Please select your home edition
Edition
Selden

Cardinalfish caught sneaking a bit on the side

by coralcoe.org.au 15 Jun 2019 02:32 UTC
Pajama Cardinalfish (Sphaeramia nematoptera) brooding his eggs. Two freshly hatched larvae can be seen swimming near his mouth. © Clive Hamilton

Scientists have revealed the torrid, adulterous love lives of the mouth-brooding cardinalfish, with cuckoldry going hand-in-hand with cannibalism of the young.

"This is a small and unassuming coral reef fish," said Dr Theresa Rueger, who led the study while she was a student at the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

The male fish of this species carries the eggs in his mouth until they are ready to hatch.

"The fish we followed in this study stayed close to each other in pairs for long periods of time, often years," Dr Rueger said.

On the surface, everything seemed to be as expected, with the pairs of fish apparently monogamous and forming larger social groups.

"Looking at the babies they produced, we saw that most of them do exclusively breed with their own partner," Dr Rueger said.

But on closer examination the researchers discovered some sneaky behaviour.

"When presented the chance, both males and females take the opportunity to mate with other individuals from outside the group."

Dr Rueger and her team carefully observed and analysed populations of the mouth-brooding cardinalfish across two years in Papua New Guinea.

Of 105 broods analysed from 64 males, 30% were mothered by a female that was not the partner, about 11% of broods included eggs from two females, and more than 7% of broods were fertilised by two males. These findings are contrary to what the researchers expected to find.

As with most apparently monogamous species who invest time and energy rearing their young, these fish make sacrifices to ensure their babies survive. Paternal care, especially, is associated with a high degree of confidence in paternity.

"Staying faithful and caring for your offspring can be a winning evolutionary strategy," added co-author Dr Hugo Harrison, also from the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

"By caring for the brood, males increase the survival of their offspring but also allow their partner to allocate more energy into producing the next clutch," Dr Harrison said.

"However, it seems that having a bit on the side might not hurt your evolutionary fitness."

"The males can't feed during that time and their swimming ability is compromised, so brooding is very costly," explained Dr Rueger.

"This means the females are in an advantageous position, because they can produce eggs quicker than the male can brood themso they can go and give eggs to another male."

"But the males can offset that advantage by eating some, or all, of the eggs. They can then accept eggs from another female."

Dr Rueger said in some cases, males even fertilise the eggs that another male is brooding. This saves them the energy they would need to brood the eggs themselves.

"What this study shows is a complicated mating system, which is something we didn't expect and could only find out by spending lots of time observing the fish and using genetic analysis to identify parentage," Dr Rueger said.

"Clearly, social interactions don't tell the whole story," added Dr Harrison. "But our parentage tests reveal the complex nature of social groups in fishes and how promiscuity could upturn theories for how monogamy arose."

The paper is out now: Rueger T, Harrison H, Gardiner N, Berumen M, Jones G (2019). Molecular Ecology. 'Extra-pair mating in a socially monogamous and paternal mouthbrooding cardinalfish'. DOI: doi.org/10.5061/dryad.557br15

Related Articles

Heatwaves risky for fish
Some fish are better than others at coping with heatwaves Scientists using sophisticated genetic analysis techniques have found that some fish are better than others at coping with heatwaves. Posted on 27 Mar
Coral disease risk factors revealed
Coral cancers are more common in reefs with fewer fish Researchers have identified key factors that increase the risk of diseases that threaten coral reefs - and their work could one day be used to predict and manage future outbreaks. Posted on 22 Feb
Coralline Algae resists ocean acidification
Coralline algae are vital not only to the survival of coral reefs but many ocean species Scientists say a type of algae crucial to the survival of coral reefs may be able to resist the impacts of ocean acidification caused by climate change. Posted on 25 Jan
Coral study prompts rethink of scientific theory
World-first study is challenging long-held assumptions about role of sunlight in coral biodiversity The research questions a classic theory that predicts coral biodiversity is highest in the shallowest waters where more energy is available in the form of sunlight. Posted on 6 Nov 2019
Clear goals but murky path to sustainability
International sustainability policies set clear goals for protecting ecosystems As biodiversity loss continues at an alarming rate across the globe a new study identifies what is needed to tackle the root causes of the problems. Posted on 6 Nov 2019
New study shows climate change is good investment
Scientists calling on world leaders to urgently accelerate efforts to tackle climate change. Almost every aspect of the environment and ecology is changing in response to global warming. Some of these changes will be profound, if not catastrophic, in the future. Posted on 23 Sep 2019
Actions to save coral reefs
A new, holistic approach to safeguarding coral reefs Scientists say bolder actions to protect coral reefs from the effects of global warming will benefit all ecosystems, including those on land. Posted on 20 Sep 2019
Marine heatwaves a bigger threat to coral reefs
With effects that go beyond coral bleaching New research reveals marine heatwaves are a much bigger threat to coral reefs than previously thought, with effects that go beyond coral bleaching. Posted on 22 Aug 2019
Fussy fish can have their coral, and eat it too
Being a fussy eater is a problem for reef fish Being a fussy eater is a problem for reef fish who seek refuge from climate change on deeper reefs. But, scientists discovered, the coral that these fussy fish eat can support them. Posted on 17 Jul 2019
Climate vulnerability of World Heritage properties
Australian scientists have created a world-first tool Australian scientists have created a world-first tool that can systematically assess climate change risks to all types of World Heritage properties: marine and terrestrial, natural and cultural. Posted on 7 Jul 2019
Sailing Holidays 2019 - BOTTOMNorth Sails 2019 - NSVictoryList - FooterGJW Direct - Yacht 2019 - Footer