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Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community

View Article: PubMed Central - PubMed

ABSTRACT

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7 h to 97.9 h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) – the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CTmax), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CTmax were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation‐resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.

No MeSH data available.


Log10 of lethal time (h) at which 50% of workers lost their muscle coordination (LT50), after they have been exposed to air (white) and desiccant (gray). The box and whisker plots are showing median of log10LT50, upper and lower quartiles, as well as the maximum values and outliers.
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ece32355-fig-0002: Log10 of lethal time (h) at which 50% of workers lost their muscle coordination (LT50), after they have been exposed to air (white) and desiccant (gray). The box and whisker plots are showing median of log10LT50, upper and lower quartiles, as well as the maximum values and outliers.

Mentions: We tested desiccation resistance of 82 ant species ranging from 0.01 to 52.70 mg in dry weight. Canopy ants from five subfamilies and 10 genera exposed to a desiccant survived almost three times longer than understory ants from seven subfamilies and 26 genera (LT50 = 32.2 ± 25.0 h vs. 11.5 ± 11, W = 1316, P < 0.001, Fig. 2). Canopy ants ranged from LT50 = 3.6 h (Azteca chartifex Emery, 1893) to 97.9 h [Camponotus simillimus (Smith, 1862)] while understory ants survived desiccation stress from LT50 = 0.7 h (Trachymyrmex isthmicus Santschi, 1931) to 42.5 h [Pachycondyla harpax (Fabricius, 1804)]. Control canopy ants survived 2.9 times longer in the air than when exposed to a desiccant (Fig. 2; W = 498, P = 0.01); understory ants survived twice as long (W = 205, P = 0.005). The increase between the difference of survival time in control and desiccation treatments increased with body mass (Fig. S2, LT50control − LT50dessicant = 0.39 mass + 1.19, R² = 0.24, P = 0.0005).


Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community
Log10 of lethal time (h) at which 50% of workers lost their muscle coordination (LT50), after they have been exposed to air (white) and desiccant (gray). The box and whisker plots are showing median of log10LT50, upper and lower quartiles, as well as the maximum values and outliers.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016648&req=5

ece32355-fig-0002: Log10 of lethal time (h) at which 50% of workers lost their muscle coordination (LT50), after they have been exposed to air (white) and desiccant (gray). The box and whisker plots are showing median of log10LT50, upper and lower quartiles, as well as the maximum values and outliers.
Mentions: We tested desiccation resistance of 82 ant species ranging from 0.01 to 52.70 mg in dry weight. Canopy ants from five subfamilies and 10 genera exposed to a desiccant survived almost three times longer than understory ants from seven subfamilies and 26 genera (LT50 = 32.2 ± 25.0 h vs. 11.5 ± 11, W = 1316, P < 0.001, Fig. 2). Canopy ants ranged from LT50 = 3.6 h (Azteca chartifex Emery, 1893) to 97.9 h [Camponotus simillimus (Smith, 1862)] while understory ants survived desiccation stress from LT50 = 0.7 h (Trachymyrmex isthmicus Santschi, 1931) to 42.5 h [Pachycondyla harpax (Fabricius, 1804)]. Control canopy ants survived 2.9 times longer in the air than when exposed to a desiccant (Fig. 2; W = 498, P = 0.01); understory ants survived twice as long (W = 205, P = 0.005). The increase between the difference of survival time in control and desiccation treatments increased with body mass (Fig. S2, LT50control − LT50dessicant = 0.39 mass + 1.19, R² = 0.24, P = 0.0005).

View Article: PubMed Central - PubMed

ABSTRACT

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7&nbsp;h to 97.9&nbsp;h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) &ndash; the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CTmax), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CTmax were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation&#8208;resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.

No MeSH data available.