Matthews-Bird, F., Gosling, W.D., Coe, A.L., Bush, M., Mayle, F.E., Axford, Y. & Brooks, S.J. (2015) Environmental controls on the distribution and diversity of lentic Chironomidae (Insecta: Diptera) across an altitudinal gradient in tropical South America. Ecology and Evolution. DOI: 10.1002/ece3.1833
I am glad to say that after almost two months out of the office running around with 8 bags of equipment, Frazer and I have finished our tour of the Americas. As the work has been so diverse, we would like to split our comments and impressions into two different posts, we hope you enjoy them!
PCRG members taking part in the Milton Keynes NSPCC Half Marathon, 8 July (left to right: Charlotte Miller, Wesley Fraser and William Gosling)
I have been really excited with the increase in the number of posts and various contributions to this blog over the last month or so. So thanks to everyone who has contributed. The excellent content allows me to focus on just a few research and teaching events which have not been previously covered.
1) Welcome to Wesley Fraser who has joined us officilally as a visiting postdoc for a few months. We hope to develop a paper and another grant submission looking at pollen/spore chemistry during this time; for further details see “Do plants wear sunblock” post.
2) Well done to Frazer and Hayley for performing well in their end of year 1 mini-vivas. Both projects are progressing well and we are all looking forward to field work at the end of the month. Hopefully most of the prepartation and equipment are now in place…
3) Potential for more exiting collaborations was also developed at two meetings. The first, at the Natural History Museum and, in conjunction with long term collaborator Steve Brooks was with old friends Mick Frogley (Sussex) and Alex Chepstow-Lusty. Both Mick and Alex taught me when I was at Cambridge and it would be super exiting to develop a new collaboration with them looking at Chironomids in Andean lakes. The second was at the Univesity of Nottingham as I took part in a UK Tropical Peatlands meeting which brought together ecologists and palaeoecologists from Nottingham, Leeds, Leicester and The OU. The aim of the meeting was to coordinate papers and grant applications.
4) At the end of July beginning of August I taught on the “Sedimentary Rocks and Fossils in the field” topic for the new Practical Science, Earth & Environment (SXG288) module which The OU now offers. Longridge Towers School (no children around this time of year) provided the perfect base for investigating the sedimentary geology of the region. The small group of students had the opportunity to make field observations and test hypotheses related to past environmental change. Everyone was very excited to find numerous fossils and interesting sedimentary structres and had fun trying to work out what they all meant! Congratulations to Angela Coe for putting together this great event.
CHIRONOMIDAE AS A PALAEO-ECOLOGICAL TOOL
Chironomidae is a family of two-winged flies more commonly referred to as non biting midges. This diverse group of insects have been known for a long time to be sensitive environmental indicators. Early research in the field showed that the trophic status of lakes could be classified according to the characteristic chironomid assemblages found within them (Thienemann, 1922). Furthermore the head capsules of the larvae are well preserved within the sedimentary record. As a result palaeolimnological researchers became increasingly interested in the potential for using Chironomids to track the trophic development of a lake through time by examining the changing assemblages within the accumulated sediments. With geographically close lakes displaying significantly different midge faunas the potential for the insects being used as climatic indicators was dismissed and the following hypothesis became established: Chironomid assemblage composition reflects in-lake variables, e.g. lake depth, pH, dissolved oxygen, trophic status and substrate. However work by Walker and Matthews (1989) demonstrated that temperature was by far the most significant variable in controlling the broad scale distribution and abundance of midge fauna.
Walker and Matthews realised the potential for the non biting midge to be used as a palaeoclimatic indicator from two initial observations. Firstly within the fossil records, as climate began warming following the deglaciation of the northern hemisphere, the relative abundance of taxa associated with cold oligotrophic lakes (Heterotrissocladius) abruptly declined. Secondly they noticed the best analogues for late glacial assemblages were found in modern day arctic and alpine settings. Overall Walker and Matthews concluded that the northern limit of temperate taxon was controlled by cold summer air and/or water temperatures. The southern limit of Arctic species was instead driven by cold oxygenated refugia in the profundal zone of deep, temperate lakes. These temperatures were significant with respect to the insect’s life cycles as many species require critical temperature thresholds to complete pupation and emergence stages.
Since the pioneering work of Walker and Matthews (1989) and others the debate linking Chironomids to temperature has raged. Debate has centred upon what controls chironomid distribution and how suitable, if at all, the insects are in the context of palaeoecological studies. Recently Velle et al. (2010) discussed some key factors which must be considered when working on chironomid based temperature resonstructions.
Below I present some of the debate around the midge-environment-temperature debate; focusing on both midge distribution and identification and the potential of this proxy as a indicator of past environmental and climatic change.