Reproductive success of monogamous and polygynous pied flycatchers (Ficedula hypoleuca)

One of the most interesting aspects of the mating system of pied flycatchers is the regular occurrence of polygyny. Here we present data on the reproductive success of polygynously paired pied flycatcher males compared to monogamous males based on paternity analyses through DNA fingerprinting. Males paired with two females suffered a higher loss in reproductive output per female compared to monogamous males due to (1) a greater proportion of unhatched eggs in their broods, (2) greater nestling mortality and (3) a greater probability of being cuckolded. Nevertheless, the number of fledglings was significantly greater for polygynous males. Based on the number of nestlings that returned for subsequent breeding seasons, however, the reproductive success of monogamous and polygynous males did not differ significantly. These data raise the question as to why males attempt polygyny. Received: 16 August 1999 / Received in revised form: 15 March 2000 / Accepted: 18 March 2000     

Assessing the Geographic Representativeness of Genebank Collections: the Case of Bolivian Wild Potatoes

Abstract: Genebank collection databases can be used for ecogeographical studies under the assumption that the accessions are a geographically unbiased sample. We evaluated the representativeness of a collection of wild potatoes from Bolivia and defined and assessed four types of bias: species, species-area, hotspot, and infrastructure. Species bias is the sampling of some species more often than others. Species-area bias is a sampling that is disproportionate to the total area in which a species is found. Hotspot bias is the disproportionate sampling of areas with high levels of diversity. Infrastructure bias is the disproportionate sampling of areas near roads and towns. Each of these biases is present in the Bolivian wild potato collection. The infrastructure bias was strong: 60% of all wild potato accessions were collected within 2 km of a road, as opposed to 22%, if collections had been made randomly. This analysis can serve as a guide for future collecting trips. It can also provide baseline information for the application of genebank data in studies based on geographic information systems.     

An Evaluation of Restoration Efforts in Fishless Lakes Stocked with Exotic Trout

Abstract: Detrimental effects of introduced fishes on native amphibian populations have prompted removal of introduced cutthroat ( Oncorhynchus clarki ), rainbow ( Oncorhynchus mykiss ), and brook trout (  Salvelinus fontinalis ) from naturally fishless lakes at Mt. Rainier National Park, Washington ( U.S.A.). Using paleolimnological indicators (diatoms, invertebrates, and sediment characteristics) in eight 480-year-old sediment cores from eight lakes, we (1) derived estimates of baseline environmental conditions and natural variation, (2) assessed the effects of stocking naturally fishless lakes, and (3) determined whether lakes returned to predisturbance conditions after fish removal (restoration). Diatom floras were relatively stable between 315 and 90 years before present in all lakes; we used this time period to define lake-specific "baseline" conditions. Dissimilarity analyses of diatoms revealed sustained, dramatic changes in diatom floras that occurred approximately 80 years ago (when fish were introduced) in four of five stocked lakes, whereas the diatom floras in two unstocked lakes had not changed significantly in the last 315 years. Diatoms were not preserved in an eighth lake. State changes also occurred in two lakes over 200 years before European settlement of the Pacific Northwest. Preserved invertebrate densities fluctuated dramatically over time in all cores, providing a poor reference for assessing the effects of fishes. Nevertheless, fish-invertebrate interactions have been demonstrated in other paleolimnological studies and may be useful for lower-elevation or more productive lakes. Because diatom communities have not returned to predisturbance assemblages in restored lakes, even 20–30 years after fish removal, we conclude that Mt. Rainier lakes were not successfully restored by the removal of fishes.     

Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Genetic differentiation in a pelagic crustacean (Meganyctiphanes norvegica: Euphausiacea) from the North East Atlantic and the Mediterranean Sea

Meganyctiphanes norvegica (M. Sars)is a pelagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We studied eight population samples collected in the European Atlantic and Mediterranean Sea. By means of single strand conformation polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by differences between populations, thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the first one represented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples. We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar). This population was found to be genetically intermediate between the NE Atlantic samples and the Ligurian sample, suggesting that the restriction to the gene flow is not associated with the Strait of Gibraltar, but possibly with the Oran–Almeria oceanographic front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop separate breeding units inside the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity, separated from the Atlantic population. Received: 2 May 1999 / Accepted: 26 November 1999     

Escape responses of four Chilean intertidal limpets to seastars

The Chilean intertidal Lottiidae limpet fauna consists of at least nine species, grouped into the monophyletic taxon Scurria and a single taxon preliminarily designated as `Lottia' orbignyi (Dall). Within the Scurria clade, the most basal species are Scurria variabilis (Sowerby), S. viridula (Lamarck), and S.zebrina (Lesson), and among the most crown groups are S. ceciliana (Orbigny) and S. araucana (Orbigny). This phylogenetic information, obtained by the analysis of molecular characters (16S mtDNA), provides a framework for a comparative study of behavioral characters. In this study, we analyze the escape responses of two basal limpet species (`L.' orbignyi and S. viridula) and two derived limpet species (S. araucana and S. ceciliana) in the presence of the limpet predatory seastar Heliaster helianthus (Lamarck) and the limpet non-predatory seastars Stichaster striatus Muller and Troschel and Patiria chilensis Lutken. Neither P.chilensis nor Stichaster striatus induced escape responses such as those observed with the predatory H. helianthus. Moreover, in the presence of H. helianthus, basal and derived limpet species differed significantly in the percentage of individuals responding, reaction time, and duration of the response. The basal species `L.' orbignyi and Scurriaviridula exhibited instantaneous and vigorous locomotor responses, whereas the derived species S. araucana and S. ceciliana displayed no locomotor responses. The same pattern was found in responses to H. helianthus homogenates. The results strongly suggest a correlation between phylogeny and anti-predator escape responses to the seastar H. helianthus. Alternative escape responses have evolved for basal and derived species within the Chilean clade. Received: 27 April 2000 / Accepted: 16 August 2000     

Phylogeny and biogeographic history of hake (genus Merluccius), inferred from mitochondrial DNA control-region sequences

 Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on the rise of the Isthmus of Panamá, which is believed to have created a barrier to dispersal between marine species of the Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved. We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa. Received: 12 December 1998 / Accepted: 15 October 1999     

Size-related aspects of arm damage, tissue mechanics, and autotomy in the starfish Asterias rubens

 Arm damage is a widely reported but superficially investigated aspect of the biology of the starfish Asterias rubens L. In the present study, the incidence of arm damage was surveyed in populations of A.  rubens at two sites in the Firth of Clyde, Scotland, and three sites in Gullmarsfjorden, Sweden. The mean (±SD) incidence across all sites of individuals with basal arm damage (resulting from detachment at the basal autotomy plane) was 19.69 ± 8.86%, the incidence of those with distal arm damage (resulting from amputation at more distal levels) was 7.74 ± 10.01%. The mean incidence of arms with basal damage was 5.28 ± 4.12%, of those with distal damage 1.83 ± 2.45%. There was a significant negative correlation between size and the incidence of basal damage at all but one site, but no significant correlation between size and distal damage at any site. Mechanical tests on specimens of the aboral body wall from the basal region of the arm (which included the autotomy plane) and from a more distal region revealed that with increasing body size there was a significant increase in yield stress, ultimate stress and Young's modulus (stiffness) but no significant change in yield strain and ultimate strain. There was no significant difference between the relationships for basal and distal specimens. It is hypothesised that in larger individuals increased mechanical toughness replaces autotomy as an effective antipredator strategy. Using two methods to induce autotomy, a significant positive correlation between size and the delay between the onset of stimulation and arm detachment was found; this may represent a size-related decline in the efficiency of the autotomy mechanism through the relaxation of selection pressure. Since size is an unreliable indicator of age in A.  rubens, the trends identified herein can be interpreted only tentatively as age-associated phenomena. Received: 4 September 1999 / Accepted: 17 February 2000     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

The nature of heat coma in Littorina littorea (Mollusca: Gastropoda)

 The nature of heat coma was examined in the edible periwinkle Littorina littorea (L.). Duration of acclimation did not influence heat-coma temperature at 12 °C, although other acclimation temperatures were important in influencing thermal tolerance, with positive shifts in coma temperature observed in response to elevated temperatures. Previous thermal history also influenced heat-coma temperatures. Individuals subjected to repeat heat-coma events on a daily basis showed significant declines (P < 0.05) in coma-temperature; in contrast individuals exposed to repeat heat-coma events on a weekly basis showed no decline in thermal tolerance. Size-effects occurred at selected sites, where decreased heat-coma temperatures were recorded in large individuals. Received: 16 August 1999 / Accepted: 13 June 2000