. In D. virgifera virgifera, although there was a general reduction in genetic diversity in invasive populations, including that associated with genetic load, we found no clear evidence for purging of genetic load, except marginally for highly deleterious mutations in one European population. Conversely, in H. axyridis, the reduction in genetic diversity was minimal, and we detected signs of genetic load fixation in invasive populations. These findings provide new insights into the evolution of genetic load during invasions, but do not offer a definitive answer to the purge hypothesis. Future research should include larger genomic datasets and a broader range of invasive species to further elucidate these dynamics.

evolutionary biology↗

bioRxiv2021

Assessing the Functionality of RNA Interference (RNAi) in the Phloem-feeding Maize pest Dalbulus maidis

Dalbulus maidis [(DeLong & Wolcott), corn leafhopper], a phloem-feeding insect, is the most efficient vector of maize stunting pathogens (Spiroplasma kunkelii, Maize bushy stunt phytoplasma, and Maize rayado fino virus) in the Americas. Studies involving gene editing in insects are rapidly providing information that can potentially be used for insect vector and plant disease control. RNA interference (RNAi), a sequence-specific gene silencing method, is one of the most widely used molecular tools in functional genomics studies. RNAi uses exogenous double-stranded RNA (dsRNA) or small interfering RNA (siRNA) to prevent the production of proteins by inhibiting the expression of their corresponding messenger RNA (mRNA). In this study, we measured the efficacy of gene silencing, and its effects on D. maidis mortality as proof of concept that RNAi is a viable tool for use in genetic pest control of phloem-feeding insects. Oral delivery of dsRNA using an artificial diet was used to silence two key insect genes, vacuolar ATP synthase subunit B, and subunit D (V-ATPase B and V-ATPase D). Our results showed reduced gene expression of V-ATPase B and V-ATPase D after ingestion of dsRNA, and significantly higher mortality, and wing deformation, associated with reduced gene expression, compared to control insects that were not orally fed dsRNA. These results reveal RNAi as a viable tool for use in genetic pest control of phloem-feeding insects, and a way for further functional genomic studies, such as identification of potential target genes for either population suppression or population replacement of this vector of maize diseases.

molecular biology↗

bioRxiv2020

Maize Biochemical Defences against a Rootworm Were Mediated by Domestication, Spread, and Breeding

Plant physiological processes generally are regulated by phytohormones, including plant biochemical responses to herbivory. Here, we addressed whether a suite of maize (Zea mays mays) phytohormones, including some precursor and derivative metabolites, relevant to herbivory defence were mediated by the crops domestication, northward spread, and modern breeding. For this, we compared phytohormone and metabolite levels among four plant types representing the evolutionary and agronomic transitions from maizes wild ancestor, Balsas teosinte (Zea mays parviglumis), to Mexican and US maize landraces, and to highly-bred US maize cultivars, as affected by root herbivory by Western corn rootworm (Diabrotica virgifera virgifera). Following ecological-evolutionary hypotheses, we expected to find changes in: (i) maize defence strategy, from reliance on induced to constitutive defences; (ii) levels of phytohormones relevant to herbivore resistance consistent with gradual weakening of defences, and; (iii) levels of a phytohormone relevant to herbivory tolerance because it positively affects plant growth. We found that with its domestication, maize seemed to have transitioned from reliance on induced defences in Balsas teosinte to reliance on constitutive defences in maize. Also, we found that while one subset of phytohormones relevant to herbivory was suppressed (13-oxylipins), another was enhanced (9-oxylipins) with domestication, and both subsets were variably affected by spread and breeding. Finally, an auxin phytohormone directly linked to growth (indole-3-acetic acid), increased significantly with domestication, and seemingly with spread and breeding. We concluded that rootworm defences in maize were mediated by domestication and ensuing processes, such as spread and breeding, and argued that agricultural intensification mediated maize defence evolution in parallel with modern breeding.

evolutionary biology↗

bioRxiv2019

Resistance and Tolerance to Root Herbivory in Maize were Mediated by Domestication, Spread, and Breeding

Plants may defend against herbivory and disease through various means. Plant defensive strategies against herbivores include resistance and tolerance, which may have metabolic costs that affect plant growth and reproduction. Thus, expression of these strategies may be mediated by a variety of factors, such as resource availability, herbivory pressure, and plant genetic variation, among others. Additionally, artificial selection by farmers and systematic breeding by scientists may mediate the expression of resistance and tolerance in crop plants. In this study, we tested whether maize defense against Western corn rootworm (WCR) was mediated by the crops domestication, spread, and modern breeding. We expected to find a trend of decreasing resistance to WCR with maize domestication, spread, and breeding, and a trend of increasing tolerance with decreasing resistance. To test our expectations, we compared resistance and tolerance among four Zea plants spanning those processes: Balsas teosinte, Mexican landrace maize, US landrace maize, and US inbred maize. We measured performance of WCR larvae as a proxy for plant resistance, and plant growth as affected by WCR feeding as a proxy for plant tolerance. Our results showed that domestication and spread decreased maize resistance to WCR, as expected, whereas breeding increased maize resistance to WCR, contrary to expected. Our results also showed that maize resistance and tolerance to WCR are negatively correlated, as expected. We discussed our findings in relation to ecological-evolutionary hypotheses seeking to explain defense strategy evolution in the contexts of plant resistance-productivity trade-offs, plant tolerance-resistance trade-offs, and varying resource availability vis-a-vis plant physiological stress and herbivory pressure. Finally, we suggested that defense strategy evolution in maize, from domestication to the present, is predicted by those ecological-evolutionary hypotheses.

ecology↗