Jouni Sorvari

Individual variation in immune function in the ant Formica exsecta; effects of the nest, body size and sex

It has been generally thought that sex differences in the immune system are the result of the differing life history strategies of the sexes, although the available data are not entirely consistent with the hypothesis. In this study, we studied the variation in the immune function in the mound-building wood ant Formica exsecta. F. exsecta has two forms of males, distinguished by size: the small males (micraners) and the large males (macraners), which die after the mating period, whereas females live tens of years laying their eggs. We found that in general males have a lower encapsulation response against nylon monofilament (i.e. lower immune function) than queens. Among males, the micraners had a lower encapsulation rate than the macraners. However, in queens, there was no correlation between size and encapsulation rate. The origin nest had an effect on the encapsulation rate of males: males from the large nests had a stronger encapsulation rate than males from small nests. However, in queens, nest size did not have any effect on encapsulation response. The observed variation between sexes and individuals in the encapsulation rate is discussed in the context of reproductive strategies and parasite-mediated sexual selection.

Wood ants are wood ants: deforestation causes population declines in the polydomous wood ant Formica aquilonia

Abstract 1. One of the main themes in ecology is adaptation for survival in different habitats and the potential of the environment to regulate populations.

Forest Clear-Cutting Causes Small Workers in the Polydomous Wood Ant Formica aquilonia

We examined whether the body size of mound building wood ant Formica aquilonia workers is affected by forest clear-cutting in a before-after logging field study. Clear-cutting is expected to decrease the availability of tree-living aphids, the main food resource of wood ants. Worker size decreased from one year to the next in clear-cuts but not in forest stands, indicating food limitation in the clear-cuts. Worker size increased with nest size in forest interiors, but not in clear-cuts, which further indicates food limitation in the clear-cuts. In addition, lower body-fat contents in ant workers in the clear-cuts supports previous suggestions of lower food resources after forest logging. Nests were cooler in the clear-cuts, which suggest that they may be poor habitats for forest-dwelling wood ants. Food resource limitation may have an effect on the ability of wood ants to regulate nest temperatures.

Habitat-related aggressive behaviour between neighbouring colonies of the polydomous wood ant Formica aquilonia

Ant species of the late succession stages usually have several queens and a polydomous colony structure, where several colonies occupy the same territory without competing. The wood ant Formica aquilonia is a good example of such a species in boreal forests. In this species, the lack of intraspecific competition may be caused by the stable environment and abundant food resources (e.g. excretions of tree-living aphids). We studied how habitat destruction, in the form of clear-cutting, affects aggressiveness between neighbouring colonies in F. aquilonia. Intercolonial relationships were more hostile in clear-cuts than in forest interiors. This aggression may be the result of increased intraspecific resource competition or alienation of neighbouring colonies caused by the loss of visual orientation cues. We suggest that the original polydomous relationships between colonies decline and colonies may start aggressive competition for the remaining resources.

The role of food and colony size in sexual offspring production in a social insect: an experiment

Abstract 1. Large colonies of ants are known to have a higher propensity for sexual offspring production, probably owing to their high capacity to exploit food resources.

Combined effects of overwintering temperature and habitat degradation on the survival of boreal wood ant

The survival of insects during diapause may be affected by overwintering temperature and other environmental stress, such as anthropogenic habitat degradation. We experimentally studied the effects of overwintering temperature (+1 and +7°C) and commercial forest clear-cutting on the overwintering survival of the forest-dwelling wood ant Formica aquilonia. We found that both the higher overwintering temperature and clear-cutting lowered the overwintering survival and body fat resources of Formica aquilonia. The survival and body fat resources were highest in lower temperature treatment forest nests and lowest in higher temperature treatment clear-cut nests. The overall survival of ants increased with higher body fat resources. It is possible that both forest clear-cutting and higher winter temperature due to possible climate warming may increase the wintertime mortality of wood ants and other forest-dwelling ants.

Species richness of associates of ants in the nests of red wood ant Formica polyctena (Hymenoptera, Formicidae)

Ant nests are rich with various other fauna, and they may be seen as resources for these guest species. We studied the species richness and abundance of ant guests in the nests of Formica polyctena by addressing the resource concentration hypothesis, which predicts that nests in high densities would support higher species richness and abundance of specialised guests. In 12 nests we found 1562 individuals belonging to 70 taxa, of which beetles were the most species rich group. The resource concentration hypothesis was supported, as we found the species richness to be higher in nests with close neighbours. There was no relationship between the abundance of associates and the nearest neighbour distance. Non‐parametric methods were applied for total species richness estimation. These suggest that additional sampling would yield more associate species. In addition, we studied the similarity of the species composition in the nests and how the distance between the nests correlates with it. Overall, nests from the same area appeared to be most similar with each other. A significant negative trend between geographical distance and similarity of the species composition was found when all species and non‐myrmecophiles were tested. For maintaining and conserving high arthropod diversity in temperate and boreal forests, forest management practices preserving dense red wood ant populations should be used if the habitat cannot be protected.

Pollution diminishes intra-specific aggressiveness between wood ant colonies.

A variety of common environmental pollutants are known to affect the animal behaviour, but the occurrence and extent of pollution-induced behavioural changes in wild populations are practically unknown. Here we show that heavy metal pollution reduces the normal intra-specific aggressive behaviour in wild populations of the wood ant, Formica aquilonia, a dominant territorial ant species in boreal forests. Ants exposed to long-term pollution around a copper smelter showed higher heavy metal concentrations and were less aggressive towards the member of foreign unpolluted colony than the ants from an uncontaminated area. A pollution-related decline in the level of aggressiveness in this keystone general predator species may potentially affect the structure of invertebrate community of boreal and temperate forests. Further studies are needed to find out whether the change in aggressiveness is directly caused by metal toxicity or indirectly via secondary pollution effects, such as changed resource levels.

Molecular identification of cryptic bumblebee species from degraded samples using PCR–RFLP approach

The worldwide decline and local extinctions of bumblebees have raised a need for fast and accurate tools for species identification. Morphological characters are often not sufficient, and molecular methods have been increasingly used for reliable identification of bumblebee species. Molecular methods often require high‐quality DNA which makes them less suitable for analysis of low‐quality or older samples. We modified the PCR–RFLP protocol for an efficient and cost‐effective identification of four bumblebee species in the subgenus Bombus s. str. (B. lucorum, B. terrestris, B. magnus and B. cryptarum). We used a short partial mitochondrial COI fragment (446 bp) and three diagnostic restriction enzymes (Hinf I, Hinc II and Hae III) to identify species from degraded DNA material. This approach allowed us to efficiently determine the correct species from all degraded DNA samples, while only a subset of samples 64.6% (31 of 48) resulted in successful amplification of a longer COI fragment (1064 bp) using the previously described method. This protocol can be applied for conservation and management of bumblebees within this subgenus and is especially useful for fast species identification from degraded samples.

Contribution of wood ants to nutrient cycling and ecosystem function

Red wood ants ( Formica rufa group) build large and long-lasting nest mounds. Due to their construction, nest mounds and especially their centres, provide a favourable microclimate for brood development (Coenen-Staβ 1980). However, constructing and maintaining the nest in addition to feeding the colony requires a considerable amount of energy and building material. The ‘central-place foraging’ strategy (Chapter 7) employed by red wood ants – retrieving food and plant material from the area surrounding the nest – means they influence not only the properties of their nests, but also those of the wider area. Wood ants influence the functioning of forest ecosystems through altering food web structure (Chapter 8), soil properties, and nutrient transport and energy flow (Frouz and Jilkova 2008). The vast accumulation of organic materials in the nest means that once the nest is no longer in use, nutrients are released during the decomposition process which is performed by microorganisms (Lenoir et al . 2001). These nutrients are then available for plant growth. This chapter addresses the effects of wood ants on nutrient flow and plant growth in forest ecosystems. Since these effects are associated with nest building and territorial activities, they can be divided into nest- and territory-related effects. Nest-related effects Foraging for food Nest-related effects are connected with foraging, nest construction and the subsequent decomposition of organic materials. Decomposition in nests is enhanced because of the abundance of microorganisms and the favourable microclimate. Mineral nutrients are released from organic materials but predominantly remain in or near the ant nests, thus creating hot spots in nutrient-limited forest ecosystems. Wood ants feed on honeydew and solid insect prey; honeydew rarely forms less than two-thirds of the energy imported to F. rufa nests (Whittaker 1991). Ants may collect more than 80% of the excreted honeydew, which constitutes 62–94% of their diet and contains 15–20% sugars, a small percentage of amino acids and c . 70% water (Rosengren and Sundstrom 1991). Thus, approximately 13–16 kg of honeydew dry mass containing a significant amount of nutrients (Table 9.1) is transported annually into the average ant nest (Frouz et al . 1997; Jilkova et al . 2012). Once transported into the ant nest, the honeydew is redistributed and used as a source of energy (Horstmann 1974).