Group stability and homing behavior but no kin group structures in a coral reef fish

Understanding the reasons behind stable group formations hasreceived considerable theoretical and empirical attention. Stablegroups displaying homing behavior have been suggested to formas a result of, for instance, benefits from knowledge of thesocial or physical environment or through kin selection andthe forming of kin groups. However, no one has disentangledpreference for grouping in a familiar location from preferencefor grouping with familiar or related individuals. To investigatethis, we conducted a series of field experiments and a groupgenetic analysis on the group-living Banggai cardinalfish (Pterapogonkauderni). We found homing behavior but no evidence for recognitionof familiar group members. Instead, homing was based on theoriginal location of their group rather than the individualsin that group. Moreover, we found no evidence for kin structureswithin these groups. We suggest that benefits from living ina known social environment drive homing behavior in this speciesand that homing behavior is not enough for the formation ofkin group structures. Instead, our results suggest that kinrecognition may be a prerequisite for the forming of kin groups.     

Postsettlement movement patterns and homing in a coral-associated fish

Coral-associated gobies are highly specialized reef fishes withhigh host-coral fidelity. Flexibility in habitat choice, however,is important to compensate for potential habitat alterationor loss, but detailed information about the postsettlement movementbehavior of such gobies is lacking. We examined movement patternsin Gobiodon histrio, both under natural conditions and duringsubsequent field experiments, involving breeding pair or partnerremoval from 3 of the 4 investigation plots. Additionally, weinvestigated homing behavior, and 2 aquaria experiments weredesigned to assess home coral and partner recognition of adultfish taken from breeding pairs. Under natural conditions, themovement rate was high for single adults, whereas breeding pairsshowed high home-coral fidelity. Manipulations revealed littlechange of natural patterns except in single adults, which slightlydecreased their movement rate in the breeding pair removal plot.In the homing experiment, 17% of tested fish returned to theirhome coral even after displacement of 4 m, and homing successwas much higher at shorter distances (100% at 0.5 m, 53% at2.25 m). In the aquarium, G. histrio exhibited higher recognitionof its home-coral colony (75%) than of its breeding pair partner(60%). Our study shows that G. histrio frequently moves betweencorals, although this depends on the social status (juvenile,single adult, breeding pair) of the individuals. The high proportionand movement rate of single adults indicate low sensitivityto habitat alteration but also limited high-quality habitatsin which breeding pairs could be established. Hence, vulnerabilityto habitat loss increases when individuals breed.     

Sexual cannibalism, competition, and size dimorphism in the orb-weaving spider Nephila plumipes Latreille (Araneae: Araneoidea)

The degree and direction of sexual dimorphism varies widely,but in several taxa of orb-weaving spiders, including Nephila,males may be less than one-tenth the size of females. This differenceis commonly attributed to selection through precopulation sexualcannibalism: females may either fail to detect very small males,or ignore them as potential prey items. However, there is oftenthe potential for male-male competition in these species becauseseveral males can be found on the web of a single female. Weinvestigated experimentally the effects of sexual cannibalismand male-male competition on male body size and hence sexualdimorphism in the Australian golden orb-weaver (Nephila plumipes).Small males were less likely to be detected and cannibalizedthan larger males. However, larger males excluded small malesfrom the central hub of the web, where mating takes place. Theconflicting effects of sexual cannibalism and male-male competitionmay be responsible for the relatively large variation in malebody size in this species.     

Impacts of Shading on Sponge-Cyanobacteria Symbioses: A Comparison between Host-Specific and Generalist Associations

The marine sponge Lamellodysidea chlorea contains large populationsof the host-specific, filamentous cyanobacterium Oscillatoriaspongeliae. Other marine sponges, including Xestospongia exigua,contain the generalist, unicellular cyanobacterium Synechococcusspongiarum. The impact of cyanobacterial photosynthesis on hostsponges was manipulated by shading these sponge-cyanobacteriaassociations. If cyanobacteria benefit their hosts, shadingshould reduce this benefit. Chlorophyll a concentrations weremeasured as an index of cyanobacterial abundance. After twoweeks, shaded L. chlorea lost more mass than controls, whileshaded and control X. exigua did not lose a significant amountof mass. Chlorophyll a concentrations in shaded X. exigua werelower than in controls, but were not significantly differentbetween shaded and control L. chlorea. In addition, L. chloreashaded in situ lost over 40% of their initial area, but didnot differ in chlorophyll a concentrations from controls. Theseresults suggest that Oscillatoria symbionts benefit their hostsponges in a mutualistic association. Synechococcus symbiontsmay be commensals that exploit the resources provided by theirsponge hosts without significantly affecting sponge mass. Whenshaded, Synechococcus symbionts may be consumed by their hostsor may be able to disperse from this unfavorable environment.These data support the hypothesis that more specialized symbiontsprovide a greater benefit to their hosts, but hypotheses concerningthe dispersal abilities of these symbionts remain to be explored.Sponge-cyanobacteria symbioses provide model systems for investigatingthe costs and benefits of symbiosis and the roles of dispersal,environmental conditions, and phylogenetic history in determiningthe specificity of endosymbionts for their hosts.     

SEXUAL DIMORPHISM OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE) IN NORTH WALES, UK

Multivariate statistical methods were employed to examine sexualdimorphism in size and shape of Nucella lapillus collected from 16sheltered sites along coasts of Anglesey and the Lleyn Peninsula, NorthWales, UK. Females were significantly larger than males in overallsize; among 12 relative measures of shell shape, two ratios (shellwidth/shell length and aperture length/shell length) were significantlydifferent between males and females, but these differences usuallydecreased with increasing age (shell length). The observed hypoallometricdimorphism could be a result of selection on increased femalefecundity, which may be positively correlated with shell sizein N. lapillus as in other gastropod species. (Received 22 November 1999; accepted 10 April 2000)     

Possible use of environmental gradients in orientation by homing wood mice,Apodemus sylvaticus

51 wood mice, Apodemus sylvaticus, tagged with chemoluminescent bulbs, were visually tracked in a series of night homing experiments. The mice did not go straight towards home, but wandered around the release area and covered distances equal to twice the radial lengths recorded. In the course of their walk, they orientated preferentially towards landscapes which resembled their usual habitat, irrespective of where their actual homeward direction lay. In spite of the randomness of their paths, homing success was good, but detailed analysis of homing time showed that the homing performances of the mice depended on the direction in which they vanished in the course of the observation period. The good fit of observed orientations with those obtained by computer simulation of klinokinesis along an axial gradient, and field observation of a vegetational gradient in the study area, are both consistent with the hypothesis that homing may have resulted from wandering, locally biased by a klinokinetic effect     

Multivariate analysis of initial orientation in homing pigeons: Is there a “preferred compass direction”?

The mean vanishing direction of homing pigeons of a given release often deviates from the home direction considerably. Any kind of geographical systematic in these deviations might give us a hint on the distribution of the information involved in the homing process. Analysis of releases arranged symmetrically around the home loft with methods of circular statistics could not resolve the pending question of site-specificity vs. directional effects in the initial orientation of homing pigeons unambiguously. In part, this ambiguity comes about by the facts that

Biogenic magnetite as a basis for magnetic field detection in animals

Bacteria, sharks, honey bees, and homing pigeons as well as other organisms seem to detect the direction of the earth's magnetic field. Indirect but reproducible evidence suggests that the bees and birds can also respond to very minute changes in its intensity. The mechanisms behind this sensitivity are not known. Naturally magnetic, biologically precipitated magnetite (Fe₃O₄) has been found in chitons, magnetotactic bacteria, honey bees, homing pigeons, and dolphins. Its mineralization in localized areas may be associated with the ability of these animals to respond to the direction and intensity of the earth's magnetic field. The presence of large numbers (～10⁸) of superparamagnetic magnetite crystals in honey bees and similar numbers of single-domain magnetite grains in pigeons suggests that there may be at least two basic types of ferrimagnetic magnetoreceptive organelles. Theoretical calculations show that ferrimagnetic organs using either type of grain when integrated by the nervous system are capable of accounting for even the most extreme magnetic field sensitivities reported. Indirect evidence suggests that organic magnetite may be a common biological component, and may account for the results of numerous high field and electromagnetic experiments on animals.     

The Interaction of Genetic, Environmental, and Hormonal Factors in Stem Elongation and Floral Development of Cucumber Plants

Hypocotyl length was found to vary between cucumber plants carryingdifferent genes controlling sex expression. Among lines havingonly unisexual flowers (genotype M/M), the homozygous monoeciousplants (st⁺/st⁺) had significantly longer hypocotyls than theirgynoecious counterparts (st/st), heterozygous gynoecious plants(st+/st) being intermediate. Similarly, hypocotyls of plantsof an andromonoecious line (st⁺/st⁺ m/m) were significantlylonger than in their hermaphrodite counterparts (st/st m/m).Differences in intemode length were also significant and inthe same direction. Since stem and particularly hypocotyl elongationin cucumber is known to be very sensitive to applied gibberellin,these findings suggest the existence of differences in the effectivelevels of endogenous gibberellins in the different sex types,higher levels being correlated with stronger male tendency.This conclusion is in good agreement with the known effect ofapplied gibberellin on sex expression (enhancement of the maletendency) in cucumber. Application of gibberellin (GA₄+GA₇) and exposure to ‘summer’conditions (long days and relatively high temperature) inhibitedthe development of pistillate flowers while ‘winter’conditions (short days, lower temperature) had a similar effecton staminate flowers. The effect was in either case specific,that is, limited to flower development. It is concluded thatexogenous and endogenous gibberellins affect not only the initiation,but also the further development, of flowers in the cucumber.     

Comparative Homing Behaviors in Two Species of Crayfish,Fallicambarus Fodiens and Orconectes Rusticus

Homing behaviors are seen across the animal kingdom, with the magnitude and scale of these movements varying to a great degree. Invertebrates, such as crayfish, prove to be excellent models for comparative research, with relatively simple nervous systems that have been extensively studied combined with a rich behavioral repertoire that has been well documented. Here we explore whether two crayfish species (a primary burrower and a tertiary burrower) can home to artificial burrows and if so, whether their homing abilities differ. The two species of crayfish, Orconectes rusticus and Fallicambarus fodiens, were examined for their ability to home to artificial burrows in a laboratory setting. Animals were placed in a homing arena, motivated to search by the presence of food, and subsequently return to the burrows. The movements of each individual crayfish were digitized and analyzed for changes in walking speed, velocity and heading angle relative to burrows, total distance travelled and path turning angles. Crayfish of both species successfully returned home, although F. fodiens had a higher homing success rate than O. rusticus. Detailed kinematic analysis showed that walking speeds almost doubled during homing to burrows and heading angles were significantly closer to zero than on the outward journeys for both species. Path turning angles were significantly lower for O. rusticus than for F. fodiens. These findings indicate that these species of crayfish can successfully home without the visual landmark of burrow chimneys and that the primary burrower (F. fodiens) appears to be more successful with straighter return paths. The differences in these two species to home and the underlying mechanisms of homing may be due to the differences in burrow use with primary burrowers showing more efficient homing than tertiary burrowers.     

Magnetic Navigation

Recent evidence suggests that some amphibians, reptiles and birds may be capable of homing using information about geographic position (“map” information) derived from subtle geographic gradients in the earth's magnetic field. The “magnetic map” hypothesis faces numerous theoretical difficulties, however, due to the extremely high level of sensitivity that would be necessary to detect natural magnetic gradients, and to the presence of spatial irregularities and temporal variation in the geomagnetic field that might make map coordinates derived from magnetic gradients unreliable. To date, the majority of studies carried out to test the magnetic map hypothesis have involved field observations of the effects on homing orientation of naturally occurring spatial or temporal variation in the geomagnetic field. While providing an important first step, these studies are subject to the criticism that the observed changes in homing orientation could result from effects on a magnetic compass, or some other unidentified component of the navigational system, rather than from effects on a magnetic map. The recent development of experimental systems in which navigational ability can be studied under controlled or semi-controlled laboratory conditions has opened up the possibility of using new experimental approaches to more rigorously test the magnetic map hypothesis. After briefly reviewing the available evidence of the geomagnetic field's involvement in the map component of homing, a simple graphical model is presented which describes how the home direction derived from a bicoordinate map varies as a function of the value of one of the map coordinates when the value of the second map coordinate is held constant. In studies of homing orientation in which the value of a specific magnetic field parameter (e.g., total intensity, inclination, etc.) can be varied independently of other putative map parameters, the graphical model can be used to generate qualitative predictions about the changes in the direction of homing orientation that should be observed if the magnetic field parameter being manipulated serves as one coordinate of a bicoordinate map. The relationship between the direction of homing orientation and the value of a putative magnetic map parameter can also be used to generate quantitative predictions about characteristics of the local gradient of that magnetic field parameter in the vicinity of the home site (i.e., the alignment and “home value” of the local gradient) which can then be compared with actual measured values. Together, the qualitative and quantitative predictions of the graphical model permit rigorous tests of whether one or both coordinates of a bicoordinate navigational map are derived from the geomagnetic field.     

Cortisol and Pacific Salmon: A New Look at the Role of Stress Hormones in Olfaction and Home-stream Migration

Pacific salmon (genus Oncorhynchus) exhibit an interesting anduncommon life-history pattern that combines semelparity, anadromy,and navigation (homing). During smoltification, young salmonimprint on the chemical composition of their natal stream water(the home-stream olfactory bouquet or "HSOB"); they then migrateto the ocean where they spend a few years feeding prior to migratingback to their natal freshwater stream to spawn. Upstream migrationis guided by the amazing ability to discriminate between thechemical compositions of different stream waters and thus identifyand travel to their home-stream. Pacific salmon demonstratemarked somatic and neural degeneration changes during home-streammigration and at the spawning grounds. The appearance of thesepathologies is correlated with a marked elevation in plasmacortisol levels. While the mechanisms of salmonid homing arenot completely understood, it is known that adult salmon continuouslyutilize two of their primary sensory systems, olfaction andvision, during homing. Olfaction is the primary sensory systeminvolved in freshwater homing and "HSOB" recognition, and willbe emphasized here. Previously, we proposed that the increasein plasma cortisol during Pacific salmon home-stream migrationis adaptive because it enhances the salmon's ability to recallthe imprinted memory of the "HSOB" (Carruth, 1998; Carruth etal., 2000b). Elevated plasma concentrations of cortisol couldprime the hippocampus or other olfactory regions of the brainto recall this memory and, therefore, aid in directing the fishto their natal stream. Thus, specific responses of salmon tostressors could enhance reproductive success.     

Predation risk and mating behavior: the responses of moths to bat-like ultrasound

In the presence of predators, animals may reduce or alter theirmating activities. There has been little experimental studyof whether mating behavior varies with the level of predationrisk. Two species of moths, Pseudaletia unipuncta (Noctuidae)and Ostrinia nubilalis (Pyralidae), significantly reduced theirmate-seeking behavior under high levels of simulated predationrisk. Male moths aborted upwind flight in a pheromone plume,and females stopped releasing pheromone in response to soundssimulating the echolocation calls of bats. For O. nubilalis,but not for P. unipuncta, the response varied significantlywith the level of predation risk. Interspecific differencesin behavioral responses likely reflect differences in physiologicalauditory sensitivity and/or behavioral thresholds. Female behavioralresponses to sounds simulating the calls of bats that gleantheir prey from surfaces were significantly weaker than theirresponses to sounds resembling the calls of aerially hawkingbats; these results support the neurophysiological data thatthe calls of gleaning bats are relatively inaudible to moths.This study indicates that some animals can modify their reproductiveactivities in response to auditory cues from predators.     

Role of olfaction and vision in homing behaviour of black rockfish Sebastes inermis

How fish find their original habitat and natal home remains an unsolved riddle of animal behaviour. Despite extensive efforts to study the homing behaviour of diadromous fish, relatively little attention has been paid to that of non-diadromous marine fish. Among these, most rockfish of the genus Sebastes exhibit homing ability and/or a strong fidelity to their habitats. However, how these rockfish detect the homeward direction has not been clarified. The goal of the present research was to investigate the sensory mechanisms involved in the homing behaviour of the black rockfish Sebastes inermis, using acoustic telemetry. Vision-blocked or olfactory-ablated rockfish were released in natural waters and their homing behaviours compared with those of intact or control individuals. Blind rockfish showed homing from both inside and outside their habitat. The time taken by blind fish to reach their home habitat was not significantly different from that of the control fish. In contrast, most olfactory-ablated fish did not successfully reach their original habitat. Our results indicate that black rockfish predominantly use the olfactory sense in their homing behaviour.     

RELATIVE IMPORTANCE OF AIRBORNE ODOURS AND TRAILS IN THE GROUP HOMING OF LIMACUS FLAVUS (LINNAEUS) (GASTROPODA, PULMONATA)

The relative importance of airborne odours and con-specifictrails in the group homing of Limacus flavus has been studiedin the laboratory using an Y-olfac-tometer and trail followingtests. The slugs showed positive anemotaxis along air flowspassing through shelters inhabited or recently inhabited byconspecifics. In the choice between single and group shelters,the animals headed preferentially towards the latter ones. L.flavus is able to discriminate between conspecific and heterospecific(Limax maximus) shelters. Trail following tests failed to showsignificant trail superimposition, but did show a significantdeflection of the test slug path towards the marker after crossing.In direct comparison, distant chemoreception prevailed overtrail following in the orientation towards conspecifics (Received 10 August 1987;     

The effect of age on encounters between male crab spiders

In males that compete aggressively for females, size and agemay determine which males obtain access to these females. Inthe present study, we use the crab spider, Misumena vatia, aspecies with males that do not grow after becoming sexuallymature adults, to test the hypothesis that age affects the successof males competing for access to females. M. vatia is an excellentspecies to test this hypothesis because it is possible to disentangleage from size, characters that typically vary together in thespecies usually tested. We staged encounters between similar-sizedolder and younger adult male M. vatia in the presence of a femaleto determine the role of age in male access to females. Encountersbetween the males occurred during 63.3% of these pairings. Youngermales won significantly more (70.2%) of the encounters thandid older ones, but did not initiate significantly more encountersthan did older ones (62.5%). Although older males won only 29.8%of these encounters, they initiated significantly more (76.5%)of them than predicted by chance. This design also allowed usto test Parker's hypothesis that older individuals should exhibita higher level of aggression than younger ones. However, attacksby younger males were most likely to include extensive bodilycontact, whereas attacks by older males involved significantlyless contact. These results counter the frequent assertion thatolder individuals usually prevail over younger ones in contestsfor access to females, and that older males are more likelyto engage in highly overt aggression than are younger ones.Aging may decrease reproductive opportunities and success ratesof male M. vatia, affecting as many as nearly one-fourth oftheir encounters.     

Ecological Aspects of Some Coral-Boring Gastropods and Bivalves of the Northwestern Red Sea

More than 17 molluscan species were obtained from burrows incoral substrata at Al-Ghardaga (Hurghada on maps) on the RedSea coast, six of which in particular bore into livingcolonies.The species reported in this paper belong to the families Mytilidae,Coralliophilidae, and Gastrochaenidae. The direction of boringin living corals is to the outside, the borers keeping pacewith the growing coral layer to maintain their burrows open.Coral growth is generally of a higher rate than that of borers,and burrows are accordingly mostly much larger than their inhabitants.There is evidence in such cases that burrows form initiallyby growth of coral around the settling young. Boring of Lithophagaspecies is mostly due to the abrasive action of the shell whichmoves straight and posteroventrally without any rotation. Incoralliophilids,boring is also executed mechanically by the turning movementsof the shell. Boring in dead coral is directed inwards, andburrows are nearly as large as the borers. The latter avoidthe blocking of their burrows (e.g., by a living coral incrustation)either by great siphonal extension (Rocellaria) or the freeends of the shell may be strengthened to maintain the capabilityof boring in the opposite direction (Lithophaga laevigata).Both L. luevigata and Modiola chmamomeus bore mainly mechanicallyby the rocking movements of the shell. Chemical boring is stilla possibility,particularly in the posterior narrow region ofburrows of Modiola lodging the extended pallial siphons whichare deprived of any effective mechanical devices for boring.Therole of boring algae in rarefying bored coral material hasalso to be included as an indirect chemical factor.     

The Meristem and Quiescent Centre in Cultured Root Apices of the gib-l Mutant of Tomato (Lycopersicon esculentum Mill.)

Cultured root apices of tomato bearing the gib-I mutation, whichreduces the levels of endogenous gibberellins, grew slower andwere thicker than wild-type contols. This was the result ofshorter and broader cells in the menstem of the mutant. Cellsof both cortex and stele were affected, but this did not causeany alteration to the volume fraction occupied by these twotissues in the root meristem. Root caps were longer in the mutantand there were also more layers of rhizodermis. All these effectscould be reproduced in wild-type roots by addition of 0.1µM2S, 3S paclobutrazol (an inhibitor of gibberellin biosynthesis)to the culture medium and could be normalized in mutant rootsby 0.1 µM GA₃. Cell doubling times in the proximal regionof the meristem were similar in mutant and wild-type roots,but were faster in both the quiescent centre (QC) and the capmeristem of the mutant. This latter feature of the mutant rootsis likely to be the cause of their longer caps, while the fasterrate of division in the QC accounts for the additional tiersof cells that were found to build up in the cortical portionof this zone These additional tiers failed to form in mutantroots grown in GA₃, but they could be induced in wild-type rootsby 2S, 3S paclobutrazol. These results suggest that endogenousgibberellins may be partly responsible for the slow rate ofcell growth and proliferation in the QC. Gibberellins, gib-I mutation, Lycopersicon esculentum, meristem, roots, 2S, 3S paclobutrazol, quiescent centre, tomato     

Elongation and Gravireactivity of Roots from an Agravitropic Maize Mutant: Implications of Growth Inhibitors

Growth of agravitropic (AGT) mutant (c.v. Kys) maize roots wassignificantly higher in comparison to that of two normal gravitropiccultivar roots. Vertical halfdecapitated roots bent towardsthe remaining half tip. This result can be explained by thefact that cap cells produced growth inhibitors (GI) moving inbasipetal direction. The curvatures of half-decapitated rootsin Kys AGT root were significantly smaller than in normal cultivarroot. One essential consequence of this AGT mutation was broughtby low GI content inside the extension zone. ¹ In honour of Professor J. Ashida (Received August 27, 1982; Accepted January 17, 1983)     

Self- and cross-adaptation to chemical stimulation of the nasal trigeminal nerve in the rat

Electrophysiological, multi-unit responses from the ethmoidbranch of the trigeminal nerve to chemical stimuli (amyl acetate,d-carvone, l-carvone, l-menthol and toluene) were examined,using self- and cross-adaptation paradigms, to address the questionof whether different chemical stimuli may stimulate trigeminalnerve fibers using different ‘receptive pathways’and thus to suggest whether qualitative distinctions betweendifferent compounds may be made by trigeminal chemoreceptors.No adaptation occurred between l-menthol and toluene, suggestingthat these two compounds activate different receptive pathwaysin the trigeminal nerve which may be capable of making qualitativediscriminations between these two compounds. Symmetrical adaptationoccurred between amyl acetate and d-carvone, amyl acetate andl-carvone, amyl acetate and toluene, and l-carvone and d-carvonesuggesting that these compounds may activate the same receptivepathways in the trigeminal nerve which may not be capable ofmaking qualitative discriminations between these compounds.Asymmetrical adaptation occurred between amyl acetate and l-menthol,d-carvone and l-menthol, l-carvone and l-menthol, d-carvoneand toluene, and l-carvone and toluene. This implies that theprocessing of these stimuli by trigeminal nerve fibers may bemore complex than anticipated previously.