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The Journal of Experimental Biology 204, 3457-3470 (2001)
© 2001 The Company of Biologists Limited

Alternative splicing, muscle contraction and intraspecific variation: associations between troponin T transcripts, Ca²⁺ sensitivity and the force and power output of dragonfly flight muscles during oscillatory contraction

James H. Marden^*, Gail H. Fitzhugh, Mahasweta Girgenrath, Melisande R. Wolf and Stefan Girgenrath

208 Mueller Laboratory, Department of Biology, Pennsylvania State University, University Park, PA 16802, USA

*e-mail: jhm10{at}psu.edu

Accepted July 23, 2001

The flight muscles of Libellula pulchella dragonflies contain a mixture of six alternatively spliced transcripts of a single troponin T (TnT) gene. Here, we examine how intraspecific variation in the relative abundance of different TnT transcripts affects the Ca²⁺ sensitivity of skinned muscle fibers and the performance of intact muscles during work-loop contraction regimes that approximate in vivo conditions during flight. The relative abundance of one TnT transcript, or the pooled relative abundance of two TnT transcripts, showed a positive correlation with a 10-fold range of variation in Ca²⁺ sensitivity of skinned fibers (r²=0.77, P<0.0001) and a threefold range in peak specific force (r²=0.74, P<0.0001), specific work per cycle (r²=0.54; P<0.0001) and maximum specific power output (r²=0.48, P=0.0005) of intact muscle. Using these results to reanalyze previously published data for wing kinematics during free flight, we show that the relative abundances of these particular transcripts are also positively correlated with wingbeat frequency and amplitude. TnT variation alone may be responsible for these effects, or TnT variation may be a marker for changes in a suite of co-regulated molecules. Dragonflies from two ponds separated by 16 km differed significantly in both TnT transcript composition and muscle contractile performance, and within each population there are two distinct morphs that showed different maturational trajectories of TnT transcript composition and muscle contractility. Thus, there is broad intraspecific variability and a high degree of population structure for contractile performance phenotypes, TnT ribotypes and ontogenetic patterns involving these traits that affect locomotor performance.

Key words: dragonfly, insect flight muscle, work loop, skinned fiber, Ca²⁺ sensitivity, cooperativity, troponin T, alternative splicing, Libellula pulchella.

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