Whale hormones

The largest mammal on Earth – the whale – has long captured the imaginations of humans. Indigenous North Americans hunted whales for thousands of years, using them for food and fuel, before commercial harvesting began in the early 1600s. The huge demand for products derived from bowhead whales (primarily lamp oil made from blubber, and buggy whips, umbrella ribs, and corset stays made from baleen, the long keratin plates that bowhead whales have instead of teeth) led to a drastic decline in their worldwide population, from 30,000-50,000 individuals before commercial whaling began to 3,000 in 1921, when large-scale hunting was banned.

Today, commercial whaling is still largely banned, but a small number of bowhead whales are taken in subsistence hunts each year.

Despite humanity’s long relationship with bowhead whales, there are some areas in which our basic knowledge of their life history is lacking, including reproduction. Scientists estimate that mature female bowhead whales go about three or four years between having calves. That estimate is largely based on three direct observations – in other words, an extremely small sample size.

Recent research conducted at the New England Aquarium in Boston suggests that a new technique might allow us to further investigate bowhead whale calving rates. A team of scientists analyzed discs of baleen, taken from 16 bowhead whales harvested during subsistence hunts in Alaska, for levels of progesterone, a hormone that can indicate pregnancy.

Because baleen grows longer over time (just as our fingernails do), the tissue closest to the gum line – the most recently grown tissue – reflects recent hormone levels, while tissue further out can serve as a record of the whale’s hormone levels in the past. The research team estimated that baleen from bowhead whales could record hormone levels from as long as 25 years ago, depending on the age and size of the animal.

Of the seven mature female bowhead whales the scientists studied, four were pregnant at the time of harvest and had elevated progesterone levels in their most recently grown baleen. All of the other whales – the non-pregnant females, immature females, and males – had lower levels of progesterone in the same area.

The researchers also found elevated progesterone levels in older sections of baleen from two of the mature females who weren’t pregnant when they were harvested, which suggests that they might have been pregnant in the past. (The researchers analyzed up to four samples from each whale, so they likely missed some baleen sections that might have shown evidence of additional past pregnancies.)

The method isn’t perfect – the scientists point out that baleen can grow at different rates in different individuals, and estimating calving intervals from baleen would require knowing the growth rate of the mother’s baleen. However, given the current scarcity of information on bowhead whale reproduction, analyzing baleen could be a fruitful area of research. It could also help scientists figure out if reproduction rates have changed since historical times, an important question with implications for conservation efforts. As the researchers note, “of particular interest is the availability of historical baleen samples in museum archives (samples collected during the era of commercial whaling) that could be used for comparisons with present-day population data.” 

Though still nowhere near as large as it once was, the bowhead whale population has rebounded since the commercial whaling moratorium in 1921; currently, there are 7,000-10,000 bowhead whales worldwide. Baleen harvest was one of the primary motivations behind the commercial exploitation of whales in the past – perhaps now we can use baleen to inform our conservation efforts, rather than in our umbrellas.

Most research labs don't have a tank large enough for a bowhead whale - adults typically weigh between 150,000 and 200,000 pounds and are 35 to 40 feet long - much less a research budget large enough to feed one, making it difficult to study bowhead whales in a controlled environment. 

(Image by NOAA Photo Library via Wikimedia Commons)

Humming hoards

The whine of a mosquito looking for a blood meal in order to develop her next batch of eggs is a constant accompaniment to summertime activities in much of the world, and all over the United States – scientists have identified over 3,000 different species of mosquitoes, 150 of which have been found in North America.

Different mosquito species have different habitats and different behaviors – some develop in swamps, others in ephemeral ponds; some are capable of transmitting malaria, some aren’t; and some don’t bite humans at all, preferring to get the blood they need for egg production from frogs, snakes, or birds.

Adult mosquitoes don’t hatch directly from eggs – they emerge in water as larvae, which mature into pupae before developing into the winged adults that ascend in humming hoards during warm summer months. Their ability to survive to adulthood is influenced by the conditions they experience early in life, and these conditions, as reported in a paper published earlier this year by a team of researchers at Rutgers University, include the species of the other mosquito larvae around them.

The team of scientists filled cups of water with varying proportions of two types of mosquito larvae, and found that, at higher temperatures, one type (the Asian bush mosquito, typically found in clear, clean water) did not survive to adulthood unless there was a small number of the other type (the southern house mosquito, well known to thrive in polluted water, and even raw sewage) present in the same cup. Left on their own, or with too many southern house mosquito larvae present, the Asian bush mosquitoes died.

The scientists observed that the cups containing only the Asian bush mosquito larvae grew yellow and cloudy with the presence of a population of flagellates – single-celled organisms with whip-like tails – which they suspect was responsible for killing the larvae. They postulate that, in the cups where both mosquito species were present, the southern house mosquito larvae saved the Asian bush mosquito larvae from the flagellate, perhaps by eating the microorganisms – but they also point out that they were a benevolent presence only in small numbers. If the southern house mosquitoes made up more than 50 percent of the mosquito population, they appeared to out-compete the Asian bush mosquitoes, whose survival plummeted. At least in cups in a lab, the presence of just the right number of one species of mosquito allowed another species of mosquito to survive.

These findings suggest that mosquitoes that are able to survive in polluted habitats may, in some cases, change those habitats to the extent that other species can move in, too; the researchers write, “if mosquitoes are capable of increasing the geographic range . . . of other mosquitoes, this could result in the establishment of new diseases or increased transmission efficiency of existing ones, with devastating impacts on native wildlife and humans alike.”

Mosquito larvae are influenced by the conditions in their immediate surroundings, including the species of their neighbors – and those dynamics have important implications for their eventual fate as adults, buzzing in our ears.

Mosquito larvae feed and develop underwater - coming to the surface to breathe - before molting into pupae and eventually emerging as adults. 

(Original image by Mary Hollinger/NOAA Photo Library via Wikimedia Commons)

Mudbugs

 

Every invasive species is a native species somewhere else. Red swamp crayfish, Procambarus clarkii, aka Louisiana crayfish, also known as crawdads, and sometimes called mudbugs, are native to the south-central United States and northeastern Mexico. Everywhere else they’ve spread to – and that’s a lot of places, including Europe, Asia, and many states outside of their native range in the United States – they’re invasive.

Not all non-native species are invasive – non-native species are organisms that don’t naturally occur in a specific place, while those that are non-native as well as destructive in some way are considered invasive. Red swamp crayfish usually fall into the later category – when introduced to a new location, they typically dominate the local habitat, to the detriment of local crayfish populations. 

Red swamp crayfish were first officially detected in Washington State in 2000, in Pine Lake, a tiny lake (just eight tenths of a mile by four tenths of a mile at its widest point) 20 miles east of Seattle. Five years after they were first recorded in Pine Lake, the invasive red swamp crayfish population was much larger than the native crayfish population. (Native crayfish population was not reported in 2008.)

Note: 2008 values were calculated from 24-hour sampling periods, with the assumption that capture rate was equal throughout the 24-hour period - because crayfish are more active at night, the calculated values may be underestimates. 

Sources: First detection in Pine Lake from Mueller 2001; 2005 values from Mueller 2007; 2008 values calculated from Larson & Olden 2008.

(Figure by Emily Benson)

The problems that invasive red swamp crayfish can cause when they spread to a new location are well known, as are the most common mechanisms of introduction. Most red swamp crayfish dispersal is due to human activity – mudbugs are considered a culinary delicacy, and live crayfish have been stocked, farmed, and traded widely throughout the world. There are, however, other ways that crayfish can spread – a study published in Aquatic Ecology earlier this year suggests that ducks and other waterfowl may be a previously unappreciated vector for transporting crayfish between lakes and ponds.

The researchers who conducted the study were interested in whether or not juvenile crayfish could cling to the feathers of a duck as it flew between bodies of water, and, if they could, how long they could hold on for. They found that crayfish are capable of hitching a ride on waterfowl, particularly in shallower water depths. With trained homing pigeons standing in as proxies for ducks, the scientists found that crayfish could survive flights as long as 37 miles in mesh bags secured to the birds.

As the researchers write, “these findings indicate that waterbird-mediated passive dispersal should be taken into account to explain P. clarkii’s rapid spread and should be considered when managing its invasions.” Humans may be responsible for the majority of the spread of this invasive species, but we’re not the only culprits.

Red swamp crayfish are freshwater crustaceans, but they can survive out of water for up to sixteen and a half hours, depending on the temperature and humidity;  Anastácio and colleagues estimate that a crayfish could walk over 700 yards in that time. 

(Image by Entomolo via Wikimedia Commons)

Pea soup

There’s a pond near where I live, a relic from a farm long since given over to forest, that often serves as a convenient turn-around point on walks with my dog. If it’s a hot day, sunlight glittering across the still surface of the water, she’ll rush down the steep mud bank and wallow in the shallows.

This morning, as we climbed the narrow dirt trail up to the edge of the pond and the water came into view, it looked like the pond had been replaced with a vat of pea soup – a bloom of algae had spread across the entire surface.

Annual algal blooms are a common summer phenomenon in many places. Depending on the dominant species of algae and the extent of the bloom, they can be harmless, or they can have extreme consequences – fish die-offs, shellfish bed closures, and drinking water bans, to name just a few.

Though researchers have long known that several factors typically control algal blooms, particularly temperature, light, nutrients, and wind patterns, individual bodies of water often respond to these environmental conditions in idiosyncratic ways. Earlier this year, researchers from the Woods Hole Oceanographic Institution reported the results of several years of monitoring blooms of the dinoflagellate Alexandrium fundyense, a microorganism that produces toxins responsible for paralytic shellfish poisoning, in Nauset Estuary on Cape Cod, Mass.

The scientists found that temperature appeared to be the most important factor controlling algal bloom inception in Nauset – the annual blooms there were triggered by a certain amount of warm weather early in the year, meaning that a warm spring might lead to an early explosion of Alexandrium fundyense, necessitating an earlier-than-usual closure of the shellfish beds in the estuary.

In fact, these conditions occurred during one of the years the scientists were monitoring the estuary – as they reported in their study, “the bloom began in Nauset about 1 month earlier in 2012 than in previous years, so the monitoring program for shellfish toxicity had not begun that year. A rapid response by state officials to sample and subsequently close parts of the estuary to shellfishing occurred on the basis of cell concentrations found in our first large-scale survey that year, but without that population sampling, the early onset might have been missed by routine monitoring.”

The scientists go on to point out that something as simple as regularly measuring the water temperature could help civic leaders anticipate when shellfish bed closures are necessary.

There are no shellfish beds on the bottom of the old farm pond where my dog likes to cool down on summer days, of course, but as we turned back toward home this morning I found myself thinking about how common an occurrence algal blooms are, from the coast of Massachusetts to northern Idaho and many places in between. 

A late summer algal bloom in an old farm pond in northern Idaho.

(Image by Emily Benson)