Maite Mascaró

Transitions during cephalopod life history: The role of habitat, environment, functional morphology and behaviour

Cephalopod life cycles generally share a set of stages that take place in different habitats and are adapted to specific, though variable, environmental conditions. Throughout the lifespan, individuals undertake a series of brief transitions from one stage to the next. Four transitions were identified: fertilisation of eggs to their release from the female (1), from eggs to paralarvae (2), from paralarvae to subadults (3) and from subadults to adults (4). An analysis of each transition identified that the changes can be radical (i.e. involving a range of morphological, physiological and behavioural phenomena and shifts in habitats) and critical (i.e. depending on environmental conditions essential for cohort survival). This analysis underlines that transitions from eggs to paralarvae (2) and from paralarvae to subadults (3) present major risk of mortality, while changes in the other transitions can have evolutionary significance. This synthesis suggests that more accurate evaluation of the sensitivity of cephalopod populations to environmental variation could be achieved by taking into account the ontogeny of the organisms. The comparison of most described species advocates for studies linking development and ecology in this particular group.

Size-selective foraging behaviour of blue crabs, Callinectes sapidus (Rathbun), when feeding on mobile prey: Active and passive components of predation

Size-selective predation by small (30-50 mm carapace width) and large (90-110 mm) Callinectes sapidus when feeding on three different size classes of Litopenaeus setiferus was investigated. Laboratory experiments using no-choice and multiple-choice designs were carried out. Active and passive components of predation were evaluated by comparing the probability of attacking (active) and capturing (passive) shrimp. Small C. sapidus consumed shrimp of all size classes in similar frequencies during multiple and no-choice experiments, and the probability of attacking and capturing shrimp of all size classes was similar. Large crabs consumed large shrimp with a significantly higher frequency during multiple than during no-choice experiments, and the probability of capturing large shrimp was significantly higher than medium and small ones. Results in the present study suggest that size-specific consumption rates of C. sapidus are mainly the result of a passive mechanism associated with the salience of shrimp to predation. However, an active component of foraging behaviour related to the decision to attack an alternative prey whilst consuming one that has already been captured, helps to explain the differences in shrimp consumption between multiple and no-choice experiments. The complex interaction between active, passive components and satiation is discussed.

The Effect of Copper on the Color of Shrimps: Redder Is Not Always Healthier

The objective of this research is to test the effects of copper on the color of pacific white shrimp (Litopenaeus vannamei) in vivo. Forty-eight shrimps (L. vannamei) were exposed to a low concentration of copper (1 mg/L; experimental treatment) and forty-eight shrimps were used as controls (no copper added to the water). As a result of this experiment, it was found that shrimps with more copper are significantly redder than those designated as controls (hue (500–700 nm): P = 0.0015; red chroma (625–700 nm): P<0.0001). These results indicate that redder color may result from exposure to copper and challenge the commonly held view that highly pigmented shrimps are healthier than pale shrimps.

Thermal biology of prey (Melongena corona bispinosa, Strombus pugilis, Callinectes similis, Libinia dubia) and predators (Ocyurus chrysurus, Centropomus undecimalis) of Octopus maya from the Yucatan Peninsula

On the Yucatan Peninsula there is an upwelling which allows access to a body of cold water that controls temperature in this area. This modulates the ecology and distribution of organisms that inhabit the continental shelf. The objective of this study was to determine the effect of different acclimation temperatures on the thermal biology of prey as mollusc, crustacean (Melongena corona bispinosa, Strombus pugilis, Callinectes similis, Libinia dubia) and predators as fish (Ocyurus chrysurus, Centropomus undecimalis) of Octopus maya. Octopus prey preferred temperatures between 23.5°C and 26.0°C, while predators preferred temperatures 26.4-28.5°C. The species with largest thermal windows were M. corona bispinosa (328.8°C(2)), C. similis (322.8°C(2)), L. dubia (319.2°C(2)), C. undecimalis (288.6°C(2)), O. chrysurus (237.5°C(2)), while the smallest thermal window was for S. pugilis (202.0°C(2)). The acclimation response ratios (ARR) estimated for prey ranged from 0.24-0.55 in animals exposed to CTMax and 0.21-0.65 in those exposed to CTMin. Amongst predators, ARR ranged from 0.30 to 0.60 and 0.41 to 0.53 for animals exposed to CTMax and CTMin, respectively. Correlating the optimal temperature limits of prey and predators with surface temperatures on the continental shelf and those 4m deep showed that the main prey, Callinectes similis and L. dubia, shared a thermal niche and that an increase in temperature could force these species to migrate to other sites to find optimal temperatures for their physiological functions. As a consequence the continental shelf community would undergo a structural change. Predators were found to be near their optimal temperatures in surface temperatures on the continental shelf. We conclude that they would remain in the area in a warming scenario. The size of the thermal window was related to the type of ecosystem inhabited by these species. These ARR intervals allowed us to categorize the species as temperate or tropical, according to the oceanographic conditions that prevail on the Yucatan Peninsula.

Morphological and molecular variability of the sea anemone Phymanthus crucifer (Cnidaria, Anthozoa, Actiniaria, Actinoidea)

The shallow water sea anemone Phymanthus crucifer exhibits three distinct morphotypes, characterized by the presence or absence of protuberances on the marginal tentacles, as well as intermediate forms. The taxonomic status of the different morphotypes and the diagnostic value of protuberances on the tentacles have been debated for this species and the family Phymanthidae. We analysed the external and internal anatomy, cnidae and three mitochondrial molecular markers for representatives of each of the three morphotypes. In addition, we address the putative monophyly of the family Phymanthidae based on molecular data. With the exception of the protuberances, our morphological and molecular results show no differences among the three morphotypes; thus, we consider this feature to be intraspecific variability within P. crucifer . Furthermore, molecular data reveal that the family Phymanthidae is not monophyletic. In addition, we discuss several diagnostic morphological features of the family Phymanthidae.

Chemical Tools of Octopus maya during Crab Predation Are Also Active on Conspecifics.

Octopus maya is a major socio-economic resource from the Yucatán Peninsula in Mexico. In this study we report for the first time the chemical composition of the saliva of O. maya and its effect on natural prey, i.e. the blue crab (Callinectes sapidus), the crown conch snail (Melongena corona bispinosa), as well as conspecifics. Salivary posterior glands were collected from octopus caught by local fishers and extracted with water; this extract paralyzed and predigested crabs when it was injected into the third pereiopod. The water extract was fractionated by membrane ultrafiltration with a molecular weight cut-off of 3kDa leading to a metabolic phase (>3kDa) and a neurotoxic fraction (<3kDa). The neurotoxic fraction injected in the crabs caused paralysis and postural changes. Crabs recovered to their initial condition within two hours, which suggests that the effects of the neurotoxic fraction were reversible. The neurotoxic fraction was also active on O. maya conspecifics, partly paralyzing and sedating them; this suggests that octopus saliva might be used among conspecifics for defense and for reduction of competition. Bioguided separation of the neurotoxic fraction by chromatography led to a paralysis fraction and a relaxing fraction. The paralyzing activity of the saliva was exerted by amino acids, while the relaxing activity was due to the presence of serotonin. Prey-handling studies revealed that O. maya punctures the eye or arthrodial membrane when predating blue crabs and uses the radula to bore through crown conch shells; these differing strategies may help O. maya to reduce the time needed to handle its prey.

Digestive Physiology of Octopus maya and O. mimus: Temporality of Digestion and Assimilation Processes

Digestive physiology is one of the bottlenecks of octopus aquaculture. Although, there are successful experimentally formulated feeds, knowledge of the digestive physiology of cephalopods is fragmented, and focused mainly on Octopus vulgaris. Considering that the digestive physiology could vary in tropical and sub-tropical species through temperature modulations of the digestive dynamics and nutritional requirements of different organisms, the present review was focused on the digestive physiology timing of Octopus maya and Octopus mimus, two promising aquaculture species living in tropical (22–30°C) and sub-tropical (15–24°C) ecosystems, respectively. We provide a detailed description of how soluble and complex nutrients are digested, absorbed, and assimilated in these species, describing the digestive process and providing insight into how the environment can modulate the digestion and final use of nutrients for these and presumably other octopus species. To date, research on these octopus species has demonstrated that soluble protein and other nutrients flow through the digestive tract to the digestive gland in a similar manner in both species. However, differences in the use of nutrients were noted: in O. mimus, lipids were mobilized faster than protein, while in O. maya, the inverse process was observed, suggesting that lipid mobilization in species that live in relatively colder environments occurs differently to those in tropical ecosystems. Those differences are related to the particular adaptations of animals to their habitat, and indicate that this knowledge is important when formulating feed for octopus species.

Effects of Different Prey and Rearing Densities on Growth and Survival of Octopus Maya Hatchlings

The present study aims to determining the isolated and combined effects of stocking and prey densities on growth and survival of Octopus maya hatchlings both at experimental level and in a pilot scale system (8 m2; 2700 L). Octopus survival was not related to prey density. Gained wet weight resulted in a significant interaction between initial stocking density and prey density indicating that octopus growth under low and high density was affected in a different manner depending on the density in which prey were offered. Prey density did not have a significant effect on growth and octopus fed with all three prey densities gained wet weight in a similar way. Results indicate the use of culture densities of 140 octopus m-2, and at least 0.27 g prey octopus-1 d-1 can be used to cultivate octopuses in small tanks. In tanks of 8m2 a higher growth rate was obtained with both 25 and 50 octopus m-2 densities were used. Survival was not affected by stocking density between 25 to 75 octopus m-2.

Health status of post-spawning Octopus maya (Cephalopoda: Octopodidae) females from Yucatan Peninsula, Mexico

The present study aimed to evaluate the health status of Octopus maya females on different days after spawning (days 0, 10, 20, 30, and 40). A total of 25 O. maya females were examined in terms of physiological (i.e., weight loss, hepatosomatic and gonadosomatic indexes, and hemocyanin, protein, glucose, cholesterol, and acylglycerides concentrations in plasma) and immunological variables (i.e., total hemocyte count, hemagglutination, and phenoloxidase activity). We hypothesized that O. maya females should maintain their physiological integrity throughout the post-spawning period until the hatching of the offspring. Results showed that the physiological and immunological indicators measured in post-spawning females significantly changed with time. Loss of body weight over time and a decrease in the hepatosomatic and gonadosomatic indexes were observed. Hemolymph components showed variations that reflect the consumption of reserves and coincide with an increased immune process of hemagglutination and phenoloxidase activity in hemocytes. Our results demonstrate that O. maya females are adapted to maintain an adequate state of health to care for their spawn despite the long period of starvation and contribute to the identification of the mechanisms involved in maintaining the integrity of these animals during one of the most critical phases of their life cycle.

Can preference for crabs in juvenile Octopus maya be modified through early experience with alternative prey

Previous studies on cephalopod feeding have suggested that predetermined preference for certain prey types can be modified by exposing newly hatched individuals to visual or chemical stimuli (imprinting), or by familiarizing them to feed on prey different from those preferred (associative learning). The aim of our study was to determine whether preference to attack crabs in Octopus maya could be modified by early experience with or without food reinforcement using palaemonid shrimp, a prey octopuses consume readily, but will reject if crabs are available. We conducted experiments on the attack response of juvenile octopuses that had been either exposed to (visual and chemical stimuli for at least 48 h before and after hatching) or had fed only on palaemonids (16 days after hatching). Octopuses were then presented with crabs and palaemonids simultaneously and attacks on either prey were recorded. Control treatments, where octopuses had to choose between two similar alternatives (no choice) were included in order to discriminate between active and passive selection. Results were analysed by means of asymmetrical χ2 contingency tables. Both, octopuses that had only been exposed to stimuli from palaemonids and those that fed on shrimp, selectively attacked crabs when first presented with both alternative prey (χ2=6.09 and χ2=5.01, respectively; both p<0.05). These results indicate that preference for crabs in early juvenile O. maya could not be modified through experience with other prey. Because octopuses had never been in contact with crabs prior to trials, such preference was not obtained through their short life experience but could be pre-determined.