Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska
Except for one unconfirmed case, chironomid larvae have been reported to pass through four larval instars between egg and pupal stages. We have observed a fifth larval instar to be a standard life-cycle feature of the podonomine Trichotanypus alaskensis Brundin 1966 in tundra ponds on the Arctic Coa...
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ftdoajarticles:oai:doaj.org/article:73a694fdcf6b40cc9bd235bbb1cf2023 2023-05-15T14:58:13+02:00 Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska Alec R. Lackmann Malcolm G. Butler 2018-06-01T00:00:00Z https://doi.org/10.4081/jlimnol.2018.1758 https://doaj.org/article/73a694fdcf6b40cc9bd235bbb1cf2023 EN eng PAGEPress Publications https://www.jlimnol.it/index.php/jlimnol/article/view/1758 https://doaj.org/toc/1129-5767 https://doaj.org/toc/1723-8633 doi:10.4081/jlimnol.2018.1758 1129-5767 1723-8633 https://doaj.org/article/73a694fdcf6b40cc9bd235bbb1cf2023 Journal of Limnology (2018) Podonominae Chironomidae Arctic Brooks-Dyar rule larval exuviae Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350 article 2018 ftdoajarticles https://doi.org/10.4081/jlimnol.2018.1758 2022-12-31T08:34:14Z Except for one unconfirmed case, chironomid larvae have been reported to pass through four larval instars between egg and pupal stages. We have observed a fifth larval instar to be a standard life-cycle feature of the podonomine Trichotanypus alaskensis Brundin 1966 in tundra ponds on the Arctic Coastal Plain near Barrow, Alaska. T. alaskensis has a one-year life cycle in these arctic ponds. Adults emerge in June ~2-3 weeks after pond thaw, then mate and oviposit; most newly-hatched larvae reach instar IV by October when pond sediments freeze. Overwintering larvae complete instar IV within a few days of thaw, then molt again to a fifth larval instar. Imaginal discs, normally seen only during instar IV in Chironomidae, develop across both instars IV & V prior to pupation and adult emergence. While monitoring larval development post-thaw in 2014, we noticed freshly-molted T. alaskensis larval exuviae a week or more prior to any pupation by that species. In 2015-16 we reared overwintering instar IV larvae from single pond sources, individually with daily monitoring, through molts to instar V, pupa, and adult. Some overwintering instar II and III larvae were reared as well, but were few in number. During 2016 we also reared T. alaskensis progeny (from eggs) through instar II, thus documenting head capsule size ranges for all five instars in a single pond’s population. Without individual rearings, the fifth larval instar was not readily apparent for two reasons: 1) The molt itself occurs immediately after thaw and is so synchronous it is difficult to discern in daily field samples. 2) The head capsule size increment between instars IV-V is much lower than the ratio predicted by the Brooks-Dyar Rule. Up through instar IV, the Brooks-Dyar ratio for T. alaskensis ranged 1.30-1.61, but during the IV-V molt head capsule dimensions (sexes pooled) increased by a ratio of 1.09 – comparable to the magnitude of sexual dimorphism in head capsule size within each of the final two larval instars. Individual rearings coupled ... Article in Journal/Newspaper Arctic Barrow Tundra Alaska Directory of Open Access Journals: DOAJ Articles Arctic Dyar ENVELOPE(139.517,139.517,71.400,71.400) Journal of Limnology |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Podonominae Chironomidae Arctic Brooks-Dyar rule larval exuviae Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350 |
spellingShingle |
Podonominae Chironomidae Arctic Brooks-Dyar rule larval exuviae Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350 Alec R. Lackmann Malcolm G. Butler Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
topic_facet |
Podonominae Chironomidae Arctic Brooks-Dyar rule larval exuviae Geography. Anthropology. Recreation G Physical geography GB3-5030 Environmental sciences GE1-350 |
description |
Except for one unconfirmed case, chironomid larvae have been reported to pass through four larval instars between egg and pupal stages. We have observed a fifth larval instar to be a standard life-cycle feature of the podonomine Trichotanypus alaskensis Brundin 1966 in tundra ponds on the Arctic Coastal Plain near Barrow, Alaska. T. alaskensis has a one-year life cycle in these arctic ponds. Adults emerge in June ~2-3 weeks after pond thaw, then mate and oviposit; most newly-hatched larvae reach instar IV by October when pond sediments freeze. Overwintering larvae complete instar IV within a few days of thaw, then molt again to a fifth larval instar. Imaginal discs, normally seen only during instar IV in Chironomidae, develop across both instars IV & V prior to pupation and adult emergence. While monitoring larval development post-thaw in 2014, we noticed freshly-molted T. alaskensis larval exuviae a week or more prior to any pupation by that species. In 2015-16 we reared overwintering instar IV larvae from single pond sources, individually with daily monitoring, through molts to instar V, pupa, and adult. Some overwintering instar II and III larvae were reared as well, but were few in number. During 2016 we also reared T. alaskensis progeny (from eggs) through instar II, thus documenting head capsule size ranges for all five instars in a single pond’s population. Without individual rearings, the fifth larval instar was not readily apparent for two reasons: 1) The molt itself occurs immediately after thaw and is so synchronous it is difficult to discern in daily field samples. 2) The head capsule size increment between instars IV-V is much lower than the ratio predicted by the Brooks-Dyar Rule. Up through instar IV, the Brooks-Dyar ratio for T. alaskensis ranged 1.30-1.61, but during the IV-V molt head capsule dimensions (sexes pooled) increased by a ratio of 1.09 – comparable to the magnitude of sexual dimorphism in head capsule size within each of the final two larval instars. Individual rearings coupled ... |
format |
Article in Journal/Newspaper |
author |
Alec R. Lackmann Malcolm G. Butler |
author_facet |
Alec R. Lackmann Malcolm G. Butler |
author_sort |
Alec R. Lackmann |
title |
Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
title_short |
Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
title_full |
Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
title_fullStr |
Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
title_full_unstemmed |
Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska |
title_sort |
breaking the rule: five larval instars in the podonomine midge trichotanypus alaskensis brundin from barrow, alaska |
publisher |
PAGEPress Publications |
publishDate |
2018 |
url |
https://doi.org/10.4081/jlimnol.2018.1758 https://doaj.org/article/73a694fdcf6b40cc9bd235bbb1cf2023 |
long_lat |
ENVELOPE(139.517,139.517,71.400,71.400) |
geographic |
Arctic Dyar |
geographic_facet |
Arctic Dyar |
genre |
Arctic Barrow Tundra Alaska |
genre_facet |
Arctic Barrow Tundra Alaska |
op_source |
Journal of Limnology (2018) |
op_relation |
https://www.jlimnol.it/index.php/jlimnol/article/view/1758 https://doaj.org/toc/1129-5767 https://doaj.org/toc/1723-8633 doi:10.4081/jlimnol.2018.1758 1129-5767 1723-8633 https://doaj.org/article/73a694fdcf6b40cc9bd235bbb1cf2023 |
op_doi |
https://doi.org/10.4081/jlimnol.2018.1758 |
container_title |
Journal of Limnology |
_version_ |
1766330298811809792 |