Population genetics of Risso’s dolphins (Grampus griseus), Fraser’s dolphins (Lagenodelphis hosei) and bottlenose dolphins (Tursiops spp.) in the North Pacific Ocean

Cetaceans are highly mobile mammals, but many species still exhibit degrees of population structure while inhabiting seemingly boundary-free open waters. Resource specialisation is hypothesized as one of the main drivers of population structure. Using multiple diploid and haploid genetic markers, this study reveals, for the first time, the population genetic structure of Risso’s dolphins, Fraser’s dolphins and common bottlenose dolphins in the tropical-temperate regions of the western North Pacific Ocean. For the Risso’s dolphins, the results showed that there are at least three populations in the North Pacific Ocean, by-and-large parallel to the existing biogeographic provinces; and the direction of gene flow corresponds with the direction of the mainstream currents. Mitochondrial DNA (mtDNA) data showed that the Pacific populations are genetically different from the three populations in the eastern North Atlantic Ocean and the Mediterranean Sea. For the Fraser’s dolphins, the genetic differentiation between Japanese and Philippine waters is consistent with the differentiation suggested in an earlier skull morphometric study. For the common bottlenose dolphins, the results suggested that there are at least four populations in the western and central North Pacific Ocean, and the differentiation appears to correspond to habitat types, resembling the scenario of inshore-offshore differentiation seen in other populations of the same species in other regions. The analysis also confirmed that there is no evident gene flow between the two “sister species”, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin (T. aduncus), occurring sympatrically in the region. The mtDNA data suggested that the Risso’s and Fraser’s dolphin populations in the western North Pacific experienced an episode of expansion in the last 10,000 years. Genetic diversity is high in most of the population examined in this study; however, a relatively low effective population size is found in some populations and that may require further conservation attention

Analysis and comparison of location strategies for reducing registration cost

Abstract. In mobile environments, a personal communication service (PCS) network must keep track of the location of each mobile user in order to correctly deliver calls. A basic scheme used in the standard IS-41 and GSM protocols is to always update the location of a mobile user whenever the mobile user moves to a new location. The problem with this approach is that the cost of location update operations is very high especially when the mobile user moves frequently. In recent years, various location management strategies for reducing the location update cost have been proposed. However, the performance issue of these proposed algorithms remains to be investigated. In this paper, we develop two Markov chains to analyze and compare the performance of two promising location update strategies, i.e., the two location algorithm (TLA) and the forwarding and resetting algorithm (FRA). By utilizing the Markov chain, we are able to quickly answer what-if questions regarding the performance of PCS networks under various workload conditions and also identify conditions under which one strategy can perform better than the others. Using the cost due to location update and search operations between two successive calls to a mobile user as a performance measure, we show that when the mobile user exhibits a high degree of locality and the mobile user’s call-to-mobility ratio (CMR) is low, TLA can significantly outperform both FRA and IS-41. On the other hand, when CMR is high, FRA is the winner. Furthermore, unlike TLA which may perform worse than IS-41 at hig