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. 2015 Apr 24;54:e36.
doi: 10.1186/s40555-015-0115-x. eCollection 2015.

Diagnosability and Description of a New Subspecies of Indo-Pacific Humpback Dolphin, Sousa chinensis (Osbeck, 1765), From the Taiwan Strait

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Free PMC article

Diagnosability and Description of a New Subspecies of Indo-Pacific Humpback Dolphin, Sousa chinensis (Osbeck, 1765), From the Taiwan Strait

John Y Wang et al. Zool Stud. .
Free PMC article

Abstract

Background: Subspecies recognition can affect how people (scientists and non-scientists alike) view organisms and thus has important implications for research on, as well as the conservation of, these entities. Recently, a small group of Indo-Pacific humpback dolphins was discovered inhabiting the waters off central western Taiwan. This geographically isolated population possesses pigmentation patterns that are subtly, but noticeably, different from their nearest conspecifics in the neighbouring waters of the Jiulong River Estuary and Pearl River Estuary of mainland China. Due to this population's low and declining numbers and the numerous threats it faces, it was assessed as critically endangered by the Red List of Threatened Species of the International Union for Conservation of Nature. The purpose of this study is to examine the degree of differentiation of the Taiwanese population to determine if subspecies recognition iswarranted.

Results: Analysis of the degree of differentiation in pigmentation patterns revealed nearly non-overlapping distributions between dolphins from Taiwanese waters and those from the Jiulong River + Pearl River estuaries of mainland China (the nearest known populations). The Taiwanese dolphins were clearly diagnosable from those of the Jiulong River + Pearl Riverestuaries under the most commonly accepted '75%rule' for subspecies delimitation (with 94% of one group being separable from 99+% of the other). Evidence of geographical isolation and behavioural differences also provided additional support for the distinctiveness of the Taiwanese dolphins.

Conclusions: Together, the evidence strongly demonstrated that the Taiwanese humpback dolphin population is differentiated at the subspecies level and on an evolutionary trajectory that is independent from that of dolphins from adjacent waters of mainland China (i.e. Jiulong River + Pearl River estuaries). As a result, the taxonomy of Sousa chinensis was revised to include two subspecies: the Taiwanese humpback dolphin, Sousa chinensis taiwanensis subsp. nov., and the Chinese humpback dolphin, Sousa chinensis chinensis (the nominotypical subspecies). These subspecies are described, and the holotype and paratype specimens for S. c. taiwanensis are established.

Keywords: ‘75% rule’; Diagnosability; Humpback dolphin; Indo-Pacific; New subspecies; Sousa chinensis taiwanensis; Taiwanese.

Figures

Fig. 1.
Fig. 1.
Figure 1 Map of the study area. Sampling locations of Indo-Pacific humpback dolphins analysed in this study. The green shaded area represents the known distribution of these dolphins, and the red star and yellow circles show the locations from where the holotype and paratype specimens of the Taiwanese humpback dolphin Sousa chinensis taiwanensis were collected, respectively. Some bathymetric contours in the Taiwan Strait are also shown.
Fig. 2.
Fig. 2.
Figure 2 Scatterplot of spotting intensity on dorsal fins and bodies of Indo-Pacific humpback dolphins. Mean scores of the spotting intensities on the dorsal fins vs. bodies of Indo-Pacific humpback dolphins from the eastern Taiwan Strait (green squares), Pearl River Estuary (yellow squares) and the Jiulong River Estuary (blue circles). Small symbols = 1 to 5 individuals; medium symbols = 6 to 10 individuals; large symbols = >10 individuals.
Fig. 3.
Fig. 3.
Figure 3 Box and whisker plots of canonical scores for Indo-Pacific humpback dolphins. The squares, boxes and whiskers represent means, standard errors and standard deviations, respectively, in (A) and medians, 25 and 75 quartiles and minima-maxima, respectively, in (B). Indo-Pacific humpback dolphins from the Jiulong River Estuary + Pearl River Estuary (JRE + PRE) and Taiwanese waters.
Fig. 4.
Fig. 4.
Figure 4 Frequency distributions of canonical scores of Indo-Pacific humpback dolphins. The distributions for Indo-Pacific humpback dolphins from Taiwanese waters and the Jiulong River Estuary + Pearl River Estuary are shown in green and yellow, respectively. The dotted lines indicate the locations where 75% of the distributions are found.
Fig. 5.
Fig. 5.
Figure 5 Typical Indo-Pacific humpback dolphins with unspotted and spotted bodies. Photographs of Indo-Pacific humpback dolphins from the Pearl River Estuary (A, C) and the eastern Taiwan Strait (B, D). Photographs by J.Y. Wang/FormosaCetus Research and Conservation Group.
Fig. 6.
Fig. 6.
Figure 6 Dorsal views of the calvariae of Sousa chinensis taiwanensis specimens. (A) holotype (NMNS-14812 (=JYW-09-01)) and paratypes (B) NMNS-6366 (=JYW-00-08) and (C) TN-2005-35 (=JYW-05-12). The white thick bars represent 10 cm in each photograph. Photographs by J.Y. Wang/FormosaCetus Research and Conservation Group.

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