Pigeon homing: a comparison between groups raised under different conditions

Summary The homing ability of a group of pigeons raised under conditions of continuous exposure to windborne information was compared to that of another group subjected to exposure to winds only during the time spent in pre-test training flights. The results of release experiments at sites that were unfamiliar to the pigeons show that both bird groups, which had been made temporarily anosmic, had impaired initial homeward orientation and homing ability. These results, which do not entirely concur with the recent findings of Wiltschko and his coworkers, show that the raising and training procedures we used do not influence the nature of the cues used in pigeon homing. If the exposure of birds to wind-borne information is reduced, this does not bring into play any effective non-olfactory mechanisms of navigation; it simply hinders the development of the olfactory map and impairs the homing ability. Offprint requests to: S. Benvenuti     

A comparison of spatial learning and memory capabilities in intertidal gobies

For the majority of animals, the ability to orient in familiar locations is a fundamental part of life, and spatial memory allows individuals to remember key locations such as food patches, shelter, mating sites or areas regularly occupied by predators. This study determined if gobies collected from rocky platforms and sandy beaches differ in their ability to learn and memorise the locations of tide pools in a simulated rocky intertidal zone. Intertidal rock pool gobies show acute homing abilities and, therefore, should be expected to display superior learning and memory capabilities. In contrast, it is unlikely that natural selection would favour similar learning skills in sandy shore fishes because they simply shift back and forth with the tides. The learning abilities of gobies were tested using small replica rock platforms, containing four tide pools that retained varying depths of water at simulated low tide. Gobies were categorised as having learnt the task if they were able to consistently locate the tide pool that retained the most water at simulated low tide as the pool with the most favourable conditions. Rock pool species were able to locate the deepest pool to wait out low tide for ~95 % of the trials, while species from sandy shores were found in the deepest pool ~10 % of trials. Despite repeated stranding, sandy shore fish continued to follow the tide out. We propose that rock pool species memorised the location of rock pools during simulated high tide enabling them to relocate the best refuge for low tide.     

Intercontinental tests of the effects of habitat patch type on the distribution of chitons within and among patches in intertidal boulder field landscapes

Patchy distributions within landscapes may be caused by migration in response to different types of habitat patches. Intertidal boulder fields are landscapes in which boulders are discrete habitat patches, often with chitons attached to their under-surfaces. Chiton densities and associations with patch edges differed between boulders overlying coarse- versus fine-sediment types, with greater densities occurring over fine sediments. We tested whether adult migration caused between-boulder distributions by measuring immigration and emigration following experimental replacement of coarse sediments with fine sediment under boulders. We also assessed whether the manipulations altered chiton positions relative to patch edges, and large-scale generality was tested by including data from two continents. The manipulations did not influence the association of chitons with edges or amounts of emigration, but chitons did display positive density-dependent immigration that mirrored their distributional patterns, indicating the importance of immigration. Strikingly, all results were consistent between continents despite involving different species and even genera of chitons. By using boulder fields as a small-scale, easily manipulated landscape, we show that, even in sedentary organisms, patchy distributions within landscapes can be caused by migration alone, without the need to invoke mortality or larval recruitment.     

The role of habitat heterogeneity in structuring the community of intertidal free-living marine nematodes

The role of habitat complexity has been widely neglected in the study of meiofaunal community patterns. We studied the intertidal nematode community of a structurally complex macrotidal beach exhibiting contrasting microhabitats (sandbars and runnels) to understand the influence of environmental gradients and habitat heterogeneity in the community structure. We tested whether topographical complexity affected (1) the zonation pattern in terms of abundance and diversity, and (2) local diversity by promoting compartmentalization into distinct faunal groups. Our analyses revealed three major faunal assemblages along the exposure gradient associated to differences in mean grain size and chlorophyll a. Diversity patterns involved a mid-intertidal peak, consistent with the intermediate disturbance hypothesis, and another peak at the limit with the subtidal region, consistent with the transition zone. These results highlight the predominance of environmental gradients in establishing intertidal zonation. However, microhabitats differed in environmental conditions and possessed significantly distinct nematofaunal communities. Runnels featured higher levels of taxonomic and functional diversity, many unique genera, and the community differed from the assemblage at the limit to the subtidal, stressing their role as distinct microhabitats. The nematofauna of the structurally complex beach was more diverse than the one from a homogeneous beach nearby, supporting the hypothesis that structural heterogeneity promotes diversity by compartmentalization and highlighting the importance of microhabitats in the assessment of biodiversity. Contrary to previous predictions, our results indicate potentially high regional marine nematode diversity in the Upper Gulf of California.     

Pigeon homing: A repetition of the deflector loft experiment

Summary Pigeons brought up in closed cages deflecting the winds to the left or to the right show, on release, a bias of the mean vanishing directions to the left or right of the mean direction of untreated control birds. The results are in full accord with the findings of Baldaccini et al. (1975).Supported by the Deutsche Forschungsgemeinschaft     

Pigeon homing: new airbag experiments to assess the role of olfactory information for pigeon navigation

Summary In three series of experiments we assessed the effects of olfactory and non-olfactory information collected en route or at the release site on the initial orientation of homing pigeons. In the first experiment, pigeons were transported in open crates to two sites located in opposite directions from the home loft. They were left at the site for 1 h, then put into airtight containers filled with air from that site and brought back to the loft. From there, controls were transported back to the original site. Experimentals were transported to the opposite site. Upon arrival at the site, the olfactory mucosae of both groups were anesthetized with Gingicain. Thus in this experiment, control and experimental pigeons were exposed to different olfactory as well as to different non-olfactory information during displacement and at the site. In the second series, controls and experimentals were treated as in the first experiment, except that they were enclosed in the airtight containers at the very beginning of the experiment and were ventilated with synthetic air until arrival at the final release site. This treatment excluded the possibility to perceive olfactory information en route or at the site. In this series, the two groups differed only with respect to non-olfactory information perceived during displacement and/or at the release site. In the third series, we exposed pigeons at the loft to air collected either at the later release site (controls) or to air collected at a site located in opposite direction of the home loft (experimentals). Here the two groups differed only with respect to their exposure to air of different origin. In all three series, the pooled controls showed a directional preference that was statistically indistinguishable from the home direction. All three experimental groups were disoriented. In the first two series, the differences in the initial orientation of control and experimental pigeons were highly significant. In the third experiment, there was only very weak statistical evidence for a difference between controls and experimentals. These results suggest that more than one factor is involved in the pigeons' navigation system. According to the present experiment with synthetic air, pigeons probably gather and process non-olfactory information during the first part of their transport from the home loft to the release site. Thus, some kind of, in this case non-olfactory, route reversal seems to be involved in the homing process. In addition, the experiment involving only manipulations of airborne information indicated some olfactory component. Previous experiments at our loft did not result in disorientation of the pigeons if either only the access to airborne information had been removed or when otherwise unmanipulated pigeons had been transported in detours to the final release site. Therefore, we assume that our pigeons' navigation system relies on several cues. Deletion of one cue can be compensated by other information. Often the initial orientation of our pigeons is disturbed only when at least one cue is removed and another one provides false information.     

The role of trail pheromones in host nest recognition of the social parasitic bumblebees Bombus bohemicus and Bombus rupestris (Hymenoptera: Apidae)

Bumblebees of the subgenus Psithyrus are obligate social parasites of Bombus colonies. Parasitic females enter host colonies and replace the host queen. The offspring of the parasite is reared by the host workers. Females locate host colonies by nest searching flights and recognition of species-specific nest odours at the entrance. We investigated inter- and intraspecific odour variation of 45 hydrocarbons of nests of potential hosts by coupled gas chromatography/mass spectrometry and tested the preferences of the parasite females of B. bohemicus and B. rupestris for these mixtures in Y-olfactometer choice tests. Interspecific and intracolonial differences in the odour bouquets of the host species were found to be predominantly due to different patterns of alkenes. Furthermore, we found intercolonial differences within the single species. In behavioural assays, females of the two species showed different preferences for the offered nest odours, implicating different host spectra. Bombus rupestris showed a clear preference for the scent of its host, B. lapidarius. Bombus bohemicus females were attracted by B. terrestris, B. lucorum, and B. cryptarum in a similar manner. The results show that volatile signals enable parasite females to discriminate between potential host species.     

Functional divergence in heat shock response following rapid speciation of Fucus spp. in the Baltic Sea

In the Baltic Sea, the broadly distributed brown alga Fucus vesiculosus coexists in sympatry over part of its range (south west Gulf of Bothnia) with the Baltic endemic F. radicans sp. nov, while further north in colder and lower-salinity areas of the Baltic F. radicans occurs alone (north west Gulf of Bothnia). F. radicans appears to have arisen via rapid speciation from F. vesiculosus within the recent history of the Baltic (ca. 7500 BP). Possible functional divergence between the two species was investigated by comparing stress-responsive gene expression in a common-garden experiment. The experiment used two allopatric populations of Fucus vesiculosus from the Skagerrak (North Sea) and Central Baltic, as well as F. radicans from the same Central Baltic site. The two species in sympatry displayed divergent heat shock responses, while F. vesiculosus populations from allopatric sites did not. F. radicans was more sensitive to heat shock at 25°C, either alone or together with high irradiance and desiccation, than Baltic or Skagerrak F. vesiculosus. The results indicate that rapid functional divergence in the inducible heat shock response has occurred between sympatric species on a timescale of thousands of years.     

Genetic divergence between colour morphs in populations of the common intertidal sea anemones Actinia equina and A. prasina (Anthozoa: Actiniaria) in the Isle of Man

A distinctive morph ofActinia equina (L.) is found at low frequency among populations on intertidal hard substrata on some shores on the Isle of Man. This morph is red with rows of green oval spots or elongate markings running longitudinally down the column. Starch gel electrophoresis of 21 allozyme loci was used to compare samples of this morph from two localities with other sympatricActinia spp. Collections were made in early summer 1986. For one sampling site the comparison was with redA. equina and greenA. prasina Gosse, whilst at the other site with redA. equina only. At both sites significant genetic differences in allele frequencies at several loci were found between the new morph and sympatricA. equina andA. prasina. The results also confirm the reproductive isolation ofA. prasina. As with much previous work on sea anemones, levels of mean heterozygosity per locus (H) were found to be high (H=0.157 to 0.342). A surprising feature of the results, although bearing out earlier unpublished data, is that high levels of genetic differentiation are found between populations of what appear to be the same morphs collected from shores only a few km apart. Among theActinia spp. studied, differentiation between populations of the same morph on different shores was of the same order as between sympatric, reproductively isolated populations.     

The Wahlund effect and the geographical scale of variation in the intertidal limpet Siphonaria sp.

Samples of Siphonaria sp. were collected between 1978 and 1982 from sites covering its known geographic range, from Kalbarri, Western Australia to Port Robe, South Australia. Geographic variation of 7 polymorphic enzymes was examined in this intertidal pulmonate limpet, and was found to be consistently small, indicating a large-scale influence of gene flow due to planktonic dispersal. Despite this large-scale uniformity, there is fine-scale genetic patchiness, which is repeated, rather than accumulated, on the larger scale. Throughout its geographic range, Siphonaria sp. shows deficits of heterozygotes for all 7 loci. The consistency among loci indicates that the causes of the deficits are populational, rather than locus-specific. A Wahlund effect, the departure from Hardy-Weinberg equilibrium due to mixing of individuals from groups with different allelic frequencies, is the simplest explanation of such deficits. The limited geographic variation of allelic frequencies, however, is grossly inadequate to produce these deficits through a Wahlund effect. Similarly, temporal variation in allelic frequencies in recruits does not explain the deficits. The largest contributor to a Wahlund effect appears to be binomial sampling variance among small local breeding groups. Thus, mixing of larvae on a scale of metres, rather than among geographical areas, apparently produces the deficits of heterozygotes.     

Factors regulating the reproductive cycles of two northeast pacific chitons,Tonicella lineata and T. insignis

The reproductive cycles of Tonicella lineata Wood and T. insignis Reeve are examined in relation to changes in physical and biotic conditions in different locations in British Columbia, Canada, over a 3 to 4 year period. A clearly annual reproductive cycle is displayed by both species, and in any one location and year reproductive events in the two species are similar. There is a progressive increase in the size of the gonads starting in the summer and continuing to mid-winter. Although no one environmental factor is likely to be correlated with this prolonged period of gonadal development, various phases of the annual temperature and photoperiod cycles do appear to coincide with particular phases of gametogenesis (such as gonial proliferation, vitellogenesis and gonadal maturation), and thus could act as external cues. There isa synchronous drop in gonadal size in T. lineata and T. insignis in the spring, as a result of spawning. The exact timing and abruptness of this event in different years can not be accounted for on the basis of temperature. However, new correlative data are presented to add further support to the hypothesis previously presented that the spring phytoplankton is the cue for natural spawning (Himmelman, 1975). Temperature may inhibit spawning in T. lineata if conditions are unseasonably cold.     

The role of cysts on population dynamics of Scrippsiella spp. (Dinophyceae) in Onagawa Bay,northeast Japan

The seasonal behavior of both vegetative cells and cysts of dinophytes Scrippsiella spp., mostly S. trochoidea, which is the dominant group among dinoflagellate populations in Onagawa Bay on the northeastern coast of Honshu, Japan, was investigated between 1990 and 1992. The germination of the cysts after 8 d incubation under favorable laboratory conditions was examined using the extinction dilution method. Incessant germination occurred throughout the year, but the germination ratio (no. of germinable cysts/total cysts) varied seasonally with a marked fluctuation during summer when vegetative cells in the water column were abundant. Although such fluctuation largely reflects the variable flux of newly deposited immature cysts produced by the vegetative cells, the regulation of germination caused by a lowered saturation of dissolved oxygen (DO) under thermally stratified conditions was also suggested. During winter, while the cysts germinated in the laboratory, vegetative cells were not found in the water column. These facts suggest that germination in situ is regulated by low temperature in winter and possibly by lowered DO and by cyst age as well in summer. Such regulation prevents simultaneous germination of all the cysts, which is disadvantageous for the population because it would be more difficult to survive adverse conditions such as successive nutrient depletion and higher grazing risk.     

Pigeon homing: sun compass use in the southern hemisphere

Although the sun compass of birds is based on learning the sun's arc during development, it was unclear whether birds can use the sun when its apparent movement is reversed, in particular, whether northern birds that have been introduced into the southern hemisphere can use the southern sun. To answer this question, clock-shift experiments were performed with local homing pigeons in Auckland, New Zealand (37°S). In three fast-shift tests and two slow-shift tests, the experimental birds showed deflections from the untreated controls that were the mirror images of those observed in the northern hemisphere. These results clearly show that homing pigeons in New Zealand use a sun compass that is adapted to the situation in the southern hemisphere. The learning processes establishing the compensation mechanisms thus appear to be free of constraints concerning the direction of the sun's movement. Differences from recent findings with migratory birds, where the direction of celestial rotation proved of crucial importance for establishing the migratory direction, are discussed: the differences may arise from the different orientation tasks, in particular, from the involvement of innate information in establishing the migratory direction. Received: 13 November 1997 / Accepted after revision: 28 February 1998     

Interactions between wave action and grazing control the distribution of intertidal macroalgae

Canopy-forming macroalgae are key species on temperate rocky shores. However, there is a lack of understanding of how the relative balance of physical and biological factors controls the establishment and persistence of intertidal macroalgae. Here we present an integrated study of the relative importance of wave-induced forces and grazing for the recruitment and survival of the canopy-forming intertidal macroalgae Fucus vesiculosus and F. spiralis. A set of overtopped breakwaters provided a nearly unconfounded gradient in wave exposure between seaward and landward sides. A biomechanical analysis was performed based on empirical measurements of maximum drag forces in breaking waves, a model of long-term maximum wave height, and the breaking stress of Fucus spp. The estimated maximum flow speed (7-8 m/s) on the seaward side of the breakwaters was predicted to completely dislodge or prune Fucus spp. larger than approximately 10 cm, while dislodgment was highly unlikely on the landward side for all sizes. Experimental transplantation of Fucus spp. supported the biomechanical analysis but also suggested that mechanical abrasion may further limit survival in wave-exposed locations. Experimental removal of the limpet Patella vulgata, which was the principal grazer at this site, resulted in recruitment of Fucus spp. on the seaward side. We present a model of limpet grazing that indicates that limpet densities >5-20 individuals/m2 provide a proximate mechanism preventing establishment of Fucus spp., whereas wave action >2 m/s reduces persistence through dislodgment and battering. In a conceptual model we further propose that recruitment and survival of juvenile Fucus spp. are controlled indirectly by wave exposure through higher limpet densities at exposed locations. This model predicts that climate change, and in particular an increased frequency of storm events in the northeast Atlantic, will restrict fucoids to more sheltered locations.     

The chemical basis for trail recognition in Lasius nipponensis (Hymenoptera: Formicidae)

Summary. In this paper we report on the chemical basis for trail recognition in Lasius nipponensis. On and near trails in the field, workers became aggressive against conspecific intruders and succeeded in protective contests, while intruders usually avoided confrontation. Such asymmetric interactions were also observed in the laboratory when two non-nestmate workers were sequentially placed in a clean glass dish, while mutual aggression was observed when they were placed simultaneously. Asymmetric aggression was also observed when the workers were placed in a dish previously conditioned by other workers, or when the dish was treated with the hexane rinse of the conditioned dish. The rinse contained a series of hydrocarbons, in which components and proportion were almost identical to those of the cuticular hydrocarbons of the workers, except for a lack of n-alkanes. Amounts of the hydrocarbons that remained on the dish were very small when all the tarsi of the workers were incapacitated. We therefore consider that the hydrocarbons are not adhesion of the cuticular hydrocarbons but secretion from the tarsi of workers, and serve as a key signal for trail recognition in this ant.