Site fidelity and homing behaviour in coral reef cardinalfishes

Tagged adult cardinalfishes Apogon doederlini , Cheilodipterus artus and Cheilodipterus quinquilineatus persisted to within an average of 36–79 cm of their initial resting positions within One Tree Reef lagoon for over 8 months in A. doederlini and over 16 months in C. artus and C. quinquilineatus . In addition, 56–81% of tagged fish displaced c. 1 km, and 33–63% of tagged fish displaced c. 2 km returned to their point of collection within 3 days. As cardinalfishes are often found densely aggregated at resting sites, their extended use of specific sites on reefs may represent a localized, predictable resource for predators and a significant source of spatial variation in nutrient input to reef systems via faeces.     

Site fidelity and homing behaviour of some kelp-bed fishes

Common species of kelp-bed fishes including adult blacksmith Chromis punctipinnis , adult senorita Oxyjulis californica , and sub-adult kelp bass Paralabrax clathratus were collected from two separate and isolated rocky reefs at Santa Catalina Island, California, U.S.A. where giant kelp Macrocystis pyrifera was present. After tagging, groups of fishes were either returned to their initial collection site or displaced to an alternative kelp-bed site to measure site fidelity and homing behaviour. No tagged fishes that were returned to their initial collection sites and subsequently resighted, exhibited any movement to another reef suggesting that these fishes have a limited home range, and handling during capture and tagging had no effect on site fidelity. Of fishes translocated to alternative kelp-bed sites, up to 80% of tagged senorita and 100% of tagged blacksmith that were resighted had returned to the site of their initial collection, indicating that these species are motivated and able to relocate previously utilized areas when displaced. However, when young-of-the-year and juvenile kelp bass were displaced, none were ever seen again suggesting that disruption of the relationship between a young kelp bass and its home site may influence its survival.     

Early survivorship of juvenile coral reef fishes

Data on early survivorship of newly settled reef fish were collected by monitoring individuals which recruited to 30 small lagoonal patch reefs over three summers. Preliminary survivorship curves spanning the first 45 days after settlement were derived for 17 species. Most species showed greatest rates of mortality in the first 1–2 weeks in the reef environment however there were substantial differences among species in the extent and the temporal pattern of this. In six species, 75% of individuals survived the 45 days, while in 5 others, 20% or fewer survived that long. In eight species, mortality was negligible after the first 14 days. In the other 9, significant mortality occurred in subsequent weeks. Patterns of survivorship did not appear to differ substantially among years in five of the six species for which data were adequate. In particular, survivorship did not appear to be different among years even when levels of recruitment varied greatly.     

Site fidelity and homing in juvenile rabbitfishes (Siganidae)

The behaviour of juvenile fishes is critical in establishing the link between recruitment and subsequent adult populations. If juvenile fishes move, they can respond to variation in local conditions before adult home ranges are established. Alternatively, if juveniles establish fixed home ranges at settlement, their decisions may determine future population densities at small spatial scales. Field observations and translocations revealed that juvenile rabbitfishes (Siganus corallinus and S. doliatus) have small home ranges and strong homing abilities (covering 6 m in 1 h or 36 m within 24 h). Only four of 22 individuals failed to return; all were transferred up-current, suggesting that olfaction is important in homing. Small home ranges and strong homing tendencies in juvenile herbivores suggest that decisions made by recruits will impact the spatial extent of both adult fishes and the functional roles they play within ecosystems.     

Local adaptation does not always predict high mating success

The hypothesis that adaptation to local environments can increase mating success was tested using ten replicate lines of Drosophila melanogaster adapted either to 16 °C or to 25 °C. Competitive mating trials at both temperatures were performed with males taken from a pair of lines, one adapted to each temperature. There was no average increase in mating success for males adapted to the local environment. Although one pair of lines showed the expected pattern, another pair showed the reverse pattern. More data are needed on this hypothesis, preferably with lines that have more strongly adapted to local environments.     

Nocturnal relocation of adult and juvenile coral reef fishes in response to reef noise

Juvenile and adult reef fishes often undergo migration, ontogenic habitat shifts, and nocturnal foraging movements. The orientation cues used for these behaviours are largely unknown. In this study, the use of sound as an orientation cue guiding the nocturnal movements of adult and juvenile reef fishes at Lizard Island, Great Barrier Reef was examined. The first experiment compared the movements of fishes to small patch reefs where reef noise was broadcast, with those to silent reefs. No significant responses were found in the 79 adults that were collected, but the 166 juveniles collected showed an increased diversity each morning on the reefs with broadcast noise, and significantly greater numbers of juveniles from three taxa (Apogonidae, Gobiidae and Pinguipedidae) were collected from reefs with broadcast noise. The second experiment compared the movement of adult and juvenile fishes to reefs broadcasting high (>570 Hz), or low (<570 Hz) frequency reef noise, or to silent reefs. Of the 122 adults collected, the highest diversity was seen at the low frequency reefs; and adults from two families (Gobiidae and Blenniidae) preferred these reefs. A similar trend was observed in the 372 juveniles collected, with higher diversity at the reefs with low frequency noises. This preference was seen in the juvenile apogonids; however, juvenile gobiids were attracted to both high and low sound treatments equally, and juvenile stage Acanthuridae preferred the high frequency noises. This evidence that juvenile and adult reef fishes orientate with respect to the soundscape raises important issues for management, conservation and the protection of sound cues used in natural behaviour.     

Predation on juvenile coral reef fishes: an exclusion experiment

The densities of recruits on caged and uncaged areas were compared in an experiment done to show the extent of predation on recently metamorphosed coral reef fishes. The design was unlike typical caging experiments, however, in that areas were caged only for short periods of 20–30 days and several independent trials, testing the same null hypothesis, were run. This was done to avoid confounding the effects of excluding herbivorous fishes with the effects of excluding piscivorous fishes. A third treatment, partially-meshed cages, revealed that the experiment was complicated by several other factors. Some prey species were attracted to the high relief offered by the experimental structures. Others responded to the differences in shelter from predators by redispersing themselves among the treatments shortly after settlement. There was also at least one significant edge effect caused by fishes preferring to settle near the boundaries of all treatments. In spite of these difficulties, observations on known individuals revealed that rates of mortality were age-dependent and decreased rapidly after metamorphosis. More than 25% of such fishes disappeared during their first five days in the benthic habitat compared with >10% of fishes aged 6–10 days and no losses of fishes aged 11–15 days. These early losses are the greatest instantaneous rates of mortality yet documented for recruited reef fishes. The experiment also suggested different rates of early mortality for various groupings of species: individuals of solitary, sedentary species disappeared approximately half as fast as individuals of the more mobile, and the more gregarious, species. This is probably a true reflection of the different vulnerability of these groups to predation and it may be caused by the different ways in which these fishes use the coral substratum. Our experience suggests that caging artifacts can have major impacts on the results obtained from this type of experiment and they must be controlled for adequately. We conclude that studies of predation on reef fishes may be done more easily using other methods.     

Accurate route demonstration by experienced homing pigeons does not improve subsequent homing performance in naive conspecifics.

We describe an experiment that uses the grouping tendencies and navigational abilities of the homing pigeon (Columba livia) to investigate the possibility of socially mediated information transfer in a field setting. By varying the composition of paired-release types, we allowed some naive birds to receive an accurate demonstration of the home route whilst others were paired with similarly naive conspecifics. After this 'paired phase', we predicted that if any learning of spatial information occurred then naive members of the former pairs would outperform their untutored conspecifics when re-released individually during the subsequent 'single phase' of the experiment. This prediction was not confirmed. Neither homing speed nor initial orientation was superior in individually released tutored versus untutored birds, despite the fact that both performance measures were better in the earlier 'paired phase' with experienced demonstrators. Our results suggest that although naive homing pigeons clearly interact with their experienced partners, they are unable to transfer any individually useful spatial information to subsequent homing flights.     

Alongshore dispersal and site fidelity of juvenile plaice from tagging and transplants

Juvenile plaice Pleuronectes platessa ( n  = 1281) were tagged and released at two locations 300 m apart on a 1 km long sandy beach. Most (>90%) of the fish were recaptured within 100 m of the release site (shown by the colour of the tag), with very few caught >200 m distance after 6 weeks. The changing spatial distribution of marked fish was adequately reproduced by a simple dispersal model with a single parameter: a 78% probability of remaining in a 100 m wide zone from one day to the next, with a 22% chance that fish move into an adjacent zone. In a subsequent similar study at the same beach, fish were either released at the point of capture ( n  = 881) or transplanted to the alternate site ( n  = 910) 100 m distant. After 6 weeks, transplanted fish moved along the shore towards their sites of original capture. Fish replaced at the point of capture showed no such movement along the shore. Further modification of the dispersal model to allow for a distinction between dispersal from home sites and from sites away from the original point of collection, was sufficient to reproduce the behaviour of the populations of both transplanted and control treatment groups. The likelihood of dispersal from home sites was much less than that seen at sites away from home. Juvenile plaice thus have a degree of long‐shore site fidelity not expected of a fish with strong depth‐related migration behaviour in a relatively homogenous habitat.     

Maternal waist-to-hip ratio does not predict child gender

It has been suggested that a high pre-conceptual waist-to-hip ratio (WHR) is a good predictor of male offspring and, thus, in cultures that value male children, an androgenous body shape may be judged as most attractive. The predictive value of WHRs is based on studies measuring women who already have children and correlating their WHRs with the proportion of existing male offspring. However, carrying a male child may alter WHRs in a different way to carrying a female child, and a high WHR may be an effect rather than a cause of male offspring. In order to test the predictive power of a pre-conceptual WHR and offspring gender, we took WHR measures from 458 women who intended to become pregnant and then correlated this with the genders of their subsequent children. We found no significant correlation. It is therefore not clear why a high WHR is preferred in some cultures. We suggest that differences in attractiveness preferences between different ethic groups are actually based on weight scaled for height (the body mass index or BMI) rather than the WHR since although there will be a preferred optimal BMI for each ethnic group, which will balance environmental and health factors, this optimal BMI may differ between groups and environments.     

Ecological speciation in tropical reef fishes

The high biodiversity in tropical seas provides a long-standing challenge to allopatric speciation models. Physical barriers are few in the ocean and larval dispersal is often extensive, a combination that should reduce opportunities for speciation. Yet coral reefs are among the most species-rich habitats in the world, indicating evolutionary processes beyond conventional allopatry. In a survey of mtDNA sequences of five congeneric west Atlantic reef fishes (wrasses, genus Halichoeres) with similar dispersal potential, we observed phylogeographical patterns that contradict expectations of geographical isolation, and instead indicate a role for ecological speciation. In Halichoeres bivittatus and the species pair Halichoeres radiatus/brasiliensis, we observed strong partitions (3.4% and 2.3% divergence, respectively) between adjacent and ecologically distinct habitats, but high genetic connectivity between similar habitats separated by thousands of kilometres. This habitat partitioning is maintained even at a local scale where H. bivittatus lineages are segregated between cold- and warm-water habitats in both Bermuda and Florida. The concordance of evolutionary partitions with habitat types, rather than conventional biogeographical barriers, indicates parapatric ecological speciation, in which adaptation to alternative environmental conditions in adjacent locations overwhelms the homogenizing effect of dispersal. This mechanism can explain the long-standing enigma of high biodiversity in coral reef faunas.     

Stress does not inhibit induced vitellogenesis in juvenile rainbow trout

Vitellogenin (Vtg) is a widely used biomarker for xenoestrogen exposure in male fishes. In female fishes Vtg can be negatively affected by stress independent of declines in estrogen. However, few data are available on the effect of stress in male fish abnormally producing Vtg, such as when exposed to xenoestrogens. The objective for these studies was to determine the effects of stress on fish forced to produce Vtg. Three weeks prior to the experiment immature juvenile rainbow trout, Oncorhynchus mykiss, were acclimated to the experimental tanks and fed a maintenance ration. We induced Vtg synthesis by injecting 17β-estradiol (E₂) 7 days prior to experimentation. Treatments in duplicate tanks were: (1) no stressor; (2) stressor; (3) E₂; (4) E₂ and stressor. Plasma was collected at time = 0 for baseline measurements from eight fish per tank and Vtg was significantly elevated in treated fish compared to uninjected controls. Water was drained from the stressor tanks then refilled to a level that just covered the backs of the fish. Eight fish were sampled again at 4 and 9 h, and 1, 7, and 14 days of continuous stress. Stressor tanks were refilled with water to pre-stress levels and the fish were sampled after another 2 weeks. Cortisol was significantly elevated from the unstressed fish at 4 h; however, plasma Vtg in the E₂-stimulated fish was not affected by the stressor at any timepoint. These results indicate that fish capture procedures employed in the field or caging experiments likely do not lead to false negative results when plasma Vtg is used as a biomarker for xenoestrogen exposure. It also suggests that the energetic load induced by stress is insufficient to cause a reduction in Vtg, during a continuous E₂ administration, at least within the timepoints examined in this study.     

Eggshell biliverdin concentration does not sufficiently predict eggshell coloration

Avian eggshell coloration may have arisen due to selection on the biological, chemical, or physical properties of the pigments embedded within the eggshell, or due to selection on the coloration that emerges due to pigment deposition. Within both hypothetical frameworks, pigment‐based eggshell coloration would be related to metrics of egg quality; however, no one has evaluated the relative strength of coloration and pigment concentration in predicting egg quality. Here, we examined 66 European starling Sturnus vulgaris eggs and quantified eggshell biliverdin concentration (an antioxidant that produces the eggshell's blue coloration) and used 28 different coloration metrics derived from both photographic and spectrophotometric data. We also measured egg size, eggshell thickness, concentration of carotenoids in the yolk, and concentration of lysozyme in the albumen to capture variation in egg quality. We found that throughout the laying sequence, biliverdin concentration increased while eggshell thickness, yolk carotenoid concentration, and lysozyme concentration in the albumen all decreased, but this variation was not captured by any eggshell coloration metric. Both eggshell coloration and biliverdin concentration were negatively associated with yolk carotenoid concentration, but only eggshell biliverdin concentration was negatively associated with yolk mass. Lastly, biliverdin concentration explained, at most, only 46% of the variation for all eggshell coloration metrics. Our results suggest biliverdin concentration is a better predictor of egg quality than egg coloration in European starlings, supporting the hypothesis that eggshell pigment concentration per se may be the target of selection.     

Seascape and life-history traits do not predict self-recruitment in a coral reef fish

The persistence and resilience of many coral reef species are dependent on rates of connectivity among sub-populations. However, despite increasing research efforts, the spatial scale of larval dispersal remains unpredictable for most marine metapopulations. Here, we assess patterns of larval dispersal in the angelfish Centropyge bicolor in Kimbe Bay, Papua New Guinea, using parentage and sibling reconstruction analyses based on 23 microsatellite DNA loci. We found that, contrary to previous findings in this system, self-recruitment (SR) was virtually absent at both the reef (0.4–0.5% at 0.15 km²) and the lagoon scale (0.6–0.8% at approx. 700 km²). While approximately 25% of the collected juveniles were identified as potential siblings, the majority of sibling pairs were sampled from separate reefs. Integrating our findings with earlier research from the same system suggests that geographical setting and life-history traits alone are not suitable predictors of SR and that high levels of localized recruitment are not universal in coral reef fishes.     

Diel feeding migrations in tropical reef fishes

Summary 1. Many tropical reef fishes that feed during the day rest at night, whereas many that feed at night rest during the day. The feeding grounds of many are some distance from their resting grounds. Thus they migrate between these two locations during twilight as part of a general changeover between diurnal and nocturnal situations.2. At least many of these migrations are predictable, both as to time and to the route taken. The distances traveled vary between species, ranging from just a few meters, to more than several kilometers.3. The pattern of migrations is strongly influenced by the relative threat from predators at different periods of the diel cycle.4. During the day, migrations of reef fishes are limited to intra-reef movements: short vertical movements by certain plankton feeders, and lateral excursions from one part of the reef to another by certain herbivores and plankton feeders. Movements into the open regions that lie adjacent to many reefs are not adaptive in daylight due largely to a danger from predators.5. Despite constant threat from predators during the day, smaller reef fishes remain relatively secure during most of this period by staying close to shelter, or by schooling. However, these defenses are less effective during twilight, when the danger from predators intensifies. The diurnal migrators return to the shelter of their resting places prior to that part of evening twilight when danger is greatest, and the nocturnal migrators usually do not expose themselves for their nightly foraging until after the period of maximum danger has passed. During morning twilight the sequence is reversed.6. The major mechanisms whereby smaller reef fishes reduce predation during the day — schooling and staying close to shelter — are less evident at night. Not only do reef fishes range freely at night into the open regions that are avoided in daylight, but their schools are more loosely defined, and many are active as solitary individuals or in small groups. The tendency for looser associations and ranging farther afield increases on darker nights.7. Most predators that threaten reef fishes are visual feeders whose mode of attack loses effectiveness when light falls below a certain level. Although they operate to some extent under moonlight, they threaten small reef fishes less at night than during the day.8. In addition to whatever other ways a shcool may be adaptive, by reducing variable behavior among its members the school is especially important to migrating species. Responses to the various cues that mark the migration routes may be refined to within acceptable limits for the population as a whole only by coordinated group action.9. Submarine topographical features are important reference points for migrating reef fishes.

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Tägliche Futtersuchwanderungen bei tropischen Riffischen

Kurzfassung Dämmerungszeiten wandern viele tropische Fische zwischen ihren Ruheplätzen auf dem Riff und ihren Futterplätzen. Diese Wanderungen, die sowohl von tag- als auch von nachtaktiven Fischen durchgeführt werden, sind bedingt durch den Licht-Dunkel-Wechsel, und für viele Arten können sogar Zeit und Weg der Wanderung vorhergesagt werden. Das Muster der tagesrhythmischen Wanderungsbewegungen wird vor allem durch das Ausmaß von Bedrohungen durch Raubfeinde beeinflußt. Bewegungen in ungeschützte Gebiete, die vom Riff wegführen, sind am Tage nicht vorteilhaft. Bei Einbruch der Dunkelheit sind diese offenen Gebiete hingegen ein Konzentrationspunkt der Wanderungen aus dem Riff, wobei sich auch der Zusammenhalt der Fischschwärme verringert. Da Schwarmverhalten und Schutzsuchen die beiden wichtigsten Verteidigungseinrichtungen gegenüber Räubern darstellen, bedeutet das Aufgeben dieser Verhaltensweisen zu Beginn der Dämmerung, daß während der Nacht kleinere Riffische weniger bedroht sind als während des Tages. Für wandernde Schwarmfische dürfte eine geringe Variabilität der Verhaltensweisen von adaptiver Bedeutung sein. Nur durch ein koordiniertes Schwarmverhalten ist es offensichtlich möglich, innerhalb bestimmter Grenzen auf die verschieden optischen Marken, welche die Wanderwege kennzeichnen, zu reagieren. Vermutlich spielen die topographischen Gegebenheiten unter Wasser eine entscheidende Rolle für die Orientierung der Riffische.