Exploring phenotypic and transcriptomic responses of Heliconius butterflies to temperature across altitudes and between species

In the face of climate change, understanding temperature response and adaptation remains a continuously relevant subject in eco-evolutionary biology, especially in insects. The tropics, which hold the wealth of the world's natural biodiversity, are thought to be the most vulnerable to rising and unstable temperatures, with species currently living close to their upper thermal limits. Altitudinal clines provide natural temperature gradients, excellent for studying how temperature influences intraspecific variation and the underlying mechanisms governing thermal tolerance and response. Heliconius butterflies are neotropical and can be found along the altitudinal slope of the Andes, and here I present them with great potential as ‘neotropical models’. Having been extensively studied for their colour patterning and mimicry, they boast numerous genomic resources, yet their thermal adaptations have been relatively understudied. In this thesis, (1) I use Heliconius sara, a heat hardy species reared in extreme but field-relevant temperatures to provide foundational insights into Heliconius thermal response across three life stages, larvae, pupae, and adults in gene expression as well as their development and thermal tolerance. 2) I then use altitudinal populations of mimetic species Heliconius erato and Heliconius melpomene reared in controlled environments to disentangle local adaptation and phenotypic plasticity in traits associated with altitude and thermal adaptation. 3) Finally, to discern the interplay between local adaptation and plasticity in gene expression responses to thermal stress. I utilized Heliconius erato samples from high and low altitudes, reared in their reciprocal temperature environments. By combining rearing experiments with transcriptomics, I aimed to effectively bridge the gap between phenotype and genotype, offering a comprehensive understanding of how species adapt and respond to temperature. This holistic approach also provides valuable insights into how species respond to future climate change scenarios.