Flying squids eat particulate organic material and fecal pellets during their early life, although they become voracious predators of crustacean and fishes in the adult stage, like other cephalopods. Flying squids, currently formed by 22 oceanic species, is the most commercially exploited family of cephalopods worldwide. The results of the work, led by CSIC scientists and published in Scientific Reports, could explain the ecological success of this group of squids.
Flying squids eat particulate organic material and fecal pellets during their early life, although they become voracious predators of crustacean and fishes in the adult stage, like other cephalopods. Flying squids, currently formed by 22 oceanic species, is the most commercially exploited family of cephalopods worldwide. The results of the work, led by CSIC scientists and published in Scientific Reports, could explain the ecological success of this group of squids.
Flying squids are one of the most widely distributed and ecologically important family of cephalopods, with a high biomass and economical importance. Although they are only 22 species of the 850 species of cephalopods, every year between 1.6 and 2.4 million tonnes are caught worldwide, representing half of the total captures of cephalopods.
Although the biology of adult flying squids has been widely studied, many fundamental biological aspects of the paralarvae are still a mystery. In cephalopods, the term “paralarvae” is applied due to they do not perform a proper metamorphosis, as larvae of other animals do. The diet of flying squid paralarvae is one of the many unknown aspects of this group during their early life.
Now, scientists of the Spanish Council for Scientific Research (CSIC), with the contribution of the Centro de Investigaciones Biológicas del Noroeste (CIBNOR, CONACYT, Mexico), demonstrate that flying squid paralarvae are detritivores: they feed on particulate organic matter and zooplankton fecal pellets, although then they become voracious predators of crustacean and fishes in posterior stages of their lives. The study has been recently published in the multidisciplinary journal Scientific Reports.
Innovative technique
Roger Villanueva, lead scientist of the study, says they had thought before flying squid paralarvae could have a radically different diet, because “the hatchlings are among the smallest cephalopod paralarvae and their morphology is very different in comparison with other species.” Villanueva is leading a scientific team at the Institute of Marine Sciences (ICM-CSIC).
The study has been done using paralarvae collected on oceanographic cruises both in the Atlantic and Pacific waters and through the ‘DNA metabarcoding´, a method that take advantage of Next-Generation Sequence to produce many copies of a particular molecular marker, which allows the identification of different organisms within a single sample.
DNA metabarcoding has been previously used to study the diet of other animals through the analysis of their gut contents, and in other environmental and ecological studies. However, when it is applied to dietary studies of very small animals, the obtained samples have, in the best case, a 90% or 95% of sequences that come from the tissues of the studied animal and not from its diet.
This, together with the fact that the digestive system of the paralarvae is extremely small, supposed a huge methodological challenge for the scientists.
To overcome this, as the ICM-CSIC scientist and first author of the study Fernando Á. Fernández-Álvarez explains, “we have used laser-capture micro dissection, which made possible to accurately isolate the gut content of the very small paralarvae (1 and 2 mm of total length) and we therefore have critically reduced the contamination of tissues from the paralarvae”.
“Next-Generation Sequencing allow to obtain a lot of information in each sample, which was essential to study the diet of these organisms”, adds Annie Machordom, a CSIC scientist at the National Museum of Natural History (MNCN-CSIC) and co-author of the study.
The DNA analysis demonstrates that the digestive tract has organisms with a continental (insects, plants and freshwater algae) and marine origin, but also fungi associated with organic matter putrefaction and microorganisms usually present in fecal pellets, strongly suggesting that flying squid paralarvae are detritivores.
This is the first time that laser-capture micro dissection and Next Generation Sequencing techniques have been used in combination to study the diet of a tiny animal.
Implications
This work might represent a further step to the experimental culture of the flying squids – until now, all the previous attempts obtained a 100% mortality rate, since paralarvae did not ingest any offered live prey item.
The obtained results are promising, since the combined methodological approach technique developed in the study might be applied to dietary studies of other tiny animals. Besides, it also represents a progress in the scientific knowledge of the early life of flying squids, a cephalopod group with a huge economic and fishery importance. “Since they are detritivores, flying squid paralarvae are devoid of the energetic costs of hunting, while particulate organic matter is an almost ubiquitous and easy-to-catch resource in marine environments. Possibly, this unique feature of the life cycle of flying squids represents an adaptive advantage compared to other cephalopods and this could therefore explain the ecological success of flying squids” considers Fernández-Álvarez.
Reference paper: Fernando Á. Fernández-Álvarez, Annie Machordom, Ricardo García-Jiménez, César A. Salinas-Zavala & Roger Villanueva Predatory flying squids are detritivores during their early planktonic life Scientific Reports volume 8, Article number: 3440 (2018) doi:10.1038/s41598-018-21501-y
Press release: CSIC Catalunya