I saw this video a couple of weeks ago and I thought it was cool. Filmed in 1910, The acrobatic fly is a silent short film made by Percy F. Smith (1880-1945).1
The 3-minute film shows a fly glued by its back to a podium and positioned so its legs point to the sky. The fly then grabs, flips, and rotates various objects placed in its grip, including a blade of grass, a small twig, a wine cork, a large ball and another fly. The video shows how strong and dexterous the fly’s legs are. After viewing this video, I think it is easy to imagine how the fly uses its magnificent legs to cling to walls, ceilings and swaying branches in its natural environment.
The acrobatic fly.
I've been busy playing around with different ways to effectively show the responses of Target-Selective Descending Neurons (TSDNs) to small targets in 3D clutter. Shown below are 4 examples from the same recording, with the same target position and direction but changes to the apparent motion of the background. The orange/red trace is the spike train/response of the TSDN, while the blue outline is indicative of the receptor field of this same neuron. As is shown in these examples, the responses of TSDNs to small targets are greatly affected by the direction of any background motion.
The last paper from Olga's PhD is now available online. Amazing work!
- By Richard
A recent paper in PLOS ONE has offered evidence for one explanation of why zebras have stripes - namely that the pattern confuses the motion perception systems of flies.
Being able to avoid bites from horseflies or tsetse flies would arguably confer an evolutionary advantage, because of the diseases that these flies often carry.
The researchers observed the behaviour of horseflies in the vicinity of, respectively, zebras and domestic horses kept on a single farm in the UK, recording the flight paths of horseflies as they approached the animals and attempted to land on them.
While the stripes were not sufficient to deter flies from approaching (roughly equal numbers of flies circled around the horses and the zebras), when the flies attempted to land on the zebras, they were far less successful in doing so than on the horses, often flying past or colliding with the zebras. Analysis of flight paths showed that the flies slowed down prior to landing on the horses, but failed to decelerate in time to successfully complete controlled landings on the zebras.
The paper also refers to earlier work by their group (https://doi.org/10.1016/j.zool.2013.10.004), in which they demonstrated that their simulation of a previously-suggested algorithm of motion detection in the fly could be confused by a pattern of moving stripes, into miscalculating the direction of movement of the pattern. Essentially, the mechanism is that, when correlating stripes from one frame of the moving stimulus to the next, the model matches up a stripe in one frame with an adjacent stripe in the next frame, rather than with the displaced original stripe. At certain speeds of motion, the whole pattern appears to move in the opposite direction from its actual motion. In the PLOS ONE paper, the authors suggest that this may be one mechanism by which the striped pattern of the zebra disrupts optic flow perception in the fly, and its subsequent landing behaviour.
Putting striped coats on the horses greatly protected them against horsefly landings, while solid black or white coats did not. Meanwhile, the flies still managed to land at the same high rate on the horses' heads, which were uncovered.
Behaviour also played a later role: in the rare event that a horsefly did manage to land on a zebra, the zebra typically responded by flicking its tail or moving away, while these behaviours were relatively absent in the horses. The authors argue that it was a consequence of both the striped pattern and behaviour of the zebra that very few horseflies were able to successfully feed on the blood of any of the zebras in this study.
Very interesting work. This almost seems to be crying out for an electrophysiological study….!
Another batch of hoverflies are being raised in the laboratory, with the larvae becoming pupae. I was curious to see how larvae transform into adults via metamorphosis and did a little reading about it.
Metamorphosis is not unique to insects, but it is one of the most recognisable organisms to undergo this process and is learnt about at an early age (such as the children’s storybook, A Very Hungry Caterpillar).
There are three major types of metamorphosis in insects, described below:
Metamorphosis is a very successful growth strategy, as it is estimated up to 60% of animal species on the planet undergo Holometabolous metamorphosis.1 As juveniles and adults have different behaviours and diets, they do not compete for the same resources in the same environment, unlike other animal species.1
So, what happens when insects enter their pupal stage? The larva contains two types of cell – the larval cells, that make up the structure of the larva (such as muscles and organs), and another cell type called imaginal discs, which are undifferentiated, like stem cells, and are involved in the development of adult structures (such as wings, genitals and antennae).2 The imaginal disc cells use the proteins of larval cells, which are degraded by enzymes in pupa to build these structures. 2 Essentially, the pupa rebuilds itself from the inside out, transitioning from a vulnerable larva to an adaptable adult.
The control of metamorphosis and moulting occurs by two insect hormones - Juvenile Hormone and 20-hydroxyecdysome respectively.2 Whilst 20-hydroxyecdysome activates moulting and gene expression needed for metamorphosis, Juvenile Hormone does the opposite, suppressing metamorphic gene suppression to prevent the insect becoming an adult prematurely.2 Juvenile Hormone thus assists the larvae to grow before becoming a non-feeding, immobile pupa.
In the final larval moult, Juvenile Hormone generation is decreased whilst its degradation is increased. This allows 20-hydroxyecdysome to increase pupal specific mRNAs that inhibit transcription of larval genes.2 A second spike of 20-hydroxyecdysome triggers the imaginal disc cells to differentiate/specialise into the cells needed for the final moult to become the adult insect.2
Lowe T, Garwood RJ, Simonsen TJ, Bradley RS and Withers PJ. (2013) Metamorphosis revealed: time-lapse three-dimensional imaging inside a living chrysalis. Journal of the Royal Society Interface, 10(84); available from: https://royalsocietypublishing.org/doi/full/10.1098/rsif.2013.0304 doi: https://doi.org/10.1098/rsif.2013.0304
Researchers used x-rays to examine the development of organs inside Painted Lady butterflies. Advantage of using fewer animals (and no harm, unlike dissection, the traditional method to view the insides of pupae) and creating 3D models from several images. Disadvantage of low resolution so could not observe muscular or neural changes.
A short 1-minute time lapse video of a large Hercules beetle during its various life stages.
Eristalis tenax is claimed to be a honeybee mimic. Indeed, when I started working on Eristalis tenax I occasionally (more than once) brought back bees from the field, instead of hoverflies. Apparently, even beekeepers struggle to tell the difference, as evidenced by the post below from the Kangaroo Island Beehive, with the heading "Busy bee" but the photo shows an Eristalis male hoverfly. Hoverflies are good pollinators, so the flower probably doesn't mind, but I doubt the Beehive people will get any honey out of this little guy.
I found myself staring at my electrophysiology setup this morning, lacking my usual motivation and enthusiasm for it. I started justifying to myself why I shouldn’t do an experiment today; I’m tired, it’s been a hectic week, it’s Friday, I’ve got other things I could do instead. The list of excuses I could have used goes on and on.
So why did I setup an experiment? Mostly because of advice I was given years ago. When you find yourself procrastinating with a list of tasks, pick the one you feel like doing the least and just get it done. Even if you achieve nothing else for the day, it forces you to stop the procrastination cycle.
Of course, it was one of the best recordings I’ve ever got, even though; I’m tired, it’s been a hectic week, it’s Friday and I had other things I could have done instead.
- By Richard
Some disturbing news has come out recently, in the form of a paper in Biological Conservation, reviewing evidence that insect populations around the world are falling at a shockingly high rate (https://doi.org/10.1016/j.biocon.2019.01.020). In a survey of 73 studies on insect populations world-wide, the authors show that according to the papers surveyed, 41% of all insect species are in decline, with a 2.5% loss in total insect biomass every year.
On land, the biggest losses in biodiversity are in dung beetles, followed by moths, butterflies and bees (the authors note that "the fate of other pollinators such as hoverflies is ... largely unknown"). However, the situation is even worse among aquatic insects (33% of species are endangered vs. 28% of terrestrial species), with major losses among dragonflies, mayflies, stoneflies and caddisflies.
The authors identify the main causes as originating in intensive agriculture during the last century, leading to habitat loss and pollution from pesticides and fertilisers. A smaller role is also played by various biological factors including diseases and the effects of other introduced species, as well as by climate change.
Plummeting insect numbers are of course highly concerning because of their fundamental position in ecosystems, playing a role in pollination, recycling nutrients and decomposition (see also Kevin's recent post) and importantly as food for many vertebrate species.
Species that have evolved as specialists in one ecological niche are the most susceptible to loss. In many cases, these species are being replaced by other generalist species, which some could argue could start to fill the roles vacated by the specialists. But as the authors point out, just as import as the loss of insects in general is the fact that the loss of individual species compromises the long-term resilience of ecosystems.
Some caveats may exist on the conclusions drawn in the paper. In some quarters there has been criticism of the search methodology used to select papers for inclusion in the survey, which may have biased the pool of papers towards ones showing declining numbers only. Also, many major species of insects were not included in the study, due to a lack of data, and vast areas of the globe were not included for the same reason.
In fact, one possible glimmer of hope is that the vast majority of the surveyed studies were based in the highly industrialised and developed countries of North America and Europe, with some evidence from the remaining studies that the rate of decline may be lower in other regions of the world.
In response to the paper, some news sites have offered suggestions for actions that people can take locally to help to alleviate the problem. For two such examples, see here and here.
The hoverfly vision group can be found at 2 locations: At Flinders University in Adelaide, Australia, and at Uppsala University in Sweden. To find out more about us and our research, browse through the pages.