Occurrence of marine resident tropical eel Anguilla bicolor bicolor in Indonesia

In order to understand the migratory history and habitat use of the tropical anguillid eels Anguilla celebesensis, A. marmorata, and A. bicolor bicolor, the otolith strontium (Sr) and calcium (Ca) concentrations were examined for eels collected in Indonesian waters. In A. bicolor bicolor collected in a lagoon, the change in Sr:Ca ratios outside the high Sr:Ca core generally indicated two patterns of habitat residence: (1) constant living in either brackish or sea waters with no freshwater life (25%) and (2) habitat shifts from fresh water to brackish or sea waters (75%). No A. bicolor bicolor had a general life history as a freshwater resident. A. celebesensis and A. marmorata from the uppermost freshwater lake showed freshwater life history patterns. The wide range of otolith Sr:Ca ratios in A. bicolor bicolor indicated that the habitat use of this tropical eel was facultative among fresh, brackish, and marine waters during the growth phase after recruitment to coastal areas similar to that for temperate eels. Thus, the migration of anguillid eels into fresh water is clearly not an obligatory.     

Intra-colony relatedness and sociality in the allodapine bee Exoneura bicolor

Summary Overwintered and newly co-founded nests of Exoneura bicolor exhibit different grades of sociality. Intra-colony relatedness was estimated for adults and female brood in both nest types using allozyme data and a multiallelic estimator. The higher relatedness among female brood from overwintered nests compared to newly-founded nests is consistent with the difference in sociality between these colony types (semisocial versus quasisocial). However, intra-colony relatedness among adults is higher in cofounded nests than in overwintered nests, suggesting that differences in sociality are determined by benefit/cost ratios associated with non-reproductive strategies, rather than relatedness between interactants. Rapid egg-production in newly founded nests allows eggs to be stockpiled. This reduceds the tasks available to non-reproductives in early phases of colony development and limits the payoffs available for reproductive altruism. It is suggested that the social flexibility characteristic of allodapines is a consequence of communal progressive rearing which allows many benefits from cooperative nesting to be gained without worker sterility.     

Dynamics of calling by tree swallow (Tachycineta bicolor) nestmates

The begging display of nestling passerine birds has become a model for examining the evolution of animal signals. A particular problem for nestlings when transmitting begging signals to parents may be interference from nestmates. The strategies used by nestlings to reduce signal interference have not been studied, yet potentially contribute to the design of these complex displays. In this study, we recorded the begging calls of nestling tree swallows (Tachycineta bicolor) when alone and with a begging nestmate, to determine whether nestlings changed the output, structure or timing of their calls in ways that would reduce acoustic interference. We found that nestlings increased their call rate in the presence of a begging nestmate, but did not alter the length, amplitude or frequency of their calls. They also appeared not to adjust the timing of their calls to avoid those of nestmates. Contrary to expectation, nestling calls became more similar in some aspects when nestmates called together. An increase in call rate in the presence of a begging nestmate should increase the likelihood that a parent detects an individual's calls. However, if all nestlings increase their calling rate in response to competitors, then the overall level of acoustic interference across the brood is potentially increased, an effect exacerbated by the tendency for call similarity to increase when calling together. We discuss how increasing call rate may improve detectability despite this effect and we also examine how an increase in rate and call similarity may serve to produce a strong brood signal.     

Occurrence of extra-pair copulation in the tree swallow (Tachycineta bicolor)

Summary A new method to mark sperm transfer events between birds, using microspheres inserted into males' cloacae, was employed to assess the frequency of extra-pair copulation (EPC) in a population of tree swallows (Tachycineta bicolor) in Ontario, Canada, during the summer of 1988. We inserted 25 males with microspheres; spheres from 8 (32%) of these males were found in extra-pair females, from which we infer that males pursue a mixed reproductive strategy of monogamy coupled with seeking EPCs. The cloacae of 10 of 41 (24.4%) females were found to contain microspheres from non-mates. EPCs occur more frequently between neighboring birds than between non-neighbors. Only two within-pair copulations were detected with this method, suggesting that it underestimates the occurrence of all copulations, extra-pair or within-pair. Copulation watches revealed that within-pair copulations occur very frequently. We propose that frequent pair copulations are used by males to ensure their paternity in their mate's offspring. Offprint requests to: R.J. Robertson     

Begging calls and parental feeding decisions in tree swallows (Tachycineta bicolor)

We conducted playback experiments to examine how parent tree swallows (Tachycineta bicolor) use nestling begging calls to distribute feedings to individuals within broods. In a first study, we used a paired-choice test to determine if parents discriminated between the taped begging calls of nestlings deprived of food and those of nestlings that had been recently fed. Our results showed that parents directed their first feeding attempt towards model nestlings near speakers playing deprived calls significantly more often than to models near speakers playing fed calls. They also made more feeding attempts overall to models with deprived calls. In the second study, we varied call rate and amplitude to examine which call features parents might use to discriminate begging calls. Parents directed significantly more first feeding attempts and more feeding attempts overall towards non-begging nestlings near speakers playing high call rates than to nestlings near speakers playing low call rates. They did not, however, discriminate between calls differing in amplitude. Previous studies have shown that parent birds use begging calls to regulate overall feeding rates to the brood. Our results suggest that parent tree swallows also use begging calls when feeding individual nestlings and, in particular, prefer calls associated with increased levels of nestling hunger. Received: 14 February 2000 / Revised: 6 October 2000 / Accepted: 16 October 2000     

Plumage characteristics, reproductive investment and assortative mating in tree swallows Tachycineta bicolor

Elaborate ornamental plumage has been associated with various measures of individual quality in many species of birds. Male plumage characteristics, which have been relatively well studied, have been shown to reflect past reproductive investment, as well as the potential for reproductive investment in the current breeding attempt. In contrast, the signalling functions of female traits remain largely unexplored. In this study, we investigated the relationship between plumage attributes of breeding adult tree swallows and past reproductive investment, current reproductive investment and social mate pairing strategy. Both males and older females possess metallic green to metallic blue iridescent plumage on their dorsal surface, making this a suitable species for this type of investigation. We did not find any effects of past reproductive investment and success on the plumage attributes of returning breeders. In contrast, female plumage hue covaried with fledging success, and female plumage brightness was positively associated with mean clutch egg mass. In addition, we found that social pairs mated assortatively with respect to plumage brightness. We argue that since plumage characteristics vary with age in both male and female tree swallows, plumage attributes in this species are indicative of breeding experience and may be honest signals of quality. Positive assortative pairing could be the result of mutual mate choice or intra-sexual competition for nest sites by both males and females.     

Genetic differentiation of bicolor damselfish (Eupomacentrus partitus) populations in the Florida Keys

Electrophoretic variation in proteins encoded by 23 loci revealed substantial genetic differentiation among populations of bicolor damselfish (Eupomacentrus partitus) collected from four coral reefs in the Florida Keys, USA, during 1986–1988. Genetic differentiation was concentrated between a sample collected from Little Grecian Rocks Reef (LGR) and the remaining samples, including fish from a reef only 600 m distant (Grecian Rocks Reef). Genetic distinction of the LGR sample derived from significantly heterogenous allelic frequencies at six of eight polymorphic loci. Aco-1 (aconitase); Ada (adenosine deaminase); Gpi-2 (glucosephosphate isomerase); Ldh-2 and Ldh-3 (lactate dehydrogenase); and Me-1 (malic enzyme); nevertheless, differentiation at cytosolic aconitase (Aco-1) far exceeded that observed for other loci (fixation index, F _ST=0.482), and differences in Aco-1 allele frequencies were largely responsible for large genetic distances (0.20) between LGR and the other reefs. Paradoxically, estimates of numbers of migrants exchanged between reefs per generation (mN _e=17.47) indicated the potential for extensive gene flow. The extent of genetic differentiation among these populations is evaluated relative to models of population genetic structure based on equilibrium between gene flow and natural selection or genetic drift.     

Individual and environmental determinants of reproductive success in male tree swallow (Tachycineta bicolor)

Evaluating the contribution of individual and environmental determinants of reproductive success is essential to improve our understanding of sexual selection. In socially monogamous bird species with high rates of extrapair paternity, traits or environmental contexts affecting the number of within-pair young (WPY) produced by males can differ from those affecting the number of extrapair young fathered (EPY). Here, we use a 4-year dataset collected in contrasted environments to assess the factors affecting male reproductive success in tree swallows (Tachycineta bicolor), a species showing high levels of extrapair paternity. Our analyses revealed that the number of WPY was higher under better environmental conditions, while the number of EPY was mainly related to male characteristics. Males nesting in more intensive agricultural areas had fewer WPY produced and a lower reproductive success. Also, males breeding earlier in the season had more WPY. The presence of parasites reduced males’ reproductive success, mainly by reducing the number of EPY. The influence of male phenotype varied according to population density: Tarsus length variation had a greater effect on reproductive success at low population density than at high density, while wing length was also positively related to the number of EPY, more so at high than at low density. Altogether, our results suggest a complex interplay between individual and environmental determinants of reproductive success and imply that sexual selection dynamics varies depending on environmental contexts.     

Individually different foraging methods in the desert ant Cataglyphis bicolor (Hymenoptera,Formicidae)

Summary Observations and field experiments on the foraging behaviour of individual workers of Cataglyphis bicolor in a Southern Tunisian shrub desert are reported. The workers search singly for their food (mostly animal carcasses) and are singleprey loaders. The individuals differ to a great extent in their persistence to re-search the place of a find on a previous foraging excursion. The differences range continuously from thoroughly researching a place to just walking by. If, in an experiment, the same reward is offered farther from the nest, each ant persists more in re-searching the place than if food is offered close to the nest. In a further experiment, some individuals persisted less in searching near the former finding site if they had collected a fly than after collecting a piece of cheese. There is, however, evidence that individuals do not differ in their food preference. Persistent individuals, which re-search the place of a former find, are faster than non-persistent ones in retrieving food that is experimentally arranged in an aggregated manner. The experiment failed to demonstrate the (reverse) superiority of non-persistent individuals foraging on homogeneously distributed food. The observations of unmanipulated foraging excursions in the field suggest such an advantage for non-persistent foragers under natural conditions where food in general occurs widely dispersed. The colony as a whole retrieves more food within the same time from an experimental lay-out that is homogeneous than from an aggregated one. The behavioural differences between individuals could be caused by a training bias of the short-lived foragers, leading to a different assessment of the profitability of a searching method which implies returning to a formerly rewarding place. Thus, each worker uses the most promising behaviour according to its individual experience. Alternatively, the individually different searching methods could mainly contribute to the welfare of the colony as a whole rather than leading to a maximal short-term efficiency of each individual. In particular, the colony, disposing of only a few highly persistent foragers, could quickly exploit occasional short-lived, but unpredictible, clumps of food within its foraging range.     

Distribution of a novel infectious agent in healthy and diseased bicolor damselfish in Florida and the Caribbean

The disease damselfish neurofibromatosis (DNF) affects bicolor damselfish (Stegastes partitus) on reefs in Florida. This disease consists of peripheral nerve sheath and pigment cell tumors that are eventually fatal. The development of DNF is correlated with the appearance of unusual, extrachromosomal DNAs in affected fish that appear to be the genome of an undescribed, virus-like agent. Probes derived from these sequences were used to determine the distribution of this agent in diseased and healthy fish from several reefs in South Florida and from selected locations elsewhere in the range of this species. These analyses demonstrated that naturally diseased fish exhibited high levels of these DNAs in tumors and, to a lesser extent, in unaffected tissues. Fish with experimentally induced DNF exhibited similar levels of this DNA. Healthy adult fish had either no detectable levels of this DNA or very low levels, depending on the sensitivity of the detection technique used. Healthy adults from high disease prevalence reefs were more likely to test positive for this DNA than those from low disease reefs. Juvenile damselfish never contained detectable levels of this agent. Very low levels of this DNA were also detected in healthy fish from the Caribbean and the Bahamas. Dose-response experiments using tumor-derived cell lines indicated that tumor development was directly related to exposure dosages and that very low concentrations of this material did not yield tumor development. Taken together, these data indicate that high levels of this agent were correlated with the appearance of this disease and the very low levels often observed in healthy fish were not a predictor of tumor development.     

Prevalence and distribution patterns of tumors in bicolor damselfish (Pomacentrus partitus) on South Florida reefs

Damselfish neurofibromatosis (DNF) is a cancer affecting bicolor damselfish (Pomacentrus partitus) on reefs in South Florida, USA. Bicolor damselfish exhibiting DNF were observed on 18 of 19 reefs surveyed, with prevalence rates varying from 0.4 to 23.8% of the adult fish in these populations. These rates were very stable over 5 to 9 yr periods (1981 to 1989) on the two reefs monitored. High disease prevalence was associated with a high population density of large size-class fish and a population structure dominated by large fish. These patterns were observed both between and within reef populations. The distribution of cases within reefs was clustered rather than uniform or random. These findings are consistent with the hypothesis that DNF is distributed primarily via fish to fish (horizontal) transmission of an infectious agent. Disease patterns are not consistent with what would be expected to result from inherited (or vertically transmitted) or water-borne agents.     

Extra-pair paternity and the reproductive role of male floaters in the tree swallow (Tachycineta bicolor)

In many avian species, a part of the population is present at the breeding grounds but does not breed. Current theories generally assume that floaters are younger or lower-quality individuals, and empirical data confirm this. However, floating could also arise as an alternative strategy to breeding, if floaters are able to reproduce via extra-pair copulations. Until the present study, there has been no evidence that floaters father offspring. We studied a population of tree swallows (Tachycineta bicolor), a species with one of the highest levels of extra-pair paternity known in birds. Using microsatellite markers, we determined the biological fathers of 65% of the extra-pair young. Of a total of 53 extra-pair young (52% of all offspring), 47% were fathered by local residents, 6% by residents breeding elsewhere (up to 2 km from the focal grid), and 13% by floaters. Residents seemed to be more successful and they were also more likely to return as territory holders in the next breeding season compared to floaters. Extra-pair males were on average in better condition than the within-pair males they cuckolded. Interestingly, resident males that disappeared (possibly to float) during the fertile period were heavier than males that stayed, and floaters were heavier than residents, but not different in any other characteristic. Although alternative interpretations of the data are possible, we propose that floating might be a conditional strategy in tree swallows whereby males in good condition gain more paternity via extra-pair copulations, whereas males in worse condition are more successful by providing parental care.     

蚯蚓对土壤中铜、镉形态及高丹草生物有效性的影响

以高沙土和黄泥土为供试土壤,采用塑料盆分装土样,分别加入3个浓度的Cu2 (100、200、300mg kg-1)或Cd2 (5、10、15mg kg-1)模拟土壤污染,待这些污染土壤平衡培养2mo后,设置接种蚯蚓(Pheretima guillemi Michaels-en)处理与不接种蚯蚓处理,并种植高丹草(Sorghum×Sudan,Sorghum bicolor×S.sudanense);采用Tessler连续提取法测定重金属各结合形态,研究蚯蚓活动对土壤中Cu、Cd的主要形态及高丹草有效性的影响,以揭示蚯蚓对铜、镉污染土壤的修复作用.结果表明,蚯蚓活动显著提高了高沙土中碳酸盐结合态铜(Carb-Cu)和铁锰氧化物结合态铜(OxMn-Cu)的含量;显著提高了Cd处理为10、15mg kg-1的高沙土中离子交换态镉(Exch-Cd)和碳酸盐结合态镉(Carb-Cd)的含量,显著提高了黄泥土离子交换态铜(Exch-Cu)和有机结合态铜(WBO-Cu)的含量;通过测定各处理高丹草Cu、Cd含量发现,接种蚯蚓后,高沙土各Cu处理的高丹草的Cu含量显著增加,高沙土5、10mg kg-1Cd处理的高丹草的Cd含量以及黄泥土各Cd处理的高丹草的Cd含量均显著增加.图3表3参32     

Geometrical Factors and Metapopulation Dynamics of the Bush Cricket, Metrioptera bicolor Philippi (Orthoptera: Tettigoniidae)

This paper presents a metapopulation study of the bush cricket, Metrioptera bicolor , living in a recently fragmented landscape. The species inhabits grass and heathland patches of varying area and isolation. Analyses are made of how these geometrical factors affect local population size and density, distribution pattern, and the probability of local extinction and colonization. The proportion of available patches occupied varied between 72 and 79% during 1985–1990. Unoccupied patches were smaller and more isolated than those that were occupied. Patches where populations became extinct during this period were smaller than those with persisting populations. Since local population size was well correlated with patch area, it was clear that stochastic extinctions only occurred in small populations. Critical patch size for population extinction was approximately half a hectare. Colonized patches were less isolated than those that had not been colonized. Critical inter-patch distance for colonization was about 100 meters. The turnover was restricted to an identifiable share of the available patches. Only 33% of the patches were so small that extinction due to stochastic causes could be considered highly probable. This metapopulation will therefore most likely persist over a considerable period in its present spatial structure. There are apparent threats of further fragmentation, however, and nothing is known about the likelihood of large-scale extinctions resulting from extremely unfavorable weather conditions. Nevertheless, our results show that it is appropriate to include geometrical factors in metapopulation models.     

C4植物甜高梁和玉米幼苗对Zn胁迫的响应差异

实验采用营养液培养法,设置2,50,100,500和1000μmol-L-1浓度ZnSO4处理,比较C4植物甜高粱(Sorghum bicolor(L.)Moench.)和玉米(Zeamays.L)幼苗对zn胁迫的响应差异.结果表明,甜高粱对重金属zn胁迫的敏感性强于玉米,随着zn处理浓度加大,前者幼苗苗高、根长、单株干物质量、叶绿素含量和根系活力的下降幅度及丙二醛含量的上升幅度皆大于后者,玉米对Zn胁迫的耐受性强于甜高粱.在处理浓度达到500 μmol-L-1之前,甜高粱和玉米体内吸收的Zn随处理浓度加大显著递增,达500μmol-L-1之后,玉米根系积累的Zn不再明显增加.在处理浓度达到和高于100μmol·L-1时,甜高粱由根系向地上部转运的Zn显著高于玉米.甜高粱和玉米对Zn胁迫的敏感性差异可能缘于它们的吸收和转运差异.     

C_4植物甜高粱和玉米幼苗对Zn胁迫的响应差异

实验采用营养液培养法,设置2,50,100,500和1000μmol·L^-1浓度ZnSO4处理,比较C4植物甜高粱（Sorghum bicolor（L．）Moench．）和玉米（Zea mays．L）幼苗对Zn胁迫的响应差异。结果表明,甜高粱对重金属Zn胁迫的敏感性强于玉米,随着Zn处理浓度加大,前者幼苗苗高、根长、单株干物质量、叶绿素含量和根系活力的下降幅度及丙二醛含量的上升幅度皆大于后者,玉米对Zn胁迫的耐受性强于甜高粱。在处理浓度达到500μmol·L^-1之前,甜高粱和玉米体内吸收的Zn随处理浓度加大显著递增,达500μmol·L^-1之后,玉米根系积累的Zn不再明显增加。在处理浓度达到和高于100μmol·L^-1时,甜高粱由根系向地上部转运的Zn显著高于玉米。甜高粱和玉米对zn胁迫的敏感性差异可能缘于它们的吸收和转运差异。     

Local variation in mortality rates and life-expectancy estimates of the coral-reef fish Centropyge bicolor (Pisces: Pomacanthidae)

Mortality rates of the coral reef fish Centropyge bicolor were based on the disappearance of known individual fish. Data were collected over three years from 1978 at four sites around Lizard Island, Queensland, Australia. To measure disappearance, membership of 36 harems (comprising about 150 fish at any one time) was determined at bimonthly intervals. Mortality rates varied significantly among the four study areas. A tenfold difference in mean mortality occurred between two of the areas. The ranking of areas according to mortality rate was similar for 1978–1979 and 1979–1980. The ranking of areas was again similar for 1980–1984 when mortality rates were determined from an additional census in June 1984. Average further life-expectancy of mature fish based on mortality rates varied from 1 yr in one study area to 5 to 13 yr in a different area.     

Sperm quantity and quality effects on fertilization success in a highly promiscuous passerine, the tree swallow Tachycineta bicolor

Sperm competition is widespread among animal taxa and considered a major force in sperm evolution. Recent comparative studies have indicated that sperm competition selects for high sperm production capacity and long and fast-swimming spermatozoa across species. Here, we examine the role of sperm quantity and quality for fertilization success of individual males in a Canadian population of tree swallows Tachycineta bicolor, a socially monogamous, but highly promiscuous passerine. Male fertilization success (the sum of withinpair and extrapair young) was significantly associated with the size of the cloacal protuberance (a proxy for sperm quantity), but not with sperm size or in vitro sperm swimming speed. In a multivariate analysis, both cloacal protuberance volume and relative sperm midpiece size (i.e. high mitochondrial loading) had significant effects on male fertilization success. However, relative sperm midpiece size was not associated with fertilization success in a simple regression. Further, both cloacal protuberance volume and relative midpiece size had significant effects on sperm velocity, both in simple regressions and in a multivariate analysis. The finding that males with large relative midpiece size had both higher fertilization success and faster swimming sperm, suggests an indirect link between sperm morphology and male fertility mediated through sperm velocity. In conclusion, both quantitative and qualitative sperm traits seem to affect male fertilization success in tree swallows.     

Management of fat reserves in tufted titmice (Parus bicolor ): evidence against a trade-off with food hoards

Caching species can manage their energy supply by adjusting body fat, number of caches, or both. It has been hypothesized that because body fat has a higher fitness cost than caches, small food-hoarding birds respond to increased starvation risk by increasing the number of their caches rather than their fat load. This hypothesis predicts that when birds cannot cache they should compensate for the loss of external energy storage by (1) shifting the time of their daily body mass accumulation toward earlier in the day and (2) increasing the overall level of their fat reserves. During the winter of 1995–1996, we tested these predictions with a caching species, the tufted titmouse (Parus bicolor). Each of six experimental birds was fed a diet of uncachable sunflower seed powder for 6 days, preceded and followed by 6-day control periods during which they were fed cachable sunflower seeds. The daily pattern of body mass gain was unaffected by the opportunity to cache. Furthermore, when unable to cache, the birds did not increase either their mean daily body mass, body mass in the middle of the day, or evening body mass compared to the two control periods. These results argue against the hypothesis of a trade-off between fat reserves and food caches in tufted titmice, and suggest that fat reserves are managed independently of external food caches. Received: 9 April 1997 / Accepted after revision: 30 August 1997