Social structure in the ant Lasius flavus: multi-queen nests or multi-nest mounds?

Abstract.

• 1 The yellow subterranean ant Lasius flavus is generally considered to have a single queen in mature nests. Yet, many anecdotal observations have suggested that the conspicuous earth mounds of this ant may, at least occasionally, contain several queens and their offspring.
• 2 To estimate the number of matrilines per mound, samples for horizontal starch gel electrophoresis were collected from a total of thirty-seven mounds in three sites of old chalk-grassland in southern England.
• 3 Allozymatic variation at an esterase and hexokinase locus showed that probably more than 50% of the mounds contained more than one queen and that the mean number of queens per mound is at least 1.5–2.
• 4 Further results strongly suggested that workers from different matrilines may share the same galleries, at least in the top of the mound.
• 5 The apparently variable social structure of Lasius flavus colonies is discussed, both technically and with reference to ecological processes related to the presence of ants in the nest mounds.

     

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri,hybridS. invicta/richteri,S. geminata) (Hymenoptera: Formicidae)

Summary In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.     

Genetic and social structure of the queen size dimorphic ant Leptothorax cf. andrei

1. The study of queen polymorphisms can provide insight into the evolution of alternative life histories in ants. In this paper, results of morphological, social and genetic investigations of the newly discovered queen size dimorphism in Leptothorax cf. andrei are presented. 2. Queens had a bimodal size distribution, and were classified as large (macrogynes) or small (microgynes) queens. Despite their small size, microgynes had a fully developed external flight apparatus and a functional reproductive tract. 3. Queen morphology was not correlated with colony social structure, and the relatedness among nestmate queens was high, indicating secondary polygyny by re‐adoption of related queens (daughters) into existing colonies. 4. The distribution of microsatellite alleles indicated that there is a genetic separation between macro‐ and micro‐gynes but the two morphs belong to the same species. 5. The results support the hypothesis that microgyny in Leptothorax has not evolved as a specialisation to inter‐ or intra‐specific social parasitism but rather is an adaptation to alternative dispersal behaviour.     

Social and genetic structure of a supercolonial weaver ant, <Emphasis Type="Italic">Polyrhachis robsoni</Emphasis>, with dimorphic queens

We studied a population of the Australian weaver ant Polyrachis robsoni with regard to variation in the morphology of its winged queens using six newlydeveloped microsatellite markers. Morphometrically the queens fell clearly into two groups, macrogynes and microgynes, with the latter an isometric reduction of the former. Aggression tests showed that hostility between ants from different nests was minimal. Nests frequently contained numbers of both queen types, with microgynes about twice as numerous as macrogynes. Nestmate workers, microgynes, and macrogynes, were significantly related to others within their caste, with macrogynes more highly related than the other castes. Relatedness values between these groups of nestmates were also significant. Pairwise relatedness values were consistent with both queen morphs producing workers. At the population level, microgynes from different nests were also significantly related and there was a weak inverse relationship between pairwise relatedness value between individuals and distance between nests.We conclude that this species is supercolonial and that the two queen morphs are part of the same population. Received 19 July 2006; revised 16 October 2006; accepted 25 October 2006.     

Dominance hierarchies and aggressive behavior among queens of the inquiline ant Vollenhovia nipponica

Social parasitism, including temporary paratisism, slave-making, and inquilinism, is one of the most intriguing phenomena in ant societies. Inquiline ants are workerless, completely rely on the worker force of their host ants, and have evolved numerous traits to exploit the host’s resources and to increase their own fitness. We examined the inquiline ant Vollenhovia nipponica, which is a social parasite of the congeneric species Vollenhovia emeryi. Host nests collected in the field usually contained multiple V. nipponica queens, suggesting that it is polygynous. However, the average number of queens in a nest decreased from spring to summer, and many old queens were found dead after the eclosion of new sexuals in late summer. Vollenhovia nipponica therefore appears to have a short life span as found in other inquiline ants. Laboratory observation revealed that inseminated queens were aggressive towards each other. Queen-queen antagonism led to the formation of dominance hierarchies, in which only a few dominant queens developed their ovaries and laid eggs. Subordinate queens frequently left the nests by themselves. The system is very similar to “functional monogyny”. Received 21 December 2006; revised 1 September 2007 and 26 February 2008; accepted 29 February 2008.     

黑翅土白蚁分飞蚁及蚁王、蚁后生殖系统结构观察

对黑翅土白蚁Odontotermes formosanus Shiraki雌雄分飞蚁及蚁后、蚁王的生殖系统进行解剖研究。结果表明,蚁后的卵巢管数量显著多于雌性分飞蚁的,蚁王的精巢管数量显著多于雄性分飞蚁的。蚁后的卵巢体积显著大于雌性分飞蚁的,卵巢也由分飞蚁时期的卵形发育到了蚁后时期的长形。蚁王的精巢体积显著大于雄性分飞蚁的,但在形状上没有明显的差异。     

Reproductive sharing among queens in the ant Formica fusca

Reproductive sharing among cobreeders, in which reproductiveshares may vary from equal contribution (low reproductive skew)to reproductive dominance by one individual (high reproductiveskew), is a fundamental feature of animal societies. Recenttheoretical work, the reproductive skew models, has focusedon factors affecting the degree to which reproduction is skewedwithin a society. We used the parameters provided by skew modelsas a guideline to study determinants of reproductive sharingin polygyne ants. As a model system we used two-queen laboratorycolonies of the ant Formica fusca in which the reproductiveshares of each queen was assessed from offspring by using allozymesand DNA microsatellites. We tested how the different variablesincluded in reproductive skew models (queen-queen relatedness,potential fighting ability, productivity, and worker relatednessreflected by queen number in the colony of origin) affect reproductivesharing among queens. The results showed that the relatednessamong queens explained 26% of the variation in reproductiveskew. The size difference between queens (reflecting potentialfighting ability), colony productivity, and worker relatednessdid not have an effect on reproductive partitioning among cobreeders.To our knowledge, this is the first study to test for the effectsof various determinants of skew in an experimental setting.     

Unmated queens in the primitively eusocial waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Summary In the primitively eusocial tropical waspRopalidia marginata, five out of eleven colonies studied had an unmated female as their queen. In two colonies this was the case despite the presence of another mated individual in the colony. We found no detectable differences between colonies with unmated queens and those with mated queens. We argue that in species such asR. marginata, where intracolony relatedness is expected to be low and where sociality is likely to be maintained because several individuals have opportunities for direct reproduction in the future, individual selection is likely to override the good of the colony and lead to such phenomena as that of unmated queens.     

Yearly variation in polygyny in the termite <Emphasis Type="Italic">Macrotermes michaelseni</Emphasis> (Sjöstedt)

Summary Macrotermes michaelseni, an abundant termite species in semi-arid ecosystems of eastern Africa, exhibits considerable fluctuations in the proportion of polygynous colonies across years (between 5 and 50%). We found a negative correlation between rainfall and the proportion of polygynous colonies with a time lag of two years. A decrease in the percentage of polygynous colonies was particularly obvious in 1999 and 2000, two years after an El Niño-event. Rainfall and subsequent primary production seem to influence the degree of polygyny. Variation in the proportion of polygynous colonies could be due to several mutually non-exclusive factors, including better survival of polygynous colonies during years with low resource availability and increased aggression between nestmate queens with decreasing resource availability. Evaluating several lines of circumstantial evidence we suggest that the degree of polygyny depends on ecological factors.Received 11 July 2003; revised 14 October and 3 February 2004; accepted 9 March 2004.