Soldiers' armature changes seasonally and locally in an eusocial aphid (Homoptera : Aphididae)

Size-frequency distribution of social insect castes has been reported to change temporally and spatially, and be influenced by external factors Such as colony size. Here, we show for the first time that the sterile soldiers of eusocial aphids change the size and shape of their armatures, seasonally and locally. Evidence is presented that, in non-soldier individuals, the sizes of armatures were seasonally constant. Two potential mechanisms causing these morphological changes in the soldiers' armatures are discussed in relation to predation pressure on the aphid.ArticleSOCIOBIOLOGY. 52(2):429-436 (2008)journal articl

The adaptation against soldier caste of a eusocial aphid: eggs are not attacked by soldiers in specialist predator Atkinsonia ignipicta (Lepidoptera: Stathmopodidae)

Predators generally have traits that enable them to efficiently capture their prey and thus improve their survival. Natural selection should also favor traits of predators that improve the survival rate of their eggs, which are immobile and incapable of active resistance. We hypothesized that eggs of Atkinsonia ignipicta, a specialist predator of the eusocial aphid Ceratovacuna japonica, exhibit a defensive trait against aphid soldiers. We found that the hatchability of A. ignipicta eggs did not differ significantly between the experimental treatments with and without soldiers, which suggests that the eggs have a defensive trait that protects them from soldier aphids. Moreover, although the soldiers occasionally exhibited attack behavior when they encountered an egg, they did not continue the attack. We have observed a similar interruption of attack behavior by soldiers that attacked their aphid siblings by mistake, suggesting that the eggs may chemically mimic the soldiers' siblings. This study thus provides evidence for adaptation in a specialist predator of a eusocial aphid.ArticleSOCIOBIOLOGY. 59(4):1315-1322 (2012)journal articl

Eggs of a Eusial Aphid’s Predator are Protected Against Attacks by Aphid Soldiers

Predators generally have traits that enable them to efficiently capture their prey and thus improve their survival. Natural selection should also favor traits of predators that improve the survival rate of their eggs, which are immobile and incapable of active resistance. We hypothesized that eggs of Atkinsonia ignipicta, a specialist predator of the eusocial aphid Ceratovacuna japonica, exhibit a defensive trait against aphid soldiers. We found that the hatchability of A. ignipicta eggs did not differ significantly between the experimental treatments with and without soldiers, which suggests that the eggs have a defensive trait that protects them from soldier aphids. Moreover, although the soldiers occasionally exhibited attack behavior when they encountered an egg, they did not continue the attack. We have observed a similar interruption of attack behavior by soldiers that attacked their aphid siblings by mistake, suggesting that the eggs may chemically mimic the soldiers' siblings. This study thus provides evidence for adaptation in a specialist predator of a eusocial aphid.

Some Properties of Multicolored-Branch Graphs

A multicolored-branch graph is such a linear graph that the branches of the graph are partitioned into several sets, and a certain color is assigned to the branches belonging to each of the sets. The assignment is called a coloring. The degree of interference of loops or cutsets in such a graph is deffned to be the minimum number of indenpedent loops or cutsets respectively containing all the colors. The maximum of the degree of interference taken over all the possible colorings is studied. Theorems concerning the colorings to give the maximum in a two-colored-branch graph are derived. Moreover, the maximum of the degree of interference is shown to be equal to the topological degree of freedom and to the maximum distance between a pair of trees in the graph. The degree of interference is also related to the rank of a certain submatrix of the fundamental loop or cutset matrix. An upper bound and a lower bound on the degree of interference in a three-colored-branch graph are given

Photosynthetic physiology and primary productivity of phytoplankton in the Australian sector of the Southern Ocean

第2回極域科学シンポジウム　共通セッション「海氷圏の生物地球化学」 11月16日（水） 統計数理研究所 3階セミナー

Demonstration of pollinator-mediated competition between two native Impatiens species, Impatiens noli-tangere and I. textori (Balsaminaceae)

Plant–plant interspecific competition via pollinators occurs when the flowering seasons of two or more plant species overlap and the pollinator fauna is shared. Negative sexual interactions between species (reproductive interference) through improper heterospecific pollen transfer have recently been reported between native and invasive species demonstrating pollination-driven competition. We focused on two native Impatiens species (I. noli-tangere and I. textori) found in Japan and examined whether pollinator-mediated plant competition occurs between them. We demonstrate that I. noli-tangere and I. textori share the same pollination niche (i.e., flowering season, pollinator fauna, and position of pollen on the pollinator's body). In addition, heterospecific pollen grains were deposited on most stigmas of both I. noli-tangere and I. textori flowers that were situated within 2 m of flowers of the other species resulting in depressed fruit set. Further, by hand-pollination experiments, we show that when as few as 10% of the pollen grains are heterospecific, fruit set is decreased to less than half in both species. These results show that intensive pollinator-mediated competition occurs between I. noli-tangere and I. textori. This study suggests that intensive pollinator-mediated competition occurs in the wild even when interacting species are both native and not invasive.ArticleECOLOGY AND EVOLUTION. 5(6):1271-1277 (2015)journal articl

Positive geographic correlation between soldiers’ weapon size and defensive prowess in a eusocial aphid, Ceratovacuna japonica

Some aphid species produce a soldier caste with enlarged forelegs and horns (weapons). It has been hypothesised that the evolution of morphological specialization by soldiers in social aphids is accelerated by high predation pressure, but this possibility has not been tested. Here, we investigated the relationship between local predator abundance and soldiers\u27 weapon size and aggressiveness in a prey-predator system comprising a eusocial aphid, Ceratovacuna japonica, and its predators (larvae of the butterfly Taraka hamada and of the moth Atkinsonia ignipicta) in two populations with different predator abundances. We found that the soldiers in the predator-abundant population had larger weapons and were more aggressive than those in the population with lower predator abundance. Furthermore, the soldiers\u27 defensive prowess (evaluated as the survival of aphids in the presence of predators) was greater in the predator-abundant population. These results provide the first evidence that a population of eusocial aphids experiencing high predation pressure has soldiers with pronounced defensive traits and defensive prowess

Convulsive Movements in Bilateral Paramedian Thalamic and Midbrain Infarction

Although some previous reports have described convulsive movements in bilateral paramedian thalamic and midbrain infarction, little is known about their nature. A 71-year-old man presented with impaired consciousness and clonic movements of both arms. Each series of movements lasted 10 to 20 s and occurred at 2-to 3-min intervals, which disappeared after intravenous administration of diazepam and phenytoin. Magnetic resonance imaging showed acute bilateral paramedian thalamic and midbrain infarction. A review of the literature revealed that convulsive movements were observed mostly at the onset of infarction. Clonic movements appeared frequently in the limbs, particularly in both arms. Clinical observations and results of animal experiments suggest that these seizures might originate from the mesencephalic reticular formation. Physicians should recognize this condition, because not only seizure control but also early management of ischemic stroke is required

Changes in pollinator fauna affect altitudinal variation of floral size in a bumblebee-pollinated herb

Geographic trait variations are often caused by locally different selection regimes. As a steep environmental cline along altitude strongly influences adaptive traits, mountain ecosystems are ideal for exploring adaptive differentiation over short distances. We investigated altitudinal floral size variation of Campanula punctata var. hondoensis in 12 populations in three mountain regions of central Japan to test whether the altitudinal floral size variation was correlated with the size of the local bumblebee pollinator and to assess whether floral size was selected for by pollinator size. We found apparent geographic variations in pollinator assemblages along altitude, which consequently produced a geographic change in pollinator size. Similarly, we found altitudinal changes in floral size, which proved to be correlated with the local pollinator size, but not with altitude itself. Furthermore, pollen removal from flower styles onto bees (plant's male fitness) was strongly influenced by the size match between flower style length and pollinator mouthpart length. These results strongly suggest that C. punctata floral size is under pollinator-mediated selection and that a geographic mosaic of locally adapted C. punctata exists at fine spatial scale.ArticleECOLOGY AND EVOLUTION. 4(17):3395-3407 (2014)journal articl