̽��ֱ�� of Cambridge - CNRS Centre d’Ecologie Fonctionnelle et Evolutive

Cuttlefish eat less for lunch when they know there’ll be shrimp for dinner

jg533 — Tue, 04 Feb 2020 23:00:59 +0000

When they know that shrimp - their favourite food - will be available in the evening, they eat fewer crabs during the day. This capacity to make decisions based on future expectations reveals complex cognitive abilities.

“It was surprising to see how quickly the cuttlefish adapted their eating behaviour - in only a few days they learned whether there was likely to be shrimp in the evening or not. This is a very complex behaviour and is only possible because they have a sophisticated brain,” said Pauline Billard, a PhD student in the ̽��ֱ�� of Cambridge’s Department of Psychology and Unicaen, France, and first author of the report.

Cuttlefish foraging behaviour can be described as either selective or opportunistic. Observing the European common cuttlefish, Sepia officinalis, when the researchers reliably provided one shrimp every evening, the cuttlefish became more selective during the day and ate significantly fewer crabs. But when they were provided with evening shrimp on a random basis, the cuttlefish became opportunistic and ate more crabs during the day.

Random provision of evening shrimp meant that the cuttlefish could not predict whether their favourite food would be available for dinner each day, so they made sure they had enough to eat earlier in the day. When conditions changed, the cuttlefish changed their foraging strategy to match.

̽��ֱ��researchers saw the animals quickly shift from one eating strategy to another based on their experience. By learning and remembering patterns of food availability, the cuttlefish optimise their foraging activity not only to guarantee they eat enough – but also to make sure they eat more of the foods they prefer. ̽��ֱ��study is published today in the journal Biology Letters.

Cuttlefish eat a wide range of food including crabs, fish and squid, depending on what is available. Despite such a generalised diet, they show strong food preferences. To test this, the researchers tested 29 cuttlefish five times a day, for five days, by putting crab and shrimp at an equal distance from the cuttlefish at the same time and watching what they ate first. All showed a preference for shrimp.

Animals must constantly adapt to changes in their environment in order to survive. Cuttlefish hatch with a large central nervous system, which enables them to learn from a young age. They are capable of remembering things that happened in the past, and using this information to adjust their behaviour in anticipation of the future.

Cuttlefish are a type of cephalopod. In evolutionary terms, cephalopods and vertebrates diverged around 550 million years ago, yet they are remarkably similar in the organisation of their nervous systems.

“This flexible foraging strategy shows that cuttlefish can adapt quickly to changes in their environment using previous experience,” said Professor Nicola Clayton in the ̽��ֱ�� of Cambridge’s Department of Psychology, who led the study. “This discovery could provide a valuable insight into the evolutionary origins of such complex cognitive ability.”

This research was funded by ANR (the French National Research Agency).

Reference
Billard, P. et al: ‘Cuttlefish show flexible and future-dependent foraging cognition.’ Biology Letters, Feb 2020. DOI: 10.1098/rsbl.2019.0743

Cuttlefish can rapidly learn from experience and adapt their eating behaviour accordingly, a new study has shown.

This discovery could provide a valuable insight into the evolutionary origins of a complex cognitive ability

Nicola Clayton

Pauline Billard

Cuttlefish

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Females protect offspring from infanticide by forcing males to compete through sperm instead of violence

fpjl2 — Thu, 13 Nov 2014 19:08:52 +0000

Previous research has shown that infanticide by males is widespread in many mammal species, but most commonly occurs in those species where females live in social groups dominated by one or a few males.

Outsiders will fight dominant males for access to females. When a rival male takes over a group, they will kill the infants of previously dominant males to render the females ‘sexually receptive’ again, so that they can sire their own offspring. This may be the main cause of infant mortality in some species, such as Chacma baboons.

Now, a new study published today in the journal Science shows that these brutal acts are strategic; males may only have a short time in charge before they themselves are deposed, and want to ensure the maternal investment of females is directed towards their own future offspring for the longest time possible.

However, the females of some species - such as the mouse lemur - have evolved a highly-effective counter-strategy to stop males from killing their offspring: by having as many mates as possible in a short amount of time. By confusing the paternity of the infants, known as ‘paternity dilution’, any male act of infanticide risks the possibility of killing his own offspring.

In such species, reproductive competition shifts to after copulation, not before - so that the most successful male is the one whose sperm outcompetes those of the others. This leads to males producing ever larger quantities of sperm, leading in turn to increases in testis size. ̽��ֱ��testes of male mouse lemurs swell 5-10 times larger during the breeding season.

“In species in which infanticide occurs, testis size increases over generations, suggesting that females are more and more promiscuous to confuse paternity,” said lead author Dr Dieter Lukas, from ̽��ֱ�� of Cambridge’s Department of Zoology.

“Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears - since males face the risk of killing their own offspring, and might not get the benefit of siring the next offspring.”

Closely related species that differ in infanticide and testes size include chimpanzees (males commit infanticide) versus bonobos (males have not been observed to kill offspring). Bonobos have testes that are roughly 15% larger than those of chimpanzees.

Male Canadian Townsend voles don’t commit infanticide, and have 50% larger testes compared to infanticidal males of close relatives the North American meadow voles, says Lukas.

He conducted the research with colleague Dr Elise Huchard, who is now based at the CNRS Centre d’Ecologie Fonctionnelle et Evolutive in Montpellier.

Fifty years ago, observations of wild Hanuman langurs shattered previous depictions of monkey groups as peaceful, supportive societies, says Lukas, as new males that had just taken control of a group of females frequently killed all juveniles.

Subsequent observations have accumulated over the years on various mammals to show that infanticide by males is a widespread phenomenon, occurring in species from house mice to lions and gorillas. In some species, he says, the biggest risk faced by infants might not actually be predators or diseases, but the adult males of their own species.

In the latest study, Lukas and Huchard compiled and compared detailed field observations for 260 mammalian species to show that male infanticide occurs in species where sexual conflict is most intense, and reproduction is monopolised by a minority of males. ̽��ֱ��researchers’ findings indicate that infanticide is a manifestation of sexual conflict in mammalian social systems.

“While it had previously been suggested that infanticide might be an evolutionary driver in mammalian societies - leading to females allying themselves with other females or forming bonds with a specific male in order to defend their offspring - we’ve now shown that this isn’t the case: male infanticide is a consequence of variation in sociality, most commonly occurring in species where both sexes live together in stable groups,” said Lukas.

̽��ֱ��researchers say the new study supports the idea that infanticide isn’t a general trait present in all species, but is strategic and occurs only when it is advantageous to males. ̽��ֱ��study reveals the reversible nature of male infanticide, and that it is successfully prevented by the ‘paternity dilution’ strategy of female sexual promiscuity.

Added Huchard: “Male infanticide appears and disappears over evolutionary times according to the state of the evolutionary arms race between the sexes. Although infanticide may not have contributed to shape the diversity of mammalian social systems, it has deeply influenced the evolution of sexual behaviour and sex roles.

“This study also highlights that some of the greatest challenges faced by mammals during their lifetime come from others of their own species.”

Inset images: A male mouse lemur with large testes (credit: Cornelia Kraus). A Chacma baboon with dead infant (credit: Alice Baniel)

Latest research shows the females of some mammal species will have many mates to ensure unclear paternity, so that males can’t resort to killing their rival’s offspring for fear of killing their own. This forces males to evolve to compete through sperm quantity, leading to ever-larger testicles. Scientists find that as testis size increases, infanticide disappears.

Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears

Dieter Lukas

Elise Huchard

Baboon fight

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