Life cycle and phenology of an Antarctic invader: the flightless chironomid midge, Eretmoptera murphyi.
My very first published paper!! HURRAH!
When I first started working on Eretmoptera murphyi I was intrigued by a few things: Firstly, that we had a good idea of its cold tolerance in final instar stages, and other stress responses including its ability to respire underwater when habitat is flooded. Yet despite decades of research into its physiology, we had not verified its parthenogenesis, life cycle or phenology. Secondly, little work had been done to investigate it's impact as an invasive species on its new, and very simple, ecosystem. These two questions leaped out at me immediately as something we should probably look into!
"Despite decades of research...we had not yet verified it's parthenogenesis, life cycle or phenology..."
So, I am pleased that over the first two years of my PhD, we were able to breakdown the lifecycle and thanks to a field trip to Signy Island in 2016/17, were able to document phenology in the field. And the result is my first chapter and paper!
Who run the E.murphyi world?
Girls do. Well, females. Without fully understanding the life cycle, it has been hard to maintain a culture of this midge in any laboratories. We knew that it had a lifecycle of 2 years already, that egg sacs were laid in Austral Spring, there were likely to be four instars, and no-one had found any males. So I set to proving if these females were asexual, by holding them in isolation from pupae through to oviposition. Et voila! Egg sacs resulted from isolated females. Simples! No males needed! On inspection of each adult that did eclose, no males were found, just as they haven't been before now. Parthenogenesis officially confirmed!
Instars in your eyes
Previous research had suspected the presence of four larval instars, and used weight classes as a divider to come to this conclusion. To verify this we tracked a few 1st instar larvae, documenting the point at which they moult to 2nd instar (a few months) and did the same with 3rd instar larvae moulting to 4th. Once we had good idea of each of the instars, they were collected from soil samples, measured for length and width with each of the instars forming a nice discrete class size. Four instars it is! Some investigation into environmental triggers found that cooler, dark, moist conditions are the most conducive to survivial, and phenological surveys suggest that it is the 2nd and 4th instars that overwinter on the island. Interestingly, even in control conditions, survival is quite low at 60%.
A Pupal State
In the only taxonomical paper on E. murphyi prior to this, just one pupae was collected and described. Unsurprisingly as pupae are understudied in the chironomidae in general. Having spent a unhealthy amount of time examining these things under a scope, I noticed that their development could be tracked via distinct phases in pupation. The first phase is undoubtably the cutest that this midge ever gets, and Im using cute at a stretch - this phase is pretty active in defense, lacks pigmentation and is still developing its compound eye. Over the next 4 phases the pupae develops gonads and pigmentation, eventually able to partially eclose into a form I call the 'walking pupae', because it does exactly that. Interestingly, some of these 'walking' phase four pupae are able to lay viable eggs. It seems to be a response to a stressful or wonky eclosion. My very first lab batch of eggs actually came from a pupae that failed to fully eclose, and in its last throws, oviposited a mangled sac of eggs. They went on to become the first lab generation. She, alas, did not survive to achieve her dream of being a neglectful mother who stumbles around a moss bank, unable to feed. C'est la vie.
What do you call a fly with no wings?
Still a fly, but just one with a deep sense of irony I suspect. Such is the case for our flightless midge. After birthing a significant effort of an egg sac that is to them what I imagine birthing a foal would be to us, the adults then stagger about for 7-10 days, before dying. They do not feed, but do seem to enjoy fair weather, coming out onto the surface of the Antarctic moss banks where they spend most of their lifecycle, on particularily sunny and still days. The eggs themselves are laid in a gelatinous ball, that I will investigate more in my next paper. For this paper, understanding gestation (max 39 days) and success (LOW! 29%) was key, as well as deciding if the eggs overwintered. Typically, Chironomids will lay large, or multiple batches of eggs - a trait that allows them to be so annoyingly abundant in areas where they swarm. But E. murphyi does neither, producing an average of 48 eggs in a single egg mass. Considering the investment in a single egg sac, the success rate of the eggs is very low. We hypothesis that perhaps the positioning of eggs and their physiology is key to understanding this strategy, and follow this up in the next paper.
Who run Signy Island?
In all things terrestrial, and excluding abiotic factors, Im going to say the newly arrived E. murphyi does! Despite a less than awesome larval survival rate, half of all pupations succeeding, and only 55% of adults successfully producing eggs, and then a quarter of all those eggs making it, we still find that the sheer abundance of E.murphyi means a doubling of the population size every two years. Last reports found it at densities of 150,000 larvae m2, and my most recent distribution surveys find that it now covers an area of 85,000m2. Huge for a flightless midge!
For more info on the new distribution surveys, check out my poster from the POLAR2018 conference and talk from the Entomological Society of America's/Canada's Joint Annual Conference in 2018