Oct 222015
 

Original story by Tim Stephens, University of California - Santa Cruz.

Scientists investigating ecological consequences of sexual dimorphism and sex ratio variation in mosquitofish populations found dramatic effects.
Mosquitofish have been introduced worldwide as a means of mosquito control. (Photo by Kevin Simon)

Mosquitofish have been introduced worldwide as a means of mosquito control. (Photo by Kevin Simon)

Female mosquitofish are not only bigger than the males, they have bigger impacts on freshwater ecosystems. In a controlled study conducted in experimental ponds, researchers found dramatic differences in pond ecosystems depending on the ratio of males to females in the mosquitofish populations. In ponds dominated by female fish, the researchers observed more pronounced ecological changes, including fewer zooplankton and a greater abundance of algae, than in male dominated ponds.

Mosquitofish, which are often used to control disease-spreading mosquitos, are probably the most widely introduced freshwater species in the world, according to Eric Palkovacs, assistant professor of ecology and evolutionary biology at UC Santa Cruz. They are also listed among the world's 100 worst invasive species by the International Union for Conservation of Nature.

Mosquitofish are known to have detrimental effects on native freshwater fauna, and in a lot of places there are efforts to control and extirpate them. It's been called the 'plague minnow' in Australia and New Zealand because its effects are so drastic," Palkovacs said.

Palkovacs and graduate student David Fryxell are senior author and first author, respectively, of a paper on the new findings published October 21 in Proceedings of the Royal Society B.

Trophic cascade

Female-biased populations (right) reduced water clarity compared to male-biased populations (left) due to the trophic cascade. (Photo by Eric Palkovacs)

Female-biased populations (right) reduced water clarity compared to male-biased populations (left) due to the trophic cascade. (Photo by Eric Palkovacs)

In addition to eating mosquito larvae, mosquitofish prey on other insect larvae, amphibian larvae, and zooplankton such as Daphnia, tiny crustaceans that graze on algae in freshwater ecosystems. Female mosquitofish prefer larger food items than males, have higher feeding rates, and spend more time foraging in the presence of other females. High levels of predation can ripple through the food web in what ecologists call a "trophic cascade." When mosquitofish consume a lot of Daphnia, the resulting trophic cascade leads to an increase in algae.

"Daphnia are the principle grazers in freshwater ponds, keeping algal populations in check," Palkovacs explained. "We found that female-dominated mosquitofish populations cause much more dramatic trophic cascades. When there are more males, the Daphnia population remains higher and algal abundance is lower."

Other effects seen in female-dominated ponds included increased temperature and pH.

Palkovacs noted that many studies have looked at the evolutionary biology of sexual dimorphism (differences between the sexes in traits such as body size or coloring) and variations in sex ratios (when populations deviate from a one-to-one ratio of males to females). But little attention has been paid to the ecological consequences of these phenomena.

"When males and females of a species differ in traits like body size, they might use different resources or interact with the ecological community in different ways. As a result, the species can shape the ecosystem differently depending on the sex ratio of the population," Palkovacs said.

Control strategies

Sex ratios in natural populations of mosquitofish vary considerably from place to place around the world. Furthermore, several of the methods used or proposed for use in controlling mosquitofish populations can lead to changes in the sex ratio. For example, trapping or netting selectively removes larger fish, so would principally target females. "In this case, removing more females than males is a good thing because females have the biggest effects on the ecosystem," Palkovacs said.

Female mosquitofish (top row) are larger than males and often display a distended abdomen due to pregnancy (mosquitofish are live-bearing fishes). Males are smaller, thinner, and characterized by an elongated gonopodium. (Photo by David Fryxell)

Female mosquitofish (top row) are larger than males and often display a distended abdomen due to pregnancy (mosquitofish are live-bearing fishes). Males are smaller, thinner, and characterized by an elongated gonopodium. (Photo by David Fryxell)

Another strategy has been proposed that would involve genetically manipulating the fish so that females only produce male offspring. "The idea was to reduce the reproductive output of the population. Our research shows that this strategy could be doubly beneficial, leading to smaller populations in the long run while also creating more male-biased populations in the short run with less severe ecological impacts," Palkovacs said.

Beyond its practical implications for mosquitofish management, the study highlights an important phenomenon that may be widespread in nature. "Sexual dimorphism is very common, as is sex ratio variation. It's not just a mosquitofish phenomenon," Palkovacs said.

To conduct the experiment, the researchers set up an array of large stock tanks on a level field at UCSC's Long Marine Laboratory. They added sediment and plankton collected from a nearby pond to establish a small freshwater ecosystem in each tank. Mosquitofish were obtained from a California mosquito vector control district, sorted by sex, and introduced into the tanks at five different sex ratios, plus a fish-free reference treatment.

Bird netting kept out birds and mammals that might prey on the fish, but allowed naturally occurring insects and amphibians to lay eggs in the tanks. In the experiment, amphibians laid eggs in all of the treatments, but larval amphibians (tadpoles) were only found in tanks without mosquitofish.

The detrimental effects of mosquitofish on native biodiversity have been widely studied. Sex ratios may play an important role in this, although additional studies in natural settings will be needed to see what the effects of sex ratio variation are in the wild, "in the midst of all the other natural variation," Palkovacs said.

In addition to Fryxell and Palkovacs, the coauthors of the paper include UCSC graduate student Travis Apgar and Heather Arnett and Michael Kinnison of the University of Maine. This work was funded by the National Science Foundation, UC Santa Cruz, and the Maine Agricultural and Forest Experiment Station.

Oct 092014
 
Rick Shine says the cane toad's evolution is different to

Rick Shine says the cane toad's evolution is different to "the sort of thing (Charles) Darwin talked about". Photo: James Purtill/ABC News

Original story by James Purtill, ABC News

Cane toads in the Northern Territory and Western Australia have evolved "very very rapidly" to hop in a straight line and cover up to six times more ground than distant cousins back in Queensland, scientists say.

Research published in the Proceedings of the Royal Society of London journal shows "a new kind of evolution" and a phenomenon dubbed "spatial sorting", according to the article's co-author and University of Sydney professor Rick Shine.

"The front has accelerated from about 10-15 kilometres per year to about 60 kilometres per year over the time toads have been in Australia," Professor Shine said.

"To move at that rate, toads have to behave in very strange ways - ways that no other frog has before. Continue reading »

Oct 062014
 

Original story at The Guardian

Spiny damselfish study suggests it would take at least several generations for fish to start coping with climate change.
Spiny damselfish, Acanthochromis polyacanthus. Photo: Flickr/creative commons.

Spiny damselfish, Acanthochromis polyacanthus. Photo: Flickr/creative commons.

Rising carbon dioxide levels in oceans adversely change the behaviour of fish through generations, raising the possibility that marine species may never fully adapt to their changed environment, research has found.

The study, published in Nature Climate Change, found that elevated CO2 levels affected fish regardless of whether their parents had also experienced the same environment.

Spiny damselfish were kept in water with different CO2 levels for several months. One level was consistent with the world taking rapid action to cut carbon emissions, while the other was a “business as usual” scenario, in which the current trend in rising emissions would equate to a 3C warming of the oceans by the end of the century.

The offspring of the damselfish were then also kept in these differing conditions, with researchers finding that juveniles of fish from the high CO2 water were no better than their parents in adapting to the conditions. Continue reading »

Sep 162014
 

Original story at ABC News

Three-quarters of the trash found off Australian beaches is plastic, a new study says, warning that the rubbish is entangling and being swallowed by wildlife.
Litter impacts wildlife through entanglement and ingestion, with 43 per cent of seabirds from study discovered with plastic in their gut.

Litter impacts wildlife through entanglement and ingestion, with 43 per cent of seabirds from study discovered with plastic in their gut.

Researchers surveyed the vast Australian coastline at intervals of about 100 kilometres, compiling the world's largest collection of marine debris data, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) said.

"We found about three-quarters of the rubbish along the coast is plastic," CSIRO scientist Denise Hardesty said.

"Most is from Australian sources, not the high seas, with debris concentrated near cities."

The report, part of a three-year marine debris research and education program developed by Earthwatch Australia with CSIRO and energy group Shell, found there were two main drivers of the pollution - littering and illegal dumping.

Rubbish found included glass and plastic bottles, cans, bags, balloons, pieces of rubber, metal and fibreglass, as well as fishing gear and other items lost or discarded in or near the sea.

The report said this marine debris not only posed a navigation hazard but could smother coral reefs, transport invasive species, harm tourism and kill and injure wildlife.

It warned that litter impacted wildlife through entanglement and ingestion, but also indirectly via the chemicals it introduced into marine ecosystems.

Smaller turtle species in particular ingested the debris, possibly because soft, clear plastic resembled its natural prey jellyfish. Continue reading »

Sep 052014
 

Original story by Cell Press via EurekAlert!

Archerfish hunt by shooting jets of water at unsuspecting insects, spiders, or even small lizards on leaves or twigs above, knocking them into the water below before gobbling them up. Now, a study in the Cell Press journal Current Biology on September 4 finds that those fish are much more adaptable and skillful target-shooters than anyone had given them credit for. The fish really do use water as a tool, the researchers say, making them the first known tool-using animal to adaptively change the hydrodynamic properties of a free jet of water. Continue reading »

Aug 292014
 

Original story by Renee Cluff, ABC News

A species of turtle native to the tip of Queensland's Cape York, the Jardine River turtle, has been officially sighted for the first time in 25 years.
Jardine River Turtle or painted turtle found in Cape York. Indigenous rangers and scientists have trapped 24 Jardine River turtles, which were last documented in 1989. Photo: Rick Gardiner

Jardine River Turtle or painted turtle found in Cape York. Indigenous rangers and scientists have trapped 24 Jardine River turtles, which were last documented in 1989. Photo: Rick Gardiner

It was thought the turtle may have been extinct, even though Indigenous locals had unofficially reported some sightings.

But Apudthama rangers and scientists from Origin Energy have trapped 24 Jardine River turtles, which were last documented in 1989.

Peta Standley from the Cape York Natural Resource Management Board said the turtles were found this week in two locations.

"They're a range of sizes and a range of sexes as well, so now the next thing is trying to get some tracking devices on them and work out where they're actually going to, because they think they're nesting at the moment," she said.

Indigenous head ranger Warren Strevens, who was involved in the rediscovery of the rare turtles in the region, said the reptiles were also known as painted turtles.

"They're striking to look at," he said.

"They're a slender turtle, on the side of their heads, especially around the cheek area they've got a bright yellow stripe.

"Then as you go under the throat and down the neck, they've got a red stripe there, and all over their chest plate is a crimson red that's almost fluorescent.

"There's no doubt they're a cute animal."

He said the finds were especially significant for local Aboriginal people.

"They're definitely sacred to one of the clan groups here," he said.

"They've got a storyline about that turtle as well, so there's a lot of significance in this find for the local region."

He said the finds were especially significant for local Aboriginal people.

"They're definitely sacred to one of the clan groups here," he said.

"They've got a storyline about that turtle as well, so there's a lot of significance in this find for the local region."

Aug 232014
 

Original story by  , Science Network WA

NEW research shows the evolution of Australian rainbowfish was most probably caused by geological changes in the region, with the divergence into separate species probably occurring much earlier than previously thought.
The research also suggests rainbowfishes may be older than experts previously thought and provides a new framework for the timing of divergence within the family. Photo: Nathan Rupert

The research also suggests rainbowfishes may be older than experts previously thought and provides a new framework for the timing of divergence within the family. Photo: Nathan Rupert

A joint research initiative between the Western Australian Museum, Brigham Young University, and National Evolutionary Synthesis Center recently finished the most comprehensive phylogenetic analysis of rainbowfishes ever undertaken, which included virtually all rainbowfish species.

The research explored the biogeographic history of rainbowfishes in Australia and New Guinea, to determine how the various species are related to one another and how the geography of the region relates to their evolution.

Dr Peter Unmack says the study shows geography is a key indicator as to whether any two species of rainbowfish are closely related.

“We had collected samples extensively over the years and I began conducting DNA sequencing and gradually built a bigger and bigger data set,” he says.

“The major finding was the importance of geographic distribution, which confirms previous findings but this was a lot more thorough in that we had virtually all of the species included.”

The research also suggests rainbowfishes may be older than experts previously thought and provides a new framework for the timing of divergence within the family.

“The central Highlands of New Guinea have been going up very fast for the past five million years, and researchers previously thought that when the mountain range began to rise, the fish in the north were isolated from the fish in the south,” Dr Unmack says.

“We have shown that rainbow fish actually diverged much earlier than that, perhaps as much as 17-20 million years before the north-south separation. The geology suggests things should be young, but the genetics says things may be older than predicted.

“There was a lot of introgression among the groups.

“Essentially, some of the species within the group have mixed with other species at particular times in the past and then separated, and so have a lingering genetic history that includes the other species they’ve mixed with.

“Species breeding with other species creates gene flow between species, and yet rainbowfishes still maintain themselves as separate entities.”

Researchers also documented 15-20 undescribed species of rainbowfish, with as many as 10 of these occurring in Australia.

“Rainbowfishes are a very important Australian group, one that we consider well studied, and that has been very actively worked on for 25 years, so to discover these undescribed species highlights how much work is still to be done on sorting out the taxonomy of Australian fishes.”