Katsusuke Yamauchi

Fighting and mating behaviors of dimorphic males in the ant

Colony composition inCardiocondyla wroughtoni and the fighting and mating behaviors of 2 types of males, alates and ergatoids, are described. This species is polygynous, with a mean of 7.0 queens per nest, and forms polycalic colonies. Within nests, ergatoid males fight with each other, leading to the death of all but one in single nests. On the other hand, alate males exhibit no aggressive behavior towards any of their colony members. Both types of males conduct intranidal mating with their sisters, though the alate males also conduct nuptial flights. Many alate females leave their maternal nest even if they have already been inseminated by intranidal mating.

Male competition in Cardiocondyla ants

Abstract The two types of males in the ant genus Cardiocondyla differ remarkably in morphology and behavior. Ergatoid males are wingless fighters whose spermatogenesis continues throughout their entire adult lives and which therefore have an “unlimited” sperm supply. They attempt to kill all eclosing ergatoid rivals and thus to increase their share in copulations with the virgin queens reared in their nests. Winged males, on the other hand, are docile and emigrate from the nests a few days after eclosion, probably to mate with queens from other colonies. By this time, their testes have fully degenerated and all sperm is stored in the seminal vesicles. Before emigration, winged males may mate with virgin queens in their maternal nests, but they are nevertheless rarely attacked by ergatoid males. In the laboratory, the life expectancy of ergatoid males is only slightly higher than that of winged males, but because of the emigration of the latter the difference is likely to be more pronounced in the field. Both male morphs are capable of inseminating more than 35 virgin queens. However, winged males older than 14 days mate less often than ergatoid males of similar age, probably due to sperm depletion in later life. The spermathecae of queens inseminated by ergatoid males contained significantly more sperm than those of queens which mated with winged males. We discuss the evolution of intranidal mating and male polymorphism in ants.

Secondary polygyny by inbred wingless sexuals in the dolichoderine ant Technomyrmex albipes

SummaryTechnomyrmex albipes makes huge polydomous colonies which consist of up to several millions of adults. In field colonies, dealate queens are rare or absent, though winged males and winged females emerge annually (synchronously) in large numbers from late may to mid June. Field and laboratory observations showed that the reproduction of established colonies was performed by wingless females inseminated by wingless males from the same colony. Dissections and morphological examinations revealed that wingless females are workers with no spermatheca and intercastes with a spermatheca. Most intercastes were inseminated, had developed ovaries, and seemed to reproduce, while workers did not seem to reproduce. Extranidal tasks were performed only by workers. Approximately half of the adult population were intercastes, and wingless males represented only a small portion of all adults, the rest being nonreproductive workers. Intercastes and wingless males were produced throughout the year except in winter. The winged females and males copulate outside the nest only after the nuptial flight and the dealate females are able to perform independent founding, but they are also eventually supplanted by intercastes. The adoption of dealate queens by an established natal colony did not seem to occur. Thus we infer that in this species the winged reproductives disperse and found new colonies, while inbred wingless reproductives allow the enlargement and budding of colonies. This species has a special trophic-flow system. There is no trophallaxis among adults, and nutrient transfer from adults to other colony members is achieved exclusively by specialized trophic eggs. All females (dealate queens, intercastes, and workers) seem to produce trophic eggs. This aphid-like life cycle, i.e., the occurrence of both winged and wingless reproductive forms, may have evolved as an adaptation supporting the development of secondary polygyny and polydomy.

Production of females by parthenogenesis in the ant,Cerapachys biroi

SummaryGroups of virginCerapachys biroi workers produced females (workers) in the laboratories. This is the first report of thelytoky in Cerapachyinae.

Colony level sex allocation in a polygynous and polydomous ant

The colony-level sex allocation pattern of eusocial Hymenoptera has attracted much attention in recent studies of evolutionary biology. We conducted a theoretical and empirical study on this subject using the dolichoderine ant Technomyrmex albipes. This ant is unusual in having a dispersal polymorphism in both males and females. New colonies are founded by an alate female after mating with one or more alate males in the nuptial flight. In mature colonies, the reproductive role of the foundress queen is taken over by wingless offspring (supplementary reproductives). Mature colonies are extremely polygynous, with many wingless queens reproducing through intea-colonial mating with wingless males (inbreeding), and producing both alate and wingless sexuals. The population sex ratio of wingless sexuals was found to be extremely female-biased, while the population allocation ratio of alates was almost 1:1. This result suggests that there is local mate competition among wingless sexuals. A specific model for this extraordinary life cycle predicted that the asymmetry of “regression relatedness” (bf/bm) will disappear during the first few generations of wingless reproductives after the foundress dies. If colonies begin to produce alates after several wingless generations, this undermines the hypotheses for intercolonial sex ratio variation based on the relatedness asymmetry. We compared the magnitude of variation in sex ratios and other characteristics between two levels (within-colony-inter-nest and between-colony). Although there was considerable within-colony variation in all the examined characteristics, between-colony variances were always larger. This means that allocation is important at the whole-colony level, not that of the nest. There was no apparent correlation between the sex ratio of alates and colony size. Furthermore, partial correlation analysis indicated that neither the number of workers nor investment in alates explained the variation in the sex ratio of alates. The only factor which was significantly correlated with the sex ratio of alates was the sex ratio of wingless sexuals (a positive correlation). We conclude that both the alate and wingless sex ratios may be influenced by a common primary sex ratio at the egg stage, the variance of which may have genetic components. In the wingless sexuals, partial correlation analysis indicated that colony size and the number of workers explained the sex allocation ratio. The number of wingless females was strongly (positively) correlated with the total investment in wingless sexuals, while the number of males showed no such correlation. There is, however, no convincing explanation for the variation in sex allocation ratio of wingless sexuals, because the estimates of investment in wingless males may have a large sampling error.

Dimorphic ergatoid males and their reproductive behavior in the ponerine antHypoponera bondroiti

SummaryWe studied the reproductive behavior of the ponerine antHypoponera bondroiti from Okinawa, Japan. This species has dimorphic wingless ergatoid males (major and minor), dimorphic reproductive females (alate queens and wingless reproductive intercastes), and workers. Workers have neither ovarioles nor spermatheca. Major ergatoid males are the largest colony members. Two major males fought one another in the nest until one disappeared, leaving the other to occupy the nest chambers where queens emerge and mate. Minor ergatoid males also fought one another, although they seemed to be less pugnacious, resulting in occasional cohabitation of multiple minor males in the same nest chamber. Major males never attacked minor ones, allowing them to coexist in the same nest chamber. Minor males seemed to mimic females. Both major and minor males mated with both alate queens and intercastes within the nest. After mating, some alate queens shed their wings and remained in the nest, while the others left the nest for dispersal in the laboratory. Intercastes remained in the nest.

Spermatogenesis of diploid males in the formicine ant, Lasius sakagamii

Summary: The diploid chromosome number in the female formicine ant, Lasius sakagamii, is 30, while the haploid number in normal males is 15. Six of the 30 studied colonies (20%), however, contained many diploid males. Although the body size of the diploid males was, on average, larger than that of the haploid males, both types of males showed normal external and internal morphologies. Furthermore, there was no reduction in chromosome numbers in either diploid or haploid males during spermatogenesis. The spermatid nuclei of diploid males, however, were significantly larger than those of haploid males, and the amount of DNA in the diploid males, as measured by flow cytometry, was twice as much as that in the haploid males, clearly indicating that diploid males produce diploid sperm.

Mating behavior of dimorphic reproductives of the ponerine ant, Hypoponera nubatama

Summary. Both wingless worker-like queens, and dealated queens of the ponerine ant, Hypoponera nubatama, engage in egg-laying activities. Corresponding to the differentiation in female reproductives, males are also dimorphic, winged and ergatoid. In Japan, wingless reproductives appear mainly from late July to mid-August, while winged ones appear mainly from late August to mid-October. Winged reproductives make nuptial flights, while wingless ones mate inside the nests. Cross-mating is, however, possible in the laboratory. The mating of ergatoid males is characterized by very long precopulation and copulation times, frequently more than 2 hours, suggesting that ergatoid males themselves play the role of mating plug. We observed no fighting among ergatoid males. However, they did seem to cause a relatively higher mortality rate in rival ergatoid males by embracing them while still in the cocoon.

A new type of male dimorphism with ergatoid and short-winged males in Cardiocondyla cf. kagutsuchi

Summary.A new type of ant male dimorphism, consisting of wingless (ergatoid) and short-winged (brachypterous) males, was found in a species of the “Cardiocondyla kagutsuchi”- complex from Malaysia. The ergatoid males show the typical morphological and behavioral characteristics of those of many other Cardiocondyla species. The brachypterous males are morphologically intermediate between ergatoid males and typical winged males of other taxa in this genus. On one hand, they share a number of morphological and behavioral features with ergatoid males that might be adaptations to the loss of flight and intranidal mating: aggressive behavior towards rival males, a prolonged spermatogenesis, which is unique in winged males, paler body coloration, smaller compound eyes, shorter antennal funiculi, more rounded heads – perhaps due to the increased development of mandibular muscles, and an angular pronotum, probably for neck protection. Their short wings appear to protect the petiolar joints during fighting. On the other hand, the brachypterous males have not become as specialized as the ergatoids and to some extent keep the nature of the winged males of other species, i.e., they escape from the nest with a higher probability and with less injuries and do not show a reduction of the ocelli. In the sexual production season, the ergatoid males emerged first in small numbers and then both male morphs emerged in large numbers. The sex ratio was extremely female-biased in the earlier stage of sexual production, probably due to local mate competition.

The caste system of the dolichoderine antTechnomyrmex albipes (Hymenoptera: Formicidae): morphological description of queens, workers and reproductively active intercastes

SummaryFemales ofTechnomyrmex albipes consist of winged queens, intercastes and workers. In established colonies, reproduction is performed by many intercastes (wingless females which have intermediate phenotypes between queen and worker characters). Dissection and morphological examination revealed that intercastes had a spermatheca, but workers did not. Intercastes can be divided into three classes: major intercastes with three ocelli, medium intercastes with one ocellus, and minor intercases without ocelli. Workers have no ocelli. The thoracic structure of intercastes gradually becomes more complex from minors to majors. The body size of intercastes gradually increases from minors to majors, and so does the number of overioles. The body size distributions of minor intercastes and workers overlap considerably, but the distributions of ovariole numbers overlap less. Winged queens had distinctly larger body sizes, more ovarioles and larger spermathecae than intercastes. Most intercastes were inseminated with developed ovaries and appeared to reproduce. The caste system and reproductive division of labour inT. albipes is compared to those of ant species in which permanently wingless females reproduce.