Apparent survival rates of a long-lived partial migrant: the Yellow-legged Gull Larus michahellis

Capsule: In Yellow-legged Gull Larus michahellis populations from the eastern Adriatic Sea, there are considerable differences in the ratio of migratory birds and apparent survival among the colonies. Survival was dependent on age, colony and area of dispersal.

Aims: To identify the ratio of migratory birds within populations of Yellow-legged Gulls, and to compare apparent survival of gulls during migration in central and northern Europe and around the Adriatic Sea.

Methods: We analysed 15 years of resighting data of Yellow-legged Gulls using a MARK multi-state model to calculate survival rates. The effects of age, natal colony and area of dispersal were examined.

Results: Almost 60% of Adriatic Yellow-legged Gulls were migratory but the ratio varied among colonies (10.3–78.3%). Survival was dependent on age, colony and area of dispersal, with average values per group ranging between 0.599 (se 0.093) and 0.684 (se 0.084).

Conclusion: The ratio of migratory and dispersive Yellow-legged Gulls from different Adriatic colonies might be affected by both inheritance and food availability.     

Aminoacylation of Bisulphite-modified Yeast Tyrosine Transfer RNA

AS part of a search for the chemical rules underlying the recognition of a tRNA by its aminoacyl-tRNA ligase¹, we are examining the effect of C?U transitions on aminoacylation of tRNA. In this paper, we describe four well-characterized modifications of yeast tRNA^Tyr induced by reaction with bisulphite ions at pH 5.8. Three of the observed changes proved to be C-?U transitions produced by the series of reactions shown in Fig. 1 (refs. 2–5).     

New distribution data and population structure of the European mudminnow Umbra krameri in Serbia and Bosnia and Herzegovina

Seventy‐six individuals of the European mudminnow Umbra krameri from two recent populations from Serbia (Bakreni Batar and Lugomir) and one from Bosnia and Herzegovina (Gromi?elj) were analysed for habitat preferences and population structure. The population from Lugomir is a newly recorded population in Serbia. Besides this new record, it is noteworthy that all three studied locations are outside the currently known species distribution range limits.     

Reproductive biology of the freshwater goby Knipowitschia croatica Mrakovčić, Kerovec,Mišetić & Schneider 1996 (Actinopterygii,Gobiidae)

The reproductive biology and gonadogenesis cycle of the Vrgorac goby, Knipowitschia croatica is described [Conservation of Endangered Freshwater Fish in Europe, Birkhauser Verlag, Basel]. The species displays sexual dimorphism during the spawning period. Sexual maturity is achieved at an early age, with 50% of males and females sexually mature at total lengths of 40–45 mm. Fecundity of gravid females ranged from 188 to 593 eggs, with an egg diameter of 0.22–1.11 mm. Though the extended spawning period lasts from March to November, the highest intensity is observed from April to September. A comparison is made of the reproductive biology of this species with other sand goby species of the genera Knipowitschia and Pomatoschistus.     

Similar breakdown rates and benthic macroinvertebrate assemblages on native and Eucalyptus globulus leaf litter in Californian streams

1. Eucalyptus globulus, a tree species planted worldwide in many riparian zones, has been reported to affect benthic macroinvertebrates negatively. Although there is no consensus about the effects of Eucalyptus on aquatic macrobenthos, its removal is sometimes proposed as a means of ecological restoration. 2. We combined the sampling of macroinvertebrates with measurement of the colonisation of leaf packs in mesh bags, to examine the effects of riparian Eucalyptus and its litter on benthic macroinvertebrates in three small streams in California, U.S.A. Each stream included one reach bordered by Eucalyptus (E‐site) and a second bordered by native vegetation (N‐site). 3. The macrobenthos was sampled and two sets of litter bags were deployed at each site: one set with Eucalyptus litter (Euc‐bags) and one with mixed native tree litter (Nat‐bags) containing Quercus, Umbellularia, Acer and Alnus. Bags were exposed for 28, 56 and 90 days and this experiment was repeated in the autumn, winter and spring to account for effects of changing stream flow and insect phenology. 4. Litter input (average dry mass: 950 g m^?2 year^?1 in E‐sites versus 669 g m^?2 year^?1 in N‐sites) was similar, although in‐stream litter composition differed between E‐ and N‐sites. Litter broke down at similar rates in Euc‐bags and Nat‐bags (0.0193 day^?1 versus 0.0134 day^?1), perhaps reflecting the refractory nature of some of the leaves of the native trees (Quercus agrifolia). 5. Summary metrics for macroinvertebrates (taxon richness, Shannon diversity, pollution tolerance index) did not differ significantly between the E and N sites, or between Euc‐bags and Nat‐bags. No effect of exposure time or site was detected by ordination of the taxa sampled. However, distinct seasonal ordination clusters were observed in winter, spring and autumn, and one of the three streams formed a separate cluster. 6. The presence of Eucalyptus was less important in explaining the taxonomic composition of the macrobenthos than either ‘season’ or ‘stream’. Similarly, these same two factors (but not litter species) also helped explain the variation in leaf breakdown. We conclude that patches of riparian Eucalyptus and its litter have little effect on stream macrobenthos in this region.     

Somatic embryogenesis in Chenopodium rubrum and Chenopodium murale in vitro

In order to establish an efficient system for in vitro plant regeneration of a short day plant Chenopodium rubrum L. and a long day plant Chenopodium murale L., optimum culture conditions for somatic embryogenesis were investigated. The effects of different growth regulators, their combination and their concentrations on somatic embryos induction in different explant types (root, hypocotyl, cotyledon and leaf) were tested. Somatic embryogenesis was induced in both plants on Murashige and Skoog (MS) medium supplemented with sucrose (3 %), agar (0.7 %) and 1 - 10 M 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole growth regulator. The largest embryogenic capacity was found in root explants of Chenopodium rubrum on 1 M 2,4-D and in basal parts of cotyledons in C. murale plants on 10 M 2,4-D.     

In vitro plant regeneration from immature zygotic embryos and repetitive somatic embryogenesis in kohlrabi (Brassica oleracea var. gongylodes)

A simple and efficient protocol for direct somatic embryogenesis and plant regeneration of kohlrabi (Brassica oleracea var. gongylodes) was developed. Somatic embryos were induced from immature zygotic embryos at different developmental stages cultured on Murashige and Skoog medium supplemented with 0, 0.5, 1.0, or 1.5 mg/l 2,4-dichlorophenoxyacetic acid. Zygotic embryos at the early cotyledonary stage, which were cultured for 4 wk on plant growth regulator-free (PGR-free) medium, displayed the highest percentage of somatic embryogenesis (80.7%). Embryogenic tissue could be subcultured on the same medium for over 1 yr. Embryogenic lines derived from early cotyledonary stage zygotic embryos displayed the highest intensity of secondary embryogenesis (highest mean number of new somatic embryos per responsive somatic embryo explant). Histological analyses confirmed the direct origin of the secondary somatic embryos. Prolonged culturing of embryogenic tissue on PGR-free medium led to somatic embryo development into plantlets that were successfully acclimated in the greenhouse with a survival rate of 72.5%. Flow cytometry analysis showed no ploidy variation in 96.7% of the acclimated plants.