Male display characters, gonadal maturation and androgens in the cichlid fish Oreochromis mossambicus

  The relationships between gonadal maturation and the expression of behavioral and morphological display characters in O. mossambicus was investigated and the possible role of androgens in the coordination of this process was evaluated using genital papilla size as a bioassay for androgen levels. Morphological and behavioral displaying characters were found to be correlated among themselves. The sexually dimorphic characters were correlated with gonad maturation and androgen levels, but not with the gonado-somatic index. Gonad maturation and androgen levels were closely related. Territoriality and other behavioral variables involved in reproduction were also correlated with gonad maturation and androgen levels. These data suggest that in O. mossambicus androgens play a mediating role between gonadal maturation and the expression of display characters, both morphological and behavioral. Received: 23 February 1999 / Received in revised form: 3 May 1999 / Accepted: 10 May 1999     

Some properties of a pheromone allowing individual recognition, from the scats of an Australian lizard, Egernia striolata

  The Australian lizard, Egernia striolata, can distinguish its own scats from those of unfamiliar conspecific individuals. This appears to be unrelated to diet, because there is no difference in the response to scats from unfamiliar lizards fed on diets that are the same or different from the test lizard. The signal that induces the response is not a visual or tactile property of scat structure, because test lizards respond equally to crushed and intact scats. We suggest that a pheromone is secreted onto the scat as it is produced. Water solutions of scats did not contain signal components that allowed lizards to distinguish their own scats from others. However, solutions of scats in dichloromethane (DCM) retained unique characteristics, and test lizards responded more strongly to the solution from scats of an unfamiliar lizard that to the solution from their own scats. Further fractionation of the DCM solution in pentane and in methanol led to loss of the unique signals needed for individual recognition, but those were restored when the pentane and methanol fractions were recombined. We infer that these lizards can distinguish between scats of different individuals on the basis of signals they receive from a complex combination of chemicals. Received: 14 December 1998 / Received in revised form: 9 April 1999 / Accepted: 12 April 1999     

MS32-regulated timing of callose degradation during microsporogenesisin Arabidopsis is associated with the accumulation of stacked rough ER in tapetal cells

  In the male sterile32(ms32)mutant in Arabidopsis thaliana, pollen development is affected during meiosis of pollen mother cells (PMCs). In normal wild-type (WT) anthers, callose is deposited around PMCs before and during meiosis, and after meiosis the tetrads have a complete callose wall. In ms32, PMCs showed initial signs of some callose deposition before meiosis, but it was degraded soon after, as was part of the cellulosic wall around the PMCs. The early dissolution of callose in ms32 was associated with the occurrence of extensive stacks of rough ER (RER) in tapetal cells. The stacks of RER were also observed in the WT tapetum, but at a later stage, i.e., after the tetrads were formed and when callose is normally broken down for release of microspores. Based on these observations it is suggested that: (1) callose degradation around developing microspores is linked to the formation of RER in tapetal cells, which presumably synthesize and/or secrete callase into the anther locule, and (2) mutation in MS32 disrupts the timing of these events. Received: 27 April 1999 / Revision accepted: 21 June 1999     

QTL analysis of tolerance to a German strain of BYDV-PAV in barley (Hordeum vulgare L.)

One hundred and forty six barley doubled-haploid lines (DH lines) were tested for variation in grain yield, yield components, plant height, and heading date after artificial infection with a German isolate of barley yellow dwarf virus (BYDV-PAV-Braunschweig). Of these 146 lines 76 were derived from the cross of the barley yellow dwarf virus (BYDV) tolerant cultivar ’Post’ to cv ’Vixen’ (Ryd2) and 70 from the cross of Post to cv ’Nixe’. Phenotypic measurements were gathered on both non-infected plants and plants artificially inoculated with BYDV-PAV by viruliferous aphids in pot and field experiments for three years at two locations. For all traits a continuous variation was observed suggesting a quantitative mode of inheritance for tolerance against BYDV-PAV. Using skeleton maps constructed using SSRs, AFLPs and RAPDs, two QTLs for relative grain yield per plant after BYDV infection, explaining about 47% of the phenotypic variance, were identified in Post × Vixen at the telomeric region of chromosome 2HL and at a region containing the Ryd2 gene on chromosome 3HL. In Post × Nixe, a QTL was found in exactly the same chromosome 2HL marker interval. In this cross, additional QTL were mapped on chromosomes 7H and 4H and together these explained about 40% of the phenotypic variance. QTL for effects of BYDV infection on yield components, plant height, and heading date generally mapped to the same marker intervals, or in the vicinity of the QTL for relative grain yield, on chromosomes 2HL and 3HL, suggesting that these regions are of special importance for tolerance to the Braunschweig isolate of BYDV-PAV. Possible applications of marker-assisted selection for BYDV tolerance based on these results are discussed. Received: 1 December 2000 / Accepted: 9 March 2001     

New hyperbenthic species of Misophriopsis and Misophriella, first record of misophrioid copepods (Crustacea) from Antarctic waters

  Misophrioid copepods are reported for the first time from Antarctic waters. A species of each of the genera Misophriopsis and Misophriella is described from hyperbenthic layers of the continental shelf of the eastern Weddell Sea. The genus Misophria is also reported from these waters. Misophriopsis australis sp. nov. is the fifth representative of this widely distributed genus, previously reported from the North Atlantic, the China Sea, and both NW and NE quadrants of the Pacific Ocean. Misophriella schminkei sp. nov. is the second representative of the genus, known to date only from a single female caught in North Atlantic bathyal depths. Traces of subdivisions on antennary exopodal segments of the latter species suggest that the first segment may be a triple segment, while the second and terminal segments may be double segments. In addition, the mandibular exopod of this taxon indicates that a six-segmented ramus with setal formula 0, 1, 1, 1, 1, 2 may represent the ground pattern in Copepoda. The presence of parts of a cyclopinid copepod in the gut of M. schminkei sp. nov. indicates that this species may be carnivorous. Received: 12 November 1998 / Received in revised form: 26 July 1999 / Accepted: 27 July 1999     

Molecular cloning of ABNORMAL FLORAL ORGANS: a gene required for flower development in Arabidopsis

 We report the cloning and characterization of the gene ABNORMAL FLORAL ORGANS (AFO), which is required for normal flower development in Arabidopsis. afo mutant flowers show defects in all four floral whorls. The number of organs in each whorl varies. Most flowers consist of reduced numbers of petals and stamens, even though supernumerary sepals and carpels may be observed. Abnormal organ structure is evident from an early stage. Mosaic first whorl organs are common, with some sepals taking on petaloid or staminoid characteristics. Stamens are often deformed, having thin filaments and reduced anthers, yet occasionally producing viable pollen. Partial fertility is indicated by some seed setting. The afo-1 mutation is caused by insertion of a gene trap Ds transposable element. The AFO gene was cloned and is predicted to encode a novel protein of 229 amino acids. The expression of AFO mRNA by northern blot analysis in combination with mutant phenotype suggests that the AFO gene product plays an important role in Arabidopsis flower development. We also report that antherless, a previously described male-sterile mutation, is allelic to afo-1. Received: 3 September 1998 / Revision accepted: 15 December 1998     

The effects of kinship and density on growth and metamorphosis of the bronze frog (Rana temporalis) tadpoles

  Five clutches of Rana temporalis eggs collected along a stream were reared separately until formation of Gosner stage 25 tadpoles. The effect of kinship and density was then studied by rearing ten siblings in 1 (sib 1) or 5 (sib 5) l water, and mixed rearing of ten tadpoles (2 from each of the 5 clutches) in 1 (mix 1) or 5 (mix 5) l water; each group replicated five times. In all the groups tadpoles showed a sigmoid growth curve. Both kinship and density interacted to affect mean proportions of individuals reaching metamorphic climax (MC), mean body mass, and size frequency at MC (day 79). The proportion of tadpoles reaching MC was highest in sib 5 (82%) followed by mix 5 (77%), sib 1 (73%), and mix 1 (64%) groups. Crowding plus mixing significantly lowered the median developmental stage mean body mass and broadened the spectrum of developmental stages or size classes at MC. The size difference of individuals at MC was inversely related to density of rearing. Frequency of different developmental stages was comparable in sib 1, sib 5, and mix 5 groups. Interestingly, small individuals were significantly greater in number in the mix 1 group compared to sib 1. The above findings suggest that genotypic heterogeneity in conjunction with crowding retards growth rate of tadpoles in comparison with those reared in a genetically homogenous (sib) environment. Further, they suggest that the adverse effect of mixed rearing is context dependent. Received: 12 April 1999 / Received in revised form: 16 June 1999 / Accepted: 18 June 1999     

Developmental effects of vasotocin and nonapeptide receptors on early social attachment and affiliative behavior in the zebra finch

Zebra finches demonstrate selective affiliation between juvenile offspring and parents, which, like affiliation between pair partners, is characterized by proximity, vocal communication and contact behaviors. This experiment tested the hypothesis that the nonapeptide arginine vasotocin (AVT, avian homologue of vasopressin) and nonapeptide receptors play a role prior to fledging in the development of affiliative behavior. Zebra finch hatchlings of both sexes received daily intracranial injections (post-hatch days 2–8) of either AVT, Manning Compound (MC, a potent V1a receptor antagonist) or saline (vehicle control). The social development of both sexes was assessed by measuring responsiveness to isolation from the family and subsequent reunion with the male parent after fledging. In addition, we assessed the changes in affiliation with the parents, unfamiliar males, and unfamiliar females each week throughout juvenile development. Compared to controls, MC subjects showed decreased attachment to the parents and MC males did not show the normal increase in affiliative interest in opposite sex individuals as they reached reproductive maturity. In contrast, AVT subjects showed a sustained affiliative interest in parents throughout development, and males showed increased interest in opposite sex conspecifics as they matured. These results provide the first evidence suggesting that AVT and nonapeptide receptors play organizational roles in social development in a bird.     

The use of fish metabolic, pathological and parasitological indices in pollution monitoring

  An integrated biological effect monitoring concept has been tested in flounder (Platichthys flesus L.) from four locations with different anthropogenic impact in the German Bight. During 3 years of sampling, biomarkers at all levels of biological organisation from the molecular to the ecosystem level were applied and tested on 742 individual fish of body lengths between 18 and 25 cm. At the ecosystem level, the fish were taken as a habitat for the parasite assemblage. The hypothesis was that changes in the environment might lead to changes in the species diversity of parasites and in the infection intensity of single species, as well as between heteroxenic and monoxenic parasite species (H/M ratio). At the molecular level, activity of the CYP1A-dependent monooxygenase ethoxyresorufin O-deethylase (EROD) was used as a biomarker of exposure. At the subcellular level, the integrity of lysosomal membranes in hepatocytes was taken as an indicator of non-specific acute and chronic toxic effects. Both biomarkers are recommended by the ICES Advisory Committee on the Marine Environment for the application in biological effects monitoring programmes. In addition, neutral lipid content in the liver was used as a marker for pathologically induced fat accumulation. In the same individual fish, a new method for the measurement of macrophage aggregate activity in the liver was tested for its application and reliability in reflecting immunosuppression. Tests were accompanied by chemical analysis of standard organochlorine and heavy metal residues in flounder tissue. A total of 33 parasite species were found. As an indicator species, the mean abundance of Trichodina sp. reflected best the pollution gradient observed with highest infection intensity at the most polluted location. Species diversity was significantly higher in fish caught near the reference site and significantly lower in fish from the polluted Elbe estuary. The use of the heteroxenous/monoxenous species ratio as a marker was not useful at the locations investigated because of the dominance of heteroxenous species at all habitats. Since EROD activity and macrophage aggregate activity were dependent on sex and maturity of female flounder, only male fish were taken into consideration for the integrated evaluation of data. All biochemical and histochemical tests were able to reflect accurately the site-specific differences, as well as an observed pollution event at the end of 1995 as determined by chemical analyses. The correlation analysis revealed a connection not only between the single parasitological and biochemical parameters but also within these groups. The non-specific immune response and Trichodina infection intensity were correlated with all other parameters, leading to the assumption that these may serve as links between the lowest and the highest levels of biological organisation. The simultaneous use of metabolic and parasitological results facilitated the interpretation of the observed variations of the data and the distinction between natural variation and pollution-mediated effects. Received: 1 March 1999 / Received in revised form: 25 May 1999 / Accepted: 7 June 1999     

Food sharing and affiliation: An experimental and longitudinal study in cockatiels (Nymphicus hollandicus)

Food sharing has attracted much attention because of its apparently altruistic nature and its link to prosociality. However, food sharing has been mostly studied in a reproductive context, during courtship and parental care, where the fitness benefits are obvious. We still lack a clear understanding of the functions of food sharing outside any reproductive context and within social groups of same‐aged peers. Previous studies suggest that cofeeding, the action to let another animal feed from the same monopolizable food source, may be used to build and strengthen bonds between individuals. This may be particularly crucial in social birds forming long‐term associations between mates or siblings such as psittacids and corvids. Here, we investigated food sharing and affiliative behaviors such as allopreening in a psittacine species, namely in a group of captive juvenile cockatiels (Nymphicus hollandicus) consisting of five siblings and five unrelated birds. Our main objective was to study the developmental pattern of food sharing over time and its implication in social bonding depending on kinship, affiliation, and sex. Studying cockatiels in this context is providing many new information since most of the studies on food sharing in birds focused on corvids. We found that, contrary to jackdaws, cockatiels continued to share food with multiple individuals, although the frequency of cofeeding as well as the number of cofeeding partners decreased over time. Cockatiels shared more food with their siblings than with other conspecifics but they were not more likely to do cofeeding with birds of the opposite sex. We also found evidence that young cockatiels exchanged more food with those from whom they received food (reciprocity) and, to a lesser extent, allopreening (interchange), than from other cockatiels. Our findings suggest that in cockatiels, food sharing within social groups serves the formation (and maintenance) of affiliative bonds, especially between siblings, rather than pair bonds, but might additionally be explained by reciprocity, interchange, and harassment avoidance.     

Social organization of a stable natal group of captive Guyanese squirrel monkeys (<Emphasis Type="Italic">Saimiri sciureus sciureus</Emphasis>)

Socioecological models suggest competition for food, foraging efficiency, predation, infanticide risk, and the costs of dispersal regulate primate social structure and organization. Wild populations of squirrel monkeys (Saimiri spp.) appear to conform to the predictions of the predation/competition socioecological model (Sterck et al. in Behav Ecol Sociobiol 41:291–309, 1997) and the dispersal/foraging efficiency model (Isbell in Kinship and behavior in primates. Oxford University, New York, pp 71–108, 2004). However, squirrel monkeys in captivity are reported to maintain patterns of social behavior observed in their wild conspecifics despite different food distribution, predation risk, and dispersal options. This behavioral similarity suggests squirrel monkeys’ social behavior has limited flexibility to respond to environmental changes. In this study, we experimentally evaluated the flexibility of social behavior within a captive group of S. sciureus. First, we determined whether dominance and affiliative relationships observed under normal laboratory conditions (with abundant, widely distributed, food; no dispersal option; and no predators) better matched published reports of relationships among wild conspecifics or the predictions of the predation/competition model. Second, we made preferred food items defensible to determine whether dominance interactions would become more frequent and linear, as predicted by the model. The model correctly predicted rates of dominance behavior in both conditions and a linear hierarchy in the defensible food condition but did not predict the consistent affiliative relationships and linear dominance hierarchy observed in normal lab conditions. Although hierarchies were linear and male dominant, manipulating food distribution changed the dominant individual within each sex. Our findings suggest interaction rates adapt more rapidly than social structure to environmental changes in Saimiri and recommend caution in interpreting tests of socioecological models.     

Whom do the sparrows follow? The effect of kinship on social preference in house sparrow flocks

Non-aggressive social interactions between group-mates, e.g. maintenance of spatial proximity or activity synchrony are basic elements of a species’ social structure, and were found to be associated with important fitness consequences in group-living animals. In the establishment of such affiliative relationships, kinship has often been identified as one of the key predictors, but this has rarely been studied in simple social groups such as flocks of gregarious birds. In this study we investigated whether kinship affects social preference, as measured by the tendency to associate with others during various social activities, in captive house sparrow (Passer domesticus) flocks where birds could interact with differently related flock-mates. We found that preference between flock-mates was correlated with familiarity from early nestling period: same-brood siblings followed their sib initiating new activities more often than non-sib birds. The strength of association between birds also tended to correlate with genetic relatedness, but this was mainly due to the effect of siblings’ affiliation. Thus we concluded that house sparrows prefer the company of their siblings during social activities even well after fledging, which may facilitate kin-biased behaviours.     

Juvenile greylag geese (Anser anser) discriminate between individual siblings

Social species that maintain individualised relationships with certain others despite continuous changes in age, reproductive status and dominance rank between group members ought to be capable of individual recognition. Tests of "true" individual recognition, where an individual recognises unique features of another, are rare, however. Often kinship and/or familiarity suffice to explain dyadic interactions. The complex relationships within a greylag goose flock suggest that they should be able to recognise individuals irrespective of familiarity or kinship. We tested whether six-week-old hand-raised greylags can discriminate between two of their siblings. We developed a new experimental protocol, in which geese were trained to associate social siblings with geometrical symbols. Subsequently, focals were presented with two geometrical symbols in the presence of a sibling associated with one of the symbols. Significant choice of the geometrical symbol associated with the target present indicated that focals were able to distinguish between individual targets. Greylag goslings successfully learned this association-discrimination task, regardless of genetic relatedness or sex of the sibling targets. Social relationships within a goose flock thus may indeed be based on recognition of unique features of individual conspecifics.     

Discrimination of sinusoidally frequency-modulated sound signals mimicking species-specific communication calls in the FM-bat Phyllostomus discolor

In the lesser spear-nosed bat, Phyllostomus discolor, maternal directive calls are characterized by an individual type of sinusoidal frequency modulation (= SFM) pattern. Beside modulation frequency, modulation depth, carrier frequency, and number of modulation cycles per call contribute to the mother's vocal signature. Since juvenile P. discolor learn to adapt their isolation calls to the corresponding call characteristics of the own mother or even to playback of a computer-stored directive call, if hand-reared in the absence of conspecifics, the bats' auditory system ought to be able to resolve interindividual differences in communication call structure. However, quantitative psychoacoustic data on the discrimination of SFM signals in this species are not available. Thus, in the present study, lesser spear-nosed bats were trained in a two-alternative forced-choice procedure to discriminate between two alternatingly presented SFM sound signals differing in modulation frequency. Other characteristics of acoustic stimuli were identical and designed to mimick the fundamental of species-specific calls. By gradually reducing the difference in modulation frequency between both stimuli within the behavioural relevant range until the animals' performance dropped below the 75%-correct level, a considerable auditory spectro-temporal resolution has been revealed. Particularly in comparison to the overall interindividual variation of this call parameter (minimal modulation frequency = 49 Hz, maximum = 100 Hz), the determined average difference limen for modulation frequency of 2.42 ± 0.29 Hz seems substantial and sufficient for labelling individuals. Accepted: 30 November 1996     

Negative association between parental care and sibling cooperation in earwigs: a new perspective on the early evolution of family life?

The evolution of family life requires net fitness benefits for offspring, which are commonly assumed to mainly derive from parental care. However, an additional source of benefits for offspring is often overlooked: cooperative interactions among juvenile siblings. In this study, we examined how sibling cooperation and parental care could jointly contribute to the early evolution of family life. Specifically, we tested whether the level of food transferred among siblings (sibling cooperation) in the European earwig Forficula auricularia (1) depends on the level of maternal food provisioning (parental care) and (2) is translated into offspring survival, as well as female investment into future reproduction. We show that higher levels of sibling food transfer were associated with lower levels of maternal food provisioning, possibly reflecting a compensatory relationship between sibling cooperation and maternal care. Furthermore, the level of sibling food transfer did not influence offspring survival, but was associated with negative effects on the production of the second and terminal clutch by the tending mothers. These findings indicate that sibling cooperation could mitigate the detrimental effects on offspring survival that result from being tended by low‐quality mothers. More generally, they are in line with the hypothesis that sibling cooperation is an ancestral behaviour that can be retained to compensate for insufficient levels of parental investment.     

The development of social behaviour between siblings and non-siblings of the voles Microtus ochrogaster and Microtus pennsylvanicus

It has been suggested that the strength and duration of sibling relations during the juvenile period may reflect the social structure of mammal species. Two Microtus species with contrasting social systems, M. ochrogaster and M. pennsylvanicus, were chosen for a comparative study of juvenile social behaviour. Young were observed in sibling and non-sibling dyadic encounters from the second until the seventh week of age. Social interactions consisted mainly of body nosing of the partner, and included behaviours interpreted as investigation, socialization and settling. Only minor sex differences in body nosing scores occurred, but some ontogenetic trends were noted. When the species were compared, M. ochrogaster received higher scores for body nosing and sitting in contact, and displayed more reciprocity in their nosing, than did M. pennsylvanicus, whether siblings or non-siblings were considered. When the sibling types were compared, non-sibling dyads received higher nosing scores than did siblings in both species, but the disparity was greater in M. ochrogaster than in M. pennsylvanicus. These results are interpreted with reference to known behavioural and developmental correlates of the extended family system in naturally occurring M. ochrogaster and the less communal social system in M. pennsylvanicus.     

Sexually dimorphic transitions revealed in the relationships of yearling rhesus monkeys following the birth of siblings

We report here that in a large captive group of monkeys, Macaca mulatta,sudden sex-related changes occur in social interactions in one short phase of an infant’s development. Social interactions of 1-year-old animals (males, N =12; females, N =8) 6 weeks before the birth of siblings were compared with interactions occurring 6 weeks after the birth. On the day of the siblings’ birth, depression-like postures were seen in two yearling males (YMs); 10 YMs showed hyperactivity. In the postbirth period, YMs refocused their attentions away from their mother and toward other, often unrelated members of the group. Although YMs initiated disengagement of interactions with their mothers, there was evidence that mothers attempted to lessen this disengagement. The YMs had close relationships with specific (“preferred”) male individuals. These relationships (particularly those with adult males) became more pronounced following the birth of the sibling. The adult-male group also took an active role in maintaining interactions with YMs. The preferred partners in the YM-other male relationship before the birth of the sibling were, however, not always the same as those in the period after the birth. Dominance relationships and probably genetic factors determined patterns of interaction between YMs and their preferred male partners. Among yearling females (YFs), no dramatic changes in interactions with their mothers or with other group members were detected after their mothers gave birth. Relationships in YF-mother and YF-other-individual pairs (especially when the other individual was kin) seemed to be consolidated during the postbirth interval. There was little evidence of jealousy between the YFs and their younger siblings. Thus, sibling birth acted as a stimulus for the occurrence of sexually dimorphic interactions in yearlings. We suggest that in natural environments, social interactions in YFs promote relationships that will serve to integrate them into the matrilineal social structure, whereas comparable behavior in YMs encourages relationships with males that they may emigrate with into, or meet again in, nonnatal troops.     

A preliminary study of selective visual attention in female mountain gorillas (Gorilla gorilla beringei)

Visually attending to conspecifics can give group-living primates important ecological information, help them to anticipate the behavior of others and to regulate interactions with them, and provide other valuable social information. Variation in the importance and quality of social relationships should influence the way individuals selectively attend to fellow group members. Preliminary data on visual monitoring of conspecifics by wild female mountain gorillas (Gorilla gorilla beringei) show that selective attention mirrors variation in social relationships. Social bonds between males and females are central to gorilla society; correspondingly, females are more likely to stop feeding, and focus their attention on males who walk into view than on females, especially when males give dislays. Females are more likely to focus on other females with whom they have antagonistic relationships than those (mostly close relatives) with whom they have affiliative, cooperative ones. Further research on the context and consequences of visual monitoring could help to address questions about the regulation of social relationships and about social cognition in gorillas.     

AFLP analysis of the phenetic organization and genetic diversity of Vigna unguiculataL. Walp. reveals extensive gene flow between wild and domesticated types

Amplified fragment length polymorphisms (AFLPs) were used to evaluate genetic relationships within cowpea [Vigna unguiculata (L.) Walp.] and to assess the organization of its genetic diversity. Nei’s genetic distances were estimated for a total of 117 accessions including 47 domesticated cowpea (ssp. unguiculata var. unguiculata), 52 wild and weedy annuals (ssp. unguiculata var. spontanea), as well as 18 perennial accessions of the wild subspecies pubescens, tenuis and alba. AFLP variation was also used to study genetic variation among and within domesticated and wild accessions based on their geographical origin (western, eastern and southern Africa). Wild annual cowpea (var. spontanea) (H _T =0.175) was more diverse than domesticated cowpea (H _T =0.108). Wild cowpea was more diverse in eastern (H _S =0.168) than in western Africa (H _S =0.129), suggesting an eastern African origin for the wild taxon. The AFLP data were consistent with earlier findings of a unique domestication event in cowpea in the northern part of the continent and suggested that domestication in eastern or southern Africa was unlikely. It did not allow a more precise localization of domestication due to extensive gene flow between wild and domesticated forms that has led to a large crop-weed complex distributed over the entire African continent. In addition, wild materials from northeastern Africa are still lacking. Overall, the superiority of the AFLP technique over isozymes resided in its ability to uncover variation both within domesticated and wild cowpea, and should be a powerful tool once additional wild material becomes available. Received: 11 September 2000 / Accepted: 14 June 2001     

Distribution patterns of bacterioplankton and chlorophyll-a in the German Wadden Sea

 In a first synoptic evaluation, the temporal and spatial distribution of bacterioplankton and chlorophyll-a were determined in the German Wadden Sea. Three surveys were undertaken in winter, spring, and summer of 1994 using up to eight ships simultaneously between the river Ems and Sylt island. Despite intensive hydrodynamic mixing of the Wadden Sea water, spatial gradients were obvious. The abundance of bacterioplankton ranged from 0.4 to 26×10⁵ ml^–1 and chlorophyll-a varied between <0.1 and 79 μg l^–1. In winter, relatively homogeneous distribution patterns of both parameters with small gradients were found. Highest chlorophyll-a values connected with a highly patchy structure were observed in spring, while in summer both total chlorophyll-a values and the complexity of the distribution pattern had decreased. In contrast, bacterial numbers increased steadily from January to July with the highest bacterial densities and greatest patchiness observed in summer. Moreover, in some regions of the Wadden Sea, a trophic succession of algae as carbon producers and bacteria as consumers was evident. Correlation analysis verified the relationship between bacteria and chlorophyll a, indicating bottom-up control of bacterial abundance in the northern part of the German Wadden Sea. Since the observed regression slope is remarkably low (0.12–0.46) compared to literature values (0.5–0.8), we suggest that the link between phytoplankton and bacteria found here is a special characteristic of the Wadden Sea as a transition zone between the coastal region and the outer North Sea. Received: 26 May 1998 / Accepted:12 November 1998