In vivo and in vitro differences in chloroplast functionality in the two north Atlantic sacoglossans (Gastropoda,Opisthobranchia) <Emphasis Type="Italic">Placida dendritica</Emphasis> and <Emphasis Type="Italic">Elysia viridis</Emphasis>

The photosynthetic functionality in chloroplasts in the two sacoglossan molluscs Placida dendritica and Elysia viridis from the Trondheim fjord in Norway was studied. P. dendritica and E. viridis with no functional chloroplasts in their digestive system were introduced to the green macroalgae Codium fragile. Our results showed that P. dendritica was not able to retain functional (photosynthetic) chloroplasts. Transmission electron microscopy (TEM) showed that chloroplasts were directly digested when phagocytosed into the digestive cells. Four stages of chloroplast degradation were observed. A corresponding operational quantum yield of chl a fluorescence (Φ_PSII ~ 0) indicated autofluorescence, and the presence of highly degraded chl a supported these observations. In contrast, E. viridis was able to retain functional chloroplasts. For this species it took only 1 week for the chloroplasts inside the digestive cells to acquire the same Φ_PSII and light utilisation coefficient (α) as C. fragile kept under the same light conditions. Data for 8 days showed a 2–6-fold increase in the maximum photosynthetic rate (P _max) and light saturation index (E _k) relative to C. fragile. This increase in available light was probably caused by a reduced package effect in the digestive gland of E. viridis relative to C. fragile, resulting in a partial photoacclimation response by reducing the turnover time of electrons (τ). Isolated pigments from C. fragile compared to E. viridis showed the same levels of photosynthetic pigments (chl a and b, neoxanthin, violaxanthin, siphonaxanthin, siphonein and β,ε-carotene) relative to μg chl a (w:w), indicating that the chloroplasts in E. viridis did not synthesise any new pigments. After 73 days of starvation, it was estimated that chloroplasts in E. viridis were able to stay photosynthetic 5–9 months relative to the size of the slugs, corresponding to an RFC of level 8 (a retention ability to retain functional chloroplasts (RFC) for more than 3 months). The reduction in Φ_PSII, P _max and α as a function of time was caused by a reduction in chloroplast health and number (chloroplast thylakoid membranes and PSII are degraded). These observations therefore conclude that chloroplasts from C. fragile cannot divide or synthesise new pigments when retained by E. viridis, but are able to partially photoacclimate by decreasing τ as a response to more light. This study also points to the importance of siphonaxanthin and siphonein as chemotaxonomic markers for the identification of algal sources of functional chloroplasts.     

Dynamics of a peculiar plant-herbivore relationship: the photosynthetic ascoglossan Elysia timida and the chlorophycean Acetabularia acetabulum

The ascoglossan mollusc Elysia timida Risso, 1818 retains functional chloroplasts from its algal food, the chlorophycean Acetabularia acetabulum (L.). Photosynthates from the plastids are an important source of organic nutrients for the mollusc. Chloroplast exploitation has an ecological function, allowing the ascoglossan to live entirely on an algal diet which is of limited, seasonal availability to other herbivores. Between October 1987 and July 1988, the annual evolution of the molluscan and algal populations was studied in a cove of Mazarrón Bay, southeast Spain. The population density of the mollusc is highly dependent on its food supply, being controlled by the seasonal life cycle of the algal population. During its life cycle, the degree of grazing by the mollusc decreases with increasing algal calcification, the cell walls of the alga progressively calcify, and the eventually highly calcificied stalks are completely resistant to ascoglossan grazing. In contrast, the exploitation of the algal chloroplasts retained by the molluscs increases during the seasonal cycle. The progressively increasing scarcity of food during the seasonal cycle may have led to the retention of symbiotic chloroplasts by E. timida. The developmental strategy of the ascoglossan also changes during the year: when food is abundant (in November, December, January, February and March) it is direct, with no planktonic larval phase, when food is scarce (in October, April, May and June) it is lecithotrophic, with a short planktonic larval phase. Chloroplast retention acts as a buffer, alleviating the effects of annual changes in density, structure and abundance of the alga on the nutritional state of the molluse.     

Relative importance and interactive effects of photosynthesis and food in two solar-powered sea slugs

Sacoglossans use chloroplasts taken from algal food for photosynthesis (kleptoplasty), but the adaptive significance of this phenomenon remains unclear. Two con-generic sacoglossans (Elysia trisinuata and E. atroviridis) were collected in 2009–2011 from Shirahama (33.69°N, 135.34°E) and Mukaishima (34.37°N, 133.22°E), Japan, respectively. They were individually maintained for 16 days under four experimental conditions (combination of light/dark and with/without food), and their survival rate and relative (=final/initial) weights were measured. Both light and food had positive effects on the survival in E. trisinuata, whereas no positive effects of light or food on survival were detected in E. atroviridis. Both light and food had positive effects on relative weights in both species, but light had smaller effects than food. A significant interaction term between light and food was detected in E. trisinuata (but not in E. atroviridis) in that only the presence of both resulted in weight gains. This result suggests that E. trisinuata can obtain sufficient additional energy from photosynthesis for sustaining growth when fresh chloroplasts are continuously supplied from algal food. In addition, fluorescence yield measurements showed that unfed individuals of both E. trisinuata and E. atroviridis lost photosynthetic activity soon (<4 and 4–8 days, respectively). In conclusion, photosynthesis may function to obtain supplementary nutrition for sustaining growth when food is available in sacoglossans with short-term functional kleptoplasty.     

Newly metamorphosed <Emphasis Type="Italic">Elysia clarki</Emphasis> juveniles feed on and sequester chloroplasts from algal species different from those utilized by adult slugs

The adult, sacoglossan sea slug, Elysia clarki (Pierce et al. in Molluscan Res 26, 2006), sequesters functional chloroplasts in cells of the digestive diverticula from four species of macroalgae in the order Bryopsidales (Penicillus capitatus, Penicillus lamourouxii, Halimeda incrassata, and Halimeda monile). Feeding experiments were conducted in December, 2003, using individuals raised in the laboratory from egg masses laid by E. clarki adults which had been collected from Grassy Key, Florida, USA, and 29 species of macroalgae collected from the Florida Keys, Tampa Bay, Tarpon Springs, Florida, or Woods Hole, Massachusetts or obtained from the Culture Collection of Algae at the University of Texas at Austin, Texas. For the first 14-day post-metamorphosis, juveniles ate only the thin filamentous species, Bryopsis plumosa or Derbesia tenuissima. Transmission electron microscopy showed that the chloroplasts from both algae were sequestered intracellularly in juvenile slugs. Individuals offered any other macroalga, including the four species fed on by adults, did not feed on or incorporate any chloroplasts, and soon died. Juveniles switched from B. plumosa to P. capitatus at a length of ∼ 1.0 cm, and fixed for microscopy 14 days later had intact intracellular chloroplasts from both algae. Nucleotide sequences of the chloroplast gene, rbcL, from DNA extracted from E. clarki, collected from Vaca Key, Florida, were aligned with 22 other available macroalgal rbcL sequences indicating that these E. clarki adults had fed on three species of algae in the Bryopsidales including Bryopsis pennata, and TEM results partially confirmed this conclusion.     

Symbiosis in sacoglossan opisthobranchs: photosynthetic products of animal-chloroplast associations

Alcohol-soluble photosynthetic products of chloroplasts symbiotic in three species of sacoglossan slugs (Elysia hedgpethi, Placida dendritica Placobranchus ianthobapsus) were analyzed and compared to products of chloroplasts in an intact alga. Animal-cell chloroplasts appear to lack the ability to synthesize either lipids or sucrose. They do, however, produce greater percentages of TCA-cycle intermediates than do chloroplasts from the intact alga investigated.     

Symbiosis in sacoglossan opisthobranchs: functional capacity of symbiotic chloroplasts

It has been previously reported that many species of the order Sacoglossa (Mollusca: Opisthobranchia) contain algal chloroplasts within the cells of their digestive gland and maintain them in a symbiotic condition. In the present study, two species, Elysia hedgpethi Marcus and Placobranchus ianthobapsus Gould, were compared as to their abilities to retain functional chloroplasts in their tissues. Animals were starved for varying lengths of time, and the functional capacity of the plastids was ascertained at intervals. The chlorophyll content of whole animals, and the ability to incorporate ¹⁴CO₂ were used as the assay for functional capacity. E. hedgpethi decreased in chlorophyll content during starvation until the tenth day, when no chlorophyll was detectable spectrophoto-metrically. Incorporation of ¹⁴CO₂ paralleled the decline in chlorophyll, and was at control levels by the tenth day. P. ianthobapsus showed no decline in chlorophyll content over 27 days starvation, although the ability to incorporate ¹⁴CO₂ showed a decrease.     

Elysia timida (Risso, 1818) (Gastropoda, Opisthobranchia): relationship and feeding deterrence to a potential predator on the south-western Mediterranean coast

The relationship between the sacoglossan Elysia timida and the ornate wrasse Thalassoma pavo was studied in two laboratory experiments using artificial models. A feeding-preference experiment was conducted to determine whether mollusc extract deterred feeding by T. pavo, by using a "realistic" mollusc model (imitating the colour pattern of E. timida) coated with mollusc extract, and a reference model (without imitation or extract), and fishes collected from two locations. It was observed that fish approached, attacked and ate more reference models than mollusc models. A second feeding-preference experiment was designed with four different coloured models: "realistic" (W), green (G), red (R) and chequered (S) pattern. Both fish populations clearly rejected the S model, and differed in their colour preferences. Although both populations seemed to prefer the R and G models equally, the W model was clearly rejected by the fish that coexist with the mollusc at one site (Mazarrón), but was not rejected by the other population of fish which does not coexist with it (Cabo de Palos). Mazarrón fishes would identify the W model with the presence of a toxic compound during their coexistence, and therefore avoid attacking conspicuously coloured E. timida models as a response to their visual signals. Therefore, it was concluded that extract of E. timida is a deterrent for T. pavo, and its effect is sufficiently noxious that the fish tend to avoid it, so that the ability of the fishes to learn to recognise colours and identify certain colour patterns associated with obnoxious prey provides the molluscs the opportunity to survive by exhibiting a conspicuous coloration.     

Photoinhibition of Symbiodinium spp. within the reef corals Montastraea faveolata and Porites astreoides: implications for coral bleaching

It is speculated that differences in coral bleaching susceptibility may be influenced by the genotype of in hospite Symbiodinium and their differential responses to bleaching stressors. Photoinhibition of photosystem II (PSII), damage to the D1 (psbA) PSII reaction centre protein and production of reactive oxygen species by in hospite Symbiodinium are likely precursors of coral bleaching. In order to assess whether photorepair rates of in hospite Symbiodinium underlie the bleaching susceptibility of their hosts, photoinhibition (net and gross), photoprotection and photorepair rates were assessed in a bleaching-‘tolerant’ coral (P. astreoides) and a bleaching-‘sensitive’ coral (M. faveolata) using non-invasive fluorometric techniques and by blocking de novo synthesis of psbA. Previous studies using such techniques have demonstrated that in vitro Symbiodinium types ‘sensitive’ to bleaching stressors had reduced rates of photorepair relative to ‘tolerant’ Symbiodinum types. Our measurements demonstrated that Symbiodinium in the more bleaching tolerant P. astreoides had higher photorepair rates than Symbiodinium in M. faveolata. Higher repair rates in P. astreoides resulted in lower net photoinhibition relative to M. faveolata, where both corals exhibited similar susceptibility to photodamage (gross photoinhibition). Photoprotective mechanisms were observed in both corals; M. faveolata exhibited higher antennae-bed quenching than P. astreoides at low-light intensities, but at and above light-saturating intensities, which are different for each coral species, P. astreoides displayed more efficient non-photochemical quenching (Stern–Volmer quenching) of chlorophyll fluorescence than M. faveolata. Increased NPQ by P. astreoides at E/E _k ≥ 1 was not driven by antennae-bed quenching. The ability of in hospite Symbiodinium in P. astreoides to mitigate the effects of photoinhibition under high light conditions compared with Symbiodinium in M. faveolata, and their high repair capacity following photoinhibition, may be a key factor to consider in future bleaching studies and may underlie the relative bleaching tolerance of P. astreoides compared to M. faveolata.     

Atypical plant–herbivore association of algal food and a kleptoplastic sea slug (Elysia clarki) revealed by DNA barcoding and field surveys

The identity of food sources and feeding preferences of specialist herbivores have been commonly inferred from spatial associations between consumer and food items. However, such basic information for well-known marine herbivores, sacoglossans (sea slugs), and their algal diets remains disappointingly lacking, especially from field studies. The sacoglossan, Elysia clarki (Pierce et al. in Molluscan Res 26:23–38, 2006), is kleptoplastic and sequesters chloroplasts from algal food to photosynthesize, so DNA identification of sequestered chloroplasts was employed to verify the algal species fed upon by the slug across its geographic range. The molecular information on the algae consumed by E. clarki was combined with field surveys of slugs and algae in slug habitats in the Florida Keys in July and August of 2008 in order to evaluate whether the diet of this herbivore could be predicted based on its spatial association with algae in the field. A considerable mismatch between food availability and kleptoplast identity was recorded. E. clarki commonly occupied areas devoid of potential food and often contained symbiotic plastids from algal species different from those most frequently found in the surveyed habitats. In three of the four study sites, algal species present were poor predictors of slug diet. These findings suggest that the photosynthetic capability of E. clarki may release the slug from the constraint of requiring proximity to its food sources and may allow for the potential lack of spatial coupling between this herbivore and its algal food. This combination of field surveys and DNA barcoding provided critical and previously unavailable information on herbivore feeding in this marine system.     

Diel cycles of activity,metabolism, and ammonium concentration in tropical holothurians

Movement rate, oxygen consumption, and respiratory tree ammonium concentration were measured in situ in the holothurians Pearsonothuria graeffei and Holothuria edulis in the Agan-an Marine Reserve, Sibulan, Philippines (9°20′30″N, 123°18′31″E). Measurements were made both day and night for both species during April–July 2005. P. graeffei had significantly higher movement rate during the day than at night (1.14 and 0.27 m h⁻¹, respectively; three-way ANOVA, P < 0.05) while H. edulis had higher movement rate at night compared to the day (0.83 and 0.07 m h⁻¹, respectively), spending the daylight hours sheltering under coral. More than 80% of H. edulis had movement rate of zero during the day. Oxygen consumption of P. graeffei was significantly higher during the day than at night (1.61 and 0.83 μmol O₂ g⁻¹ h⁻¹, respectively; two-way ANCOVA, P < 0.05), but the reduction at night was not as pronounced as the reduction in movement. H. edulis had a 75% reduction in oxygen consumption during the day compared to night (0.51 and 1.96 μmol O₂ g⁻¹ h⁻¹, respectively), matching this species’ reduced movement rates during the day. Ammonium concentration in water withdrawn from the respiratory trees of P. graeffei during the day (12.0 μM) was three times higher than in respiratory tree water sampled at night (4.3 μM) and 15 times higher than ambient seawater (0.8 μM; three-way ANOVA, P < 0.05). Ammonium concentration in the respiratory tree water of H. edulis was six times higher at night (14.6 μM) than during the day (2.2 μM) and 16 times higher than that of ambient seawater (0.9 μM). Even though H. edulis and P. graeffei are found within the same coral reef environment, they may affect different substrates and reef organisms due to their different habitats and distinct but opposite diel cycles.     

“An eye for an eye?”—on the generality of the intimidating quality of eyespots in a butterfly and a hawkmoth

Large eyespots on the wings of butterflies and moths have been ascribed generally intimidating qualities by creating a frightening image of a bird or mammal much larger than the insect bearing the eyespots. However, evidence for this anti-predator adaptation has been largely anecdotal and only recently were peacock butterflies, Inachis io, shown to effectively thwart attacks from blue tits, Parus caeruleus. Here, we test whether large eyespots on lepidopterans are generally effective in preventing attacks from small passerines and whether the size of insect or bird can influence the outcome of interactions. We staged experiments between the larger eyed hawkmoths, Smerinthus ocellatus, and the smaller peacock butterflies, I. io, and the larger great tits, Parus major, and the smaller blue tits, P. caeruleus. Survival differed substantially between the insect species with 21 of 24 peacock butterflies, but only 6 of 27 eyed hawkmoths, surviving attacks from the birds. Thus, surprisingly, the smaller prey survived to a higher extent, suggesting that factors other than insect size may be important. However, great tits were less easily intimidated by the insects’ eyespots and deimatic behaviour and consumed 16 of 26, but the blue tits only 8 of 25, of the butterflies and hawkmoths. Our results demonstrate that eyespots per se do not guarantee survival and that these two insects bearing equally large eyespots are not equally well protected against predation.     

Effects of light exposure on the retention of kleptoplastic photosynthetic activity in the sacoglossan mollusc <Emphasis Type="Italic">Elysia viridis</Emphasis>

The effects of light exposure on the photosynthetic activity of kleptoplasts were studied in the sacoglossan mollusc Elysia viridis. The photosynthetic activity of ingested chloroplasts was assessed in vivo by non-destructively measuring photophysiological parameters using pulse amplitude modulation (PAM) fluorometry. Animals kept under starvation were exposed to two contrasting light conditions, 30 μmol photons m⁻² s⁻¹ (low light, LL), and 140 μmol photons m⁻² s⁻¹ (high light, HL), and changes in photosynthetic activity were monitored by measuring the maximum quantum yield of photosystem II (PSII), F _v/F _m, the minimum fluorescence, F _o, related to chlorophyll a content, and by measuring rapid light-response curves (RLC) of relative electron transport rate (rETR). RLCs were characterised by the initial slope of the curve, α_RLC, related to efficiency of light capture, and the maximum rETR level, rETR_m,RLC, determined by the carbon-fixation metabolism. Starvation induced the decrease of all photophysiological parameters. However, the retention of photosynthetic activity (number of days for F _v/F _m > 0), as well as the rate and the patterns of its decrease over time, varied markedly with light exposure. Under HL conditions, a rapid, exponential decrease was observed for F _v/F _m, α_RLC and rETR_m,RLC, F _o not showing any consistent trend of variation, and retention times ranged between 6 and 15 days. These results suggested that the retention of chloroplast functionality is limited by photoinactivation of PSII reaction center protein D1. In contrast, under LL conditions, a slower decrease in all parameters was found, with retention times varying from 15 to 57 days. F _v/F _m, α_RLC and rETR_m,RLC exhibited a bi-phasic pattern composed by a long phase of slow decrease in values followed by a rapid decline, whilst F _o decayed exponentially. These results were interpreted as resulting from lower rates of D1 photoinactivation under low light and from the gradual decrease in carbon provided by photosynthesis due to reduction of functional photosynthetic units.     

Production, hatching success and surface ornamentation of eggs of calanoid copepods during a winter at 57°N

Close to 50 species of marine Calanoid copepods have been reported to produce diapause eggs (Engel and Hirche in J Plankton Res 26:1083–1093, 2004); eggs that are viable but require a refractory phase before they hatch, sometimes after months. Diapause eggs are often described as morphologically different with respect to egg membrane ultrastructure and having a thicker egg shell with surface ornamentation as opposed to the smooth shell found in subitaneous eggs that hatch within days (Belmonte in J Mar Syst 15:35–39, 1998; Chen and Marcus in Mar Biol 127:587–597, 1997; Castro-Longoria in Crustaceana 74:225–236, 2001). Egg production rates, egg surface ornamentation, and hatching success were monitored in large aquaculture fish enclosures during winter with close to zero water temperatures (N57°). Surprisingly, all female copepods (Acartia spp.—presumably A. tonsa, and Centropages hamatus) produced eggs all through the winter with no obvious pattern with respect to light, temperature and food availability, and no diapause eggs were observed. However, individual females produced several categories of eggs with or without surface spines even within the same egg batch as evidenced by scanning electron microscopy (SEM). Four egg categories were distinguishable: ‘no spines’, smooth eggs; ‘short spines’, 5–15 μm long; ‘truncated spines’, with the spine tips cut-off <10 μm long; and ‘long spines’, up to 30 μm long. All egg categories remained unchanged with respect to surface structures from when we took them out of the incubation bottles until they hatched. In general, the frequency of ‘no spines’ was 10–40%, and most eggs were ornamented with ‘short-’ or ‘long spines’. Further, a given egg can be ornamented with all types of surface spines simultaneously, which might even be a fifth egg category. The different egg categories were all able to hatch within days when exposed to normoxic conditions suggesting that they were subitaneous.     

Wanted dead or alive: high diversity of macroinvertebrates associated with living and ‘dead’ Posidonia oceanica matte

The Mediterranean endemic seagrass Posidonia oceanica forms beds characterised by a dense leaf canopy and a thick root-rhizome ‘matte’. Death of P. oceanica shoots leads to exposure of the underlying matte, which can persist for many years, and is termed ‘dead’ matte. Traditionally, dead matte has been regarded as a degraded habitat. To test whether this assumption was true, the motile macroinvertebrates of adjacent living (with shoots) and dead (without shoots) matte of P. oceanica were sampled in four different plots located at the same depth (5–6 m) in Mellieha Bay, Malta (central Mediterranean). The total number of species and abundance were significantly higher (ANOVA; P<0.05 and P<0.01, respectively) in the dead matte than in living P. oceanica matte, despite the presence of the foliar canopy in the latter. Multivariate analysis (MDS) clearly showed two main groups of assemblages, corresponding to the two matte types. The amphipods Leptocheirus guttatus and Maera grossimana, and the polychaete Nereis rava contributed most to the dissimilarity between the two different matte types. Several unique properties of the dead matte contributing to the unexpected higher number of species and abundance of motile macroinvertebrates associated with this habitat are discussed. The findings have important implications for the conservation of bare P. oceanica matte, which has been generally viewed as a habitat of low ecological value.     

δ<Superscript>13</Superscript>C and δ<Superscript>15</Superscript>N values in reef corals <Emphasis Type="Italic">Porites lutea</Emphasis> and <Emphasis Type="Italic">P. cylindrica</Emphasis> and in their epilithic and endolithic algae

In summer 1998, shallow water corals at Sesoko Island, Japan (26°38′N, 127°52′E) were damaged by bleaching. In August 2003, partially damaged colonies of the massive Porites lutea and the branching P. cylindrica were collected at depths of 1.0–2.5 m. The species composition of epilithic algal communities on dead skeletal surfaces of the colonies (‘red turfs’, ‘green turfs’, ‘red crusts’) and the endolithic algae (living in coral skeletons) growing close to and away from living coral polyps was determined. Carbon and nitrogen stable isotope values of organic matter (δ¹³C and δ¹⁵N) from all six of these biological entities were determined. There were no significant differences in the isotope composition of coral tissues of the two corals, with P. lutea having δ¹³C of −15.3 to −9.6‰ and δ¹⁵N of 4.7–6.1‰ and P. cylindrica having similar values. Polyps in both species living close to an interface with epilithic algae had similar isotope values to polyps distant from such an interface. Despite differences in the relative abundance of the algal species in red turfs and crusts, their δ¹³C and δ¹⁵N values were not significantly different from each other (−18.2 to −13.9, −20.6 to −16.2, 1.1–4.3, and 3.3 to 4.9‰, respectively). The green algal turf had significantly higher δ¹³C values (−14.9 to −9.3‰) than that of red turfs and crusts but similar δ¹⁵N (1.2–4.1‰) to the red algae. The data do not suggest that adjoining associations of epilithic algae and coral polyps exchange carbon- and nitrogen-containing metabolites to a significant extent. The endolithic algae in the coral skeletons had δ¹³C values of −14.8 to −12.3‰ and δ¹⁵N of 4.0–5.4‰. Thus they did not differ significantly from the coral polyps in their carbon and nitrogen isotope values. The similarity in carbon isotope values between the coral polyps and endolithic algae may be attributed to a common source of CO₂ for zooxanthellae and endolithic algae, namely, from respiration by the coral host. While it is difficult to fully interpret similarity in the nitrogen isotope composition of coral tissue and of green endolithic algae and the difference in δ¹⁵N between green epilithic and endolithic algae, the data are consistent with nitrogen-containing metabolites from the scleractinian coral serving as a significant source of nitrogen for the endolithic algae.     

Mating behavior of <Emphasis Type="Italic">Abdopus aculeatus</Emphasis> (d’Orbigny 1834) (Cephalopoda: Octopodidae) in the wild

The mating system of Abdopus aculeatus incorporates sneaker matings, mate guarding, sex-specific body patterns, frequent copulations, and male–male competition for mates, making it more similar to that of aggregating decapod cephalopods than any previously known octopus social system. Large male–female A. aculeatus occupy ‘Adjacent’ (G_A) dens and copulate frequently in mate-guarding situations over successive days. Nearby individuals copulate in ‘Temporary guarding’ (G_T) and ‘Transient’ (T; non-guarding) situations, the latter of which can involve ‘Sneaker’ (S) mating. In a focal animal study of these octopuses in the wild (Sulawesi, Indonesia) we addressed the hypotheses that they demonstrate: (1) precopulatory mate choice, (2) differential copulation rates by individuals employing different mating tactics, and (3) distant sex identification. We quantified daily copulation rates of A. aculeatus of reproductive size as well as aspects of copulation duration, display, mate-competition, and mate rejection. Mating tactic correlated with daily copulation rates. ♂G_A spent significantly more time copulating than did ♂T, while ♀G_A spent more than twice as much time per day in copula than did other females. Sneaker copulations lasted longer than those by males adopting other tactics. Mate-guarding was an effective and important tactic used by males to temporarily monopolize mating with apparently non-selective females. Males demonstrated clear pre-copulatory mate choice by guarding and mating repeatedly with large females (typically ♀G_A). While foraging alone away from the den, ♂G procured ‘Transient’ copulations with unguarded females. However, mate-guarding reduced the amount of time ♂G were alone and may impede their ability to seek out new mates. Low-copulation rates by ♀T, the smallest female tactic on average, may reflect this trade-off between mate preference and mate-searching by males, or non-receptivity of some females. A male-typical body pattern (black and white stripes) appeared to facilitate distant sex identification. Although mating and aggression were often initiated before contact between individuals, same-sex copulations and intense male–female aggression were rare. By contrast frequent male–female copulations and intense male–male aggression were consistent behavioral components of mating in A. aculeatus at these sites. Because the behavioral and ecological characters conducive to this complex system are not exclusive to A. aculeatus, it is possible that other octopuses exhibit some or all of these behaviors. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

What fraction of the organic carbon in sacoglossans is obtained from photosynthesis by kleptoplastids? An investigation using the natural abundance of stable carbon isotopes

any sacoglossans (opisthobranch gastropods) have the potential for carbon acquisition from photosynthesis by plastids sequestered from their macroalgal food as well as by ingestion, digestion and assimilation of the organic carbon derived from the alga. A new method for obtaining a minimum estimate of the fraction of sacoglossan carbon supplied from photosynthesis by kleptoplastids is suggested, based on the mass balance of stable carbon isotopes at the natural abundance level. The method involves comparison of ¹³C/¹²C ratios in sacoglossans with those of the algae on which they are found. Differences in ratios between alga and sacoglossan are used to give a minimum estimate of carbon acquisition by kleptoplasty, granted assumptions about the range of ¹³C/¹²C fractionation values which can occur for marine photolithotrophs. The new method is applied to several green (ulvophycean) alga–sacoglossan associations from Rottnest Island, Western Australia, and the values compared with those obtained previously by other means. The method suggests values of up to 0.6 of the total carbon input to the sacoglossans from photosynthesis by their kleptoplastids. To improve the estimates of the minimum role of kleptoplastidy in the carbon nutrition of sacoglossans, further information is needed: (1) on the fidelity of a given sacoglossan to a given algal individual (or species), (2) on the ¹³C/¹²C ratio of the part of the alga ingested by the sacoglossan, and (3) on the allocation of dietary organic carbon and of kleptoplastidic photosynthate to carbon lost in respiration, mucopolysaccharide production and gametes (and hence not sampled with the animal). Received: 24 November 1999 / Accepted: 20 October 2000     

Composition and temporal fluctuations of inshore juvenile fish populations in the Kornati Archipelago, eastern middle Adriatic

Temporal fluctuations of species composition and abundance of fish juveniles in the National Park Kornati were studied over 12 months from January to December 1992. A total of 40 168 individuals, representing 24 families and 69 species, were collected using a 50 m long beach seine. The community was dominated numerically by a few species: Atherina hepsetus (45.90%), Sarpa salpa (21.21%), Diplodus vulgaris (10.49%), and Symphodus ocellatus (6.98%), constituting over 84.58% of the total catch. Similarity between patterns in the abundance of the 17 most common species were examined using correlation matrix-based principal component analysis. Results were compared to the abiotic factors leading to the conclusion that only a low amount of variation in the abundance field can be explained by temperature, salinity and dissolved oxygen. Received: 23 March 1997 / Accepted: 11 April 1997     

Greenhouse effect of clusterization of CO2 and CH4 with atmospheric moisture

Carbon dioxide and methane are major compounds involved in global warming. The process of CO₂ and CH₄ molecules absorption by water clusters was investigated by the molecular dynamics method. The frequency spectra of dielectric permittivity for systems consisting of (H₂O) _n , (CO₂) _i (H₂O)₁₀ and (CH₄) _i (H₂O)₁₀ clusters mixed in various proportions were determined. The IR radiation absorption spectra of these systems were calculated and compared. Also, the radiating power of these systems was established. The capture of greenhouse gases’ molecules by ultra disperse water media reduces the ability of the media to absorb the Earth’s radiation, i.e., it reduces the greenhouse effect.     

Species-specificity and individual variation in the song of male Nathusius’ pipistrelles (<Emphasis Type="Italic">Pipistrellus nathusii</Emphasis>)

Sequences of the advertisement calls produced by male Nathusius’ pipistrelles (Pipistrellus nathusii) during the autumn mating period were recorded from individuals at two separate sites in Antrim, Northern Ireland, in August 2004. Several male roosts were found at these sites in close proximity to a single maternity roost, each containing approximately 200 adult females and their young. Analysis of measured parameters of four identified call types revealed that there were significant differences in call structure between sites and between individuals. Playback experiments, performed outside the adult female and juvenile roost sites, comprised of experimental advertisement call sequences of P. nathusii, Pipistrellus pygmaeus and Pipistrellus pipistrellus and control sound recorded without bats present (silence). Response was measured by simultaneously recording ultrasound during playbacks and counting the number of echolocation pulses identified as those of P. nathusii above a predetermined amplitude threshold. Significantly greater numbers of P. nathusii echolocation pulses were recorded during playback of male P. nathusii advertisement calls than during playback of congeners’ advertisement calls and control sound. The number of echolocation pulses recorded was similar during playback of P. pipistrellus and P. pygmaeus advertisement calls and silence. We suggest that, due to call complexity, male P. nathusii advertisement calls should be classified as ‘song’. Species-specificity and individual variation suggests that the songs of male P. nathusii have the potential to play a role in mate attraction and mate assessment.