Showing papers by "Fuminori Ito published in 2017"

Transcriptome profiling of the spermatheca identifies genes potentially involved in the long-term sperm storage of ant queens.

Abstract: Females of social Hymenoptera only mate at the beginning of their adult lives and produce offspring until their death. In most ant species, queens live for over a decade, indicating that ant queens can store large numbers of spermatozoa throughout their long lives. To reveal the prolonged sperm storage mechanisms, we identified enriched genes in the sperm-storage organ (spermatheca) relative to those in body samples in Crematogaster osakensis queens using the RNA-sequencing method. The genes encoding antioxidant enzymes, proteases, and extracellular matrix-related genes, and novel genes that have no similar sequences in the public databases were identified. We also performed differential expression analyses between the virgin and mated spermathecae or between the spermathecae at 1-week and 1-year after mating, to identify genes altered by the mating status or by the sperm storage period, respectively. Gene Ontology enrichment analyses suggested that antioxidant function is enhanced in the spermatheca at 1-week after mating compared with the virgin spermatheca and the spermatheca at 1-year after mating. In situ hybridization analyses of 128 selected contigs revealed that 12 contigs were particular to the spermatheca. These genes have never been reported in the reproductive organs of insect females, suggesting specialized roles in ant spermatheca.

Worker reproduction of the invasive yellow crazy ant Anoplolepis gracilipes

Abstract: Reproductive division of labor is one of the key features of social insects. Queens are adapted for reproduction while workers are adapted for foraging and colony maintenance. In many species, however, workers retain functional ovaries and can lay unfertilized male eggs or trophic eggs. Here we report for the first time on the occurrence of physogastric workers and apparent worker reproduction in the invasive yellow crazy ant Anoplolepis gracilipes (Fr. Smith). We further examined the reproductive potential and nutritional role of physogastric workers through multidisciplinary approaches including morphological characterization, laboratory manipulation, genetic analysis and behavioral observation. Egg production with two types of eggs, namely reproductive and trophic eggs, by physogastric workers was found. The reproductive egg was confirmed to be haploid and male-destined, suggesting that the workers produced males via arrhenotokous parthenogenesis as no spermatheca was discovered. Detailed observations suggested that larvae were mainly fed with trophic eggs. Along with consumption of trophic eggs by queens and other castes as part of their diet, the vital role of physogastric workers as “trophic specialist” is confirmed. We propose that adaptive advantages derived from worker reproduction for A. gracilipes may include 1) trophic eggs provisioned by physogastric workers likely assist colonies of A. gracilipes in overcoming unfavorable conditions such as paucity of food during critical founding stage; 2) worker-produced males are fertile and thus might offer an inclusive fitness advantage for the doomed orphaned colony.

Social structure of the polygynous ant, Crematogaster osakensis

Abstract: The colony structures of social insects vary greatly among species. In ant societies, the number of queens within a colony is variable during colony maturation. We investigated the social structure of a polygynous ant Crematogaster osakensis in a series of field and laboratory experiments. First, the initial colonies headed by multiple queens were found in the field. In laboratory experiments, queens that were artificially cohabited after their nuptial flight harmoniously co-existed even in the presence of newly emerged workers, suggesting that mated queens of this species can establish their colony cooperatively as primary polygynous colonies. In addition, the mating frequency of a queen was typically more than one, estimated from the sperm number stored in field-collected males and queens, and from genetic relatedness among daughters of lab-reared monogynous colonies. Second, our assessment of genetic relatedness in a mature field colony of this species revealed that dealated queens, as well as workers and alates, were relatives. The number of developed oocytes identified reproductive skew in two of five field-collected nests. Moreover, under laboratory conditions, the most fertile egg layer altered over 3 months of observation. Based on these lines of evidence, we propose that in C. osakensis, polygynous foundresses might either be unrelated and subsequently be replaced by daughter queens of particular foundresses, or be related in the first place.

Discovery of wood nesting by a subterranean halictine bee, Lasioglossum (Evylaeus) vulsum (Hymenoptera: Halictidae): Nesting plasticity of halictine bees

Abstract: An unusual nesting substrate of a subterranean halictine bee, Lasioglossum (Evylaeus) vulsum (Vachal), was found at Mt Ishizuchi‐san, Ehime, Japan. Two nests were obtained from a decaying log in a display sign for a local restaurant. Brood cells, forming a cell cluster, were constructed in a wood hollow with rotted wood fibers pressed together. Nests in the decaying log show the same structural elements as those made in soil. This is the first report of wood nesting by subterranean halictine bees belonging to the subgenus Evylaeus.

Colony composition and behavioral characteristics of Myrmoteras iriodum and M. jaitrongi in Ulu Gombak, Peninsular Malaysia (Hymenoptera: Formicidae)

Abstract: Gesomyrmex (subfamily Formicinae) is a poorly known arboreal ant from the Oriental tropics. We sampled colonies in three localities (NE Thailand, peninsular Malaysia, and Sabah) and examined inhabitants of ten nests inside living branches. None of the nests had a reproductive dealate queen, indicating colonies are polydomous. We distinguished three sterile castes using discrete morphological traits, morphometry and total body size. Observations of behaviour are challenging in tree canopies, and we use functional morphology to predict the specialised functions of different castes. Disproportionately large eyes and piercing mandibles are consistent with workers being agile hunters. Soldiers and supersoldiers share robust mandibles, but the latter have a rectangular head and substantially larger body size, like the queens. This suggests both supersoldiers and queens have the muscular power necessary to chew entrance tunnels in healthy wood. Queens and supersoldiers also share frontal lobes (protection for antennal bases), suggesting that they block nest entrances with their heads. When founding a nest, newly mated queens need to chew an entrance tunnel that reaches the innermost soft pith. Supersoldiers are mostly restricted inside nests where they store nutrients in their gaster, but they may also chew the entrance tunnels of additional nests as the colony expands.

Harvesting fig seeds from bird feces by an Oriental myrmicine ant species, Acanthomyrmex ferox Emery, 1893 (Hymenoptera: Formicidae)

Abstract: Nests of the Oriental endemic genus Acanthomyrmex often contain fig seeds (Moffet 1985). This genus is well known for having remarkably dimorphic worker castes (Moffet 1986), and the soldiers have huge heads that appear to be important for crushing fig seeds (Moffett 1985; Bushinger & Maschwitz 1998). However, no direct observations of seed crushing behavior by soldiers have been reported and, so far, seed-harvesting behavior has not been observed in nature. Acanthomyrmex ferox Emery, 1893 is one of the most common and widespread species in Southeast Asia and has been recorded from Java, Sumatra, Borneo, Peninsular Malaysia and southern Thailand (Moffett 1986). We have been investigating several aspects of the biology of this species in Ulu Gombak, Peninsular Malaysia, since 1992 (Gobin & Ito, 2000, 2003). In this short paper, the seed-foraging behavior of A. ferox workers is reported, based on field observations carried out in the Ulu Gombak field station from 1998 to 2002.All of the foraging workers found by us on the forest floor (N = 100) were minor workers; no foraging soldiers were found. Foraging minor workers were frequently observed in small gapsin the forest, and along the forest edge, where sunshine filtering through the foliage reached the forest floor. In such microhabitats, minor workers walked on accumulated dead leaves, small dead twigs, ground, and leaves of lower vegetation. Nests of this species, which are usually found in small dead twigs and in the accumulation of dead leaves, were also abundant in such microhabitats.In order to reveal the sources of fig seeds, we carefully searched for workers of A. ferox on the trunks of 20 fig trees, and on and around several decayed fig fruits fallen on the forest floor. However, no workers harvesting fig seeds were observed. On the other hand, minor workers harvesting fig seeds were observed on 20 bird feces on the leaves of lower vegetation. These observations suggest that A. ferox workers harvest fig seeds exclusively from bird feces dropped on the ground level (forest floor and lower vegetation). Even though we do not have quantitative data of the distribution of bird feces on the forest floor and lower vegetation, anecdotal observations suggest that feces are more abundant along the forest edge and in the gaps of the forest, perhaps because feces dropped by birds can easily reach the ground level without being intercepted by

The rove beetle Drusilla sparsa (Coleoptera: Staphylinidae) is a myrmecophilous species associated with a myrmicine ant, Crematogaster osakensis (Hymenoptera: Formicidae)

Abstract: The rove beetle genus Drusilla includes some myrmecophilous species. The Japanese species Drusilla sparsa (Sharp, 1874) has been regarded as a non-myrmecophilous beetle. In Kagawa Prefecture, Shikoku Island, western Japan, however, we often observed that D. sparsa adults were walking in the vicinity of foraging workers of the myrmicine ant Crematogaster osakensis Forel, 1990. The body color of the beetle is similar to C. osakensis as in other myrmecophilous beetles found near the trails of the host ants. To examine whether D. sparsa is myrmecophilous, we investigated the distribution of D. sparsa and C. osakensis in the field, as well as their behavior including prey preference of the beetle in the laboratory. Drusilla sparsa beetles were collected only in sites where C. osakensis ants occurred. When the beetles encountered the ant workers, they bent the abdominal tip toward the ants. The ants licked the abdominal tip, and then the beetles usually walked away. Such behavioral reaction of the ants was not observed when the beetles encountered workers of the formicine ant Nylanderia flavipes (Smith, 1874) that continuously attacked the beetles. Drusilla sparsa preferred to feed on dead workers of C. osakensis even when other ants were available as food, indicating that D. sparsa is a myrmecophilous species associated with C. osakensis. Crematogaster osakensis was frequently found in the stomach in the ant predator, the Japanese treefrog Hyla japonica Gunther, 1859. Thus, the significance of body color similarity between the host ants and beetles is not a case of Batesian mimicry.