NatureWatch: Tales of scents and movement

Restoring chemical communication

Scientists have studied the impact of high ozone air pollution on the chemical communication between flowers and pollinators, and made a remarkable discovery.

They showed that tobacco hawkmoths (Manduca sexta) lose attraction to the scent of their preferred flowers when that scent had been altered by a pollutant, but when given the chance they quickly learn that an unpleasantly polluted scent may lead to nutritious nectar.

The work by researchers from Germany’s Max Planck Institute (MPI) and the University of Virginia, US, is described in a paper in the Journal of Chemical Ecology.

They first tested the response of moths in behavioural assays in a wind tunnel, allowing them to investigate both an original floral odour and one that had been altered using ozone concentrations that can be measured on hot days in their natural habitat.

“We were surprised, even shocked, that the innate attraction to the odour of tobacco flowers was completely lost in the presence of increased ozone levels,” says lead author Markus Knaden, from MPI.

The team then developed an experiment where the moth had to follow the ozone-altered odour to the flower, but was presented with the original scent at the flower containing the sugar reward.

“While we anticipated that Manduca sexta could learn new floral scents and hoped that they would be able to learn the polluted floral scent of their host flower, we were amazed to see that Manduca sexta could learn the polluted floral blend in a number of different ways, including learning a polluted scent that was decoupled from a sugar reward,” says Virginia’s Brynn Cook.

What is especially noteworthy, he adds, is that the response to a changing environment occurred in real time, not over evolutionary timescales.

A rudimentary digit of real value

African wild dogs (Lycaon pictus) are known for a unique hunting style often referred to as exhaustive predation; they just keep chasing their prey until it drops. Now a team of US anatomists has found some clues as to how they do it.

It seems the species is not fully tetradactyl (four-toed) as previously thought. It has a rudimentary first digit, buried deep, which results in a reconfiguration of some of the associated forelimb muscles to assist with proprioceptive functions – the body’s perception of its own position and movement.

“We now not only know that this vestigial digit exists, but how its presence completely reorganises and repurposes the muscles typically associated with the first digit,” says Heather F Smith, lead author of a paper in the journal PeerJ.

Smith and colleagues from Midwestern University, US, also discovered a stout ligament in the wrist which may act as a strut, assisting with passive flexion and rebound of the forefoot. It provides non-muscular propulsion during push-off of the forepaw, they say, which may help sustain endurance running and prevent the wrist muscles from tiring.

This morphology is similar in function to the suspensory ligaments of the horse “spring foot”, which provides passive “spring” action by absorbing and transferring forces experienced during locomotion. Several other muscular adaptations to long-distance endurance running also were identified in the forelimb muscles.

Also known as the African painted dog or Cape hunting dog, L. pictus is native to southern and eastern Africa. It has a nomadic lifestyle, with packs travelling up to 50 kilometres a day over home ranges of as much as 3000 square kilometres.

The fluid physics of marine snails

Hyalocylis striata, a thecosomatous pteropod with an elongated shell. Credit: David Murphy and coauthors

Billions of tiny marine snails (a form of plankton) commute daily between the oceans’ surface waters, where they feed at night, to depths of several hundred metres during the day to rest while avoiding predators.

But they’re not easy to see, so their behaviour has not been well understood – until now.

A team of oceanographers and engineers who specialise in research at the intersection of fluid physics and biology has filmed tropical marine snails and analysed them from both a fluid physics and an ecological perspective.

They found that each species has a distinct style of swimming and sinking depending on the shape of its shell, its body size, the presence or otherwise of flapping “wings”, and its speed.

“We found that [a] species with a shell shaped like an airplane wing swims faster and is more manoeuvrable than those with snail-like coiled shells,” says David Murphy from the University of South Florida, US, corresponding author of a paper in the journal Frontiers in Marine Science.

“Understanding the swimming ability of these animals is helping us better understand their ecological importance and distribution in the ocean.”

The engineers also hope they can learn some snail tricks that will help in the design of a new generation of bio-inspired underwater vehicles.

Murphy and colleagues from Florida and the Bermuda Institute of Ocean Sciences caught multiple individuals of nine species of marine snails (0.9-13.1 millimetres long) then recorded them in a salt-water aquarium with high-speed stereophotogrammetry, a technique that tracks movement in 3D with a pair of cameras.

“It’s absolutely mesmerising to watch these tiny, delicate animals flap their wings in really complex motions in order to essentially fly through the water,” he says.

Heliconoides inflatus, a thecosomatous pteropod with a coiled shell. Credit: David Murphy and coauthors