Xyloryctidae: Thyrocopa Spp.)

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ScholarSpace at University of Hawai'i at Manoa JPumpingroceedings in flightless of the h awaiianmoths entomological society (2012) 44:55–61 55 Jumping Performance in Flightless Hawaiian Grasshopper Moths (Xyloryctidae: Thyrocopa spp.) Matthew J. Medeiros1 and Robert Dudley2 1The Urban School of San Francisco, San Francisco, California, 94117, USA, and Depart- ment of Integrative Biology, University of California, Berkeley, California, 94720, USA; [email protected] 2Department of Integrative Biology, University of California, Berkeley, California, 94720, USA and Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Republic of Panama; [email protected] Abstract. Saltatorial locomotion has evolved multiple times in flightless Lepidop- tera, particularly on oceanic islands and in habitats with high winds. The kinematics of this behavior are unknown but are clearly relevant to escape performance in the absence of wings. We investigated jumping in two non-sister species of brachypterous Hawaiian moths (genus Thyrocopa). Moths were collected from the islands of Maui and Hawaii. Lateral views of jumps were recorded on video and then digitized. Jump distances of both species averaged about ten body lengths. In males of Thyrocopa apatela, jump distance was significantly correlated with the maximum horizontal component of jump velocity. Jumping ability may become enhanced as a means of evading predators when selection for flight performance is relaxed under high-wind regimes. Key words: Brachyptery, kinematics, Lepidoptera, locomotion, morphology, predation Jumping is a specialized locomotor be- formance in brachypterous insects more havior that has evolved numerous times in generally (see Dudley 2000). insects. Within the Lepidoptera, second- Here, we evaluate jumping in two rare ary flightlessness and concomitantly en- species of flightless grasshopper moths in hanced jumping abilities are particularly Hawaii, Thyrocopa apatela (Walsingham) noted on islands, in habitats with scattered and T. kikaelekea Medeiros. These species vegetation, and under high–wind regimes are unusual in that both sexes, although (Carlquist 1965; Medeiros 2008; Powell partially winged, are flightless. Brachyp- 1976; Sattler 1988, 1991). The jumping tery in Lepidoptera is typically restricted “grasshopper moths” of the Hawaiian to females (Roff 1990), and selection for islands (Xyloryctidae: Thyrocopa spp.) flightlessness inThyrocopa might accord- are of particular interest given that their ingly have been particularly strong. T. apa- jumping motions are similar to those of tela occurs on Haleakala Volcano (Maui) Orthoptera and likely serve a similar role at high elevations, historically above 2200 in escaping from terrestrial predators. The m (although two specimens were collected kinematics of jumping in grasshopper in 1976 at 1524 m; Medeiros 2009). The moths have never been investigated but species is now restricted to elevations are relevant to understanding possible above ~2900 m (M. Medeiros, pers. obs.), tradeoffs between flight and escape per- probably due to predation by introduced 56 medeiros and dudley ants (Krushelnycky et al. 2005). T. ki- moths were then placed into a clear acrylic kaelekea typically occurs at elevations of chamber (27 x 13.5 x 10.5 cm) with a sheet 2800–3000 m but is occasionally found of graph paper attached to the rear wall as low as 2100 m. The high-elevation for scale. A Sony DCR–HC26 Handycam habitats of both species are characterized digital video camera was positioned ~1 m by high winds, low air temperatures, only in front of the jumping chamber such that scattered vegetation, an absence of native its optical axis was perpendicular to the vertebrate predators, and low relative front wall of the chamber. The camera humidity. The larvae are detritivores on was used to film at 30 frames/s both a dead leaves under rocks (Howarth 1979, lateral view of the chamber and a vertical Medeiros 2008), and adults probably perspective, as reflected from a mirror do not feed, though they have a normal set up at a 45° angle above the chamber. proboscis and may drink water droplets. Jumping was induced by gently touching Locomotor behavior of adults in the field moths with a probe. Because no features is restricted to walking and intermittent of jumps have been described for any moth jumping (M. Medeiros, pers. obs.). Here, taxon, we sought to provide a preliminary we quantify jumping performance, infer description of jumping performance using important jump kinematics, and investi- a filming rate of 30 frames/s, including gate morphological correlates of jumping distances and angles for which such a film- in Thyrocopa. ing rate is sufficient. Jump trajectories and velocities are, by contrast, undersampled Materials and Methods in time but are still informative relative Individual Thyrocopa apatela were col- to the absence of any information on such lected in 2006 from the Sliding Sands area behaviors. (~2925 m) of Haleakala National Park, Only those jumps for which the pro- Maui. T. kikaelekea were collected from jected planar trajectory was <15º from above the Hale Pohaku area (~2900 m) the vertical image plane of the camera of the Mauna Kea Forest Reserve, island were used for analysis; this restriction of Hawaii. The inability to fly was con- was necessary to ensure accurate two- firmed for both species using a “drop test” dimensional reconstruction of the jump identical to that used for cave-dwelling (i.e., an angular displacement of the Schrankia (Noctuidae) moths (Medeiros trajectory by 15º from the plane of view et al. 2009). Individuals were collected by will maximally underestimate projected hand, kept within plastic vials, and were values of the x coordinate by (1 – cos 15º), brought indoors within two hours of cap- or 3.4%). The average trajectory angle ture for filming and morphological mea- relative to the image plane was 6º for all surements. For T. apatela, filming took analyzed sequences, corresponding to a place at an elevation of ~975 m, whereas reconstruction error of only 1%. Following filming ofT. kikaelekea occurred near sea a recording bout, specimens were pinned level; both filming locations were at room and later accessioned to the National Park temperature (approx. 20°C). At both loca- Service (Maui) and the Bishop Museum. tions, weight of individual moths was first Video sequences of interest were up- measured on a portable balance (Acculab loaded into a Macintosh computer, and PP2060D), and the body length was then individual movie files containing one measured from the anterior tip of the head jump each were made using QuickTime. to the tip of the abdomen (excluding the ImageJ software was used to digitize for ovipositor length in females). Individual each frame the (x, y) coordinates of the Jumping in flightless moths 57 centroid of the moth’s image, with the Results absolute length scale determined from the A range of 1–3 individuals per sex per graph paper in the immediate background. species was captured in the field, and 1–5 The distance traveled during a jump was jumps were filmed for each individual defined as the horizontal difference be- (Table 1). The extreme rarity of these two tween the frame immediately preceding species precluded larger sample sizes, and that following a jump. Takeoff angle with the field collecting effort for the relative to horizontal was measured from samples obtained here exceeding twenty the first aerial point of a jump and the hours. Moths always jumped forwards immediately preceding frame using the relative to their anteroposterior axis via coordinates of the moth’s centroid. Hori- hindleg extension, and also extended zontal and vertical velocity components their wings laterally when in the air. No were determined from a three–point roll- abdominal contact with the ground was ing average of frame-to-frame displace- noted during jumps. ments in x and y, respectively. These two Jumps by individuals were highly vari- orthogonal components were summed able, but averaged about 10 body lengths vectorially to calculate the magnitude of (Table 1; Fig. 1). Application of one-way the two–dimensional velocity vector; the ANOVA to kinematic data for jumps of maximum magnitude was determined for T. apatela males showed no effect of in- each jump. One-way ANOVA was used dividual identity on either takeoff angle, for jump data for T. apatalea males (the maximum velocity, horizontal and vertical only sex-by-species class with more than components of velocity, or jump length ten jumps); see Table 1 to assess effects of (d.f.=2,10; F>0.5 and P>0.25 in all cases). individual identity on kinematic variables. Data for these individuals were accord- For an additional set of dried and pinned ingly pooled. Jump distance in T. apatela specimens of T. apatela and T. kikaelekea, males was significantly correlated with measurements were made with digital maximum velocity (r2=0.53, P<0.005), calipers of the interocular distance (the and this correlation derived from variation transverse distance between the two in the maximum horizontal component compound eyes, as a proxy for overall of velocity (see Fig. 2). Jump distance size), and of both the femur and the tibia was, not surprisingly, independent of the lengths for the right hindlimb. To deter- maximum vertical component of velocity mine if leg morphology between volant (r2=0.05, P<0.40). and flightless species is different, the same Relative hindlimb size was substantially morphological data were also taken from different among females of different spe- dried and pinned specimens of T. abusa cies but not males (Table 2). For females, Walsingham, a typical non-jumping and the three species differed significantly flightedThyrocopa species of comparable in the ratio of the interocular distance to body length (~ 10 mm). None of the three femur length (d.f. =2, 10, F=5.9, P<0.02; T.

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