Cutaneous respiration by diving beetles from underground aquifers of Western Australia (Coleoptera: Dytiscidae)

Abstract

Insects have a gas-filled respiratory system, which provides a challenge for those that have become aquatic secondarily. Diving beetles (Dytiscidae) use bubbles on the surface of their bodies to supply O 2 for their dives and passively gain O 2 from the water. However, these bubbles usually require replenishment at the water's surface. A highly diverse assemblage of subterranean dytiscids has evolved in isolated calcrete aquifers of Western Australia with limited/ no access to an air-water interface, raising the question of how they are able to respire. We explored the hypothesis that they use cutaneous respiration by studying the mode of respiration in three subterranean dytiscid species from two isolated aquifers. The three beetle species consume O 2 directly from the water, but they lack structures on their bodies that could have respiratory function. They also have a lower metabolic rate than other insects. O 2 boundary layers surrounding the beetles are present, indicating that O 2 diffuses into the surface of their bodies via cutaneous respiration. Cuticle thickness measurements and other experimental results were incorporated into a mathematical model to understand whether cutaneous respiration limits beetle size. The model indicates that the cuticle contributes considerably to resistance in the O 2 cascade. As the beetles become larger, their metabolic scope narrows, potentially limiting their ability to allocate energy to mating, foraging and development at sizes above approximately 5 mg. However, the ability of these beetles to utilise cutaneous respiration has enabled the evolution of the largest assemblage of subterranean dytiscids in the world.

Elucidating stygofaunal trophic web interactions via isotopic ecology

“…Under those conditions, increased oxygen levels [38] may play a role in shaping changes in stygofaunal niche occupation. Subterranean beetles’ body size has been found to drive differential physiological responses to increased exoskeleton respiration rates (inversely proportional to the body size) which ultimately affect the ability to allocate energy for breeding and foraging [80]. As the smallest species P .…”

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago

“…Over 100 species have been described to date from more than 45 individual calcretes, each showing troglomorphic traits such as eye, pigment and wing loss, and adaptive traits such as cutaneous respiration (Watts and Humphreys 2004, 2006, 2009; Jones et al. 2019). Beetle species within individual calcretes have repeatedly evolved distinct size variation (small, medium, and/or large; see Fig.…”

Stygofaunal community trends along varied rainfall conditions: Deciphering ecological niche dynamics of a shallow calcrete in Western Australia

“…These patterns suggest that the shifts in environmental conditions, and therefore resource availability, provided by rainfall (HR) do not shape differential inter-specific competition. As suggested by Allford et al (2008), vertical partitioning down the water column, as a result of contrasting oxygen requirements (Jones, Cooper, & Seymour, 2019), is likely to play an important role in beetles' interactions at Sturt Meadows, and further investigations will help unravel these ecological dynamics.…”