André Francoeur

Variations and Taxonomic Significance of the Chromosome Numbers in The Nearctic Species of the Genus Leptothorax (S.S.) (Formicidae: Hymenoptera)

SUMMARYThe taxonomic situation of the genus Leptothorax (sensu stricto = subgenus Leptothorax sensu Smith 1950) appears particularly puzzling in North America when using morphological characters alone. This paper analyses the taxonomic impact of the complex variations observed in the chromosome numbers of the presently recognized species. The method of Imai modified for some details was applied to specimens obtained from colonies reared in laboratory. These were collected between 1978 and 1984, in different regions of Quebec and in Alberta for Canada, in New Hampshire and Utah for USA. Over 250 slides of testes (male pupae) or brain (female prepupae) were prepared. Results for the nearctic species are compared to European data. For the traditional muscorum taxon as applied in North America the haploid numbers varied from 15 to 23 including supernumerary chromosomes. At least four distinct species can be extracted from these results. Male diploidy is documented. Different tendencies are stressed between th...

Soil modifications created by ants along a post-fire chronosequence in lichen-spruce woodland

Abstract Ants appeared to be an important component of the soil fauna in azonal lichen-spruce woodland in southern Québec, but their role in nutrient distribution and vegetation dynamics remained unknown. A study was undertaken to compare physical, chemical, and microbial properties of nest mound soils to those of surrounding soils to test the hypothesis that ants create patches of fertile soil and that these modifications are greater than changes in soil fertility due to forest succession. We also quantified ground cover, sexually regenerated black spruce seedlings, and ant nests along the chronosequence and verified whether nest mounds constituted safe sites for black spruce seedling establishment. Surface nest mounds had a significant effect on most measured soil variables. Compared to surrounding soils, nest soils had lower moisture content and bulk density, higher organic matter content and pH, higher available C for microbial growth, higher plant-available N, and were enriched in several major nutrients (K, Ca, Mg). Extractable-P was, however, lower in nest mounds than in surrounding soils. On the other hand, age-class significantly affected fewer soil variables (moisture, microbial biomass, extractable Na, and total Ca), and these changes could be explained by fire disturbance and the subsequent development of the tree stratum. Exposed mineral soil was the dominant ground cover in the 1-year-old and 9-year-old plots, while lichen cover was dominant in the three older age-classes. Sexually regenerated black spruce seedlings occurred mainly in the sparse moss layer in the 1-year-old and 9-year-old age-classes and almost exclusively in the lichen layer in the two older age-classes. Seedling density was 15 ha-1 the year following fire disturbance, but varied between 52 and 121 ha-1 in the four older age-classes. The average densities of occupied ant nests varied between 137-188 nests ha-1 across age-classes and occurred directly in lichen or moss, under bare mineral soil, in coarse woody debris, or under conspicuous sand mounds. We found no seedlings growing on occupied or abandoned nest mounds, which numbered only 15 ha-1 in the 1-year-old age-class and between 44 and 74 ha-1 in subsequent age-classes. We conclude that ants in this lichen-spruce woodland create nutrient-rich patches that can have a positive effect on tree growth and accelerate canopy closure, but we reject the hypothesis that nest mounds are safe sites for black spruce seedling establishment.

Ground-Nesting Ant Assemblages and Their Relationships to Habitat Factors Along a Chronosequence of Postfire-Regenerated Lichen–Spruce Woodland

Abstract Ground-nest densities and nesting habits of 13 ant species were quantified in five postfire age classes (1, 9, 23, 47, and 79 yr old) in the lichen–spruce woodland of Quebec, Canada. There were no significant differences in ant nest densities between age-classes (average of 163 nests/ha), but there were significant differences in ant community structure. Ant communities were dominated by Formica podzolica, F. aserva, F. hewetti, and Myrmica detritinodis, which accounted for 77% of occupied nests. Some species (e.g., F. podzolica) were specialists in their nesting habits, whereas others (e.g., F. aserva) were generalists and built their nest in a variety of substrates. Nest densities of F. aserva correlated with several habitat factors, but these correlations could have been spurious because they were not related to this species’ nesting habits. However, significant positive correlations found between Camponotus herculeanus and Leptothorax canadensis and coarse woody debris (CWD) may be biologically significant, because these two species nested exclusively within CWD. Nest densities of M. detritinodis and M. fracticornis were relatively high in the youngest and the oldest age classes, resulting in a negative correlation with CWD. We suggest that the distribution of these two species is caused by their preference for older forests to a high rate of fire survival and possibly to competitive release in the year after disturbance. According to canonical correspondence analysis, at least 75% of the variation in ant species cannot be explained by the habitat factors measured. Future research should include, therefore, experimental manipulations to determine the extent to which other factors, such as interspecific interactions, may structure ant communities in lichen–spruce woodland.

Effects of early experience on interactions between the parasite ant Formicoxenus provancheri and its host Myrmica incompleta (Hymenoptera: Formicidae)

Abstract The influence of early experience on interspecific recognition in the parasite ant Formicoxenus provancheri and its host Myrmica incompleta was studied by investigating the interactions of each species with adults and with larvae. The adults tested were reared heterospecifically (host and parasite together) or homospecifically (with or without mature conspecific ergates). Adults of each species were tested with both conspecific and allospecific larval brood. Homospecifically reared M. incompleta were more aggressive towards their parasite than when reared with the latter. Formicoxenus provancheri were always attracted to M. incompleta brood and adults. This parasite thus prefers to rear the hostbrood, especially when the parasites early experience has been either of its own species or where it has been reared alone.

Postfire Succession of Ants (Hymenoptera: Formicidae) Nesting in Dead Wood of Northern Boreal Forest

ABSTRACT Dead wood decomposition begins immediately after tree death and involves a large array of invertebrates. Ecological successions are still poorly known for saproxylic organisms, particularly in boreal forests. We investigated the use of dead wood as nesting sites for ants along a 60-yr postfire chronosequence in northeastern coniferous forests. We sampled a total of 1,625 pieces of dead wood, in which 263 ant nests were found. Overall, ant abundance increased during the first 30 yr after wildfire, and then declined. Leptothorax cf. canadensis Provancher, the most abundant species in our study, was absent during the first 2 yr postfire, but increased steadily until 30 yr after fire, whereas Myrmica alaskensis Wheeler, second in abundance, was found at all stages of succession in the chronosequence. Six other species were less frequently found, among which Camponotus herculeanus (Linné), Formica neorufibarbis Emery, and Formica aserva Forel were locally abundant, but more scarcely distributed. Dead wood lying on the ground and showing numerous woodborer holes had a higher probability of being colonized by ants. The C:N ratio was lower for dead wood colonized by ants than for noncolonized dead wood, showing that the continuous occupation of dead wood by ants influences the carbon and nitrogen dynamics of dead wood after wildfire in northern boreal forests.

The Guest Ant, Symmyrmica Chamberlini, Rediscovered Near Salt LakeCity, Utah (Hymenoptera, Formicidae)

In a series of recent papers we investigated the social structures of Formicoxenus nitidulus, F. hirticornis, and Leptothorax provancheri (Buschinger und Winter 1976, Buschinger 1979, Buschinger, Francoeur and Fischer 1980). They are all so-called guest ants, small species living in independent colonies within the larger nests of their host species. Formicoxenus gains its food by soliciting it from the Formica hosts, or by stealing food when two Formica workers feed each other (Stiiger 1925, Buschinger 1976). L. provancheri are often seen licking the head and body of their Myrmica hosts; however, it remains uncertain how they really get their food. Our observations revealed that these guest ants had some interesting features in common, such as a functional monogyny, a queen polymorphism with dealate and intermorphic females, and a tendency to mate within or on the upper surface of the host nest. The Formicoxenus species recognized up to now have wingless, workerlike males, whereas the L. provancheri male exhibits an ordinary winged shape. It was a challenging task, therefore, to search for Symmyrmica chamberlini Wheeler (1904), another guest ant with wingless males and living together with Manica mutica, in order to study its biology and to find out its relationship to the species mentioned above. We took the opportunity of visiting the type area of S. chamberlini in the vicinity of Salt Lake City, Utah, after the 9th Congress of IUSSI in Boulder, Colorado. We were able to rediscover this ant and to collect some new material which yielded additional support for an incorporation of Symmyrmica into Formicoxenus.