The evolution of longevity in Heliconius butterflies

Abstract

The diversity of lifespans across the animal kingdom has long been of interest to evolutionary biologists. With maximum longevities ranging from a single day in adult mayflies up to several centuries in the ocean quahog, how have some organisms managed to evolve such long lives? With a globally ageing population, this question is of growing biomedical interest – and the high conservation of ageing mechanisms has researchers increasingly looking to non-model systems for the answers. The remarkable lifespans of the Heliconius butterfly genus, stretching almost up to a year, rank among the longest recorded in butterflies. This represents a dramatic lifespan extension up to 25 times longer than their close relatives in the Heliconiini tribe, and is thought to be related to a unique pollen-feeding behaviour in Heliconius. Despite the popularity of Heliconius as a model system, however, little attention has been paid to this aspect of their biology. Employing a comparative framework encompassing data across Heliconiini, before focusing on comparisons between one representative long-lived pollen-feeder, Heliconius hecale, and one representative shorter-lived non-pollen-feeder, Dryas iulia, I use survival analyses, behavioural assays, and molecular approaches to investigate the evolutionary and mechanistic bases of Heliconius’ extended longevity. My results show that along with their lifespan extension, Heliconius have evolved a slowed actuarial and physiological senescence. I also conclusively demonstrate that while pollen-feeding provides some direct plastic fitness benefits to Heliconius, their longevity is the result of evolved, heritable mechanisms of longevity. I then use evidence from transcriptomics to implicate an enhanced investment into proteostasis as an important pro-longevity mechanism in the ageing Heliconius brain, and show that accordingly, Heliconiini butterflies are surprisingly cognitively robust in old age. My results serve to add a new case study to the canon of noteworthy agers, and provide valuable insights into the evolution of long life.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Stephen H Montgomery (Supervisor), James J L Hodge (Supervisor) & Araxi Urrutia (Supervisor)