Developing at low mean temperatures, arctic chironomids often have prolonged larval growth yet adult emergence is typically a brief and highly synchronous event. How does a midge population achieve synchronous emergence? Under the Absolute Spring Species Hypothesis (AbSS), adult eclosion by early-emerging species may be synchronized by overwintering as fully mature larvae. Such prepupal larvae would neither feed nor grow after spring thaw, only pupate and emerge. The podonomine Trichotanypus alaskensis Brundin is an abundant midge in tundra ponds on Alaska’s Arctic Coastal Plain, and one of the earliest-emerging species in this chironomid-dominated insect community. T. alaskensis is univoltine in these arctic ponds, with most emergence from any one pond occurring within less than a one-week span during late June, typically about three weeks after pond thaw. We evaluated T. alaskensis for conformity to the AbSS model by documenting the overwintering state of this species in a tundra pond near Barrow, Alaska, then monitoring larval growth and development of the population from spring thaw to pupation. Most T. alaskensis were immature instar IV larvae when collected in late September of both 2010 and 2011, with 10-30% still in late instar III. Immediately after pond thaw in 2011, all collected larvae had imaginal disc primordia showing early stages of instar IV development. Within the first two weeks following pond thaw, most larvae had doubled their dry mass and developed into mature (prepupal) final-instar larvae. Highly synchronized emergence by T. alaskensis is not a consequence of a population overwintering as fullymature larvae, as per the Absolute Spring Species Hypothesis. Rather, larvae in a given tundra pond appear to develop synchronously throughout the life cycle, including a period of substantial growth and rapid prepupal development between spring thaw and earlysummer emergence.

中文翻译：

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北极蠓 Trichotanypus alaskensis Brundin 出苗前的生长发育

在低平均温度下发育，北极摇蚊通常具有延长的幼虫生长时间，但成虫出现通常是一个短暂且高度同步的事件。一只蠓种群如何实现同步出现？在绝对春季物种假说 (AbSS) 下，早期萌发物种的成虫羽化可能与完全成熟的幼虫越冬同步。这种预蛹幼虫在春季解冻后既不会进食也不会生长，只会化蛹和出现。podomine Trichotanypus alaskensis Brundin 是阿拉斯加北极沿海平原苔原池塘中的一种丰富的蠓，也是这个以摇蚊为主的昆虫群落中最早出现的物种之一。T. alaskensis 在这些北极池塘中是单生的，在 6 月下旬，任何一个池塘的大多数出现都在不到一周的时间内出现，通常在池塘解冻后约三周。我们通过在阿拉斯加巴罗附近的苔原池塘记录该物种的越冬状态，然后监测从春季解冻到化蛹的幼虫生长和种群发育，评估了 T. alaskensis 是否符合 AbSS 模型。2010 年和 2011 年 9 月下旬收集的大多数 T. alaskensis 是未成熟的 IV 龄幼虫，其中 10-30% 仍处于晚龄 III 期。2011 年池塘解冻后，所有收集的幼虫都具有成虫盘原基，显示出 IV 龄发育的早期阶段。在池塘解冻后的前两周内，大多数幼虫的干重增加了一倍，并发育成成熟的（预蛹）终龄幼虫。T. alaskensis 的高度同步出现并不是种群作为完全成熟的幼虫越冬的结果，根据绝对弹簧物种假说。相反，给定苔原池塘中的幼虫似乎在整个生命周期中同步发育，包括春季解冻和初夏出现之间的大量生长和快速前蛹发育时期。