Blog 8/1: Lucie Duffy and Gretchen Schreiner
What We Learned: Michigan Thermoregulation Study
It seems like ages ago we were in Grayling, Michigan studying C. aequabilis and C. maculata, but we now have some data to report from our extended thermoregulation study. Recall that Svensson and Waller (2013) used surface temperature to investigate the thermoregulation response in damselflies of two European Calopteryx species, C. splendens and C. virgo, the latter of which extends further north and has darker wings. They found that C. virgo had a significantly higher body temperature than C. splendens at low ambient temperatures, and C. virgo body temperature had a suprisingly negative relationship with ambient temperature while C. splendens body temperature had a positive relationship. The negative slope of the more northern species could be adaptive, raising body temperatures in cooler, wetter northern climates and cooling temps in a warm southerly climate. This study inspired our work with C. aequabilis and C. maculata, two North American species that display a similar northern and southern distribution, respectively, and exist over a broad region sympatrically. In contrast to the European species, however, the more northerly distributed species has less darkly pigmented wings.
Comparing thorax temperature to ambient temperature is a way to quantify ectotherm thermoregulation. Here are some of our main questions about the thermoregulation of C. aequabilis and C. maculata:
- How do thorax temperatures of different species and sexes change as ambient temperatures increase?
- Do our findings support or contradict those of Svensson and Waller (2013)?
As we mentioned earlier on the blog, while we were in Michigan we measured thorax temperatures of more than 1000 damselfly individuals using a SeekThermal camera, while simultaneously measuring ambient temperature. We used this data to answer our proposed questions. Here is what we learned!
Figure 1. Effect of ambient air temperature on thorax surface temperature of C. aequabilis and C. maculata damselflies collected from AuSable River in Michigan. C. aequabilis females: n=89. C. aequabilis males: n=295. C. maculata females: n=324. C. maculata males: n=485.
Question 1: How do thorax temperatures of different species and sexes change as ambient temperatures increase?
As we expected, ambient temperature significantly determined the internal temperature of C. maculata and C. aequabilis thorax muscles (see Figure 1 above). All species and sexes had lower thorax temperatures at lower ambient temperatures, and all thorax temperatures increased as ambient temperatures increased. We have evidence that these damselflies are not perfect conformers, since their body temperatures did not perfectly match the air temperature. If they were perfect conformers, the slopes of all regression lines would be 1. As the figure above shows, slope = 1 is represented as a black line, which none of the other lines match. Instead, we believe these damselflies are behavioral thermoregulators, or there is a slight time lag between air temperature rising and body temperature increasing. Overall, our analysis revealed that the bodies of all four groups of damselflies – C. maculata and C. aequabilis males and females – heat up at about the same rate.
Question 2: Do our findings support or contradict those of Svensson and Waller (2013)?
Our findings provide inconclusive evidence about the thermal melanism hypothesis, which predicts the most pigmented phenotype will have the greatest rate of temperature gain. Our data supports the thermal melanism hypothesis for three reasons: (1) males, the more melanized phenotype, increase in heat faster than females (slopes of male regression lines were the steepest, although not significantly greater than those of females), (2) males are hotter than females, given the ambient temperature, and (3) although not statistically significant, C. aequabilis females, the least melanized phenotype, heated up most slowly. However, our data also contradicts this hypothesis, as there was no significant difference between species thermoregulatory ability, despite pigment differences between species and sexes; all four groups of damselflies – C. maculata and C. aequabilis males and females – increase in internal temperature at about the same rate. Our findings also do not support those of Svensson and Waller (2013) in finding (in European species) that the more northerly species had a negative slope for thorax vs. ambient temperature.
What We Learned: Exposure Trials
In addition to immersing ourselves in local culture while living and working in Hawai’i, the overarching goal of the summer was to prepare M. calliphya samples for biochemical assays to quantify oxidative damage in the fall. To prepare these damselfly samples, we performed the exposure experiment that many of us have posted about thus far in our blog, in which we exposed a portion of damselflies to solar radiation for 1 hr and left half unexposed. Recall that in Grinnell we will analyze these samples to see which morph – green females, red females, or (red) males – underwent the most oxidative damage during the 1 hr UV exposure.
In previous years of doing exposure experiments as part of this project, several unanswered questions were raised. Particularly…
- How much hotter are exposed damselflies than unexposed damselflies?
- Do our data support the thermal melanism hypothesis?
- How does UV radiation affect the internal temperature of the damselflies during the experiment?
- Does damselfly temperature affect how much they are damaged by UV radiation?
- How does weather (namely, ambient air temperature and wind speed) affect the oxidative damage the damselflies incur during exposure?
In order to answer these questions, we measured the ambient air temperature, average wind speed, and damselfly temperature throughout the exposure experiment. Here is what we learned!
Question 1: How much hotter are exposed damselflies than unexposed damselflies?
Figure 2. Average thorax surface temperatures of M. calliphya morphs during 1 hr exposure experiment. Green females: n=98. Red females: n=86. Males: n=92. Bars represent ± 1 S.E. of the mean. ANOVA Treatment: F=553.76, p<0.001; Morph: F=0.47, p=0.627; Treatment*Morph: F=4.59, p=0.011.
Figure 3. Deviation of mean thorax temperature from ambient air temperature of M. calliphya morphs during 1 hr exposure experiment. Green females: n=98. Red females: n=86. Males: n=92. Bars represent ± 1 S.E. of the mean. ANOVA Treatment: F=770.89, p<0.001; Morph: F=0.25, p=0.781; Treatment*Morph: F=7.11, p=0.001.
Overall, the damselflies in the exposure group were 6.7 ºC warmer than those in the unexposed group (see Figure 2 above)! This makes sense, because those damselflies receiving solar radiation for an hour, while the rest were in the shade. Additionally, the exposed damselflies had thorax temperatures that were 6.6ºC higher than the ambient air temperature, while those in the unexposed group had temperatures the same or just slightly higher than ambient air temperature (see Figure 3 above). This supports unpublished data of Dr. Idelle Cooper (James Madison University), who found in a similar experiment that the different morphs of damselflies – males, red females, green females – have about the same internal thorax temperature after exposure. After we test the oxidative damage of these Hawaiian damselflies, we will analyze whether oxidative damage is related to temperature.
Question 2: Do our data support the thermal melanism hypothesis?
The thermal melanism hypothesis predicts that the most pigmented – or darkest – phenotype will have the highest rate of temperature gain and higher body temperatures, which, in the M. calliphya model system, expects males to have the greatest thorax temperature during the exposure experiment. While we did not measure color quantitatively, our results confirm Cooper’s previous study that illustrates that color differences do not result in differences in brightness (or darkness!) or in internal thorax temperatures. (see Figure 2 above). Thus, the thermal melanism hypothesis is perhaps not relevant for this species, since brightness varies within, rather than between morphs.
Question 3: How does UV radiation affect the internal temperature of the damselflies during the experiment?
We used a UV meter to determine how much UV radiation was hitting the damselflies in the exposed group during the 1 hr exposure. As we expected, the amount of UV hitting the damselflies significantly affected the temperature of their thorax muscles, with higher levels of UV related to higher thorax temperatures. Within the exposed group, all morphs had similar deviations from ambient temperatures, and the effect of UV radiation levels was the same across all morphs. We will eventually use these UV levels in our final analysis, to investigate the relationship between UV level and oxidative damage.
Question 4: Does damselfly temperature affect how much they are damaged by UV radiation?
Question 5: How does weather (namely, ambient air temperature and wind speed) affect the oxidative damage the damselflies incur during exposure?
To address these two questions, we will need to wait until we complete the biochemical assays in the fall, which will reveal the level of damage from these Hawaiian M. calliphya samples are. Only then can we investigate whether a relationship between thorax temperature, ambient air temperature, mean wind speed, and oxidative damage exists.
What We Learned: Pool Mapping and Physical Parameters
We collected damselflies from four sites – Gulch 56, Waterfalls, Waia’ele, and Upper Mountain House – during the portion of our summer on the Big Island. At each site, we identified about 25 pools and analyzed the physical conditions of each (conductivity, pH, temperature, dissolved oxygen, and area) to learn more about the environment in which damselfly larvae live. Since Eve and Bella took the lead on analyzing this data, they will discuss their findings in a different post!
Side note: Today was Jackie’s birthday, and we all celebrated together! We performed a hula dance about the beauty of Ka’u – the region we are staying in – that we had been practicing over the last couple of days, we ate pineapple upside-down cake (with fresh pineapple), and we tried soursop for the first time. It was a great final day in Hawai’i.