Natural hybridization produced dolphin species

A newly published study on the clymene dolphin, a small and sleek marine mammal living in the Atlantic Ocean, shows that this species arose through natural hybridization between two closely related dolphins species, according to authors from the Wildlife Conservation Society, the American Museum of Natural History's Sackler Institute for Comparative Genomics, the University of Lisbon, and other contributing groups.

In a molecular analysis including the closely related spinner and striped dolphins, scientists conclude that the clymene dolphin is the product of natural hybridization, a process that is more common for plants, fishes, and birds, but quite rare in mammals.

The study appears in the online journal PLOS ONE. The authors include: Ana R. Amaral of the University of Lisbon, Portugal, and the American Museum of Natural History; Gretchen Lovewell of the Mote Marine Laboratory; Maria Manuela Coelho of the University of Lisbon; George Amato of the American Museum of Natural History; and Howard Rosenbaum of the Wildlife Conservation Society and American Museum of Natural History.

"Our study represents the first such documented instance of a marine mammal species originating through the hybridization of two other species," said Ana R. Amaral, lead author of the study and research associate at the American Museum of Natural History. "This also provides us with an excellent opportunity to better understand the mechanisms of evolution."

The classification of the clymene dolphin has been a longstanding challenge to taxonomists, who initially considered it to be a subspecies of the spinner dolphin. Then in 1981, thorough morphological analyses established it as a recognized distinct species. In the current study, researchers sought to clarify outstanding questions about the dolphin's origin and relationships with rigorous genetic analyses.

"With its similar physical appearance to the most closely related species, our genetic results now provide the key insights into this species origin" said Dr. Howard Rosenbaum, Director for WCS's Ocean Giants Program and a senior author on the study. "Very little is known about the clymene dolphin, whose scientific name translated from Greek is oceanid, but ironically also can mean fame or notoriety. Hopefully, our work will help draw greater attention to these dolphins in large parts of their range."

Based on research conducted at the American Museum of Natural History's Sackler Institute for Comparative Genomics, the authors examined the nuclear and mitochondrial DNA from skin samples obtained from both free-ranging dolphins by means of biopsy darts and deceased dolphins obtained through stranding events. Using samples from 72 individual dolphins (both clymene dolphins and the closely related spinner and striped dolphins), the researchers amplified one mitochondrial DNA marker and six nuclear DNA markers as a means of analyzing the evolutionary relationship between the clymene dolphin and its closest relatives.

The level of discordance among the nuclear and mitochondrial markers from the three species, the authors assert, is best explained as an instance of natural hybridization. Specifically, the team discovered that while the mitochondrial genome of the clymene dolphin most resembled the striped dolphin, the nuclear genome revealed a closer relation to the spinner dolphin. The authors also noted that continued hybridization may still occur, although at low levels.

The clymene dolphin grows up to nearly seven feet in length and inhabits the tropical and temperate waters of the Atlantic Ocean. Threats to the species include incidental capture as bycatch in fishing nets, which in some parts of the range has turned into direct hunts for either human consumption or shark bait.

The authors thank NOAA Fisheries for funding to initiate this project.

New species of dolphin found in Australian waters

A species of humpback dolphin previously unknown to science is swimming in the waters off northern Australia, according to a team of researchers working for the Wildlife Conservation Society, the American Museum of Natural History, and numerous other groups that contributed to the study.

To determine the number of distinct species in the family of humpback dolphins (animals named for a peculiar hump just below the dorsal fin), the research team examined the evolutionary history of this family of marine mammals using both physical features and genetic data. While the Atlantic humpback dolphin is a recognized species, this work provides the best evidence to date to split the Indo-Pacific humpback dolphin into three species, one of which is completely new to science.

"Based on the findings of our combined morphological and genetic analyses, we can suggest that the humpback dolphin genus includes at least four member species," said Dr. Martin Mendez, Assistant Director of WCS's Latin America and the Caribbean Program and lead author of the study. "This discovery helps our understanding of the evolutionary history of this group and informs conservation policies to help safeguard each of the species."

The authors propose recognition of at least four species in the humpback dolphin family: the Atlantic humpback dolphin (Sousa teuszii), which occurs in the eastern Atlantic off West Africa; the Indo-Pacific humpback dolphin (Sousa plumbea), which ranges from the central to the western Indian Ocean; another species of Indo-Pacific humpback dolphin (Sousa chinensis), which inhabits the eastern Indian and western Pacific Oceans; and a fourth Sousaspecies found off northern Australia yet to be named (the formal adjustment of the naming and number of species occurs through a separate and complementary process based on these findings).

"New information about distinct species across the entire range of humpback dolphins will increase the number of recognized species, and provides the needed scientific evidence for management decisions aimed at protecting their unique genetic diversity and associated important habitats," said Dr. Howard Rosenbaum, Director of WCS's Ocean Giants Program and senior author on the paper.

A new as-of-yet unnamed species of humpback dolphin is shown off the coast of northern Australia.

Working to bring taxonomic clarity to a widespread yet poorly known group of dolphins, the authors assembled a large collection of physical data gathered mostly from beached dolphins and museum specimens. Specifically, the team examined features from 180 skulls covering most of the distribution area of the group in order to compare morphological characters across this region.

The researchers also collected 235 tissue samples from animals in the same areas, stretching from the eastern Atlantic to the western Pacific Oceans, analyzing both mitochondrial and nuclear DNA for significant variations between populations.

The humpback dolphin grows up to 8 feet in length and ranges from dark gray to pink and/or white in color. The species generally inhabits coastal waters, deltas, estuaries, and occurs throughout the Indian and Pacific oceans to the coasts of Australia. The Atlantic humpback dolphin is considered "Vulnerable" according to the IUCN Red List, whereas the Indo-Pacific dolphin species Sousa chinensis is listed as "Near Threatened." Humpback dolphins are threatened by habitat loss and fishing activity.

Dolphin whistle warnings: Remotely monitoring acoustical changes in dolphin whistles may be powerful new tool for conservation

A team of researchers in Italy, Portugal, Spain, France, Britain and the United States has demonstrated that remotely monitoring the acoustical structures of dolphin vocalizations can effectively detect "evolutionarily significant units" of the mammal -- distinct populations that may be tracked for prioritizing and planning conservation efforts.

Two dolphins.

This finding, presented at the 167th meeting of the Acoustical Society of America, to be held May 5-9, 2014, in Providence, Rhode Island, suggests that placing remote acoustical monitoring platforms on ocean buoys and the like may be a viable, low-cost and automated way of monitoring populations of dolphins and rapidly alerting ecologists to the threats that confront them.

"Acoustical changes can be used for constant and continuous monitoring of population belonging to endangered species," said Elena Papale of the University of Torino, who led the research. "We found that [by remotely monitoring dolphin whistles], it is possible to distinguish between evolutionary significant units."

The discovery emerged from a large, multinational collaboration that pulled together data from five research groups based in Italy, Portugal, Spain, Britain and France. Those groups were already monitoring dolphins for a number of existing scientific studies. Other groups in the United States collaborated by providing sound analysis equipment. Shepherding all these groups of people and the flood of data they produced was a challenge, Papale said, but the greater challenge was working out how to distinguish the flood of whistles from one group of dolphins from another.

Animal vocalizations have acoustic characteristics that reflect an organism's genes, its adaptation to ecological conditions and the interactions between their genes and the environment. The differences between groups of dolphins within the same species may be slight and hard to detect however, because morphological features, ecological conditions and socio-behavioral aspects of the creatures influence the structure of whistle. The problem is also a dynamic one, since vocalizations may vary in short time scale.

So at the start of the research, it was not clear whether acoustical analyses alone would be able to tease apart the common threads for given groups of dolphins and differentiate between them.

Papale and her colleagues compared 123 sightings of three dolphin species from the Atlantic Ocean and the Mediterranean Sea (Stenella coeruleoalba, Delphinus delphis and Tursiops truncatus). They analyzed whistles from 49 hours of audio recordings made at the same time as the sightings and tested whether they could definitively identify dolphin populations by analyzing the acoustical parameters of the whistles.

This allowed them to correctly assign more that 82 percent of data to the correct dolphin population, based solely on the acoustic structure, a proof of principle that the acoustic structure of whistles can be used to monitor recent or rapid changes in the local population biology.

"More work is still needed to develop an automatic system for population recognition," Papale said. She added that other research groups are focusing on the development of software but for the moment only for species-specific identification, not intra-specific recognition.