Geographic patterns of genetic differentiation and plumage colour variation are different in the pied flycatcher (Ficedula hypoleuca)

The pied flycatcher is one of the most phenotypically variable bird species in Europe. The geographic variation in phenotypes has often been attributed to spatial variation in selection regimes that is associated with the presence or absence of the congeneric collared flycatcher. Spatial variation in phenotypes could however also be generated by spatially restricted gene flow and genetic drift. We examined the genetic population structure of pied flycatchers across the breeding range and applied the phenotypic Q(ST) (P(ST))-F(ST) approach to detect indirect signals of divergent selection on dorsal plumage colouration in pied flycatcher males. Allelic frequencies at neutral markers were found to significantly differ among populations breeding in central and southern Europe whereas northerly breeding pied flycatchers were found to be one apparently panmictic group of individuals. Pairwise differences between phenotypic (P(ST)) and neutral genetic distances (F(ST)) were positively correlated after removing the most differentiated Spanish and Swiss populations from the analysis, suggesting that genetic drift may have contributed to the observed phenotypic differentiation in some parts of the pied flycatcher breeding range. Differentiation in dorsal plumage colouration however greatly exceeded that observed at neutral genetic markers, which indicates that the observed pattern of phenotypic differentiation is unlikely to be solely maintained by restricted gene flow and genetic drift.

Experimental evidence for species-specific habitat preferences in two flycatcher species in their hybrid zone

Hybrid zones are often found in areas where the environmental characteristics of native habitat of both parental species meet. One of the plausible mechanisms that maintain species distinctiveness, or limit hybridization, is the existence of local species-specific preferences for the natal habitat type. We evaluated this hypothesis for two passerine bird species, the pied Ficedula hypoleuca and collared flycatcher F. albicollis, in their narrow hybrid zone in Central Europe. Both species have quite distinct habitat distributions, and they have also been reported to differ in their foraging niches. In a series of aviary experiments, we demonstrated that both species show distinct preferences for trees from their native area. The pied flycatcher preferred coniferous vegetation, while the collared flycatcher favored deciduous vegetation. In addition, both species differed in foraging substrate preferences. The pied flycatcher preferred to forage in the lower strata on the ground than the canopy, whereas the collared flycatcher foraged more at the canopy level. Both males and females of each species were highly consistent in their preference patterns. Due to the widespread nature of hybrid zones as places with transitional habitat features and the well-known habitat tight associations of various animal taxa with particular habitat types, we propose that habitat preferences might be an important and common mechanism that enhances the formation of conspecific pairs.

Flycatcher song in allopatry and sympatry--convergence, divergence and reinforcement

The theory of reinforcement predicts that natural selection against the production of unfit hybrids favours traits that increase assortative mating. Whether culturally inherited traits, such as bird song, can increase assortative mating by reinforcement is largely unknown. We compared songs of pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) from two hybrid zones of different ages with songs from allopatric populations. Previously, a character divergence in male plumage traits has been shown to reinforce premating isolation in sympatric flycatchers. In contrast, we find that the song of the pied flycatcher has converged towards that of the collared flycatcher (mixed singing). However, a corresponding divergence in the collared flycatcher shows that the species differences in song characters are maintained in sympatry. Genetic analyses suggest that mixed song is not caused by introgression from the collared flycatcher, but rather due to heterospecific copying. Circumstantial evidence suggests that mixed song may increase the rate of maladaptive hybridization. In the oldest hybrid zone where reinforcement on plumage traits is most pronounced, the frequency of mixed singing and hybridization is also lowest. Thus, we suggest that reinforcement has reduced the frequency of mixed singing in the pied flycatcher and caused a divergence in the song of the collared flycatcher. Whether a culturally inherited trait promotes or opposes speciation in sympatry may depend on its plasticity. The degree of plasticity may be genetically determined and accordingly under selection by reinforcement.

Egg size and offspring performance in the collared flycatcher (Ficedula albicollis): a within-clutch approach

Adaptive within-clutch allocation of resources by laying females is an important focus of evolutionary studies. However, the critical assumption of these studies, namely that within-clutch egg-size deviations affect offspring performance, has been properly tested only rarely. In this study, we investigated effects of within-clutch deviations in egg size on nestling survival, weight, fledgling condition, structural size and offspring recruitment to the breeding population in the collared flycatcher ( Ficedula albicollis). Besides egg-size effects, we also followed effects of hatching asynchrony, laying sequence, offspring sex and paternity. There was no influence of egg size on nestling survival, tarsus length, condition or recruitment. Initially significant effect on nestling mass disappeared as nestlings approached fledging. Thus, there seems to be limited potential for a laying female to exploit within-clutch egg-size variation adaptively in the collared flycatcher, which agrees with the majority of earlier studies on other bird species. Instead, we suggest that within-clutch egg-size variation originates from the effects of proximate constraints on laying females. If true, adaptive explanations for within-clutch patterns in egg size should be invoked with caution.

Sources and timing of calcium intake during reproduction in flycatchers

Calcium availability may limit the reproductive output of birds and snail shells are considered to be the main source of calcium in many passerine species. This study of collared ( Ficedula albicollis) and pied ( F. hypoleuca) flycatchers evaluates calcium intake of a natural diet in Central Europe, and sex differences in the utilization of experimentally supplemented sources of calcium during the entire breeding period in aviary birds. The study provides the first evidence that successful reproduction of these species depends on the availability of woodlice (Isopoda) and millipedes (Diplopoda). Each of these two components provided about 3 times more calcium than the snail shells contained in a natural nestling diet. The breeding performance of aviary birds was poor when only snail shells and the fragments of eggshells were provided in food, i.e., irregular laying, smaller clutches, eggshell defects (25 of 53 eggs), and eggs dried-up during incubation. In contrast, no defective eggshell or dried-up eggs were found and the overall breeding performance increased 2-3 times when woodlice were added to the food. Females increased their intake of woodlice during both the pre-laying and laying periods, and both sexes did so during the nestling period. Both sexes took more woodlice in the evening than in the morning, independent of the nesting stage. Intake by females was low until 4 days before laying the first egg, then increased to the highest level, dropping immediately after laying the last egg. Intake of woodlice by both sexes increased steadily from hatching until the nestling age of about 10-12 days decreasing thereafter, which corresponds with the period of rapid skeletal growth. In contrast, the intake of mealworms increased until the nestling age of 13-14 days leveling off thereafter which corresponds with the growth curve of nestling body mass.

Hybridization and adaptive mate choice in flycatchers

Hybridization in natural populations is strongly selected against when hybrid offspring have reduced fitness. Here we show that, paradoxically, pairing with another species may offer the best fitness return for an individual, despite reduced fitness of hybrid offspring. Two mechanisms reduce the costs to female collared flycatchers of pairing with male pied flycatchers. A large proportion of young are sired by conspecific male collared flycatchers through extra-pair copulations, and there is a bias in favour of male offspring (which, unlike females, are fertile) within hybrid pairs. In combination with temporal variation in breeding success, these cost-reducing mechanisms yield quantitative predictions about when female collared flycatchers should accept a male pied flycatcher as a mate; empirical data agree with these predictions. Apparent hybridization may thus represent adaptive mate choice under some circumstances.

Computer keyboards and faucet handles as reservoirs of nosocomial pathogens in the intensive care unit

PURPOSE

We postulate that computer keyboards and faucet handles are significant reservoirs of nosocomial pathogens in the intensive care unit (ICU) setting.

METHODS

Sterile swab samples were obtained from 10 keyboards and 8 pairs of faucet handles in the medical ICU at Tripler Army Medical Center during a period of 2 months. Methicillin-resistant Staphylococcus aureus (MRSA) obtained from the environmental and patient specimens were sent for DNA identification by using pulsed-field gel electrophoresis.

RESULTS

A total of 144 samples were obtained (80 keyboards and 64 faucet handles), yielding 33 isolates. The colonization rate for keyboards was 24% for all rooms and 26% in occupied rooms. Rates for faucet handles in all rooms and occupied rooms were 11% and 15%, respectively. The environmental isolates annd their prevalence were: MRS, 49%; Enterococcus, 18%; Enterobacter, 12%; and all other gram-negative rods, 21%. Fourteen individual patient isolates were recorded: MRSA, 43%; Enterobacter, 21%; other gram-negative rods, 36%; and Enterococcus, 0%. By using pulsed-field gel electrophoresis, an indistinguishable strain of MRSA was identified in two patients, the keyboards and faucet handles in their respective rooms, and on other keyboards throughout the ICU, including the doctors' station.

CONCLUSIONS

The colonization rate for keyboards and faucet handles, novel and unrecognized fomites, is greater than that of other well-studied ICU surfaces in rooms with patients positive for MRSA. Our findings suggest an associated pattern of environmental contamination and patient infection, not limited to the patient's room. Pulsed-field gel electrophoresis results have documented an indistinguishable strain of MRSA present as an environmental contaminant on these two fomites and in two patients with clinical infections patients during the same period. We believe these findings add evidence to support the hypothesis that these particular surfaces may serve as reservoirs of nosocomial pathogens and vectors for cross-transmission in the ICU setting. New infection control policies and engineering plans were initiated on the basis of our results.

The effect of nestling condition on risk-taking in meadow pipits

The harm to offspring hypothesis, which says that parental investment should be related to the harm that offspring without parental care would suffer, was tested on meadow pipits, Anthus pratensis. We placed a stuffed European weasel, Mustela nivalis, 5 m from seven nests with exothermic 1-3-day-old nestlings. We measured air temperature and the cloacal temperature of the nestlings at the start of the trial and the time elapsing between the removal of the weasel model and the parent's first entry into the nest. We compared pairs of trials at each nest when nestling condition was good (normal cloacal temperature) and when it was temporarily poor (reduced cloacal temperature). The hypothesis predicts a shorter elapsed time when nestling condition was poor. In all cases the females entered the nest before the males and entered more quickly when nestling condition was poor. The results thus supported the harm to offspring hypothesis.Copyright 1997 The Association for the Study of Animal Behaviour