Coping with the cold: minimum temperatures and thermal tolerances dominate the ecology of mountain ants

1. Ants (Hymenoptera: Formicidae) are often cited as highly thermophilic and this has led to a range of studies investigating their thermal tolerances. It is unknown, however, if the geographic distribution of ant thermal tolerance conforms to the two major macropyhsiological rules that have been found in other taxa: Janzen's and Brett's rules. In addition, there is a paucity of data on how the lower thermal tolerances of ants are able to influence behaviour. 2. These two knowledge gaps were addressed here by sampling ants across a 1500 m elevational gradient in southern Africa and estimating the upper (CTmax) and lower (CTmin) thermal tolerances of 31 and 28 species, respectively. Ant abundances and soil temperatures were also recorded across the gradient over 6 years. 3. It was found that the average CTmin of the ants declined with elevation along with environmental temperatures. It was also found that the correlation between abundance and local temperature depended on the ant species' CTmin. The activity of species with a low CTmin was not constrained by temperature, whereas those with a high CTmin were limited by low temperatures. 4. For the first time, evidence is provided here that the thermal tolerances of ants are consistent with two major macrophysiological rules: Brett's rule and Janzen's rule. A mechanistic link between physiology, behaviour and the environment is also shown, which highlights that the ability of ants to deal with the cold may be a key, but often overlooked, factor allowing multiple ant species to succeed within an environment.     

A preliminary investigation of temporal patterns in semiarid ant communities: Variation with habitat type

Abstract This study reports on preliminary findings of habitat‐contingent temporal variability in ant assemblages in Purnululu National Park in northern Australia's semiarid tropics, by sampling at the end of the dry season (October 2004) and the end of the wet season (April 2005). Six grids of 15 pitfall traps were established in each of the spinifex, sandplain and gorge habitats. Community composition was dominated by behaviourally dominant ants (Iridomyrmex spp.) and climate specialists (Melophorus and Meranoplus spp.). Ant activity was higher in the wet season sampling period, with greater species richness and abundance. Interestingly, temporal variation in ant assemblage richness, abundance and composition varied markedly with habitat type. While there were large differences between sampling periods for the spinifex and sandplain habitat, this was not the case in the gorges. These temporal changes in ant assemblages are postulated to be linked with major environmental differences between the two sampling periods, driven by seasonal climatic conditions. It is likely that these changes influenced the ant assemblages through species differences in physiological tolerance levels, ecological requirements and competitive ability. This study demonstrates the need, in highly seasonal environments, to consider the temporal context of studies in relation to habitat type, particularly when undertaking biodiversity surveys and monitoring.     

Discordant patterns of evolutionary differentiation in two Neotropical treefrogs

Comparative studies of codistributed taxa test the degree to which historical processes have shaped contemporary population structure. Discordant patterns of lineage divergence among taxa indicate that species differ in their response to common historical processes. The complex geologic landscape of the Isthmus of Central America provides an ideal setting to test the effects of vicariance and other biogeographic factors on population history. We compared divergence patterns between two codistributed Neotropical frogs ( Dendropsophus ebraccatus and Agalychnis callidryas ) that exhibit colour pattern polymorphisms among populations, and found significant differences between them in phenotypic and genetic divergence among populations. Colour pattern in D. ebraccatus did not vary with genetic or geographic distance, while colour pattern co-varied with patterns of gene flow in A. callidryas . In addition, we detected significant species differences in the phylogenetic history of populations, gene flow among them, and the extent to which historical diversification and recent gene flow have been restricted by five biogeographic barriers in Costa Rica and Panama. We inferred that alternate microevolutionary processes explain the unique patterns of diversification in each taxon. Our study underscores how differences in selective regimes and species-typical ecological and life-history traits maintain spatial patterns of diversification.     

Crops that stay green1

Genetic variation exists for foliar senescence and has, usually incidentally or empirically, been exploited for crop improvement. We review the incidence of delayed or inoperative senescence in maize, sorghum, oats, rice, wheat, fescue, soybean, french bean, fruit crops, trees and other species. The insights such variants give into the genetic control of leaf senescence, and the practical implications of improved understanding of the stay-green phenomenon are discussed.     

Using multitemporal digital elevation model data for detecting canopy gaps in tropical forests due to cyclone damage: An initial assessment

Abstract The detection and mapping of canopy disturbance caused by natural events such as cyclones in tropical rainforests is important for monitoring and understanding rainforest dynamics and recovery. In February 1999 tropical cyclone Rona crossed the coastline of Far North Queensland, Australia, causing significant damage to the rainforest canopy in some areas. This paper examines the application of multitemporal canopy digital elevation models (DEMs) generated by a NASA‐operated airborne radar mapping system called TOPSAR in 1996 and 2000, for detection of canopy disturbance caused by cyclone damage. Canopy damage was mapped here by identifying areas with a significant decrease in canopy height estimated from the difference of the 1996 and 2000 TOPSAR DEMs. Conventional aerial photographs, flown shortly after the cyclone (March 1999), were used to validate the resulting map of cyclone damaged rainforest canopy. The results showed that the DEM‐derived canopy damage map performed reasonably well when comparing the spatial distribution and size of damaged areas, while taking into account the time difference between cyclone damage and the second radar acquisition. Some errors were encountered on the steeper slopes which were related to terrain distortions inherent in radar images of steep terrain. The height accuracy of the DEM was close to the depth of some of the gaps being mapped, which also contributed to errors. Even so, the results demonstrate there may be potential for weather‐independent, regional‐scale mapping of forest canopy change from imaging radar that is not always possible from traditional optical means of measuring canopy elevation, for example, airborne laser data and stereo aerial photography. This may be possible in relatively flat areas, provided the second radar acquisition occurs within months of the damaging event. Further algorithm refinement is required to improve its robustness and the range of topographies where this approach can provide reliable estimates of the extent of canopy disturbance.     

Geographical variation of mitochondrial DNA between populations of the white-clawed crayfish Austropotamobius pallipes

1. The white-clawed crayfish Austropotamobius pallipes has a widespread distribution in Europe, but since the last century its distribution has been severely affected by a combination of factors, particularly the disease crayfish plague, introduced by foreign crayfish species. At present A. pallipes is considered as vulnerable and endangered and measures are being taken in a number of countries to conserve it.
2. The application of genetics to conservation is of practical value particularly where restocking is being considered. This study assesses levels of genetic differentiation from an analysis of mitochondrial DNA (mtDNA) variation by restriction fragment length polymorphism of four populations sampled on a European scale. Six different composite haplotypes were detected among sixty-four crayfish representing the four populations. mtDNA nucleon diversity values within species ranged from 0.63% to 12.35%. A close genetic similarity was found between British and French populations of A. pallipes .
3. Results show that mtDNA can be as a suitable diagnostic marker for measuring genetic diversity between crayfish populations and that such information is of use in planning crayfish conservation strategies.     

Growth Regulation of Galium mollugo L. Cell Suspensions by a-Naphthalene Acetic Acid

Fidgeon, C. and Wilson, G. 1987. Growth regulation of Galiummollugo L. cell suspensions by -naphthalene acetic acid.—J.exp. Bot. 38: 1491–1500. Galium mollugo cell suspension cultures were found to requirethe plant growth regulator -naphthalene acetic acid (-NAA) forcontinued growth and cell division. This requirement could notbe substituted in either batch or semi-continuous culture byindole-3-acetic acid (IAA) or 2,4-dichlorophenoxy acetic acid(2,4-D) at any concentration tested. However, ß-naphthaleneacetic acid (ß-NAA) and indole-3-butyric acid (IBA)were found to support growth when supplied at a concentrationtwo orders of magnitude greater than the normal media level(0–5 mg dm³). The growth of Galium cells was found to be influenced not onlyby the -NAA initially supplied in the medium but also by theexposure to -NAA in previous growth cycles. Preculture of cellsfor 3 d in an -NAA containing medium, followed by cell washingand re-inoculation into -NAA free medium, supported a quantitativegrowth response similar to that obtained after 14 d in the control-NAA containing medium. Even short-term exposures between 0·5and 6·0 h stimulated a detectable growth response 14d later. These observations raise questions relating to theuptake and perception of exogenously supplied growth regulatorsby cultured cells. The delayed kinetics of this form of response is of significancein culture regimes in which cells are transferred from one mediumto another, differing in their growth regulator composition,in order to induce morphogenesis     

Load size selection by foraging leaf-cutter ants (Atta cephalotes)

ABSTRACT.

• 1 Velocity of load-carrying Atta cephalotes (L.) foragers increases with increasing ant size and decreasing load size.
• 2 Foragers are selective in the sizes of loads they carry, but heavier loads would apparently increase their rate of leaf transport to the nest (mg of leaf m s^?1).
• 3 Even for very thin leaves, leaf diameter is not correlated with ant body size despite the method of cutting (rotating around a fixed point on the leaf edge).
• 4 When cutting leaves of different densities, load mass is more closely matched to ant size than is load surface area. This implies that ants choose loads based on mass rather than surface area, and thus the several possible disadvantages associated with carrying loads of large surface area (e.g. increased disturbance by wind or rain) are unlikely explanations of why ants do not select larger loads.
• 5 The relationship beween forager size and load size is made more complex by further selectivity at the level of colony recruitment: larger ants recruit to higher-density (thicker) leaf types.
• 6 Gross leaf transport rate is not maximized by foraging A.cephalotes, but net rate of energy intake cannot be assumed to follow the same pattern. If costs/time (not measured) are constant with changing load size, then the net rate of energy intake is not maximized. An alternative hypothesis is that costs/time increase with larger loads, thereby decreasing net rate of gain for larger loads.