Biology subjects

Kronforst, M.

Publications and source records attributed to Kronforst, M..

6 recordsLinked to original sources

bioRxiv2025

Environmental, Developmental, and Genetic Conditions Shaping Monarch Butterfly Migration Behavior

Monarch butterflies in North America migrate south each autumn, but the mechanisms that initiate their migratory flight remain incompletely understood. We investigated environmental, developmental, and genetic factors that contribute to directional flight by testing summer and autumn-generation monarchs in three flight simulators: two at ground level (with and without wind blockage) and a novel balloon-based system that raised butterflies 30 meters into the air. Monarchs reared under autumn-like conditions in a growth chamber during the summer were also tested to explore the influence of developmental cues. Autumn generation monarchs demonstrated significant southwestern flight orientation, observed exclusively in the balloon simulator, underscoring the importance of high-altitude flight for migratory behavior. Summer generation monarchs reared under autumn-like conditions displayed southward orientation, larger wing sizes, and partial reproductive diapause, indicating specific seasonal environmental cues that are sufficient to induce migratory traits. In contrast, a lab line of monarchs reared in captivity since 2016 exhibited diminished wing size and reduced orientation ability, even when raised outdoors in the autumn, consistent with a loss of migratory traits in the absence of migration. Surprisingly, butterflies in the balloon simulator tended to orient upwind, which suggests that wind may also serves as a directional cue during migration. These findings highlight the critical roles of altitude, wind, and environmental cues in monarch migration and validate the balloon flight simulator as a powerful tool for studying migratory behavior. This research advances our understanding of the initiation of monarch migration and informs strategies for conservation efforts amidst environmental change.

animal behavior and cognition↗

bioRxiv2022

Conserved signaling pathways antagonize and synergize with co-opted doublesex to control development of novel mimetic butterfly wing patterns

Novel phenotypes are increasingly recognized to have evolved by co-option of conserved genes into new developmental contexts, yet the impact of co-option on existing developmental programs remains obscure. Here we provide insight into this process by characterizing the consequences of doublesex co-option on wing color pattern development in Papilio swallowtail butterflies. doublesex is the master regulator of insect sex differentiation but has been co-opted to control the switch between discrete mimetic and non-mimetic, male-like color patterns in Papilio polytes and its close relatives. Here we show that development of the mimetic color pattern in P. polytes is caused by a pulse of dsx expression early in female wing development that results in a corresponding pulse of differential expression that both alters color pattern development and quickly becomes decoupled from dsx expression itself. Differentially expressed genes were enriched in canonical Wnt and Hedgehog signaling pathway genes, but case studies of key genes using RNAi and antibody stains suggested opposing, novel roles for the two pathways in mimetic color pattern development. The pulse of Dsx expression caused Engrailed, the key transcription factor effector of Hh signaling, to gain anterior expression in early pupal wing development. However, Dsx and En became decoupled by mid-pupal development when En pre-figured melanic and red patterns and Dsx pre-figured white patterns. In contrast, Wnt signaling antagonizes Dsx in restricted regions of the wing to refine the mimetic color pattern. Our results therefore provide strong experimental evidence that dsx co-option significantly altered spatiotemporal activities of conserved wing patterning pathways to promote and refine the development of a novel adaptive color pattern. Altogether, our findings provide strong evidence for how co-opted genes can both cause and elicit changes to established gene regulatory networks during the evolution and development of novel phenotypes.

evolutionary biology↗

bioRxiv2022

Seasonal plasticity in morphology and metabolism differs between migratory North American and resident Costa Rican monarch butterflies

Environmental heterogeneity in temperate latitudes is expected to maintain seasonally plastic life-history strategies that include the tuning of morphologies and metabolism that support overwintering. For species that have expanded their ranges into tropical latitudes, it is unclear the extent to which the capacity for plasticity will be maintained or will erode with disuse. The migratory generations of the North American (NA) monarch butterfly Danaus plexippus lead distinctly different lives from their summer generation NA parents and their tropical descendants living in Costa Rica (CR). NA migratory monarchs postpone reproduction, travel thousands of kilometers south to overwinter in Mexico, and subsist on little food for months. Whether recently dispersed populations of monarchs such as those in Costa Rica, which are no longer subject to selection imposed by migration, retain ancestral seasonal plasticity is unclear. To investigate differences in seasonal plasticity, we reared NA and CR monarchs in summer and autumn in Illinois, USA, and measured seasonal reaction norms for aspects of morphology and metabolism related to flight. NA monarchs were seasonally plastic in forewing and thorax size, increasing wing area and thorax to body mass ratio in autumn. While CR monarchs increased thorax mass in autumn, they did not increase the area of the forewing. NA monarchs maintained similar resting and maximal flight metabolic rates across seasons. However, CR monarchs had elevated metabolic rates in autumn. Our findings suggest that the recent expansion of monarchs into habitats that support year-round breeding may be accompanied by (1) the loss of some aspects of morphological plasticity as well as (2) the underlying physiological mechanisms that maintain metabolic homeostasis in the face of temperature heterogeneity.

evolutionary biology↗

bioRxiv2021

From the formation of embryonic appendages to the color of wings: Conserved and novel roles of aristaless1 in butterfly development

Highly diverse butterfly wing patterns have emerged as a powerful system for understanding the genetic basis of phenotypic variation. While the genetic basis of this pattern variation is being clarified, the precise developmental pathways linking genotype to phenotype are not well understood. The gene aristaless, which plays a role in appendage patterning and extension, has been duplicated in Lepidoptera. One copy, aristaless1, has been shown to control a white/yellow color switch in the butterfly Heliconius cydno, suggesting a novel function associated with color patterning and pigmentation. Here we investigate the developmental basis of al1 in embryos, larvae and pupae using new antibodies, CRISPR/Cas9, RNAi, qPCR assays of downstream targets and pharmacological manipulation of an upstream activator. We find that Al1 is expressed at the distal tips of developing embryonic appendages consistent with its ancestral role. In developing wings, we observe Al1 accumulation within developing scale cells of white H. cydno during early pupation while yellow scale cells exhibit little Al1 at this timepoint. Reduced Al1 expression is also associated with yellow scale development in al1 knockouts and knockdowns. We also find that Al1 expression appears to downregulate the enzyme Cinnabar and other genes that synthesize and transport the yellow pigment, 3-Hydroxykynurenine (3-OHK). Finally, we provide evidence that Al1 activation is under the control of Wnt signaling. We propose a model in which high levels of Al1 during early pupation, which are mediated by Wnt, are important for melanic pigmentation and specifying white portions of the wing while reduced levels of Al1 during early pupation promote upregulation of proteins needed to move and synthesize 3-OHK, promoting yellow pigmentation. In addition, we discuss how the ancestral role of aristaless in appendage extension may be relevant in understanding the cellular mechanism behind color patterning in the context of the heterochrony hypothesis.

developmental biology↗

bioRxiv2018

Genomic architecture and introgression shape a butterfly radiation

We here pioneer a low-cost assembly strategy for 20 Heliconiini genomes to characterize the evolutionary history of the rapidly radiating genus Heliconius. A bifurcating tree provides a poor fit to the data, and we therefore explore a reticulate phylogeny for Heliconius. We probe the genomic architecture of gene flow, and develop a new method to distinguish incomplete lineage sorting from introgression. We find that most loci with non-canonical histories arose through introgression, and are strongly underrepresented in regions of low recombination and high gene density. This is expected if introgressed alleles are more likely to be purged in such regions due to tighter linkage with incompatibility loci. Finally, we identify a hitherto unrecognized inversion, and show it is a convergent structural rearrangement that captures a known color pattern switch locus within the genus. Our multi-genome assembly approach enables an improved understanding of adaptive radiation.

evolutionary biology↗

bioRxiv2017

Female mate choice is a reproductive isolating barrier in Heliconius butterflies

In sexually reproducing organisms, speciation involves the evolution of reproductive isolating mechanisms that decrease gene flow. Premating reproductive isolation, often the result of mate choice, is a major obstacle to gene flow between species because it acts earlier in the life cycle than other isolating barriers. While female choice is often considered the default mode in animal species, research in the butterfly genus Heliconius, a frequent subject of speciation studies, has focused on male mate choice. We studied mate choice by H. cydno females by pairing them with either conspecific males or males of the closely related species H. pachinus. Significantly more intraspecific trials than interspecific trials resulted in mating. Because male courtship rates did not differ between the species when we excluded males that never courted, we attribute this difference to female choice. Females also performed more acceptance behaviours towards conspecific males. Premating isolation between these two species thus entails both male and female mate choice, and female choice may be an important factor in the origin of Heliconius species.

animal behavior and cognition↗