John J. Videler

The social and mating system of the herbivorous reef fish Sparisoma viride: One-male versus multi-male groups

SynopsisWe present a detailed description of the social and mating system of the protogynous reef herbivoreSparisoma viride at the fringing reef of Bonaire (Netherlands Antilles). Initial phase (IP) fish and terminal phase (TP) males occur either in one- or in multi-male groups, which are compared quantitatively with respect to the use of space, size composition, social interactions and sexual activity. One-male groups consist of one TP male plus 1–14 IP females, whereas in multi-male groups up to 14 TP males and about twice as many IP fish share a common home range. The two social units further show marked differences in vertical distribution (one-male groups are restricted to depths between 3 and 22 m, multi-male groups mainly residing < 3 m), size composition (a larger proportion of small adults live in multi-male groups), size and stability of the range (larger in one-male groups) and sexual activity (daily spawning of one-male group members inside their normal home range; no activity in multi-male groups on the shallow reef). Sexual activity occurred daily, throughout the year, with no evidence for tidal tracking or major seasonal or lunar patterns. The one-male groups constitute less than 20% of the adult stock but control up to 77% of the inhabited reef. As a result they have access to higher-yield food patches and to suitable spawning sites inside their home range. Although members of both units appear to defend their common home range against intruding conspecifics, the degree of territoriality is clearly higher in one-male groups. We discuss the relative importance of food, shelter, mates and mating sites as defended resources and some life history implications. The complex social and mating system ofS. viride shows much resemblance to that of another Caribbean scarid,Scarus iserti. This complexity seems to reflect the capacity of individuals to flexibly adapt their feeding, mating and life history styles to an unpredictable environment. We propose thatS. viride is a good study animal to test adaptive explanations for its territorial organization and complex life history patterns.

Escape from viscosity : the kinematics and hydrodynamics of copepod foraging and escape swimming

SUMMARY Feeding and escape swimming in adult females of the calanoid copepod Temora longicornis Müller were investigated and compared. Swimming velocities were calculated using a 3-D filming setup. Foraging velocities ranged between 2 and 6 mm s-1, while maximum velocities of up to 80 mm s-1 were reached during escape responses. Foraging took place at Reynolds numbers between 2 and 6, indicating that viscous forces are considerable during this swimming mode. Inertial forces are much more important during escape responses, when Reynolds numbers of more than 100 are reached. High-speed film recordings at 500 frames s-1 of the motion pattern of the feeding appendages and the escape movement of the swimming legs revealed that the two swimming modes are essentially very different. While foraging, the first three mouth appendages (antennae, mandibular palps and maxillules) create a backwards motion of water with a metachronal beating pattern. During escape movements the mouth appendages stop moving and the swimming legs beat in a very fast metachronal rhythm, accelerating a jet of water backwards. The large antennules are folded backwards, resulting in a streamlined body shape. Particle image velocimetry analysis of the flow around foraging and escaping copepods revealed that during foraging an asymmetrical vortex system is created on the ventral side of the animal. The feeding motion is steady over a long period of time. The rate of energy dissipation due to viscous friction relates directly to the energetic cost of the feeding current. During escape responses a vortex ring appears behind the animal, which dissipates over time. Several seconds after cessation of swimming leg movements, energy dissipation can still be measured. During escape responses the rate of energy dissipation due to viscous friction increases by up to two orders of magnitude compared to the rate when foraging.

Riding the waves: the role of the body wave in undulatory fish swimming

Abstract A continuously swimming mullet modulates its thrust production by changing slip-the ratio between its swimming speed U and the speed V with which the body wave travels down its body. This variation in thrust is reflected in the wake of the fish. We obtained 2-dimensional impressions of the wake behind a mullet swimming at a slip of 0.7 equivalent to active swimming, at a slip of 0.9 close to free-wheeling, and at a slip of 1.1 when the fish is braking. Independent of the slip, vortices are shed at the tail when the tail tip reaches its maximum lateral excursion. The manner in which the wake changes as it decays depends on the degree of slip: At a slip well below unity, the wake decays without any qualitative changes in shape, the medio-frontal cross section of the mature wake consists of a double row of alternating vortices separated by an undulating jet, and the angle between the jet flow and the mean path of motion is close to 45°; at a slip above unity, the vortices stretch out laterally and the mature wake resembles a single row of oval vortices with two vortex cores, and the jet between the vortices is almost perpendicular to the mean path of motion; the wake at slip of 0.9 exhibits a pattern intermediate between the wakes at slips 0.7 and 0.9 with slightly elongate vortices and a jet angle of 61°.

Behaviour and time allocation of the burrowing shrimp Callianassa subterranea (Decapoda, Thalassinidea)

Abstract The behaviour and allocation of time of the endobenthic shrimp Callianassa subterranea from the central North Sea was studied in the laboratory. Animals were allowed to construct a two-dimensional burrow in large transparent sediment filled cuvettes tailored to their body width. The behaviour of the animals was found to consist of 12 behavioural States which were described in an ethogram. The allocation of time of animals in cuvettes was recorded to the nearest 0.1 s during 1 or 2 h observation periods randomly distributed over the day. All records were statistically tested for their validity with respect to visibility of the animals studied. The behavioural states were grouped into six classes using a type of Markov-chain sequence analysis: Wandering, Resting, Burrowing, Surveying, Grooming and Ventilating. An average time budget of 10 animals based on 98 valid 1 h protocols shows that C. subterranea spends 27.4 ± 2.2% (SEM) of the time Burrowing. This is a little more than 40% of the time the animal is active. Wandering and Grooming each take about half that amount, with 12.6 ± 0.9% and 14.9 ± 1.4% respectively. Ventilating takes 8.6 ± 1.5% and only little time is spent Surveying the burrow (2.6 ± 0.4%). The animal is Resting during 33.9 ± 2.4% of the time. Circumstantial evidence indicates that feeding is part of the burrowing behaviour. No major periodicity in the behaviour of C. subterranea was encountered.

Copepod feeding currents: flow patterns, filtration rates and energetics

SUMMARY Particle image velocimetry was used to construct a quasi 3-dimensional image of the flow generated by the feeding appendages of the calanoid copepod Temora longicornis. By scanning layers of flow, detailed information was obtained on flow velocity and velocity gradients. The flow around feeding T. longicornis was laminar, and was symmetrical viewed dorsally, but highly asymmetrical viewed laterally, with high levels of vorticity on the ventral side. The flow rate through the feeding appendages varied between 77 and 220 ml day-1 per individual. The morphology of the flow field ensured that water was entrained over the full length of the first antennae. These were kept out of areas with high velocity gradients that could interfere with distant mechano- or chemoreception. The volume of influence, i.e. the volume of water around the foraging copepod, where shear rates were significantly higher than background levels, was calculated. Implications for encounter probability and mechanoreception are discussed. The average rate of energy dissipation within the copepods volume of influence is several times higher than the levels of turbulent energy dissipation these animals are likely to encounter in their environment. Even in highly turbulent environments, adult T. longicornis will not experience very significant effects of turbulence. Within the volume of influence of the copepods the energy dissipation due to viscous friction varied between 6.6×10-11 and 2.3×10-10W. Taking mechanical efficiency and muscle efficiency into account, this results in a total energetic cost of the feeding current of 1.6×10-9W per copepod. This value represents only a small percentage of the total energy budget of small calanoid copepods.

Radular teeth as models for the improvement of industrial cutting devices

Limpets (Gastropoda) and chitons (Polyplacophora) feed on epi- and endolithic organisms by means of the radula, a specialized feeding apparatus located in the mouth cavity. The radula owes most of its abrasive capability to the presence of numerous mineralized teeth. Here we report on the shape, internal structure, wearing pattern, feeding position, and distribution of hardness and elastic properties of these teeth in an attempt to generate ideas for the innovation of industrial cutting devices. The teeth remain sharp during their entire working-life mainly due to the fact that wearing preferentially occurs along surfaces formed by the internal structure of the tooth. It is shown that shape, internal structure, positioning and material characteristics concertedly function in minimizing the rate at which the teeth wear down and in maintaining optimal cutting behaviour. Implementation of these self-sharpening characteristics into industrial cutting devices is discussed.

MATE CHOICE IN AIDABLENNIUS-SPHYNX (TELEOSTEI, BLENNIIDAE) - FEMALES PREFER NESTS CONTAINING MORE EGGS

Criteria for female mate choice were investigated in a natural population of a Mediterranean blenny, Aidablennius sphynx. Removable test tubes in concrete blocks were offered as nests. Each tube was guarded by a male and females laid eggs in the tubes. Nests with larger broods received significantly more spawning females. The numbers of eggs laid increased with brood size from empty nests to intermediate brood sizes, but this tendency is reversed if nests contain very large broods. Nests with and without broods were exchanged experimentally among males. The number of eggs a male received, after an empty tube was replaced by a tube with eggs, was significantly higher. Conversely, the number of eggs received after a tube with eggs was replaced by an empty tube, was significantly lower. Male display did not increase the probability that females spawned. Male size did not correlate with the numbers of eggs received. It is discussed that female preference for large broods might be adaptive because the number of eggs present in the nest is probably a reliable predictor of the survival chances of the eggs.

Differences between the reproductive biologies of Tripterygion tripteronotus and T. delaisi (Pisces, Perciformes, Tripterygiidae): the adaptive significance of an alternative mating strategy and a red instead of a yellow nuptial colour

This paper contributes to the understanding of the evolution of alternative mating strategies by comparing morphological, ecological and ethological aspects of the reproductive systems of two closely related fish species studied near the marine biological station “STARESO” at Calvi, Corsica, between March 1982 and May 1985. The Mediterranean breeding areas of Tripterygion tripteronotus and T. delaisi partly overlap. The red territorial males of T. tripteronotus defend territories in the upper 6 m of the water column and the yellow territorial males of T. delaisi breed between a depth of 3 and 40 m. Small male T. tripteronotus possess relatively large gonads exhibit “sneaking” behaviour, while small male T. delaisi do not participate in mating. T. tripteronotus expends more effort in reproduction than T. delaisi. This is expressed in larger gonads, a higher density of and stronger competition for nest sites, and a longer breeding season and shorter spawning bouts with a higher fertilization rate in the former species. We hypothesize that the sneaking strategy of non-territorial male T. tripteronotus evolved in response to competition for nest sites in the shallow, upper water layers, which are limited in depth, but contain a good food supply. The depth restriction is imposed by the light-reflecting properties of the red territorial males. We suggest that the evolution of T. tripteronotus began with the appearance of a red morph of T. delaisi after the invasion of this latter species into the tideless Mediterranean Sea.

Resource and habitat sharing by the stoplight parrotfish, Sparisoma viride, a Caribbean reef herbivore

SynopsisWe compare the vertical distribution, substrate preferences, grazing behaviour and social interactions of the stoplight parrotfish,Sparisoma viride, with that of other scarids at a fringing reef off Bonaire (Netherlands Antilles). Earlier reports thatS. viride only displays territorial behaviour against conspecifics are confirmed by the non-aggressive nature of this parrotfish and the low time expenditure on interactions with other herbivores. The vertical distribution ofS. viride is largely identical to that of several other scarids, acanthurids and pomacentrids, whose ranges may completely coincide withS. viride territories. Comparison of the substrate use of the five most common scarids inside a singleS. viride territory yields no evidence of food partitioning. We suggest that the lack of interspecific territorial behaviour inS. viride is explained by the inability to economically defend a territory against all potential food competitors. Factors that may favour territory sharing between herbivores are fine-scale resource partitioning and shared defence, both of which would reduce the costs of territorial life. However, more detailed investigation of herbivore food selection is required before definite conclusions can be drawn.

Local variability in population structure and density of the protogynous reef herbivore Sparisoma viride

SynopsisWe compare the (relative) abundance of life phases [juveniles (JU), initial phase (IP) and terminal phase (TP) fish], social categories (territorial and group adults), and fish following alternative mating styles, in three local populations of the protogynous reef herbivore,Sparisoma viride, on the fringing reef of Bonaire (Netherlands Antilles). In order to determine the adaptive significance of variations in social organization, they are related to the density of conspecifics and other herbivores and to the availability of food, shelter and mating sites. The most striking difference is the high abundance of JU and group fish at one location (Playa Frans) and the total absence of group fish at another (Red Slave). These differences are coherent with a gradient in population density, total herbivore density, scarid grazing pressure, and reproductive output, all of which are highest at Playa Frans and lowest at Red Slave. Exposure to waves and currents shows an inverse trend. The differences in the relative abundance of territorial fish can be explained by the concept of economic defendability, which is reduced at higher population density. In a life history context, small TP group males represent ‘bachelors’ that sacrifice current reproduction for better future prospects. As predicted by life history theory, early sex change is promoted at sites where the future rewards are higher (higher spawning rates of large TP males) and where the costs incurred during the bachelor phase are reduced (more spawning opportunities for group TP males). At Red Slave an alternative male mating style (‘streaking’) appears to be promoted by the lack of a refuge for group TP males and by a dense gorgonian canopy, allowing IP males to reside inside territories. We conclude that most observed differences in population structure can be considered adaptive in an ecological and in a life history context. Population density is a major factor in both contexts. Analysis of the variability in adult density in relation to JU density and the availability of food and shelter indicates that theS. viride populations at Bonaire are not totally controlled by stochastic processes. Considering the small spatial scale and the high dispersal of the planktonic embryos and larvae, the observed variability in behavioural and life history traits ofS. viride points to a high degree of phenotypic plasticity.