Vertical movements, behavior, and habitat of bigeye tuna (Thunnus obesus) in the equatorial eastern Pacific Ocean, ascertained from archival tag data

The results presented in this report are based on analyses of 16,721 days of data downloaded from 96 archival tags recovered from bigeye tuna (Thunnus obesus; 54–159 cm in length, 0.97–5.44 years of age) at liberty from 31 to 1,508 days in the equatorial eastern Pacific Ocean. Analyses of daily timed depth and temperature records resulted in the classification of the data into three daily behavior types: characteristic, associative (associated with floating objects), and other. There is a significant positive correlation between the proportion of time fish exhibit characteristic behavior and increasing length, and significant negative correlations between the proportion of time bigeye exhibit associative and other behavior with increasing length. For the smallest (54–80 cm) to largest (100–159 cm) length classes, the vertical habitats utilized when exhibiting non-associative behaviors were 99 and 98% of the time above the thermocline depth (60 m) during the night, at the same average depth of 34 m, and 60 and 72% of the time below the thermocline during the day at average depths of 163 and 183 m, respectively. For the same smallest to largest length classes, when exhibiting associative behavior, the average nighttime and daytime depths were 25 and 21, and 33 and 37 m, respectively. The apparent effects of the environment on the behavior of the fish are discussed.     

On the consortium of the tintinnid <Emphasis Type="Italic">Eutintinnus</Emphasis> and the diatom <Emphasis Type="Italic">Chaetoceros</Emphasis> in the Pacific Ocean

The morphology and distribution of the diatoms Chaetoceros tetrastichon and Ch. dadayi as epiphytes on the loricae of the tintinnids Eutintinnus apertus and E. pinguis investigated in the open waters of the Pacific Ocean. The Eutintinnus–Chaetoceros consortia was encountered in 38 of the 52 sampling stations from 34°N to 33°S, and together were among represented the most wide-spread species. The abundance was low with a maximum of 32 consortia l⁻¹ and E. apertus was often the most abundant species of the genus. The free-living Eutintinnus congeneric species showed a wider vertical distribution, whereas E. apertus–Chaetoceros tended to be near the surface. The success of E. apertus in consortium with Chaetoceros may be due to increase of the clearance rate and/or the lower susceptibility to predation. Chaetoceros modifies its morphology to adapt the epiphytic life, especially Ch. dadayi. The shorter curved setae may facilitate the transfer to the lorica of the daughter tintinnid after the cell division. The free-living Ch. tetrastichon and Ch. dadayi are very rare and Chaetoceros remained attached to empty loricae or encysted tintinnid cells. This suggests that the Eutintinnus–Chaetoceros consortium is obligate for the success of the diatom and renders the tintinnid more competitive versus congeneric species.     

Cardiac output during exposure to <Emphasis Type="Italic">Chattonella</Emphasis><Emphasis Type="Italic">marina</Emphasis> and environmental hypoxia in yellowtail (<Emphasis Type="Italic">Seriola</Emphasis><Emphasis Type="Italic">quinqueradiata</Emphasis>)

The experiments were undertaken to measure, for the first time, cardiac output in yellowtail (Seriola quinqueradiata) during exposure to a harmful red tide flagellate (Chattonella marina). The responses were compared with those during exposure to environmental hypoxia to evaluate the significance of the drop of arterial oxygen partial pressure (PaO₂) in the fish-kill mechanisms by C. marina. PaO₂ immediately decreased, whereas heart rate (HR) was maintained until shortly before death during exposure to C. marina. Suffocation developing during the exposure resulted from a decrease in blood oxygen content, but not from lowered blood flow to the tissue. Although exposure to both C. marina and hypoxia immediately decreased PaO₂, arterial oxygen content (CaO₂) and pH (pHa) were significantly lower, whereas HR and cardiac output (&Qdot;) remained significantly higher, for the C. marina-exposed fish than for hypoxia-exposed fish. Although the drop in PaO₂ appears to play a pivotal role in the mechanisms of fish death by C. marina, other physiological response(s) should also be considered.     

Evidence of a spawning area of <Emphasis Type="Italic">Anguilla</Emphasis><Emphasis Type="Italic">marmorata</Emphasis> in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3-36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9-20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.     

Individual specialization in the hunting wasp <Emphasis Type="Italic">Trypoxylon</Emphasis> (<Emphasis Type="Italic">Trypargilum</Emphasis>) <Emphasis Type="Italic">albonigrum</Emphasis> (Hymenoptera,Crabronidae)

Individual-level variation in resource use occurs in a broad array of vertebrate and invertebrate taxa and may have important ecological and evolutionary implications. In this study, we measured the degree of individual-level variation in prey preference of the hunting wasp Trypoxylon albonigrum, which inhabits the Atlantic Forest in southeastern Brazil. This wasp captures several orb-weaving spider genera to provision nests. Individuals consistently specialized on a narrow subset of the prey taxa consumed by the population, indicating the existence of significant individual-level variation in prey preferences. The population niche was broader in the wet season in terms of both prey size and taxa. In the case of prey size, the population niche expansion was achieved via increased individual niche breadths, whereas in the case of prey taxa, individual niches remained relatively constrained, and the population niche expanded via increased interindividual variation. The observed pattern suggests the possibility of functional trade-offs associated with the taxon of the consumed prey. The nature of the trade-offs remains unknown, but they are likely related to learning in searching and/or handling prey. We hypothesize that by specializing on specific prey taxa, individuals increase foraging efficiency, reducing foraging time and ultimately increasing reproductive success.     

Oceanographic preferences of Atlantic bluefin tuna, <Emphasis Type="Italic">Thunnus thynnus</Emphasis>, on their Gulf of Mexico breeding grounds

Electronic tagging and remotely sensed oceanographic data were used to determine the oceanographic habitat use and preferences of Atlantic bluefin tuna (Thunnus thynnus L.) exhibiting behaviors associated with breeding in the Gulf of Mexico (GOM). Oceanographic habitats used by 28 Atlantic bluefin tuna exhibiting breeding behavior (259 days) were compared with available habitats in the GOM, using Monte Carlo tests and discrete choice models. Habitat utilization and preference patterns for ten environmental parameters were quantified: bathymetry, bathymetric gradient, SST, SST gradient, surface chlorophyll concentration, surface chlorophyll gradient, sea surface height anomaly, eddy kinetic energy, surface wind speed, and surface current speed. Atlantic bluefin tuna exhibited breeding behavior in the western GOM and the frontal zone of the Loop Current. Breeding areas used by the bluefin tuna were significantly associated with bathymetry, SST, eddy kinetic energy, surface chlorophyll concentration, and surface wind speed, with SST being the most important parameter. The bluefin tuna exhibited significant preference for areas with continental slope waters (2,800–3,400 m), moderate SSTs (24–25 and 26–27°C), moderate eddy kinetic energy (251–355 cm² s⁻²), low surface chlorophyll concentrations (0.10–0.16 mg m⁻³), and moderate wind speeds (6–7 and 9–9.5 m s⁻¹). A resource selection function of the bluefin tuna in the GOM was estimated using a discrete choice model and was found to be highly sensitive to SST. These habitat utilization and preference patterns exhibited by breeding bluefin tuna can be used to develop habitat models and estimate the probable breeding areas of bluefin tuna in a dynamic environment.     

Flexible habitat selection and interactive habitat segregation in the marine congeners <Emphasis Type="Italic">Idotea baltica</Emphasis> and <Emphasis Type="Italic">Idotea emarginata</Emphasis> (Crustacea,Isopoda)

Habitat segregation among competing species is widespread yet very little is know how this is achieved in practice. In a case study, we examined short-term effects of conspecific and congeneric density on habitat selection in two competing marine isopod species, Idotea emarginata and Idotea baltica. Under semi-natural conditions in large outdoor cylindrical tanks (4 m high; volume 5.5 m³), animal groups of different size and composition had the choice between a set of relevant habitat samples (surface-floating seaweed, the water column, seaweed on the bottom). Habitat selection in both I. baltica and I. emarginata proved to be largely independent of conspecific density (level of intraspecific competition). In single-species treatments, both species showed a similar and stable pattern of distribution, with a clear preference for seaweed on the bottom. In mixed-species treatments (MST), however, the species were largely separated by habitat. While the distribution of I. emarginata was completely unaffected by the mere presence of interspecific competitors, habitat selection of I. baltica changed notably when I. emarginata was present. The habitat use patterns observed in MST conformed to those realized in geographical areas where the two species overlap in distribution: I. emarginata is dominant among decaying seaweed on the sea floor, and I. baltica is the dominant species among surface-floating seaweed. Our findings suggest that habitat segregation between the two species is essentially interactive, resulting from rapid decision-making of I. baltica with respect to habitat selection. The underlying mechanism is discussed. I. emarginata is highly superior to I. baltica in interference competition and rapidly eliminates the latter from one-habitat systems which do not allow I. baltica to escape from this interaction. In more natural, heterogeneous environments, however, I. baltica seems to be able to coexist with the superior competitor due to its broader habitat niche, flexibility in habitat selection, and a behavioural disposition to avoid normally preferred habitats when these are occupied by I. emarginata.     

Viable algae released by the seastar <Emphasis Type="Italic">Dermasterias</Emphasis><Emphasis Type="Italic">imbricata</Emphasis> feeding on the symbiotic sea anemone <Emphasis Type="Italic">Anthopleura elegantissima</Emphasis>

Echinoderms are major predators of anemones in temperate ecosystems. The fate of two algae, zooxanthellae and zoochlorellae, after their host anemone (Anthopleura elegantissima Brandt) was consumed by the leather star Dermasterias imbricata Grube was determined in experiments conducted in July and August 2004. Productivity, photosynthetic pigments, and mitotic index (percent of cells dividing) were used as indicators of algal health; algae released after leather stars consumed their host were compared with algae freshly isolated from anemones. Two types of waste products contained algae: pellets resulting from extraoral digestion, and feces. Zooxanthellae and zoochlorellae isolated from these waste products were photosynthetic, although to different extents. For algae from feces and pellets, light-saturated photosynthetic rates (P _max) were 85 and 13%, respectively, of P _max of freshly isolated zooxanthellae; and were 20 and 46%, respectively, for zoochlorellae. The photosynthetic pigments and mitotic index (percent of dividing cells) were not altered by the feeding activities of the leather star. These results show that algae released by seastar predation on their hosts remain viable, and are hence available for establishing symbioses in A. elegantissima and other potential hosts.     

Effects of substrate type on growth and mortality of blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) exposed to the predator <Emphasis Type="Italic">Carcinus</Emphasis><Emphasis Type="Italic">maenas</Emphasis>

Structure and complexity of the substrate are important habitat characteristics for benthic epifauna. The specific growth and mortality rates and inducible defence characters on medium-sized blue mussels (Mytilus edulis L.) exposed to shore crabs (Carcinus maenas L.) were examined on three different substrate types in combined field and laboratory experiments. The experiments showed that complexity of the substrate increased blue mussel survival significantly, through a decrease in predation pressure. However, increased intraspecific competition for food on the complex substrate resulted in significantly lower growth rates of the mussels. Inducible defence characters were also influenced by substrate type. Blue mussels were more affected by predators on the structurally simple substrate, where they developed thicker shells and a larger posterior adductor muscle.     

Mate preferences in <Emphasis Type="Italic">Drosophila</Emphasis> infected with <Emphasis Type="Italic">Wolbachia</Emphasis>?

The maternally inherited bacterium Wolbachia pipientis generates strong reproductive incompatibilities between uninfected females and infected males (cytoplasmic incompatibility), significantly reducing both female and male reproductive success. Such fitness costs are thought to place selective pressure on hosts to evolve pre-copulatory preferences for mating with compatible mates, thereby enabling them to avoid the reproductive incompatibilities associated with Wolbachia. Therefore, uninfected females are predicted to prefer mating with uninfected males, whereas infected males are predicted to prefer mating with infected females. Despite these predictions, previous investigations of pre-copulatory mate preferences in Wolbachia-manipulated Drosophila have not found evidence of female preference for uninfected or compatible males. However, none of these studies utilised a design where focal individuals are provided with a simple choice in a relatively non-competitive situation. We examined both female and male pre-copulatory mate preference based on mate infection status in Drosophila simulans and D. melanogaster using simple choice assays involving between 30–50 replicates per treatment. Although we found no evidence of female pre-copulatory mate preferences in either species, male D. simulans exhibited some preference for mating with females of the same infection status. However, this preference was not evident when we repeated the experiment to confirm this finding. Consequently, we conclude that neither male nor female D. melanogaster and D. simulans exhibit significant Wolbachia-associated pre-copulatory mate preferences.     

Settlement of the wreckfish (<Emphasis Type="Italic">Polyprion</Emphasis><Emphasis Type="Italic">americanus</Emphasis>)

The wreckfish (Polyprion americanus) is a panoceanic, long-lived, deep-water demersal species, characterized by an extended pelagic juvenile phase associated with floating objects. In the present study morphometric data from 435 specimens collected from Greece (Crete), Italy (Ionian Sea) and the Atlantic coast of France from September 1999 to March 2001 were analyzed to estimate the settlement size of the species and associated changes in morphology. The fishery sample included specimens from both the pelagic and the demersal stage. Length-at-settlement (TL₅₀) and 95% confidence intervals were estimated by fitting a logistic function. Eleven morphometric characters were analyzed, and the existing inflection points, reflecting alterations in body shape, were defined: (1) iteratively, as the transition point, splitting the data set into two groups, for which the reduced major axis functions, between a character and total length, of the successive groups best fit (minimum sum of squares of residuals) the combined data set and (2) where the second derivative of the fitted third-order polynomial functions to morphometric ratios equaled zero. The main size range within which wreckfish settled was 56-65 cm, and the means of the inflection points defined by the two methods were 61 and 64 cm. These results indicate changes in functional morphology associated with settlement. The monitoring of wreckfish juveniles caught in the wild and kept individually in captivity showed changes in growth and food intake at approximately the estimated settlement length and suggested that temperature was the most likely factor triggering settlement.     

Molecular population structure of the kuruma shrimp <Emphasis Type="Italic">Penaeus</Emphasis><Emphasis Type="Italic"> japonicus</Emphasis> species complex in western Pacific

In a previous study on the kuruma shrimp Penaeus japonicus from the South China Sea, we detected high genetic divergence between two morphologically similar varieties (I and II) with distinct color banding patterns on the carapace, indicating the occurrence of cryptic species. In the present study, we clarify the geographical distribution of the two varieties in the western Pacific by investigating the genetic differentiation of the shrimp from ten localities. Two Mediterranean populations are also included for comparison. Based on the mitochondrial DNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises populations from Japan and China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam, Singapore and the Philippines), Australia and the Mediterranean. Population differentiation is evident in variety II, as supported by restriction profiles of two mitochondrial markers and analysis of two microsatellite loci. The Australian population is genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship. Variety I does not occur in these three localities, while a small proportion of variety II is found along the northern coast of the South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean, are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery management and aquaculture development programs of this important biological resource.     

Movements of bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis>) in the northwestern Atlantic Ocean recorded by pop-up satellite archival tags

Pop-up satellite archival tags were implanted into 68 Atlantic bluefin tuna (Thunnus thynnus Linnaeus), ranging in size from 91 to 295 kg, in the southern Gulf of Maine (n=67) and off the coast of North Carolina (n=1) between July 2002 and January 2003. Individuals tagged in the Gulf of Maine left that area in late fall and overwintered in northern shelf waters, off the coasts of Virginia and North Carolina, or in offshore waters of the northwestern Atlantic Ocean. In spring, the fish moved either northwards towards the Gulf of Maine or offshore. None of the fish crossed the 45°W management line (separating eastern and western management units) and none traveled towards the Gulf of Mexico or the Straits of Florida (known western Atlantic spawning grounds). The greatest depth recorded was 672 m and the fish experienced temperatures ranging from 3.4 to 28.7°C. Swimming depth was significantly correlated with location, season, size class, time of day, and moon phase. There was also evidence of synchronous vertical behavior and changes in depth distribution in relation to oceanographic features.Communicated by J.P. Grassle, New Brunswick     

Altered c-Fos expression demonstrates neuronal stress in mummichog, <Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>, exposed to <Emphasis Type="Italic">Pfiesteria shumwayae</Emphasis> and <Emphasis Type="Italic">Chaetoceros concavicornis</Emphasis>

To better understand sublethal effects of harmful algal blooms (HABs) on fish, mummichog, Fundulus heteroclitus (L.), were exposed in the laboratory to varying, environmentally relevant densities of Pfiesteria shumwayae (Glasgow et Burkholder, CCMP 2089, dinoflagellate) and Chaetoceros concavicornis (Mangin, CCMP 169, diatom). Two experiments were conducted during the spring of 2003 and 2004 to quantitatively examine the effects of acute (2 h) P. shumwayae and C. concavicornis algal exposure on mummichog brain activity using c-Fos expression as a marker of altered neuronal activity. Brains from HAB-exposed fish were removed, sectioned, and stained using immunocytochemistry prior to quantifying neuronal c-Fos expression. Fish exposed to P. shumwayae and C. concavicornis showed increased c-Fos expression compared to unexposed control fish. A significant dose-response relationship was observed, with increased labeling in brains of fish exposed to higher cell densities for both HAB species tested (P ≤ 0.01). Increased labeling was found in the telencephalon, optic lobes, midbrain, and portions of the medulla. The greatest increases in expression were observed in the telencephalon of P. shumwayae-exposed fish, and in the telencephalon and optic lobes of C. concavicornis-exposed fish (P ≤ 0.01). These increases in c-Fos expression are consistent with other physical and chemical stress exposures observed in fish. Neuronal stress, evidenced by c-Fos expression, demonstrates a sublethal effect of exposure and changes in brain activity in fish exposed to HAB species.     

Reduced planktotrophy in larvae of <Emphasis Type="Italic">Clypeaster</Emphasis><Emphasis Type="Italic">rosaceus</Emphasis> (Echinodermata,Echiniodea)

Phylogenetic analyses have demonstrated that nonfeeding larvae have evolved from feeding larvae many times among marine invertebrates. In light of this observation, it is surprising that an intermediate strategy, a larva that can feed but is provisioned with enough energy to metamorphose without acquiring exogenous food (i.e., facultative planktotrophy), is rare. A hypothesis for the lack of facultative planktotrophic species among marine invertebrates is that the transition from feeding to nonfeeding is rapid due to this intermediate stage being evolutionarily unstable. Evidence that would support this hypothesis is if species with facultative planktotrophy have reduced food assimilation when compared with obligate planktotrophs. We studied a species with facultative planktotrophic larvae, Clypeaster rosaceus, that is very near the boundary between facultative and obligatory planktotrophy, to answer two questions: (1) does feeding during the larval stage result in energy gains in larval or juvenile stages and (2) if not, are larvae capable of assimilating exogenous food at all. Our measurements of energetics in larval and juvenile stages show that C. rosaceus larvae accumulate very little if any energy when fed, but stable isotope data indicate that larvae are able to assimilate some food. Our results are consistent with similar studies on facultative planktotrophic larvae suggesting poor food assimilation and rapid loss of larval feeding after a population evolves the ability to reach metamorphosis without feeding (lecithotrophy).     

Annual migrations,diving behavior,and thermal biology of Atlantic bluefin tuna, <Emphasis Type="Italic">Thunnus thynnus</Emphasis>, on their Gulf of Mexico breeding grounds

Electronic tags were used to examine the biology of Atlantic bluefin tuna (Thunnus thynnus L.) on their breeding grounds in the Gulf of Mexico (GOM). The hypothesis that movement patterns, diving behavior, and thermal biology change during different stages of the breeding migration was tested. Mature Atlantic bluefin tuna tagged in the western Atlantic and the GOM, were on their breeding grounds from February to June for an average of 39 ± 11 days. The bluefin tuna experienced significantly warmer mean sea surface temperatures (SSTs) within the GOM (26.4 ± 1.6°C) than outside the GOM (20.2 ± 1.9°C). As the bluefin tuna entered and exited the GOM, the fish dove to daily maximum depths of 568 ± 50 and 580 ± 144 m, respectively, and exhibited directed movement paths to and from the localized breeding areas. During the putative breeding phase, the bluefin tuna had significantly shallower daily maximum depths (203 ± 76 m), and exhibited shallow oscillatory dives during the night. The movement paths of the bluefin tuna during the breeding phase were significantly more residential and sinuous. The heat transfer coefficients (K) were calculated for a bluefin tuna in the GOM using the recorded ambient and body temperatures. The K for this fish increased rapidly at the high ambient temperatures encountered in the GOM, and was significantly higher at night in the breeding phase when the fish was exhibiting shallow oscillatory dives. This suggests that the fish were behaviorally and physiologically thermoregulating in the Gulf of Mexico. This study demonstrates that the movement patterns, diving behavior, and thermal biology of Atlantic bluefin tuna change significantly at different stages of the breeding migration and can be used to define spawning location and timing. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

<Emphasis Type="Italic">Semibalanus</Emphasis><Emphasis Type="Italic">balanoides</Emphasis> in winter and spring: larval concentration,settlement, and substrate occupancy

This study measured the progression from pelagic larvae to juvenile barnacles, and examined whether recruitment of barnacles, Semibalanus balanoides Linnaeus, at two intertidal sites in contrasting hydrodynamic regimes was determined by pre-settlement or post-settlement processes. The two sites were 1.5 km apart in the vicinity of Woods Hole, Mass., USA. Quantitative plankton samples were taken twice weekly from December 1997 to May 1998 at a nearby site as an estimate of nearshore larval abundance. The presence of S. balanoides nauplii was noted, and cyprids were enumerated and measured. Larval settlement at the two sites [Gansett Point, Buzzards Bay (GP) and Little Harbor, Vineyard Sound (LH)] was estimated from examination of replicate settlement plates exposed for 2 or 3 days throughout the settlement season, and from replicate plots on marked rock quadrats at each site. On both plates and rocks settled cyprids and metamorphs were enumerated. Space occupancy on unmanipulated rock quadrats by all stages from cyprids to adult barnacles was also examined. Settlement occurred from 2 January to 20 May, and major settlement peaks coincided with peaks in pelagic cyprid concentration at LH, but not at GP. Space occupied by juvenile barnacles was close to zero up until late February despite substantial settlement prior to that. At LH, juvenile barnacle cover was zero at the end of the observations; all settlement failed. Almost 100% of settled cyprids failed to metamorphose within 2 days from late January to late March. Then the proportion metamorphosing increased sharply coinciding with a sudden increase of 3°C in water temperature. Observed site differences in space occupancy by juvenile barnacles suggest that while cyprid supply is a necessary condition for barnacle settlement, other factors affecting metamorphosis of settled cyprids and early juvenile mortality determine recruitment.     

Antennal responses to floral scents in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae)

Summary. To better understand the biological role of floral scents for butterflies, electrophysiological responses to floral scents were investigated using combined gas chromatography and electroantennographic detection (GC-EAD). The antennal responses of three butterfly species, Aglais urticae L. (Nymphalidae), Inachis io L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae) to floral scent compounds from both natural and synthetic mixtures were examined. Floral scents were collected from the butterfly nectar plants Cirsium arvense (L.) (Asteraceae), and Buddleja davidii Franchet cv. (Loganicaeae) with dynamic head-space methods on Tenax-GR and eluted with pentane. These eluates, composed of natural floral scent blends, represent an array of compounds in their natural state. In the GC-EAD analyses eleven compounds were identified from C. arvense with the benzenoid compound phenylacetaldehyde in highest abundance. Seventeen compounds were identified from B. davidii with the irregular terpene oxoisophorone in highest abundance. Thirty-nine synthetic floral scent compounds were mixed in pentane, in equal amounts; about 35 ng were allowed to reach the antennae. The butterflies showed antennal responses to most of the floral scent compounds from both natural and synthetic blends except to the highly volatile monoterpene alkenes. Certain benzenoid compounds such as phenylacetaldehyde, monoterpenes such as linalool, and irregular terpenes such as oxoisophorone, were emitted in relatively large amounts from C. arvense and B. davidii, and elicited the strongest antennal responses. These compounds also elicited strong antennal responses when present in the synthetic scent blends. Thus, the butterflies seem to have many and /or sensitive antennal receptors for these compounds, which points to their biological importance. Moreover, these compounds are exclusively of floral scent origin. For B. davidii, which depends highly on butterflies for pollination, the exclusive floral scent compounds emitted in high abundance could be the result of an adaptive pressure to attract butterflies. Received 2 Septemter 2001; accepted 9 September 2002.