Visual aspects of species recognition in the damselfish Dascyllus aruanus L. (Pisces,Pomacentridae)

Attraction was found to be a reliable indicator of species recognition in the damselfish Dascyllus aruanus. Isolated fish are attracted to live or dead conspecifics significantly more than to heterospecifics. Attraction persists towards black and white photographs. Using photographs it was shown that certain parts of the pattern are more important for recognition than others. Of the three black bars of the normal colour pattern, the central is the most important, and the anterior the least so. Two alternative criteria for demonstrating species recognition in a boldly coloured reef fish, aggression and attraction, are contrasted.     

Field experiments on species recognition by the threespot damselfish, Eupomacentrus planifrons, (Pisces: Pomacentridae)

The threespot damselfish, Eupomacentrus planifrons, defends differently sized territories against individuals of different species. Tests were conducted in the field to determine the mechanism(s) by which this interspecific recognition occurs. It was found to be based largely on visual cues, the most important of which was body form. Both colour and movement had different effects for intra- and inter-specific intruders. Based on these data, it is proposed that different mechanisms underlie the recognition of and territorial defence against the two groups. Further, interspecific territoriality need not be an ‘accidental’ form of intraspecific territoriality nor a transitional phase in the divergence of already established species, but, rather, may be a stable system based on the simple need to defend an area against non-related competitors.     

Sexual selection and reproductive success in males of the bicolor damselfish, Eupomacentrus partitus (Pisces: Pomacentridae)

Relative reproductive success of male bicolor damselfish, Eupomacentrus partitus, was measured as the number of egg batches obtained per week per male during a 14-month field study. Large and consistent differences in spawning success, observed in seven colonies containing 23 males, demonstrated that mating was non-random. Various physical and behavioural characteristics of males were also monitored. Significant correlations (P<0.05) were found between reproductive success and four variables: frequency of courtship, inter- and intraspecific aggression, and total length. The importance of other factors such as size and location of male territories and time allotment to various activities was also considered. The interactions between these variables, as well as preliminary observations of spawning, suggest that intersexual selection, that is female choice of mates, is the dominant process in sexual selection in this species.     

Daily carbon, nitrogen and phosphorus budgets for the Mediterranean planktivorous damselfish Chromis chromis

The planktivorous damselfish Chromis chromis is one of the most numerous fish species in the Mediterranean rocky littoral, yet the role this species plays in the overall functioning of the ecosystem is poorly understood. In this study nitrogen, carbon and phosphorus budgets were constructed for C. chromis from the Bay of Calvi, Corsica and an attempt was made to resolve the possible fates of these nutrients from ingested materials, to somatic growth (P_s), reproductive tissues (P_r), respiration (R), assimilation (A′), faeces (F) and dissolved wastes (U). C. chromis were estimated to consume on average 4.7% of their own body mass of zooplankton per day, in two separate feeding episodes — at dawn and at dusk. This is equivalent to 8288 individual copepods or 42.1 mg carbon, 9.7 mg nitrogen, 0.8 g phosphorus. 44% of all phosphorus ingested was shown to be excreted as dissolved waste, and 46% as faeces; this may be of considerable importance in the Mediterranean, where littoral macrophytes are often severely phosphorus-limited. 85% of all nitrogen was excreted as dissolved waste (mostly ammonia) and local nutrient enrichment may enhance littoral primary productivity, particularly around C. chromis night-shelters.     

Territorial behaviour of beaugregory damselfish (Stegastes leucostictus) in response to egg predators

To test the hypothesis that territorial male beaugregory damselfish (Stegastes leucostictus) can assess the degree of threat from egg predators, the aggressive behaviour of both males guarding eggs and males without eggs was recorded when they were presented with either one or five individuals of the wrasse egg predator Thalassoma bifasciatum. Presentations were made in a clear plastic bottle 0.5 m from artificial beaugregory breeding sites in the field. Two measures of aggressive behaviour (downhead threats and time spent within 10 cm of the presentation bottle) were significantly greater for multiple wrasse presentations than for single wrasse presentations, while a third measure (chase attempts) was not. In contrast, chase attempts were significantly greater for males guarding eggs than for males without eggs, but there was no significant difference in the level of downhead threats or bottle proximity time for this comparison. Levels of the three aggressive measures were not correlated with either the amount of eggs or the number of egg clutches present. These results indicate that territorial male beaugregories respond to an increase in the number of intruding egg predators by increasing the levels of low-cost threat behaviour, while the presence (but not the amount) of eggs results in an increase in the amount of higher cost attack behaviour. These experiments, therefore, support the hypothesis that male beaugregories can assess the degree of threat from egg predators, and indicate that they use this assessment to alter the strategies used in territorial defence.     

Linking larval history to juvenile demography in the bicolor damselfish Stegastes partitus (Perciformes: Pomacentridae)

Otolith-based reconstructions of daily larval growth increments were used to examine the effect of variation in larval growth on size and age at settlement and post-settlement growth, survival and habitat preferences of juvenile bicolor damselfish (Stegastes partitus Poey). During August 1992 and 1994, newly settled S. partitus were collected from Montastraea coral heads and Porites rubble piles in Tague Bay, St. Croix, U.S. Virgin Islands (17 degrees 45'N, 64 degres 42' W). Daily lapillar otolith increments from each fish were counted and measured with Optimas image analysis software. S. partitus pelagic larval duration was 23.7 d in 1992 (n = 70) and 24.6 d in 1994 (n = 38) and larval age at settlement averaged 13.0 mm total length both years. Analysis of daily otolith increments demonstrated that variation in larval growth rates and size and age at settlement had no detectable effect on post-settlement survivorship but that larger larvae showed a preference for Montastraea coral at settlement. Late larval and early juvenile growth rates showed a significant positive relationship indicating that growth patterns established during the planktonic stage can span metamorphosis and continue into the benthic juvenile phase. Larval growth rates during the first two weeks post-hatching also had a strong effect on age to developmental competence (ability to undergo metamorphosis) in both 1992 and 1994 with the fastest growing larvae being 8 d younger and 0.8 mm smaller at settlement than the slowest growing larvae. These differential growth rates in early stage larvae established trajectories toward larval developmental competence and may prove important in biogeographical studies of larval dispersal.     

Effect of mobbing toward predators by the damselfishPomacentrus coelestis (Pisces: Pomacentridae)

Field observations on prey-predator interactions, focusing on mobbing behavior byPomacentrus coelestis, were made in the shallow water of Shirahama, Japan. Within the breeding colony of the damselfish, indirect group mobbing toward 6 ambushers and direct mobbing with physical contact only by nesting males toward a stalker were observed. The direct mobbing toward the stalker (moray eel) is suggested to have involved an element of egg-guarding. Group mobbing was usually released by large and quick attacking motion of the predator. Attack intervals of a predator were much longer after it was mobbed than when it was not mobbed, but there was no significant difference in success ratio of the next attack whether mobbing was elicited or not. Consequently, it is concluded that mobbing effectively reduced future predation risk of each mobber.     

Copulation in the lycosid spider (Lycosa rabida walckenaer): A quantitative study

An event recorder was used to obtain information on the temporal patterning of palpal insertions and palpal moistening in wolf spider matings. The series of insertions of each palp was characterized by a linear increase in insertion duration. The rate of change of insertion duration was fairly constant for the species. Asymmetry in the mechanism underlying palpal insertion was indicated by differences between the palps of some males in mean insertion duration and repetition rate. Termination of mating was initiated by the male's decreasing activity. Defensive behaviours described for the first time in spiders included spine erection in both sexes during mounting and ‘cheliceral pinching’ by the male when dismounting.     

Mating rendezvous in monogenean gill parasites of the humbug Dascyllus aruanus (Pisces: Pomacentridae)

The gills of the humbug, Dascyllus aruanus (Pomacentridae), were infected by a monogenean genus Haliotrema at a high prevalence (83%) but with a low mean intensity (5.6 worms/fish). All the gill arches of 365 fish, caught on the fringing reef of Moorea Island (French Polynesia), were examined for parasites. Each hemibranch was divided into 12 subequal sections. Monogeneans showing microhabitat overlap were defined as couples. Hosts with low intensity of infection (fewer than 5 monogeneans per gill) were selected and couples were recorded. Among the 37 hosts harboring 2 worms on their gills, 18 fish were infected with these 2 monogeneans on the same gill side of the body; 50% (n = 9) of these harbored monogeneans within the same gill arch and 55% (n = 5) of these last fish showed individual parasites within the same section of the gill. In the case of hosts with few monogeneans (3 and 4 individuals; n = 37) on the same arch, more than 40% (n = 16) harbored worms in couples. There may be some chemical communication that allowed these monogeneans to migrate toward each other and thus enhance mating success. Mating rendezvous appears to be a more important factor than site location for these gill monogeneans.     

Social spacing in the mormyrid fish Gnathonemus petersii (Pisces): A multisensory approach

The sensory basis of group cohesion in the weak-electric fish Gnathonemus petersii was investigated in a circular tank with groups of four fish each, interacting through a wide-meshed plastic screen with intact or operated conspecifics, or with other stimulus objects. We confined these stimuli to one or two peripheral holding compartments. The response measures were obtained from the free swimming fish and included (1) the time the fish spent together as a group, (2) the time they spent in front of the holding compartments, (3) the circular distribution of the fish's positions, and (4) the mean nearest neighbour distances. Under empty compartment conditions, four different groups were tested, consisting of either (1) intact, electrically active fish, or (2) electrically ‘silent’ fish (with their electric organ surgically rendered inoperative), or (3) blind, or (4) ‘silent’ and blind animals. The loss of either sensory modality, vision or feedback from electric organ discharge, led to changes of comparable size, decreasing the time spent as a group and increasing the mean nearest neighbour distance. In fish lacking both modalities, group cohesion was further impaired. With stimuli present in one or both holding compartments, the strength of social attraction depended on the nature of the stimulus: the more intact stimulus conspecifics were present, the more densely did the fish group in front of the stimulus compartment. ‘Wired-in’ electric organ discharges (simulating waveform and intensity) and electrically ‘silent’ fish were equally attractive, but only half as attractive as intact fish. Blind free swimming fish aggregated with intact and also with ‘silent’ conspecifics. Under dim light conditions, group cohesion was predominantly, though not exclusively, affected by electrosensory feedback from the electric organ discharge and visual input. Mechanical and olfactory cues may also be involved.     

Night and day service: Distyly and mixed pollination system in Faramea cyanea (Rubiaceae)

Currently, pollination is seen as involving more generalist interactions than specialized ones. Supporting this trend, some nocturnal distylous flowers may also receive floral visitors during the day, and since the latter contribute to fruit set, the pollination system is mixed and less specialized. Common among the Rubiaceae, distyly has been regarded as a reproductive strategy which requires a precise and specialized pollination system, and in this important tropical family, environmental disturbance and pollination failure have been used to explain anomalies in distylous features. Faramea cyanea Müll. Arg. is a common tree species in forest formations in the increasingly threatened Cerrado biome, the Neotropical savannas in Central Brazil. We evaluated the floral morphology, pollination biology and breeding system of a population of F. cyanea. Despite their moth pollination features, flowers were visited by diurnal (bees) as well as nocturnal (moths) pollinators. Experimental results showed that both pollinator groups contributed equally to pollen flow and legitimate pollination. The population presented distyly, isoplethy and heteromorphic self-incompatibility. Although F. cyanea did not present exact reciprocal herkogamy between floral morphs, pollination and reproductive success were not impaired. Floral features, which allowed pollination by complementary groups of pollinators, may explain the absence of anomalies in the isoplethy and distylous features in the studied population, anomalies which have been observed in other sympatric distylous Rubiaceae.     

Karyotypic changes associated to the dispersive potential on Pomacentridae (Pisces, Perciformes)

When comparing karyotypic diversification between freshwater and marine fish, a notable increase in modifications associated to the former environment can be noticed in relation to the latter one. This fact is related to the great number of physical partitions (barriers) that exist in continental waters. Furthermore, in the marine environment, the barriers to the gene flow are complex and not always identifiable, especially when considering the participation of dynamic factors such as currents and winds associated to the dispersive potentialities of a living group. Within Perciformes fish, the Pomacentridae family stands out from the others for its intimate relation with the coral reefs, as well as for its diversity of forms and biological characteristics, providing an adequate model for studying the influence of the pelagic period of the larval stage upon the karyotypic evolution. In the present work, cytogenetic analyses were carried out on three Pomacentridae species, typical representatives of the coral reefs, Abudefduf saxatilis (2n=48, FN=52, 2 m+2sm+44a), Microspathodon chrysurus (2n=48, FN=64, 6 m+10st+32a) and Amphiprion frenatus (2n=48, FN=92, 14 m+22sm+8st+4a) that have different pelagic larval periods. The analyses between subfamilies showed a trend that the lower the dispersive potential, the greater the quantity of fixed pericentric inversions based on the basal karyotype of the Perciformes.     

The effect of territorial damselfish (family Pomacentridae) on the space use and behaviour of the coral reef fish, Halichoeres bivittatus (Bloch, 1791) (family Labridae)

Most demersal species of damselfish (family Pomacentridae) are territorial herbivores that aggressively chase other fishes away from their nests. This study investigates whether the aggressive territorial damselfish, Stegastes leucostictus, modifies behaviours and home range area use in a less aggressive, non-territorial species, the slippery dick wrasse, Halichoeres bivittatus (family Labridae). Damselfishes and wrasses are ubiquitous and abundant members of coral reef fish assemblages around the world; hence, this study has broader implications beyond the two Caribbean species chosen for this study. A manipulative field experiment consisted of transplanting one or three S. leucostictus into artificial shelters positioned within adult or adjacent to juvenile H. bivittatus home ranges. The introduction of damselfish had little effect on the size of home range areas of juvenile or adult wrasses, but had a significant effect on the location of their home ranges. The damselfish also affected adult microhabitat use but did not affect use by juveniles. In addition, there was an increase in damselfish-wrasse interactions that resulted in a significant reduction in the amount of time adult wrasses could spend foraging or in a foraging assemblage. It was concluded that aggressive interactions with territorial damselfish affect individual H. bivittatus space use and may consequently affect the spatial distribution of H. bivittatus populations.     

Isolation and characterization of 16 microsatellite loci in the humbug damselfish, Dascyllus aruanus (family Pomacentridae)

Here we report on 16 microsatellite loci designed for the damselfish Dascyllus aruanus. All loci were tested on 98 individuals and were polymorphic (seven to 35 alleles). Expected heterozygosity ranged from 0.705 to 0.942. Six loci showed Hardy-Weinberg disequilibrium due to the occurrence of null alleles. Cross-species amplifications conducted within the genus Dascyllus (D. carneus, D. strasburgi, D. trimaculatus) lead to polymorphic fragments in 32 out of 48 tests. These 16 loci will enable future research into the behavioural ecology and population ecology of Dascyllus aruanus throughout the Indo-Pacific.     

Direct mate choice for simultaneous acoustic and visual courtship displays in the damselfish, Dascyllus albisella (Pomacentridae)

Acoustic signals are well established as key components of mate selection in terrestrial species, but not in aquatic species. It has long been known that damselfish (Pomacentridae) use a combined visual and acoustic display in their courtship.. This study examined several male qualities including individual size, courtship vigor, territory size and complexity, as well as components of the acoustic call including dominant frequency, pulse characteristics and repetition rate. The objective was to determine which male traits were correlated with mating success. Observations made over ten reproductive cycles revealed that female mate choices were not random and that male mating success was correlated with courtship rate (a simultaneous visual and acoustic cue) and the number of neighboring females, but not with male morphological traits, territory quality, or acoustic call structure. These results suggest that females choose mates based on a condition-dependent trait (courtship rate) that advertises quality of paternal care, which supports good parent models of sexual selection, thereby demonstrating the importance of the combined acoustic/visual display for sexual selection in fishes