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An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts.

ABSTRACT: The adaptive nature of discontinuous gas exchange (DGE) in insects is contentious. The classic 'hygric hypothesis', which posits that DGE serves to reduce respiratory water loss (RWL), is still the best supported. We thus focused on the hygric hypothesis in this first-ever experimental evolution study of any of the competing adaptive hypotheses. We compared populations of the migratory locust (Locusta migratoria) that underwent 10 consecutive generations of selection for desiccation resistance with control populations. Selected locusts survived 36% longer under desiccation stress but DGE prevalence did not differ between these and control populations (approx. 75%). Evolved changes in DGE properties in the selected locusts included longer cycle and interburst durations. However, in contrast with predictions of the hygric hypothesis, these changes were not associated with reduced RWL rates. Other responses observed in the selected locusts were higher body water content when hydrated and lower total evaporative water loss rates. Hence, our data suggest that DGE cycle properties in selected locusts are a consequence of an evolved increased ability to store water, and thus an improved capacity to buffer accumulated CO2, rather than an adaptive response to desiccation. We conclude that DGE is unlikely to be an evolutionary response to dehydration challenge in locusts.

SUBMITTER: Talal S

PROVIDER: S-EPMC5206591 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature

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An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts.

Talal Stav S Ayali Amir A Gefen Eran E

Biology letters 20161201 12

The adaptive nature of discontinuous gas exchange (DGE) in insects is contentious. The classic 'hygric hypothesis', which posits that DGE serves to reduce respiratory water loss (RWL), is still the best supported. We thus focused on the hygric hypothesis in this first-ever experimental evolution study of any of the competing adaptive hypotheses. We compared populations of the migratory locust (Locusta migratoria) that underwent 10 consecutive generations of selection for desiccation resistance w ...[more]

PMID: 28003523

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Project description:The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance.A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion.Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion.Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

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An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts.

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An experimental evolution study confirms that discontinuous gas exchange does not contribute to body water conservation in locusts.

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