Alternative strategies by thermophilic ants to cope with extreme heat: individual versus colony level traits

Abstract

Cataglyphis is a fairly homogeneous ant genus which is widespread over the arid regions of the Old World. All Cataglyphis species are thermal specialists which are adapted to extreme environments where they forage at nearly lethal temperatures. This study focusses on two Cataglyphis species which differ considerably in their physical caste systems. These species have developed two alternative mechanisms facing extreme heat. In C. velox, foraging at high surface temperatures is clearly dependent on size: large C. velox workers forage at midday and are able to withstand higher temperatures than small workers. On the other hand, C. rosenhaueri has not developed great physical specialization, but the workers of this species have achieved physiological (such as low cuticular transpiration and metabolic rate), and behavioural adaptations (such as raising their abdomen to protect the vital organs contained in it from high temperatures) to tolerate thermal stress. The result is that small C. rosenhaueri workers may withstand extreme heat conditions in a similar way to large C. velox workers, and much better than small C. velox workers. The different mechanisms used by these two species to withstand extreme heat could reflect fundamental patterns of independent evolution. In some situations, selection may act to promote a relatively narrow size range of adult workers, all of them able to withstand thermal extremes, while in others it may act by producing different worker sizes with different tolerance to environmental conditions.

The evolution of worker–queen polymorphism in Cataglyphis ants: interplay between individual- and colony-level selections

“…Interestingly, the legs of both ergatoids and brachypters are quite similar and shorter than those of workers. In thermophilic Cataglyphis ants, long legs procure an ecological advantage by reducing workers' body exposure to extreme ground temperature (Cerdá and Retana 2000;Clémencet et al 2010). Queens are always assisted by workers and almost never leave their nest, which explains why they may not need such an adaptation.…”

Genetic diversity, worker size polymorphism and division of labour in the polyandrous ant Cataglyphis cursor

“…Analogous results were reported in C. velox, another polymorphic species belonging to the genus Cataglyphis. In this species, only large and mediumsized workers withstand extreme heat conditions and can leave the nest at higher daily temperatures to forage (Cerdá et al 1998;Cerdá & Retana 2000). The relationship between workers' morphology and the task that she usually does has been documented in several other polymorphic ants (reviewed in: Hölldobler & Wilson 1990;Passera & Aron 2005) and is supposed to confer an ergonomic advantage to the colony through a better and more efficient division of labour among workers (Oster & Wilson 1978;Gordon 1996;Passera et al 1996;Waser 1998).…”

Assembling an ant community: species functional traits reflect environmental filtering

“…An alternative explanation is thermal constraints drive assemblage-wide diVerences in relative leg length. The greater surface temperatures and VPD in the sandy soil shrub habitats (Table 3) could promote relatively longer legs as they increase the distance between an ant's body and the heat-radiating soil (Cerdá 2001;Cerdá and Retana 2000). However, we found no relationship between relative leg lengths and foraging thermal limits (F 1,14 = 2.58, P = 0.130, R 2 = 0.10) or lethal temperatures (F 1,14 = 1.71, P = 0.212, R 2 = 0.05) in common species, showing that leg morphology is not associated with greater thermal tolerance at Archbold.…”