Mothers adjust egg size to helper number in a cooperatively breeding cichlid

Mothers should adjust the size of propagules to the selective forces to which these offspring will be exposed. Usually, a larger propagule size is favored when young are exposed to high mortality risk or conspecific competition. Here we test 2 predictions on how egg size should vary with these selective agents. When offspring are cared for by parents and/or alloparents, protection may reduce the predation risk to young, which may allow mothers to invest less per single offspring. In the cooperatively breeding cichlid Neolamprologus pulcher, brood care helpers protect group offspring and reduce the latters' mortality rate. Therefore, females are expected to reduce their investment per egg when more helpers are present. In a first experiment, we tested this prediction by manipulating the helper number. In N. pulcher, helpers compete for dispersal opportunities with similar-sized individuals of neighboring groups. If the expected future competition pressure on young is high, females should increase their investment per offspring to give them a head start. In a second experiment, we tested whether females produce larger eggs when perceived neighbor density is high. Females indeed reduced egg size with increasing helper number. However, we did not detect an effect of local density on egg size, although females took longer to produce the next clutch when local density was high. We argue that females can use the energy saved by adjusting egg size to reduced predation risk to enhance future reproductive output. Adaptive adjustment of offspring size to helper number may be an important, as yet unrecognized, strategy of cooperative breeder

Putting fish in the tank: An Agent Based Model with flow interaction

Water Qualit

Context-dependent impacts of anthropogenic noise on individual and social behaviour in a cooperatively breeding fish.

Keywords: antipredator behaviour boat noise Cichlidae global change Lake Tanganyika Neolamprologus pulcher parental investment Anthropogenic (man-made) noise is a global problem and present in virtually all terrestrial and aquatic environments. To date, most studies investigating the potential impact of this pollutant have focused on individual behavioural responses and simply considered whether noise has an effect. However, most animals engage in social interactions, which may be vulnerable to the adverse effects of noise, and work in other fields suggests that individuals might react differentially to comparable noise stimuli depending on their own characteristics and the current situation. We used controlled experiments and standardized tests to investigate the impacts of playback of the noise of a passing boat, a dominant acoustic stressor in the aquatic environment, on nest-digging behaviour, antipredator defence and social interactions in small groups of Neolamprologus pulcher, a territorial and cooperatively breeding cichlid fish. Our results show that, in comparison to ambient noise, playback of boat noise: (1) reduced digging behaviour, which is vital to maintain hiding and breeding shelters; (2) decreased defence against predators of eggs and fry, with direct consequences for fitness; and (3) increased the amount of aggression received and submission shown by subordinates. Moreover, the context (presence or absence of eggs) affected individual and social behaviours in response to the same noise source. Our results demonstrate the need to consider whole behavioural repertoires for a full understanding of the impact of anthropogenic noise, and indicate that the effects of this global pollutant are likely to be context dependent.

Influence of pile driving on the clearance rate of the blue mussel, Mytilus edulis (L.)

Underwater pile driving is typically undertaken during construction of offshore oil and gas platforms and wind farms and harbours. These structures generally need solid foundations - provided by large steel piles - that are driven into the seabed. Impact pile driving generates water-borne pressure and particle motions, which propagate through the water column and the seabed. Few studies have investigated the potential effects of underwater noise stimuli on bivalves. In current study, the influence of impact pile driving on clearance rate of the blue mussel (Mytilus edulis) was investigated in a semi-open field experiment. An experimental pile driving setup was constructed using a pile-driver and a steel pile. Under controlled conditions, individual mussels were exposed to experimental pile driving and ambient conditions, with the possibility to feed upon microalgae (Tetraselmis suecica). Mussels had significantly higher clearance rates during exposure to pile driving compared with individuals tested in ambient conditions. We suggest that mussels under pile driving conditions moved from a physiologically maintenance state to active metabolism to compensate for the stress caused by pile driving.</p

Exposure of benthic invertebrates to sediment vibration: From laboratory experiments to outdoor simulated pile-driving

Activities directly interacting with the seabed, such as pile-driving, can produce vibrations that have the potential to impact benthic invertebrates within their vicinity. This stimuli may interfere with crucial behaviors such as foraging and predator avoidance, and the sensitivity to vibration is largely unknown. Here, the responsiveness of benthic invertebrates to sediment vibration is discussed in relation to laboratory and semi-field trials with two marine species: the mussel (Mytilus edulis) and hermit crab (Pagurus bernhardus). Sensory threshold curves were produced for both species in controlled laboratory conditions, followed by small-scale pile-driving exposures in the field. The merits of behavioral indicators are discussed, in addition to using physiological measures, as a method of determining reception and measuring responses. The measurement and sensors required for sediment vibration quantification are also discussed. Response and threshold data were related to measurements taken in the vicinity of anthropogenic sources, allowing a link between responsiveness and actual operations. The impact of pile-driving on sediment-dwelling invertebrates has received relatively little research, yet the data here suggest that such activities are likely to impact key coastal species which play important roles within the marine environment

Relationships of sound pressure and particle velocity during pile driving in a flooded dock

Underwater sound is characterized by two different components, directional particle motion and scalar pressure waves. Here, we studied sound pressure and particle motion during experimental pile driving in a confined industrial-sized shipbuilding dock. The pile driving noise was generated by a 200 kg hammer striking a 7.5m steel pile. Noise data were collected using a hydrophone and a 3-axis accelerometer along 27 equally spaced locations. The results show that the relationship between the two components is approximately linear, as theory suggests, but the recorded values of particle velocity are generally larger than expected, particularly for the z-axis velocity which is shown to have a magnitude of 1 to 10 times (average 3.5) that of the theoretical velocity for a plane wave at the same sound pressure.Moreover, sound pressure and particle motion showed a different frequency distribution. For sound pressure, a shallow water cut-off frequency below approximately 400 Hz was observed in the power spectrum, which was not observed for particle velocity. This could be due to ground roll waves, but also wind induced waves and vibration on the cable could cause an increase in the low frequency vertical velocities.</p