Aerobic and anaerobic movement energetics of hybrid and pure parental abalone

The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly understood. We used pure blacklip (Haliotis rubra) and greenlip (Haliotis laevigata) abalone, as well as their hybrid, to test whether differences in movement and/or aerobic versus anaerobic energy use are linked to a purported increased growth rate in hybrids. Abalone were acclimated to control (16 °C) and typical summer temperatures (23 °C), each with oxygen treatments of 100% air saturation (O₂sat) or 70% O₂sat. The experiment then consisted of two phases. During the first phase (chronic exposure), movement and oxygen consumption rates (ṀO₂) of abalone were measured during a 2 day observation period at stable acclimation conditions. Additionaly, lactate dehydrogenase (LDH) and tauropine dehydrogenase (TDH) activities were measured. During phase two (acute exposure), O₂sat was raised to 100% for abalone acclimated to 70% O₂sat followed by an acute decrease in oxygen to anoxia for all acclimation groups during which movement and ṀO₂ were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting ṀO₂, LDH and TDH activities, however, were similar between abalone types but were increased at 23 °C compared to 16 °C. During the acute exposure, the initial increase to 100% O₂sat for individuals acclimated to 70% O₂sat resulted in increased movement compared to individuals acclimated to 100% O₂sat for hybrids and H. rubra when compared within type of abalone. Similarly, ṀO₂ during spontaneous activity of all three types of abalone previously subjected to 70% O₂sat increased above those at 100% O₂sat. When oxygen levels had dropped below the critical oxygen level (P_crit), movement in hybrids and H. laevigata increased up to 6.5-fold compared to movement above P_crit. Differences in movement and energy use between hybrids and pure species were not marked enough to support the hypothesis that the purportedly higher growth in hybrids is due to an energetic advantage over pure species.

Nitrate causes deleterious effects on the behaviour and reproduction of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)

Nitrate (NO3 (-)) is present in aquatic ecosystems as a natural component of the nitrogen cycle. However, in the last decades, several human activities are the causes of the rising amounts of organic matter and inorganic nitrogen nutrients in aquatic ecosystems, causing notable increase of nitrate above background natural levels. In spite of the toxicity of nitrate to aquatic animals, there are relatively few studies on the chronic toxicity of this compound to invertebrates. The aim of our study is to assess the effect of chronic (35 days) exposure to nitrate on the behaviour (velocity of movement) and reproduction (number of newborns) of the aquatic snail Potamopyrgus antipodarum. Four actual concentrations of nitrate were used (21.4, 44.9, 81.8 and 156.1 mg N-NO3 (-)/L). In each treatment, 12 animals were individually monitored for velocity (weekly) and newborn production (every 3-4 days). Velocity was recorded using quantitative video monitoring. Our results showed that nitrate did not cause mortality, but it reduced the velocity of movement (at 44.9, 81.8 and 156.1 mg N-NO3 (-)/L) and number of live newborns (in all tested concentrations). Reproductive impairment was caused at realistic nitrate concentrations which is relevant to the risk assessment of this compound. Our study contributes to the knowledge of the chronic effects of nitrate on the behaviour and reproduction of an aquatic snail.

A video-based tracking analysis to assess the chronic toxic effects of fluoride ion on the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)

Short-term lethal bioassays are not suited for assessing the real effects of pollutants in natural ecosystems, as their concentrations are usually unrealistic under an ecological point of view. By contrast, chronic bioassays are more realistic for assessing effects on aquatic animals, especially when behavioural endpoints are used. These endpoints are a good link between physiological and ecological effects. Among behavioural bioassays, those based on automated image analysis following video-recording have the advantage of being quantitative and non-subjective tests. The present study focuses on the assessment of chronic (63 days) effects of fluoride ion (F⁻) on the survival, proportion of affected animals (dead plus immobile animals) and several behavioural endpoints (monitored by video-recording and image analysis system) of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca). The bioassay consisted of one control and three actual fluoride concentrations (4.68, 18.6, and 37.1 mg F⁻/L) with 12 replicates in each treatment. The endpoints were monitored every 7 day of continuous exposure to fluoride ion. The highest fluoride concentrations killed all animals at the end of the bioassay. By contrast no animals died in the lowest fluoride treatment, but snails showed several alterations of behaviour: increase heterogeneity of velocity among successive recording periods, increase of the time to escape from a marked circle, and reduction of the heterogeneity in the utilization of space. Therefore, most of the behavioural endpoints were sensitive to environmentally realistic non-lethal fluoride concentrations, being useful parameters for ecological risk assessment. The ecological relevance of these findings is discussed.

Subchronic toxic effects of fluoride ion on the survival and behaviour of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)

Short-term bioassays usually assess lethal effects of pollutants in animals, whereas subchronic bioassays are more suited for assessing effects on animal behaviour. Among them, videotaped bioassays are an improvement in the behavioural monitoring because they are easily and cheaply implemented. The present study focuses on the assessment of subchronic (14-day) effects of fluoride ion on the survival, proportion of dead plus immobile animals, and velocity (monitored by a videotaping and image analysis system) of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca). One control and three nominal fluoride concentrations (5, 20, and 40 mg F(-)/l [actual mean concentrations of 5.2, 17.5, and 37.0 mg F(-)/l, respectively]) were used. Each treatment (including the control) was replicated 12 times. Mortality, number of dead plus immobile animals, and velocity were monitored after 0, 7, and 14 days of exposure. After 14 days, animals exposed to 40 mg F(-)/l showed higher mortality, number of dead, and immobile individuals than control animals. Snails exposed to 5 and 20 mg F(-)/l were not affected by fluoride ion regarding these endpoints. In contrast, snails exposed to 20 mg F(-)/l for 7 and 14 days showed lower velocity than control animals. Therefore, velocity was sensitive to environmental fluoride concentrations and as such is a useful parameter for ecologic risk assessment. In addition, videotaping allowed us to detect behavioural patrons in velocity at very short exposures (seconds) during the monitoring process by showing that the velocity of snails must be monitored at least during the course of several minutes. We conclude that in P. antipodarum, velocity is a more sensitive endpoint than the classic mortality and immobility endpoints.