Category Archives: Ethology

Newly Discovered Squid Pheromone Sparks Extreme Aggression on Contact

Loligo squids approaching and touching the egg capsules, which harbor the contact pheromone that initiates high-level aggression among males. (Credit: Roger Hanlon)

ScienceDaily (Feb. 11, 2011) — Scientists have identified a pheromone produced by female squid that triggers immediate and dramatic fighting in male squid that come into contact with it. The aggression-producing pheromone, believed to be the first of its kind discovered in any marine animal, belongs to a family of proteins found in vertebrates, including humans. Results of the study appear in the February 10th issue of Current Biology.

Male-male aggression is a complex process that involves neural, hormonal, physiological, and psychological stimuli and is widespread in the animal kingdom, where it is associated with the acquisition or retention of shelter and food, and in sexual competition. “The identification of this pheromone as a key component of this signaling system is highly unusual because the male squids need only to come into contact with these protein molecules to initiate the complex cascade of behaviors that we term aggressive fighting,” says Roger Hanlon, senior scientist at the Marine Biological Laboratory (MBL) and study co-author.

Squid are highly advanced marine invertebrates with a complex mating system rivaling that of vertebrates. Most mating and egg laying in the longfin squid (Loligo pealeii), the focus of this study, occurs in the spring when the animals migrate from deep offshore waters to shallower waters along the eastern seaboard, from North Carolina to Maine. Females mate multiple times with multiple males, who compete fiercely for females.

In field studies, the scientists observed a visual attraction by male squid to eggs laid on the sea floor followed by an escalation from calm swimming to the highest level of aggressive fighting — even in the absence of females — when they physically contacted eggs. Seeking to identify what was triggering the behavior, Hanlon and his colleagues, including Scott Cummins of The University of the Sunshine Coast, Australia, Bernard Degnan of Queensland University, Kendra Buresch of the MBL, Jean Boal and Johanna Holm of Millersville University, and Gregg Nagle of the Medical College of Georgia/University of Georgia Medical Partnership, conducted laboratory experiments at the MBL.

They discovered a protein pheromone produced in the female reproductive tract and embedded in the outer surface of eggs. After purifying the pheromone and presenting it to male squid in the lab, they found the same extreme aggressive responses, even when the protein was “painted” translucently on a glass vial that contained squid eggs. “The contact pheromone was incredibly resistant to degradation,” says Nagle. “It appears to remain intact for an extended period of time until the eggs are seen and contacted by male squid.”

“Our lab experiments show that the male squid that touches the eggs first becomes aggressive faster than other males who have not yet touched the eggs,” says Hanlon. “This leads to dominance by the males that encounter the pheromone. Dominant males pair with the females and mate more often, and they gain greater fertilization success so the extremely competitive aggression has a payoff.”

“It was exciting to map an important behavior back to the molecular level,” adds Boal. “The research involved careful teamwork among people with very different backgrounds and skills. It was great to be part of such a far-flung and interesting group of scientists.”

While there are multiple discoveries of pheromones that can elicit aggression in land-based animals, the scientists maintain that this discovery in squid will help them to understand the critical signaling beneath our oceans. “Squid may have revealed a more direct way of stimulating aggression,” says Hanlon. “We doubt that many researchers have thought that contact with molecules in the external world could stimulate such complex and extreme aggressive behavior.”

Interestingly, the protein pheromone found in squid has some similarity with beta-microseminoproteins (ß-MSP), a family of proteins found in humans and other animals. “The functions of ß-MSP in vertebrates have not been determined, but our findings in squids may inspire other researchers to consider similar functions in higher vertebrates,” says Hanlon.

Journal Reference:

  1. Scott F. Cummins, Jean G. Boal, Kendra C. Buresch, Chitraporn Kuanpradit, Prasert Sobhon, Johanna B. Holm, Bernard M. Degnan, Gregg T. Nagle and Roger T. Hanlon. Extreme Aggression in Male Squid Induced by a β-MSP-like Pheromone. Current Biologoy, (in press)


Moonstruck Primates: Owl Monkeys Need Moonlight as Much as a Biological Clock for Nocturnal Activity

This is the Azara owl monkey. (Credit: University of Pennsylvania)

ScienceDaily (Sep. 3, 2010) — An international collaboration led by a University of Pennsylvania anthropologist has shown that environmental factors, like temperature and light, play as much of a role in the activity of traditionally nocturnal monkeys as the circadian rhythm that regulates periods of sleep and wakefulness.

The study also indicates that when the senses relay information on these environmental factors, it can influence daily activity and, in the case of a particular monkey species, may have even produced evolutionary change. It is possible, according to the study results, that changes in sensitivity to specific environmental stimuli may have been an essential key for evolutionary switches between diurnal and nocturnal habits in primates. The study also provides data to better understand all life cycles.

Researchers set out to examine the hypothesis that masking, the chronobiology term for the stimulation or inhibition of activity, was largely caused by changing environmental factors that affected the Azara’s owl monkeys’ internal timing system, or synchronized circadian rhythm. Put simply, changes in temperature and light make Azara’s owl monkeys the only anthropoid primate (monkeys, apes and humans) with a propensity for both early bird and night owl behavior.

The observational nature of field studies has generally limited science’s understanding of the mechanisms responsible for the change in activity patterns of these species, whose behavior traditionally takes place in the dimmest of light. Researchers monitored the activity of these wild owl monkeys continually for as long as 18 months using actimeter collars fitted to them.

The results represent the first long-term study of wild primates providing direct evidence for environmental masking, according to researchers.

The data indicate that, although regular daytime activity is represented by the output of a circadian clock, nocturnality is the result of fine-tuned masking of circadian rhythmicity by environmental light and temperature.

Specifically, date showed that nocturnal activity was more consolidated during the relatively warmer months of September to March than during the colder months of April to August, when temperatures in the Argentine province of Formosa regularly fall below 10ºC. Throughout the year, nocturnal activity was higher during full-moon nights than during new-moon ones, and these peaks of nocturnal activity were consistently followed by mornings of low activity. Conversely, new-moon nights were usually followed by mornings of higher diurnal activity than mornings following full-moon nights.

“The behavioral outcome for these owl monkeys is nocturnal activity maximized during relatively warm, moonlit nights,” said Eduardo Fernández-Duque, lead investigator and an assistant professor in the Department of Anthropology in Penn’s School of Art and Sciences.

“While laboratory studies have pointed to the importance of masking in determining the environmental factors that cause animals to switch from nocturnal activity patterns to diurnal ones or vice versa, our study underscores the importance of masking in determining the daily activity patterns of animals living in the wild. It also suggests that moonlight is a key adaptation for the exploitation of the nocturnal niche by primates,” he said.

Conclusive evidence for the direct masking effect of light was provided when three full lunar eclipses completely shadowed moonlight, coinciding with diminished monkey activity. Temperature also negatively masked locomotor activity, and this masking was manifested even under optimal light conditions.

“If there was a biological clock that they were depending on to regulate this activity, you could expect the activity to continue even in the absence of lunar light,” said Horacio de la Iglesia of the Department of Biology at the University of Washington.

Primates — even humans — conduct their daily tasks in patterns ranging from nocturnality to diurnality, with a few species showing activity both during day and night. Among anthropoids (monkeys, apes and humans), nocturnality is only present in the Central and South American owl monkey genus Aotus. But unlike other tropical Aotus species, the Azara’s owl monkeys (A. azarai) of the subtropics, and this study, have actually switched their activity pattern from strict nocturnality to one that also includes regular daytime activity. The phenomenon led researchers to question the causes of such a behavioral change.

“Harsher climate, food availability and the lack of predators or daytime competition have all been proposed as factors favoring evolutionary switches in primate activity patterns,” Fernández-Duque said.

“The lunar day has not been a stable force as much as the solar day to evolutionarily select for a clock,” de la Iglesia said. “We still have to prove it in the lab, but the evidence in this paper points to a lack of a lunar biological clock.”

The article appears in the current issue of the journal PLoS ONE.

The study was conducted by Fernández-Duque, de la Iglesia and Hans G. Erkert of the University of Tübingen.

The research was funded by the Zoological Society of San Diego, Leakey Foundation, Wenner-Gren Foundation and National Geographic Society. It was authorized by the Ministerio de la Producción, Subsecretaría de Ecología y Recursos Naturales and Dirección de Fauna from Formosa Province.

University of Pennsylvania (2010, September 3). Moonstruck primates: Owl monkeys need moonlight as much as a biological clock for nocturnal activity. ScienceDaily. Retrieved September 6, 2010, from­ /releases/2010/09/100903210414.htm