Fur seal pups and hookworms
In this interview we’re off to Patagonia, where veterinary pathologist Mauricio Seguel explains to Chris Smith how he has discovered that climate change, by forcing their mothers to spend longer at sea foraging, is making fur seal pups much more susceptible to parasitic hookworms...
Mauricio - Fur seals live between land and the ocean; so they find their food in the ocean - mostly fish - but they reproduce on land, so they need a good piece of land where they can mate, give birth, and then take care of those pups for about one year. Usually they stay with a pup for one or two days, and they they go to the ocean to find food, produce more milk during that trip, and then two, three days later they come back to the mainland where they nurse their pup for another one or two days; and then they go back to the ocean to find food again, and again...
Chris - And what was the question you were specifically trying to find out about that life cycle?
Mauricio - So in this population, we saw that there is a significant amount of mortality in the young animals - in the pups - because of a parasite disease - a nematode, like a worm -that lives in the intestines of the pups and it sucks the blood of these animals causing disease and mortality.
Chris - And on what sort of scale do you see mortality because of this?
Mauricio - In some years it could be up to 25 percent of the pups that are born.
Chris - That's a very significant proportion isn't it! Tell us about the lifecycle of the parasite itself. What does it do how does it spread and how does it cause disease.
Mauricio - This is a very unique parasite. The way the parasite reach these pups is only through the milk of their mothers. The very first milk that their mothers give these pups get the larval stages of these worms. These worms goes go to the intestine where they mature and they start releasing eggs; these eggs reach the environment where the larval stages remain for a little bit in the soil, and then these larvae, which are very little, they are worms and can penetrate the skin; then these larvae they just remain in the subcutaneous tissues in the blubber of these animals. But if the animal that got infected through the skin is a female, when this female gets pregnant, these larvae sense somehow that this female is pregnant and they migrate to the mammary gland; and in the mammary gland they migrate through the milk to get transmitted to the pup again.
Chris - So what did you actually do to study how the parasite is imposing a burden on the first population?
Mauricio - The first thing that we did was to measure the mortality and to try to understand, well, what's driving this mortality? So we first saw that there were pups that they were able to fight this infection by creating a very strong immune response against this worm; but we saw that other animals were not able to fight this infection and they ended up dying.
Chris - Is that death owing to the fact that the animals are just susceptible for some reason - genetics for instance - or is there some other reason that they're more susceptible than other animals?
Mauricio - That was one of the main questions of our study and we saw that most of the explanation of why some animals cannot fight infection is driven by the care that they get from their mothers. So the animals that spend more time with their mothers tend to have a better immune response and they can fight these infection better and they survive.
Chris - That sounds logical; but what determines why some of them get more maternal input than others?
Mauricio - So, the mothers can spend more time with their pups when the conditions in the ocean are better. So when the conditions are good and there is a lot of fish in the ocean, these females they can easily find food in the ocean so they return very early to nurse their pups. However, when the conditions and the ocean are not that good and there is less fish and these females cannot find food that easily, they tend to leave their pups alone for a longer period of time.
Chris - So putting that together then, when you've got less plentiful food in the ocean - for a variety of reasons - the mothers are forced to make more frequent and longer forays out fishing to feed themselves. So, therefore, the pups are not getting the same input from their mother in terms of milk and therefore energy. So they're being deprived of food for longer, and that makes them more susceptible to succumbing to the parasite?
Mauricio - Yes, exactly. Additionally, we saw that this link is mostly given by the energy balance of the pup. So these pups that spend more time with their mothers, they potentially receive more milk because they tend to have a better energy balance: they have higher levels of blood sugar, blood fatty acids that are very important for the body of these pups to have enough energy to devote to the immune system.
Chris - Again that's logical isn't it that there should be that relationship; but what are the factors that you refer to that affect how plentiful the fishing is for the females and therefore how long they're forced to spend away from their pups or not?
Mauricio - There is this link between the temperature of the ocean and the flow of nutrients for phytoplankton and zooplankton. So these cycles are driven by temperature mostly, and by winds in the ocean. Basically they dictate what is the productivity, or how much life there is, in certain period of time in a particular zone of the ocean. We saw that in this place where we were doing the study, in the Northern Pacific Patagonia, when the temperature of the ocean is too warm there tends to be lower productivity. So there is lower concentration of, for instance, phytoplankton. We saw that, during these years, the fur seal females spend more time in the ocean trying to find food.
Chris - So, if warmer temperatures mean fewer fish and that means hungry females and therefore hungrier pups, what might be the implications of climate change then?
Mauricio - The implications of climate change are big in this case. So the temperature in the ocean is impacting the health of these first seal pups and their survival. Not directly, because they don't swim; they don't go to the ocean, but through their mothers; their mothers are feeling this effect and, even though it's not killing their mothers, it's affecting how much energy these mothers can transfer to their pups and this affects the chances of survival of these pups...