Hiroki Yamagishi

Nest density, genetic structure, and triploid workers in exotic Bombus terrestris populations colonized Japan

A commercialized pollinator introduced from Europe, Bombus terrestris, has colonized Japan. We investigated nest density and genetic structure in two sites based on worker genotypes at 12 microsatellite loci. We confirmed that five workers were triploids using multilocus genotypes and flow cytometry, indicating that queens mated with diploid males and produced triploid workers. The inbreeding coefficient of diploid workers representing individual colonies was significantly positive (FIS = 0.048) in a site where triploids were found. Genetic diversity in the sites was as high as that in native regions in Europe, and genetic differentiation between the sites was low (FST = 0.006). The maximum distance between sampling locations of full-sib worker pairs indicated that the radius of a foraging range was at least 782 m. The estimates of nest density were 31 and 89 km−2 in the two sites, suggesting that the nest density in a colonized region can be higher than that in the native regions.ZusammenfassungDie kommerziell aus Europa eingeführte Bestäuberart Bombus terrestris hat sich inzwischen über ganz Japan verbreitet und beeinflusst dadurch möglicherweise einheimische Bienenund Pflanzenarten. In den Verbreitungsgebieten scheint die genetische Diversität geringer zu sein als in ursprünglichen Regionen, da die Gründerpopulationen meist recht klein sind. Durch Inzucht in kleinen Gründerpopulationen entstehen diploide Männchen, die bei der Paarung triploide Individuen zeugen. Trotz der Inzucht und der verringerten genetischen Variabilität vergrößern wilde Populationen ihr Verbreitungsgebiet und kommen dann teilweise recht häufig vor. Wir untersuchten die Nestdichte und die genetische Struktur bestimmter Genotypen an zwei Untersuchungsstandorten in Nordjapan auf der Basis von 12 Mikrosatelliten-Loci von sammelnden Arbeiterinnen (Abb. 1). Wir bestätigten anhand von Multilocus-Genotypanalysen, dass fünf Arbeiterinnen triploid waren (Abb. 2); deren Königinnen hatten sich vermutlich mit diploiden Männchen verpaart und danach triploide Arbeiterinnen produziert. Die Ergebnisse lassen Inzucht vermuten. Folgerichtig war der Inzuchtkoeffizient von diploiden Arbeiterinnen aus Einzelvölkern signifikant positiv (FIS = 0, 048), wenn an den Standorten triploide Arbeiterinnen gefunden wurden (Tab. II). Die genetische Diversität an diesen Standorten war genauso hoch wie in den Ursprungsregionen in Europa und die genetische Differenzierung zwischen den Standorten war gering (FST = 0, 006; Tab. II). Diese Ergebnisse lassen vermuten, dass diese Wildpopulationen von verschiedenen Linien kommerziell eingeführter Völker abstammen und dass es durch Migration zur Vermischung verschiedener Populationen kam. Die maximale Distanz zwischen Sammelorten von Vollgeschwister-Paaren zeigt, dass der Sammelradius mindestens 782 m beträgt (Abb. 3). Die geschätzte Nestdichte von 31 und 89 km−2 an zwei verschiedenen Standorten (Tab. I) zeigt, dass die Dichte im neuen Verbreitungsgebiet höher sein kann als in den Ursprungsregionen. Unsere Befunde lassen vermuten, dass reduzierte Paarungsmöglichkeiten für die Inzucht in eingeschleppten B. terrestris-Populationen verantwortlich sind.

Reproductive ecology of Viola mirabilis var. subglabra representing intermediate flowering characteristics between stemless and stemmed Viola

Viola (Violaceae) is one of the largest genera in angiosperms. This genus is essentially classified into stemless and stemmed groups based on growth morphology. However, Viola mirabilis var. subglabra is an exception in having intermediate flowering characteristics; cleistogamous (CL) flowers are formed in the axils of stem leaves, whereas chasmogamous (CH) flowers arise from basal rosettes (radical CH (CH(r)) flowers) and also in the axils of the stem (axially CH (CH(a)) flowers). To understand why the pattern of flower production varies in this Viola species, flower production was investigated in 10 Japanese populations from Hokkaido to the western part of Honshu in 2014 and 2015. Furthermore, flower characteristics were also compared between CH(r) and CH(a) flowers in Hokkaido. In this species, the production of CH flowers varied among individuals, and they were categorized into three groups, individuals that produced (i) only CH(r) flowers, (ii) only CH(a) flowers and (iii) both CH flowers. The frequency of these groups differed among populations, but some individuals changed the category between 2014 and 2015. Thus, the production of CH(r) and CH(a) flowers plastically changes depending on individual conditions and/or environmental factors. On the other hand, CH(r) and CH(a) flowers differed in flower size and flowering phenology. These results suggest that two types of CH flowers may play different roles in reproduction in each population, but fruit sets and seed sets did not differ between two types of CH flowers.

Vascular plants from Kunashiri Island, the southernmost island of the Kuril Islands, island arc between Hokkaido and Kamchatka peninsula

Vascular plants of the Kunashiri Island, the southernmost island of the Kuril Islands, were inventoried during an expedition to Kunashiri, 19–25 July 2013. This study was conducted as a part of the Sika Deer ( Cervus nippon yezoensis ) management program in Shiretoko World Natural Heritage Site, to assess vegetation damage under strong browsing pressure by the deer. A checklist of the vascular plants was made from each study locality. As Kunashiri Island is very close to Shiretoko Heritage Site, with similar climatic and geographical conditions, this plant list will provide a preliminary comparison of the floral composition between Kunashiri and Shiretoko or Hokkaido. Our research revealed that vegetation is well preserved on Kunashiri, and this floral list will serve as a reference of the original floral composition of Shiretoko World Natural Heritage Site prior to damage by deer.