Biology subjects

van der Burg, K. R. L.

Publications and source records attributed to van der Burg, K. R. L..

5 recordsLinked to original sources

bioRxiv2026

Canalization masks high levels of cryptic epigenetic and transcriptional plasticity in butterflies

Phenotypic plasticity is a common adaptation to heterogeneous environments. While it is well documented that trait plasticity can rapidly evolve, little is known about the developmental mechanisms that underlie variation in plasticity. Here, we compare diverged populations of the common buckeye butterfly (Junonia coenia): one population with canalized wing patterns that are insensitive to environmental conditions and another population that has distinctive seasonal color patterns. In common garden trials we were surprised to find dramatically elevated levels of transcriptional and chromatin accessibility plasticity during wing development of the canalized population compared to the seasonally plastic population. Further, using machine learning analysis of accessible chromatin sequences, we observed a broad heterochronic shift in motifs enriched in plastic putative regulatory elements to earlier stages of development in the canalized population, which we speculate may cause phenotype-related gene expression to move outside a wing color critical period. Together, our data lead us to propose a model where cryptic genetic processes are masked by a shift in chromatin remodeling, which in turn could produce a capacitor-like effect to maintain developmental genetic variation in the canalized population.

evolutionary biology↗

bioRxiv2024

Major changes in gene expression between strains of diapausing and non-diapause spruce budworm despite little evidence of genetic divergence

To survive harsh winter conditions, many insects enter a state of dormancy called diapause which allows them to withstand extreme temperatures and lack of food. When diapause is induced, insects enter a state of arrested development and low metabolic rate. Because diapause and environmental conditions are closely linked, variation within and between species in diapause induction, depth, and duration is extremely common. Studies investigating the genetic underpinnings of diapause tend to focus on either different populations and/or environmental variation, which runs the risk of confounding the genetic signal either due to isolation-by-distance or variation in environmental conditions. We use the eastern spruce budworm (Choristoneura fumiferana) to circumvent these issues and investigate within-population variation in diapause. C. fumiferana usually diapauses as second instar larvae, but a small subset of individuals does not diapause and instead continues through development. This non-diapause phenotype can be selected to create a non-diapause strain. Here, we present a chromosome-level assembly of such a non-diapause strain, and compare it to an earlier published genome assembly of the diapause strain. We did not find evidence of major chromosome rearrangements, indicating that the genetic variation between strains is likely small and multi-genic. Gene expression comparisons between the strains indicate major gene expression changes, where genes associated with glycolysis and environmental signaling processing increase in expression in the diapause strain. Lastly, we found that gene expression diverges halfway through the first instar, and not before, indicating that the signal to induce diapause happens early in the first instar. Significance statementThe ability to enter diapause is a crucial adaptation for many insects to survive cold winters. The genetic underpinnings of the diapause phenotype has been the target of many investigations. However, many of these studies focus on variation in diapause on between geographic regions or changes in environmental conditions, which can lead to confounding factors. Here, we focus on within-population variation in diapause in the eastern spruce budworm, with two strains established from the same source population that vary in their ability to induce diapause. We present a chromosome level assembly of the non-diapause strain, and report that genetic changes between the diapause and the non-diapause line are likely small and involve multiple loci. Gene expression differences were extensive, and mostly associated with mechanisms to avoid freezing. This work sets the stage to further investigate how minimal genetic changes can lead to large-scale phenotypic changes as impactful as diapause.

genetics↗

bioRxiv2024

Plasticity in cryoprotectant synthesis involves coordinated shunting away from pyruvate production

Insects living in temperate regions often accumulate a large amount of glycerol during winter to avoid freezing. This seasonal accrual of glycerol is generally produced from glycogen reserves through the pentose phosphate pathway. An alternative pathway to produce glycerol is through glycolysis, normally used for pyruvate production for eventual ATP synthesis. Aside from seasonal accumulation, some insects will also rapidly increase glycerol production as a short-term response to a sudden cold event, thereby increasing cold hardiness when necessary. In the eastern spruce budworm Choristoneura fumiferana, this plasticity in cold hardiness is locally adapted, where northern populations produce more glycerol upon cold shock. Here we investigate how glycerol is produced during the rapid plastic response to fluctuating cold conditions, and whether this pathway could be a target of local adaptation. After a period of repeated cold exposure, we found evidence of increased enzyme activity and increased mRNA abundance of several proteins associated with glycolysis, and a downregulation in expression of glucose-6-phosphate dehydrogenase, associated with pentose phosphate. Pyruvate production is prevented through downregulation of glyceraldehyde-3-phosphate dehydrogenase. We found higher overall enzyme activity and glycerol accumulation in a northern population from Alberta, although there was no evidence of an interaction effect between population and cold shock treatment. This is one the first studies to show a mechanistic basis of such plasticity in cold hardiness.

physiology↗

bioRxiv2021

Allochronic isolation on a latitudinal gradient in the polyphagous moth Hyphantria cunea

O_LIAllochronic speciation, where reproductive isolation between populations of a species is facilitated by a difference in reproductive timing, depends on abiotic factors such as seasonality and biotic factors such as diapause intensity. These factors are strongly influenced by latitudinal trends in climate, so we hypothesized that there is a relationship between latitude and divergence among populations separated by life history timing. C_LIO_LIHyphantria cunea (the fall webworm), a Lepidopteran defoliator with red and black colour morphs, is hypothesized to be undergoing an incipient allochronic speciation. However, given their broad geographic range, the strength of allochronic speciation may vary across latitude. We annotated >11,000 crowd-sourced observations of fall webworm to model geographic distribution, phenology, and differences in colour phenotype between morphs across North America. C_LIO_LIWe found that red and black morph life history timing differs across North America, and the phenology of morphs diverges more in warmer climates at lower latitudes. We also found some evidence that the colour phenotype of morphs also diverges at lower latitudes, suggesting reduced gene flow between colour morphs. C_LIO_LIOur results demonstrate that seasonality in lower latitudes may increase the strength of allochronic speciation in insects, and that the strength of sympatric speciation can vary along a latitudinal gradient. This has implications for our understanding of broad-scale speciation events and trends in global biodiversity. C_LI

evolutionary biology↗

bioRxiv2017

Genetic basis of melanin pigmentation in butterfly wings

Despite the variety, prominence, and adaptive significance of butterfly wing patterns surprisingly little known about the genetic basis of wing color diversity. Even though there is intense interest in wing pattern evolution and development, the technical challenge of genetically manipulating butterflies has slowed efforts to functionally characterize color pattern development genes. To identify candidate wing pigmentation genes we used RNA-seq to characterize transcription across multiple stages of butterfly wing development, and between different color pattern elements, in the painted lady butterfly Vanessa cardui. This allowed us to pinpoint genes specifically associated with red and black pigment patterns. To test the functions of a subset of genes associated with presumptive melanin pigmentation we used CRISPR/Cas9 genome editing in four different butterfly genera. pale, Ddc, and yellow knockouts displayed reduction of melanin pigmentation, consistent with previous findings in other insects. Interestingly, however, yellow-d, ebony, and black knockouts revealed that these genes have localized effects on tuning the color of red, brown, and ochre pattern elements. These results point to previously undescribed mechanisms for modulating the color of specific wing pattern elements in butterflies, and provide an expanded portrait of the insect melanin pathway.

genetics↗