Thursday, 28 February 2019 12:41

What Is a Species? Insight From Dolphins and Humans

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More than 70 definitions exist for what makes a species New species of insects, worms and other creepy-crawlers are announced on a monthly basis. Similarly, just last week, two new humpback dolphin species splashed into the headlines. And in October, news broke that early humans may have included fewer species than previously thought. This forces the question: what does it take to be a distinct species?

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Name me! Australian humpback dolphins eagerly await their very own scientific name. Photo by Mendez More than 70 official species definitions exist, of which 48 are widely accepted and used by scientists. And there’s no hard rule that scientists must stick to just one definition; some apply a handful of species definitions when approaching the topic. “I personally go to my lab every day and use five species definitions to conduct research,” says Sergios-Orestis Kolokotronis, a molecular ecologist at Fordham University, and co-author of the new dolphin study, published in Molecular Ecology. “And I sleep just fine amidst this uncertainty.” Species definitions oftentimes do not translate from one organism to another. Dolphins may become isolated by distance and behavior that prevents them from reproducing, but in other cases–such as bacteria, which reproduce asexually–these distinguishing markers do not apply. Thus, the definition of what constitutes a species varies depending on whether scientists are studying dolphins, monkeys, insects, jellyfish, plants, fungi, bacteria, viruses or other organisms, Kolokotronis explains. And likewise, methods for investigating those species also vary. In the case of the four dolphin species, each occupy different sections of ocean around the world, including in the Atlantic off West Africa (Sousa teuszii), in the central to western Indo-Pacific (Sousa plumbea), in the eastern Indian and western Pacific (Sousa chinensis) and in northern Australia (researchers are in the process of working on a name for that one–Sousa bazinga, anyone?).

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Two members of the newly identified Australian dolphin species. Photo by Mendez et. al., Molecular Ecology While the humpback dolphins look quite similar, their genetics tells a different story. Researchers collected 235 tissue samples and 180 skulls throughout the animals’ distribution, representing the biggest dataset assembled to date for the animals. The team analyzed mitochondrial and nuclear DNA from the tissue, which revealed significant variations between those four populations. They also compared the skulls for morphological differences. Although the line between species, sub-species and populations is a blurry one, in this case, the researchers are confident that the four dolphins are divergent enough to warrant the “species” title. The mitochondrial DNA turned up genetic signatures distinct enough to signal a separate species, and likewise, differences in the dolphins skulls supported this divergence. Although the nuclear DNA provided a slightly more confounding picture, it still clearly showed differences between the four species. “We can confidently say that such strong divergence means these populations are demographically and evolutionarily isolated,” says Martin Mendez, a molecular ecologist at the American Museum of Natural History and lead author of the dolphin paper. “The key is that all the evidence–mitochondrial DNA, nuclear DNA and morphology–exhibited concordant patterns of distinct units,” he continues, which are “usually a must for species proposals.” The genetic data the team collected does not have enough resolution to reveal how long ago the humpback dolphins diverged, and the team has yet to examine the drivers that fueled those speciation events. But Mendez and his colleagues have found that, in some dolphin populations, environmental factors such as currents and temperature play a role in separating populations and encouraging speciation. Different behaviors can help reinforce that separation, too. Most likely, however, geographic isolation plays a significant role in this case. “For populations living a couple hundred kilometers from one another, it’s perfectly possible for them to meet,” Mendez says. “But the distance from Africa to Australia is so great, it’s difficult to imagine those populations would ever be linked.” Dolphins, Mendez and his colleagues are finding, evolve relatively quickly once isolated from parent populations. New cryptic–or hidden–species have similarly turned up in waters near South America. There may very well be other species of dolphins–or any type of animal, in fact–lurking undetected within an already-discovered species. ”This really applies to most taxa,” Mendez says. Across the board, “we’re adding many more species by looking at genetic data.” Nonetheless, pondering the speciation of humans in dolphins in light of these two findings raises lots of questions: Are we fractally subdividing genetic information and brain cavity size to group and regroup organisms, or is there vast genetic diversity in even familiar species that we’ve yet to uncover? What does it mean for a species to gain or lose members of its family tree? The world and its organisms await more research. Hermanus Online Website 

White whales, such as the recently spotted humpback nicknamed Migaloo, are rare and elusive creatures. How many are there and why are they white?

First spotted in 1991, he’s been seen more than 50 times since, including a few times around the Great Barrier Reef this summer.

 
Migaloo, the white whale. Photo by Jenny Dean. “Call me Migaloo,” would start the memoir of the most famous white humpback whale out there. He’s not quite from the pages of Moby Dick—Herman Melville’s white whale was a sperm whale and not entirely white—but Migaloo still makes quite a splash when he lifts his head or tail above the waves. Photo by Jenny Dean What do we know about Migaloo? In the past 22 years since whale watchers first spotted the exceedingly social Migaloo—so-called after the Aboriginal word for “white fella”—scientists have been able to learn a bit about him. They think he was around 3-5 years old when first spotted, which makes him 25-27 now. Barring an unfortunate accident, he may have another 50 years ahead of him, although scientists don’t know for sure how long humpback whales live because they don’t have teeth—like tree rings, analyzing concentric layers in teeth is a common way to measure age in mammals. They know he’s a male from his song. While both male and female humpback whales produce sound, only males sing the melodic humpback songs that long ago captured our imaginations. In 1998, researchers first recorded Migaloo singing—and his knack for melody gave it away. His maleness was further confirmed by DNA after researchers from Lismore, Australia’s Southern Cross University, collected skin samples from Migaloo in 2004. Are white humpbacks rare? As far as we know, exceedingly so. Besides Migaloo, there are three other known white humpbacks. Willow lives up in the Arctic and was spotted along the coast of Norway in 2012. Meanwhile, Bahloo lurks in Migaloo’s territory in the Great Barrier reef, first seen in 2008. But these two are not as gregarious as Migaloo, rarely showing their faces. The other known white humpback is a calf first seen swimming around the Great Barrier Reef in 2011. Unofficially named “Migaloo, Jr.,” the calf is not known to be the child of Migaloo—in fact, the two whales may not even be related. If a DNA sample from the calf is obtained someday, they could compare it with Migaloo’s genetic profile to find out. {youtube}http://www.youtube.com/watch?v=PswQUvMCgcM{/youtube} Why is he white anyway? Many articles describe Migaloo and the other white whales as albino. But making that diagnosis is easier said than done. Albinism is a genetic disorder in which the protein tyrosinase, which helps to produce the pigment melanin, is completely absent or damaged by a variety of possible mutations. Fully albino animals and people have no melanin whatsoever; they are white or pink from head to toe, including their eyes. Willow and Bahloo are not albino: they have black spots or patches on their bodies. It’s more likely that they have leucism, a condition where all pigment types are lost in patches of cells. Even though Migaloo is all white, scientists are skeptical that he is albino because he doesn’t have red or pink eyes—like other humpbacks, he has brown eyes. Instead, he’s considered the more conservative “hypo-pigmented,” describing a generic loss of skin color. It’s also possible that Migaloo is leucistic. The Southern Cross University researchers could analyze his DNA for different genetic variants associated with pigment disorders to pinpoint the exact form. But there are many variants and, as Megan Anderson, who originally tested Migaloo’s DNA, said in a press release, “It’s going to be a long and complex process to test for albinism in this humpback whale as it has not ever been done before.” And what about the calf? There isn’t enough known about it to be sure.  

Are there other white whales that aren’t humpbacks? Yes! These skin disorders are not exclusive to humpbacks. There have been several other wild spottings of white whales recently.

Last April, researchers spotted a white killer whale off the coast of Alaska, and they named it “Iceberg.” And a truly albino pink dolphin has been seen around Florida and the Gulf of Mexico repeatedly over the years. In fact, whales aren’t the only creatures that can lack pigment. A plethora of other all-white examples—such as koalas, penguins, and gorillas—can be found throughout the animal kingdom.

 

 

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