Kazuo Horikoshi

Diet analysis by next-generation sequencing indicates the frequent consumption of introduced plants by the critically endangered red-headed wood pigeon (Columba janthina nitens) in oceanic island habitats

Oceanic island ecosystems are vulnerable to the introduction of alien species, and they provide a habitat for many endangered species. Knowing the diet of an endangered animal is important for appropriate nature restoration efforts on oceanic islands because introduced species may be a major component of the diets of some endangered species. DNA barcoding techniques together with next-generation sequencing may provide more detailed information on animal diets than other traditional methods. We performed a diet analysis using 48 fecal samples from the critically endangered red-headed wood pigeon that is endemic to the Ogasawara Islands based on chloroplast trnL P6 loop sequences. The frequency of each detected plant taxa was compared with a microhistological analysis of the same sample set. The DNA barcoding approach detected a much larger number of plants than the microhistological analysis. Plants that were difficult to identify by microhistological analysis after being digested in the pigeon stomachs were frequently identified only by DNA barcoding. The results of the barcoding analysis indicated the frequent consumption of introduced species, in addition to several native species, by the red-headed wood pigeon. The rapid eradication of specific introduced species may reduce the food resources available to this endangered bird; thus, balancing eradication efforts with the restoration of native food plants should be considered. Although some technical problems still exist, the trnL approach to next-generation sequencing may contribute to a better understanding of oceanic island ecosystems and their conservation.

Genetic characteristics of the Black-footed Albatross Diomedea nigripes on the Bonin Islands and their implications for the species' demographic history and population structure

Abstract The Black-footed Albatross Diomedea nigripes is an endangered seabird that is endemic to the North Pacific. The genetic structure of Black-footed Albatross populations on three of the Hawaiian Islands and on Izu-Torishima Island, Japan, has been studied previously, using the mitochondrial cytochrome b region. Hawaiian and Japanese breeding groups are genetically different, and the genetic diversity of the birds on Izu-Torishima is lower than that of birds in the Hawaiian Islands. We analyzed 50 Black-footed Albatrosses from the Bonin Islands, where a relatively stable population persisted throughout the twentieth century. Although albatrosses in the Bonin Islands do not differ significantly from those on Izu-Torishima in their cytochrome b region sequences, they do exhibit higher genetic diversity (as high as those from the Hawaiian colonies). A statistical parsimony network revealed two clades, one primarily in the western North Pacific colonies and the other primarily in eastern North Pacific colonies. The total network appears as a dumbbell-shaped phylogeny, suggesting recent population expansion in both populations, although the population breeding in the western North Pacific is only about 5% of the size of that in the eastern North Pacific. Our results suggest that Black-footed Albatrosses in the Bonin and the Hawaiian Islands differ genetically but are comparable natural biological units for conservation and management purposes.

The foraging ranges of Black-footed Albatross Diomedea nigripes breeding in the Bonin Islands, southern Japan, as determined by GPS tracking

ABSTRACT The foraging movements of six Black-footed Albatross Diomedea nigripes (an endangered species) breeding in the Mukojima Islands (a subset of the Bonin Islands) were successfully tracked over a period of two weeks using back-mounted global positioning system (GPS) data loggers (GDBL-II) during the nest-guarding period. Ninety percent of foraging was done over relatively shallow waters within 200 km of the breeding site. The population of this species in the Bonin Islands has not decreased during last ten years, while the area of long-line fishing is likely to overlap with the albatross foraging area around the islands. The effect on population should be assessed carefully.

Bryan's Shearwaters Have Survived on the Bonin Islands, Northwestern Pacific

Abstract. Bryans Shearwater (Puffinus bryani) was described in 2011 on the basis of a specimen collected on the Midway Atoll in 1963. This specimen and another recorded on Midway in the early 1990s are the sole reliable records to date. Since 1997, we have found six specimens of a remarkably small Puffinus shearwater morphologically similar to Bryans Shearwater on the Bonin Islands, northwestern Pacific. In this study, we examined the Bonin samples genetically and confirm that they are of Bryans Shearwater. A morphological analysis suggests that the small body size and relatively long tail are characteristics of this species. Because the most recent individual was found on an islet to the north of Chichijima Island in 2011, the species has evidently survived in the Bonin Islands, where it may breed, although the exact location remains unclear. Three of the individuals found on an islet off Chichijima Island were carcasses preyed upon by black rats (Rattus rattus). Attempts were made to eradicate rats from this island in 2008, and rats may pose a problem on other islands where the shearwaters may breed. Regardless, Bryans Shearwater appears to be very rare and threatened on the Bonin Islands. To conserve this species effectively, its breeding sites must be identified and the infesting rats eradicated.

Limited Overwater Dispersal and Genetic Differentiation of the Snake-Eyed Skink (Cryptoblepharus nigropunctatus) in the Oceanic Ogasawara Islands, Japan

The genetic differentiation and speciation of lizards on oceanic islands may be affected by their rate of overwater dispersal. Cryptoblepharus is one of the most geographically widespread scincid lizards throughout the Indo-Pacific and Australian regions. Cryptoblepharus nigropunctatus is the northernmost species of the genus, dwelling on several small Pacific islands. To examine the colonization history of this lizard, mitochondrial 16S rDNA and D-loop sequences were compared among populations of the Ogasawara Islands consisting of four island groups (the Muko-jima, Chichijima, Haha-jima, and Kazan groups), and an isolated island, Minamitori-shima (Marcus Island). These four groups and Minamitori-shima have not been connected to each other because each is surrounded by deep sea (>100 m). DNA analyses showed that the lizard populations on individual islands had each representative haplotypes. The ancestors of C. nigropunctatus probably arrived on the islands from the southern Pacific Ocean via wave dispersal and differentiated to produce the present state. They appear to have dispersed from their origin along two independent pathways: one between Kitaiwo-to (Kazan group) and the Muko-jima and Chichi-jima groups, and the other among the Minamitori-shima, Minamiiwo-to (Kazan group), and Haha-jima groups. Limited long-distance overwater dispersal may be responsible for the genetic structure of the C. nigropunctatus populations on these oceanic islands. However, among the small islands within the same island group, D-loop haplotypes were shared and the local genetic diversity was usually high, suggesting frequent gene flow across the same group of islands.

Subfossil Land Snail Fauna (Mollusca) of Central Chichijima, Ogasawara Islands, with Description of a New Species.

ABSTRACT The fossil record provides useful information to estimate what island communities were like before human colonization. We examined the species composition of the subfossil land snail fauna of dune deposits at the Yatsuse River, central Chichijima, Ogasawara Islands, and compared it with the species recorded in Chichijima since the nineteenth century. The 22 species in the dune deposits included 13 species that are now extinct in Chichijima. Live specimens of 11 of these extinct species were recorded in the early twentieth century, but no living Mandarna pallasiana and Ogasawarana obtusa Chiba et al., n. sp., have ever been recorded. Age of the sediment, estimated by radiocarbon (14C) dating, was 720 years B.P., and it is possible that these two land snail species became extinct as a result of the impact of human colonization of the island, which started in 1830. Specifically, Ogasawarana obtusa, n. sp., became extinct before the start of taxonomic studies of the land snails of Ogasawara. The sample included Hawaiia minuscula, which is generally now considered a cosmopolitan species introduced from North America. This finding suggests that Hawaiia minuscula is not alien in Ogasawara but indigenous.

Impacts of Predation by the Invasive Black Rat Rattus rattus on the Bulwer's Petrel Bulweria bulwerii in the Bonin Islands, Japan

The black rat Rattus rattus is one of the most invasive alien species in the Bonin Islands and has been recorded on at least 16 of the islands. Higashijima, an uninhabited satellite island of Chichijima, provides breeding sites for thousands of Bulwers petrels ( Bulweria bulwerii), and a massive die-off of this small petrel caused by rat predation was detected there in 2006. In total, 237 adult carcasses and 61 broken eggs were found in small plots totaling 0.035 ha in area during the year; this predation was estimated to have had devastating impacts on the population. Rat eradication was conducted in 2008, and although the petrel population was small, chicks were observed in 2009. The prompt eradication efforts during the early stages of rat predation prevented local extinction of the Bulwers petrel. Broken eggs, a sign of rat predation, have also been found on other islands, and rats have been detected on most islands >2 ha in size. Eradication programs should be promoted on islands that currently support both small petrel populations and introduced rat populations before a crisis occurs.

DNA barcoding reveals seasonal shifts in diet and consumption of deep-sea fishes in wedge-tailed shearwaters

The foraging ecology of pelagic seabirds is difficult to characterize because of their large foraging areas. In the face of this difficulty, DNA metabarcoding may be a useful approach to analyze diet compositions and foraging behaviors. Using this approach, we investigated the diet composition and its seasonal variation of a common seabird species on the Ogasawara Islands, Japan: the wedge-tailed shearwater Ardenna pacifica. We collected fecal samples during the prebreeding (N = 73) and rearing (N = 96) periods. The diet composition of wedge-tailed shearwater was analyzed by Ion Torrent sequencing using two universal polymerase chain reaction primers for the 12S and 16S mitochondrial DNA regions that targeted vertebrates and mollusks, respectively. The results of a BLAST search of obtained sequences detected 31 and 1 vertebrate and mollusk taxa, respectively. The results of the diet composition analysis showed that wedge-tailed shearwaters frequently consumed deep-sea fishes throughout the sampling season, indicating the importance of these fishes as a stable food resource. However, there was a marked seasonal shift in diet, which may reflect seasonal changes in food resource availability and wedge-tailed shearwater foraging behavior. The collected data regarding the shearwater diet may be useful for in situ conservation efforts. Future research that combines DNA metabarcoding with other tools, such as data logging, may provide further insight into the foraging ecology of pelagic seabirds.

Phylogenetic Position of Endangered Puffinus lherminieri bannermani

Abstract Puffinus lherminieri bannermani is a small black-and-white shearwater, which is endemic to the Ogasawara Islands, Japan. The taxonomic position of this shearwater is contentious. It is treated as a subspecies of Audubons Shearwater P. lherminieri or the Tropical Shearwater P. bailloni in some checklists, while it is as considered monotypic, as Bannermans Shearwater P. bannermani, in others. We examined the mitochondrial cytochrome b region to determine the taxons phylogenetic position. While on the one hand the results showed that it was not genetically related to either P. lherminieri or P. bailloni, but formed a clade with P. myrtae, P. newelli, and P. auricularis, on the other hand, bannermani has diverged substantially from the other three taxa in both genetic and morphological features. This shearwater was first described as Bannermans Shearwater, and our results confirm that P. lherminieri bannermani should be split from Audubons Shearwater, and the monotypic Bannermans Shearwater is recommended to be restored as a distinct species.

Small Mass of Rattus norvegicus (Rodentia: Muridae) on the Ogasawara Islands, Japan

Abstract We investigated the cause of extraordinarily small body mass in Norway rats (Rattus norvegicus) living in the Ogasawara (Bonin) Islands in the subtropical climate zone in Japan. We compared body masses of Norway rats living in four localities, the Hahajima group of the Ogasawara Islands, uninhabited islands in Hokkaido in the subarctic climate zone, a business district in Yokohama, and an artificial islet in Tokyo Bay in the temperate climate zone. Regressions of body mass and age (in months; estimated from lens weight) showed that weights of Norway rats on the Hahajima Islands were about half the weights of rats in the other three localities. Crown length of the maxillary molar row was similar in three localities ( Hahajima, Hokkaido, and Yokohama), and both the head — body length and the tail length were similar in Hahajima and Hokkaido, suggesting that the low body mass of the Hahajima rats was due to environmental factors rather than genetic factors. Stomach contents of Norway rats on the Hahajima Islands were predominantly (95.2% by vol.) plant matter, which is not the usual food preference for the species. We hypothesize that a low-protein diet restricts body mass of Norway rats on the Ogasawara Islands.