Group living is a common behavioural feature in many different animal species. It offers a multitude of fitness benefits, such as increased opportunities to find resources, improved predator ...vigilance and potentially even social learning. In cephalopods, social grouping behaviour has mainly been reported for squid species, with up to several thousand individuals displaying different forms of shoaling and even schooling behaviour. Despite being held in groups in captivity, cuttlefish (Cephalopoda: Sepiidae) have long been considered rather asocial animals. However, reports of breeding aggregations and one recent schooling observation from the wild started to bring this characterisation into question. Following this, we here present 10 observations of the European cuttlefish Sepia officinalis (Linnaeus 1758) forming groups of up to 30 individuals along the South Coast of the UK. The majority of the observed cuttlefish appeared to be juveniles or subadults and showed different shoaling orientations, such as linear or spherical‐shaped formations. This indicated the grouping behaviour did not derive from coincidental accumulations. No mating or courtship behaviour could be identified in these groups, and as all observations were made in August or September, and therefore outside their mating season (March to June), it is unlikely that reproductive behaviour motivates these aggregations. As S. officinalis is known to migrate to deeper overwintering grounds in autumn, we propose that cuttlefish may temporarily form groups in late summer/early autumn as part of their migration pattern, and that their shoaling behaviour likely offers similar fitness benefits as in other migrating shoaling species.
Cephalopods of the family Sepiidae, commonly known as cuttlefish, have long been considered asocial. In this study, we report grouping behaviour of the European cuttlefish Sepia officinalis from the South Coast of the UK, with group sizes up to 30 individuals. All observed groups showed distinct shoaling behaviour previously reported for social squid species, such as (a) linear‐shaped formations with all individuals facing one direction expect one cuttlefish potentially acting as a sentinel by facing the other way, and (b) spherical formations with all cuttlefish facing outwards.
Previous research into public perceptions of live prey feeding has been focused on terrestrial animals. The reasons for this likely relate to the difficulty humans have in being compassionate to ...animals who are phylogenetically distantly related. In order to test these assumptions, the general public (two groups; one who had just visited an aquarium; and one group who had just visited a zoo), aquarium professionals in the UK/US and terrestrial zoo animal professionals (UK) were investigated to see how they would differ in their responses when asked about feeding various live aquatic animals to one another. Likert based surveys were used to obtain data face to face and via online social media. Demographics in previous research identified a lower acceptance of live prey feeding by females, however in aquatic animals this was not reflected. Instead, separations in perception were seen to exist between participants dependent on whether they had just visited a zoo or aquarium, or worked with animals.
Amongst cephalopods microplastics have been reported only in jumbo squid gut. We investigated microplastics in the digestive system of wild cuttlefish (Sepia officinalis) as they are predators and ...prey and compared the stomach, caecum/intestine and digestive gland (DG) of wild and cultured animals, exposed to seawater from a comparable source. Fibers were the most common type (≈90% of total count) but were ≈2× higher in relation to body weight in wild vs. cultured animals. Fibers were transported to the DG where the count was ≈2× higher /g in wild (median 1.85 fibers/g) vs. cultured. In wild-caught animals the DG was the predominant location but in cultured animals the fibers were more evenly distributed in the digestive tract. The potential impact of microplastics on health of cuttlefish is discussed. Cuttlefish represent a previously unrecognized source of microplastic trophic transfer to fish and finding fibers in cultured animals has implications for aquaculture.
•Microplastics were found in the digestive tract/digestive gland of wild and cultured cuttlefish.•Fibers were the predominant type (~90% total count) in both wild and cultured cuttlefish.•Plastic fragments, beads and microfilm pieces were also found in animals from both sources.•The fiber count/g digestive gland of wild-caught animals was twice that of the cultured animals.•The potential implications for cuttlefish health, trophic transfer and aquaculture are reviewed.
Balancing selection is important for the maintenance of polymorphism as it can prevent either fixation of one morph through directional selection or genetic drift, or speciation by disruptive ...selection. Polychromatism, the presence of multiple genetically determined colour phenotypes, can be maintained if the fitness of alternative morphs depends on the relative frequency in a population. In aggressive species, negative frequency‐dependent antagonism can prevent an increase in the frequency of rare morphs as they would only benefit from increased fitness while they are rare. Heterospecific aggression is common in nature and has the potential to contribute to rare morph advantage. Here we carry out field observations and laboratory aggression experiments with mbuna cichlids from Lake Malawi, to investigate the role of con‐ and heterospecific aggression in the maintenance of polychromatism and identify benefits to rare morphs which are likely to result from reduced aggression. We hypothesize that rare morph individuals receive less aggression than common morph individuals and therefore have an ecological advantage. Within species we found that males and females bias aggression towards their own morph, adding to the evidence that inherent own‐morph aggression biases can contribute to balancing selection. Over‐representation of rare morph territory owners may be influenced by two factors; higher tolerance of different morph individuals as neighbours, and the ability of rare morphs to spend more time feeding. Reduced aggression to rare morph individuals by heterospecifics may also contribute to rare morph advantage.
The rocky‐shore habitat of Lake Malawi (top) is home to densely‐packed multi‐species communities of highly‐aggressive “mbuna” cichlids (middle). Maylandia callainos is a colour polymorphic species comprised of common blue and rare white morph individuals. Using field observations we identified advantages to being rare: white morph individuals are over‐representation among territory owners (bottom‐left), able to hold territories closer to blue morph males (bottom‐middle), and spend more time feeding (bottom‐right). Laboratory aggression experiments showed an own‐morph aggression bias, which indicates that negative frequency‐dependent antagonism is likely contributing to the balancing selection necessary for the maintenance of polychromatism.
Bobtail squids (Cephalopoda: Sepiolidae) are emerging model organisms for a wide range of genetic, anatomical, neurophysiological and behavioural studies. However, the knowledge about their ...behavioural ecology is scarce and derives mainly from laboratory-based studies, whereas observations from the wild are rare. Here, we use photo and video footage collected through the
Cephalopod Citizen Science Project
to describe the hunting, burying, mating and spawning behaviour of the stout bobtail squid
Rossia macrosoma
(Delle Chiaje, 1830) from Scottish waters. Based on our long-term observations, we were able to determine a spawning period from August to November based on different behavioural traits for this species. Furthermore, we observed
R. macrosoma
to be able to adhere a sand grain layer (‘sand coat’) to its dorsal mantle. This behavioural feature has only been reported for two genera of the sepiolid subfamily Sepiolinae so far, and therefore represents the first of this kind for the subfamily Rossiinae. Lastly, we identified a local sea urchin species as an active predator of egg batches of
R. macrosoma
and discussed the cryptic egg laying behaviour of this bobtail squid species in terms of its protective traits to avoid egg predation.
•The study identified significant preferences for sand as a substrate compared to gravel or a bare tank, and significantly avoided black coloured sand over white or yellow sand.•The experiments ...involving group size showed significant increases in stereotypies with increasing numbers of individuals.•Rays spent more time resting in sand substrate and differed in type of resting in different depths of substrate.
There are few studies investigating captive conditions for commonly kept public aquaria species. Here the thornback ray (Raja clavata) was used to determine preferred captive conditions via choice tests and behavioural observations. Substrate type, substrate colour, substrate depth, group size and refuge use were all used to assess usage, number of stereotypic behaviours and activity in captive born rays. Sand was the preferred choice of substrate which also brought fewer surface breaking behaviours (a possible stereotypic behaviour) compared to gravel or bare tanks. Lighter colours of sand were preferred, as were deeper depths whilst increasing group size increased possible stereotypic behaviours. Type of resting behaviour (horizontal vs vertical) also differed within experiments − rays switched from horizontal to vertical resting, on the side of the tank when using gravelled versus sandy areas of the tank. The rays in this study appeared not to use refuges. Very few published studies have focused on what aquatic animals want, here we use preference tests, which are a useful way of determining what the animal wants, and can help aquarists provide the best conditions for captive thornback rays.
The rocky shore habitats of the African Great Lakes support high densities of cichlid fishes, including many closely related/ecologically similar species. Aggressive behaviours between conspecifics, ...and perhaps heterospecifics, influence this unusually high level of species coexistence. In dichotomous choice aggression trials, male
Maylandia thapsinogen
were presented simultaneously with two heterospecific intruders (
Maylandia emmiltos
and
Maylandia zebra
).
M. thapsinogen
were significantly more aggressive towards intruders from an allopatric species (similar orange dorsal fin colour—
M. emmiltos
), than towards a different allopatric species (blue dorsal fin—
M. zebra
). Aggression biases disappeared when colour differences were masked using monochromatic lighting. A second experiment compared female aggression biases between
M. emmiltos
with
M. thapsinogen
, species similarly coloured to one another, the former possessing a yellow, as opposed to a black throat as the latter does.
M. thapsinogen
preferentially attacked females of their own species in full but not monochromatic light, while female
M. emmiltos
showed no significant bias in aggression under any lighting. Responses were not affected by olfactory cues provided by the stimulus fish. These results indicate that divergence in colour might facilitate species coexistence in some cases, but not all, which could be important should populations rejoin through lake level drops.
In representative species of all vertebrate classes, the oral ejection of upper digestive tract contents by vomiting or regurgitation is used to void food contaminated with toxins or containing ...indigestible material not voidable in the feces. Vomiting or regurgitation has been reported in a number of invertebrate marine species (
Exaiptasia diaphana
,
Cancer productus
, and
Pleurobranchaea californica
), prompting consideration of whether cephalopods have this capability. This “hypothesis and theory” paper reviews four lines of supporting evidence: (1) the mollusk
P. californica
sharing some digestive tract morphological and innervation similarities with
Octopus vulgaris
is able to vomit or regurgitate with the mechanisms well characterized, providing an example of motor program switching; (2) a rationale for vomiting or regurgitation in cephalopods based upon the potential requirement to void indigestible material, which may cause damage and ejection of toxin contaminated food; (3) anecdotal reports (including from the literature) of vomiting- or regurgitation-like behavior in several species of cephalopod (
Sepia officinalis
,
Sepioteuthis sepioidea
,
O. vulgaris
, and
Enteroctopus dofleini
); and (4) anatomical and physiological studies indicating that ejection of gastric/crop contents
via
the buccal cavity is a theoretical possibility by retroperistalsis in the upper digestive tract (esophagus, crop, and stomach). We have not identified any publications refuting our hypothesis, so a balanced review is not possible. Overall, the evidence presented is circumstantial, so experiments adapting current methodology (e.g., research community survey,
in vitro
studies of motility, and analysis of indigestible gut contents and feces) are described to obtain additional evidence to either support or refute our hypothesis. We recognize the possibility that further research may not support the hypothesis; therefore, we consider how cephalopods may protect themselves against ingestion of toxic food by external chemodetection prior to ingestion and digestive gland detoxification post-ingestion. Reviewing the evidence for the hypothesis has identified a number of gaps in knowledge of the anatomy (e.g., the presence of sphincters) and physiology (e.g., the fate of indigestible food residues, pH of digestive secretions, sensory innervation, and digestive gland detoxification mechanisms) of the digestive tract as well as a paucity of recent studies on the role of epithelial chemoreceptors in prey identification and food intake.
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