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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.

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(A) Total water content (%) of canopy and ground nesting ants. (B) Total water loss (%) in canopy and ground nesting ants. The box and whisker plots are showing median of % water content (A) and % total water loss (B), upper and lower quartiles, as well as the maximum values and outliers.
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ece32355-fig-0004: (A) Total water content (%) of canopy and ground nesting ants. (B) Total water loss (%) in canopy and ground nesting ants. The box and whisker plots are showing median of % water content (A) and % total water loss (B), upper and lower quartiles, as well as the maximum values and outliers.

Mentions: We studied the role of hydration in desiccation resistance in 10 common ant species – five from each habitat – ranging in dry mass from 1.5 to 27.2 mg. These ants varied in % water content from 48% in Eciton hamatum (Fabricius, 1782) to 75% in Camponotus sericeiventris (Guérin‐Méneville, 1838), but % water was not related to body mass (F1, 8 = 0.004, P = 0.95). Water content of canopy ants averaged 2.5% higher than the water content of understory ants (Fig. 4A, 61.3 ± 6.0% vs. 58.8 ± 4.5%, W = 3280, P = 0.016). Water content, however, was not a good predictor of desiccation resistance (F1, 8 = 0.41, P = 0.54) or CTmax (F1, 7 = 0.017, P = 0.90).


Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community
(A) Total water content (%) of canopy and ground nesting ants. (B) Total water loss (%) in canopy and ground nesting ants. The box and whisker plots are showing median of % water content (A) and % total water loss (B), 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-0004: (A) Total water content (%) of canopy and ground nesting ants. (B) Total water loss (%) in canopy and ground nesting ants. The box and whisker plots are showing median of % water content (A) and % total water loss (B), upper and lower quartiles, as well as the maximum values and outliers.
Mentions: We studied the role of hydration in desiccation resistance in 10 common ant species – five from each habitat – ranging in dry mass from 1.5 to 27.2 mg. These ants varied in % water content from 48% in Eciton hamatum (Fabricius, 1782) to 75% in Camponotus sericeiventris (Guérin‐Méneville, 1838), but % water was not related to body mass (F1, 8 = 0.004, P = 0.95). Water content of canopy ants averaged 2.5% higher than the water content of understory ants (Fig. 4A, 61.3 ± 6.0% vs. 58.8 ± 4.5%, W = 3280, P = 0.016). Water content, however, was not a good predictor of desiccation resistance (F1, 8 = 0.41, P = 0.54) or CTmax (F1, 7 = 0.017, P = 0.90).

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.