Water relations in nocturnal and diurnal foragers of the desert honeypot ant Myrmecocystus: Implications for colony‐level selection

Abstract

The desert honeypot ant genus Myrmecocystus contains both diurnal and nocturnal species, which are subject to very different desiccation challenges when foraging. We measured water loss rates (WLRsj of live and dead M. mexicanus and M. mendax workers (nocturnal and diurnal foragers, respectively) in still and moving air a t 30°C. In M. mendax, air flow and vital state significantly affected WLR; death increased WLR, as did air flow (but only in live ants). The WLR of M. mexicanus was unaffected by flow or vital state and was generally equivalent to that of M. mendax. Cuticular permeabilities of both species 10-20 pg HzO cm-' h-' Ton-') are similar to values for other xeric insects. The mean body water content of both species was very high at 84% of live body mass. Coordination failed after losing 71% (M. mexicanus), and 51% (M. mendax), of total original body water reserves. Paradoxically, therefore, the diurnal M. mendex workers are operationally more sensitive to desiccation; accordingly, in a desiccating environment they lost coordination more rapidly than M. mexicanus workers (mean 27 vs. 59 hr). We therefore found no evidence that WLRs or dehydration sensitivities of these worker ants reflected the differing dehydration challenges imposed by diurnal vs. nocturnal foraging strategies and suggest that this may reflect similar selective pressures not on workers, but on female reproductives during colony foundation.

The hyperoxic switch: assessing respiratory water loss rates in tracheate arthropods with continuous gas exchange

“…The WLR of F. mccooki has not been previously described but is typical for a xeric ant (Duncan and Lighton, 1994). That of P. californicus is far higher on an area-specific basis than that of the other two insects, but this is to be expected in view of its higher measurement temperature (40°C vs 20°C).…”

A Comparative Study between Solenopsis invicta and Solenopsis richteri on Tolerance to Heat and Desiccation Stresses

“…Since the same food source (sugar water and crickets) was used for maintaining colonies, such differences might not be the result of diet, as previously found in other ant species [24]. In addition to the difference in body water requirement (physiological trait), S. richteri might just store more fluid in the crop (behavioral trait) as for Linepithema humile and Forelius mccooki when being compared to Myrmecocystus spp [24]. Insects with a high fat content are generally those that also have a low water content [25].…”

Respiratory physiology and water relations of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae)

“…Similar values have been measured in Myrmecocystus mendax (21.1 μg/cm 2 / h/Torr), Cataglyphis bicolor (23.6 μg/cm 2 /h/Torr) and Solenopsis invicta (25.2 μg/cm 2 /h/Torr) ( Appel et al . 1991 ; Lighton & Wehner 1993; Duncan & Lighton 1994). However, our values are somewhat higher than those determined by Lighton & Feener (1989a) for P. rugosus .…”

“…Adsorbed cuticular water can affect water loss for hours in some insects ( Loveridge 1980). Water loss from ants can be surprisingly complex and factors such as air flow, hydration state, body size and vital state may all influence water loss in unpredictable ways ( Duncan & Lighton 1994; Lighton et al . 1995 ).…”