Hawaiian monk seals are one of the world’s most endangered marine mammals. Only about 1,600 individuals still exist in the wild. They are threatened from multiple angles. Overhunting has decimated their historic population. Overfishing has threatened their food source. They’re suffering from habitat loss and they’re prime prey for sharks. Even marine debris can ensnare and kill them.
In addition to these threats, there is another danger looming: The seals face an extreme lack of genetic diversity.
“Genetic variation is the raw material for adaptation to changing environments. If you lack genetic variation, you don’t have (new) options available to you as the environment changes,” explained UWM Biological Sciences Professor Emily Latch.
Currently, she said, Hawaiian monk seals have among the lowest levels of genetic variation ever reported.
“So, they are in trouble,” Latch concluded.
Luckily for the seals, Latch and her colleagues stood ready to help.
Latch is the coauthor of a paper titled, “Genomic analysis of population history for Hawaiian monk seals” that was recently published in the journal Endangered Species Research. In it, she and colleagues detailed a new method of analyzing the genomic diversity in monk seal populations. Latch hopes that the research will help conservation experts gain a better picture of how to help the threatened population.
The problem of similar genomes
Hawaiian monk seals are scattered in small colonies throughout the Hawaiian Islands. Any time there are small, isolated populations like these, said Latch, it’s a recipe for genetic erosion. The seals have a limited number of partners to breed with, and over time, the seals have become more and more genetically similar.
“When you try to take a baby seal and (genetically) assign it to a mom, everybody looks like mom – even if the seals are from different islands,” Latch said. In other words, the monk seals’ genomes are so closely related that it’s almost impossible to tell which seal pup was born from which seal mom by looking at their genes, let alone if there is genetic variation across the population.
So, Latch and her colleagues had to find a new method to take a deeper look at the genome.
In genomic testing in other endangered species, scientists will typically look at a few key points scattered throughout the genome in the DNA samples that they have. Those markers will usually vary between individual animals, and give a picture of what genetic variation is like throughout the species’ genome as a whole.
But in monk seals, there is so little variation in those key markers that it is difficult to draw any meaningful conclusions about the genetic variation of the species. Latch and her colleagues needed more data.
“What we’re doing with this approach is really deep sampling within the genome to uncover what variation there is, and pull out every variant that we can possibly find,” she explained. “It’s like sampling in any other way. If you did a phone call survey and only asked five people a question, you might not get a very accurate estimate of what the population thinks. But if you called 5 million people, now you’ve got some power to look at … differences between groups.”
It’s still not enough to tell which seal pup goes with which seal mom – but it is enough to draw conclusions about island-level and regional-level patterns within the populations. For a long time, Latch said, scientists at the National Oceanic and Atmospheric Administration (NOAA) wondered if monk seal populations on the main Hawaiian Islands differed genetically from the ones living in the archipelago’s northwest islands. Now, thanks to this new method of analyzing DNA, scientists can begin to answer those questions.
Conservation through genetics
Using their new method on monk seal DNA samples collected by NOAA, Latch and her colleagues were able to gain a broader picture of the genetic differences between different colonies of seals in various locales throughout Hawaii. That data is critical in protecting the seals.
For instance, Latch said, if one monk seal group shows a bit more genetic diversity than another group, conservation experts might try to initiate a translocation program to transfer some seals from the more diverse group to the more homogenous population in an effort to increase that group’s genetic variances.
“We can help to target conservation efforts toward the populations that are most in need that would benefit the most, and also tailor them to specific threats (the seals face),” Latch said.
Not only that, but they can quantify the amount and patterns of seals’ natural movements between groups. If the seals are naturally visiting different islands and aren’t as isolated as scientists fear, then Latch and her colleagues will be able to tell based on the variations in the genomes.
Monk seals are outside of Latch’s usual wheelhouse; for most of her career, she’s focused on land vertebrates. But monk seals have captured a piece of Latch’s heart, and she wants to help preserve and promote what little genetic diversity there is. To do that, her next project will be to complete whole genome sequences of Hawaiian monk seals to find where in the genome variations occur.
It’s important, she added, because monk seals are an essential part of Hawaii’s delicate ecosystem. If they go extinct, their loss will echo throughout the environment of the islands. Groups like NOAA and other conservation organizations are working to preserve the monk seals through awareness campaigns, educational programming, and other protective measures.
And now, Latch is doing her part, too.
By Sarah Vickery, College of Letters & Science