QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online April 23, 2004
Journal of Experimental Biology 207, 1903-1913 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00970

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lighton, J. R. B. Articles by Turner, R. J. Search for Related Content PubMed PubMed Citation Articles by Lighton, J. R. B. Articles by Turner, R. J. Social Bookmarking                         What's this?

Thermolimit respirometry: an objective assessment of critical thermal maxima in two sympatric desert harvester ants, Pogonomyrmex rugosus and P. californicus

John R. B. Lighton^1,2,* and Robbin J. Turner²

¹ Department of Biological Sciences, University of Nevada at Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4004 USA
² SpanLabs Inc., 8445 Westwind Road, Las Vegas, NV 89139, USA

View larger version (32K): [in a new window]   Fig. 1. Thermolimit respirometry diagram. Simplified and not to scale. Gas streams are denoted by thick lines, and their directions by arrowheads. Thin lines are electrical connections. PTC, Peltier-effect temperature control cabinet (controlled area within hatched walls); PELT-4, controller for cabinet, in turn controlled by the adjacent computer; A, ant; AD-1, activity detector with infrared emitter (E) and detector (D); T, thermocouple in chamber, connected to thermocouple meter (TC1000); RC, respirometry chamber; EQ, equilibration coil; CA, CO2 analyzer; RA, room air; DAD, Drierite/Ascarite/Drierite drying and CO2 scrubber column; P, pump; MFCV, mass flow control valve; MFC2, mass flow control electronics unit; UI2, 16-bit data acquisition interface attached to the adjacent computer. See text for details.

View larger version (20K): [in a new window]   Fig. 2. Thermolimit respirometry on an ant, Pogonomyrmex rugosus, mass 10.2 mg (run no. AFPR_011). Clearly visible on the CO2 trace (left scale adjacent to graph; µl h-1) are the seven stages of the ant's response: equilibration (1; ca. 0–10 min), ramping (2; ca. 10–36 min), premortal plateau (3; ca. 36–40 min), mortal fall (4; ca. 40–44 min), postmortal valley (5; ca. 45 min), postmortal peak (6; ca. 50 min) and exponential decay (7; >ca. 50 min) phases. See text for details and definitions. The equilibration temperature (right scale) was 44.84°C. The ramping rate was 0.254°C min-1. The CTmax of this ant was 51.87°C (spiracular) and 51.68°C (locomotor), defined as the temperature at the breakpoint of the lag-corrected CO2 ADS trace and the activity ADS trace, respectively. CO2 begins with a brief baseline. The units of the activity ADS scale are arbitrary (left scale); the CO2 ADS trace is similar and is not shown. Note that the absolute value of the ADS trace is shown; where activity is more intense (especially during the premortal plateau) the slope of the ADS trace vs. time increases dramatically, only to inflect to near zero at the theta point (see Fig. 3). Only the slopes vs. time of the ADS traces, and not their absolute magnitudes, were used for analysis.

View larger version (18K): [in a new window]   Fig. 3. Objective determination of CTmax, using the residuals of the linear regressions vs. time of the absolute difference sums (ADS) of CO2 and of activity. Each ADS is a cumulative sum of the absolute differences between adjacent sample points in the respective data channel; the residuals of the linear regressions of each ADS vs. time clearly shows an inflection point for each ADS at which spiracular control (in the case of CO2) or motor control (in the case of activity) ceases. See Fig. 2 for reference. We operationally define the inflection point, as measured using our methodology, as the theta point and consider it to be congruent with behavioral measures of CTmax. See text for details.

View larger version (11K): [in a new window]   Fig. 4. Entering the premortal plateau section of the ramp response (see text and CO2 trace in Fig. 2) at a higher temperature predicts a higher exit temperature. A type 1 (predictive least squares) regression fit shows that 64% of the variance of exit temperature is explained by entry temperature (line equation: XT=12.1+0.779NT, where XT = exit temperature in °C and NT = entry temperature in °C; P<10-6). Squares, P. californicus; triangles, P. rugosus; the species do not differ significantly (see text).

View larger version (11K): [in a new window]   Fig. 5. A high activity ADS-derived CTmax predicts a high spiracular control (CO2)-derived CTmax. This holds true in spite of the relatively narrow range of CTmax values. A type 1 (predictive least squares) regression fit shows that 59% of the variance of CO2 ADS-derived CTmax is explained by activity-derived ADS CTmax (line equation: VT=8.1+0.845AT, where AT = activity-derived ADS CTmax in °C and VT = CO2 ADS-derived CTmax in °C; P<10-6). Squares, P. californicus; triangles, P. rugosus; the species do not differ significantly (see text).

View larger version (11K): [in a new window]   Fig. 6. A high premortal plateau CO2 predicts a high CO2 at CTmax. A type 1 (predictive least squares) regression fit shows that 46% of the variance of premortal plateau CO2 is explained by CO2 at CTmax (line equation: TV=–10.5+0.998PV, where TV = CO2 at CTmax in µl h-1 and PV = premortal plateau CO2 in µl h-1; P<10-6). The CO2 at CTmax is the CO2 at the CO2 ADS breakpoint; the breakpoint is also the marker for CTmax. Squares, P. californicus; triangles, P. rugosus; the species do not differ significantly, in spite of the large difference in body mass between the two species (see text for statistics).

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter