Rudolf F. Verheyen

Male song as a cue for mate choice in the European starling

This study had two aims. First, we looked at individual differences in song characteristics between males of the European starling, and we related song behaviour to factors such as male age, pairing date, polygyny and male breeding success. Second, we experimentally tested whether song has an effect on female mating decisions. 1. During the breeding season, male starlings sing a very long and complex song consisting of a rapid succession of large number of different song types. We observed marked differences between males in average song bout length (a song bout was defined as a period of at least five seconds of song containing no pauses larger than 1.5 seconds) and in song repertoire size. Average song bout lengths ranged from 16 to 35 seconds. The individual repertoire size ranged from 23 to 67 song types. Repertoire size and average song bout length were positively correlated. 2. Both in the field and in captivity, yearling males sang shorter average song bout lengths and had smaller repertoire sizes than older males. 3. Males singing longer average song bouts and having larger repertoire sizes attracted females for pairing before their rivals with shorter average song bouts and smaller repertoire sizes.

Comparison of vitellogenin responses in zebrafish and rainbow trout following exposure to environmental estrogens

In this comparative study, the suitability of the commonly used in vivo biomarker for estrogenicity, vitellogenin (VTG), upon waterborne exposure to known environmental estrogens is evaluated in both male zebrafish (Danio rerio) and juvenile rainbow trout (Oncorhynchus mykiss). The results from initial experiments in which both species were exposed to 4-tert-octylphenol (OP) or 17 alpha-ethynylestradiol under semistatic conditions for 3 weeks demonstrated a difference in species sensitivity for OP exposure. Additional dose-response studies (semistatic, 3 weeks) with 4-nonylphenol (20, 100, and 500 microg/L), bisphenol A (40, 200, and 1000 microg/L), dibutylphthalate (40, 200, and 1000 microg/L DBP), and 17beta-estradiol (20 and 100 ng/L E2) were conducted. All these compounds, except for DBP, were found to be estrogenic to both fish species. The results demonstrated a difference in species sensitivity for NP with the zebrafish being about 5 times less sensitive. For the other compounds tested, no indications for a difference in species sensitivity was found. The results from this study demonstrated that both fish species can be used for the detection of VTG as biomarker for estrogenicity, taken into the potential interspecies differences in sensitivity which might be important for the evaluation of fish population effects.

Altitudinal variation of the thermal biology and running performance in the lizard Podarcis tiliguerta

SummaryWe studied, in the field and laboratory, aspects of the thermal biology in two populations of the lizard Podarcis tiliguerta along a 1450 m altitudinal gradient. Body temperatures (Tb) at high altitudes average lower, are more variable, but are more elevated above environmental temperatures than at sea level. Lizards partially reduced the impact of altitudinal changes in thermal loads through presumable subtle behavioural adjustments. A comparison of the thermal preferences in the laboratory, the maximal operative temperatures predicted from a biophysical model, and the activity Tbs at both sites, indicates that the main response to changing environmental conditions is an active shift in thermoregulatory set points. Integration of field Tbs and laboratory data on temperature specific sprint speeds, predicts that the mountainous lizards experience reduced running abilities that are especially acute in the early morning. Despite this impairment of running performance, the thermal sensitivity of running speed has not evolved to match the Tbs experienced by both populations. This result supports the view that the thermal physiology of this lizard is evolutionarily conservative, but the lack of information on the relation between running performance and fitness components impedes rejection of alternative hypotheses.

Effects of 17α-ethynylestradiol in a partial life-cycle test with zebrafish (Danio rerio): effects on growth, gonads and female reproductive success

In this study, the impact of an exposure of zebrafish embryos (Danio rerio) until 3 months post fertilization to 17alpha-ethynylestradiol (EE2: 0; 0,1; 1; 10; 25 ng/l) was evaluated for growth and development, gonad development and body vitellogenin (VTG) content. After a recovery period of 5 months, the female reproductive success was evaluated. The results demonstrated a significant reduction in total body length, body weight, whole body Ca and P content and an increase in morphological abnormalities for fish exposed to 25 ng/l EE2 as a function of exposure time. An increase in total body VTG content was observed for fish exposed for a period of 3 months down to levels of 1 ng/l EE2. At the age of 3 months, a dose-dependent increase of the number of fish with no macroscopic recognizable gonads was observed (up to 100% at 25 ng/l EE2). After a recovery period on clean tap water for 5 months, all fish had developed either ovaries or testis with a gonadosomatic index not different from control fish and the sex ratio was similar in EE2 treatment groups and controls. Nevertheless, a reduced number of spawning females and a reduced egg production were found for the female fish exposed to 10 or 25 ng/l EE2 for 3 months and which were allowed to recover for 5 months. Although the underlying mechanism could not be elucidated, these findings did indicate that the reproduction potential of fish populations might be disturbed by a long-term exposure to EE2 (> or =10 ng/l) from fertilization until sexual maturity.

Selected body temperatures in the lizard Lacerta vivipara: variation within and between populations

Abstract 1. 1.|Selected body temperatures (SBT) of adult male, female and subadult Lacerta vivipara from a Belgian population, were measured monthly in a laboratory thermogradient. 2. 2.|Monthly mean SBTs varied between 29.9 and 34.0°C and differed significantly among months in all three lizard groups, and among lizard groups in 4 out of 6 months. 3. 3.|Evidence for a positive relationship between monthly SBT and air temperature was found in the subadults, but not in the adult lizards. 4. 4.|Monthly mean SBTs measured in this study were consistently higher (mean difference = 2.0°C) than those obtained by Patterson and Davies (1978) in a similar study on Lacerta vivipara from southern England.

Evolutionary rigidity of thermal physiology: the case of the cool temperate lizard Lacerta vivipara

We compared the thermal dependence of sprint speed in two populations of the common lizard, Lacerta vivipara, from different altitudes. Although field body temperatures in the montane population were consistently 3-5°C below those of the lowland population, we found no parallel shift in the optimal temperatures for sprint speed. Lizards from both populations also selected similar temperatures in the laboratory. In the field, lizards from the montane population were frequently active at body temperatures that seriously impair locomotion. These observations give support to the static view of thermal physiology, which claims that thermal physiology is evolutionary stationary and resistant to directional selection.

Nutrient limitation in species‐rich lowland fens

. Nitrogen, phosphorus and potassium were supplied to some Belgian fens of varying nutrient status and productivity. Plant growth in the lowest productive fen with a species-rich Caricion davallianae vegetation was strongly P-limited. N was ineffective when applied alone, but increased the effect of P-addition when applied together. Summer biomass and plant nutrient concentrations were monitored for four years, and showed partial recovery of nutrient limitation. In a more productive fen dominated by Carex lasiocarpa and in a fen meadow, nutrient limitation was less strong. N limited growth in the productive fen, and N and K were co-limiting in the fen meadow. The P-concentration in the productive fen vegetation showed a marked increase after P-fertilization, but it did not result in higher standing crop. The significance of P-limitation for the conservation of species rich low productive fens is discussed. P-limitation may be an essential feature in the conservation of low productive rich fens: because it is less mobile in the landscape than N and/or because it is an intrinsic property of this vegetation type. Plant nutrient concentrations and N:P-ratios may be used as an indication for the presence and type of nutrient limitation in the vegetation. We found N:P-ratios of 23 to 31 for a P-limited site and 8 to 15 in N-limited sites. This was in agreement with critical values from the literature: N:P > ca. 20 for P-limitation and N:P < 14 for N-limitation. Thus, this technique appears valid in the vegetation types that were studied here.

On the function of singing and wing-waving in the European Starling Sturnus vulgaris

Experiments were performed using captive starlings to examine whether Starling song functions primarily in intersexual communication. Male Starlings showed a significant increase in the time spent at the nestbox, as well as in the total time spent singing, after the introduction of a female into the aviary. After the introduction of a male, only the time spent at the nestbox increased significantly. Wing-waving (a visual display associated with singing) and singing in the nest box occurred only after introduction of a female. Our results strongly suggest that Starling song functions largely in male-female interactions. The primary function of wing-waving seems to be mate attraction.

Song learning in captive European starlings, Sturnus vulgaris

Abstract The song of captive Euroepan starlings was recorded in successive years to see if changes occurred in song repertoire size and average song bout length. Seven out of nine males sang new song types in their second year of recording. Three males, which were yearlings when recorded for the first time, increased their average song bout length significantly while the average song bout length of six older males did not increase. The three yearling males also increased their repertoire size significantly more than the six older males. Nevertheless, four of the six older males modified their repertoire. These results indicate that starlings are ‘open-ended’ learners, but also suggest that the ability to incorporate new song types into the song decreases with age. Choices of song models by four male starlings raised in captivity were also investigated. All four males copied a large proportion of their song from adult males with whom they shared the aviary. The captive-hatched males often copied precise sequences of different song types from the adult males. Direct evidence that starlings copy heterospecific imitations from other, starlings is also presented.

Relationships between river sediment characteristics and trace metal concentrations in tubificid worms and chironomid larvae.

Surficial sediments, midge larvae (Chironomidae, Diptera) and tubificid worms (Tubificidae, Oligochaeta) were collected at 65 sampling sites located in four different river basins in Flanders (Belgium). Concentrations of the trace metals Cu, Zn, Cd and Pb were measured in organisms and sediments by atomic absorption spectrophotometry. Sediments were subjected to a simultaneous extraction scheme to identify trace metal partitioning among various geochemical phases. Three geochemical characteristics of the sediment were analysed; Total Organic Carbon (TOC), Fe oxides and Mn oxides. Non-linear regression models were constructed to determine the relative importance of the different sediment factors contributing to the variation in metal accumulation by the tubificid worms and chironomids. Generally, the amount of variation that could be explained by these models was limited, with coefficients of determination ranging from 0.05 to 0.66. In most cases, metal levels in organisms were positively related to the easily reducible and reducible metal fractions, and negatively related to the TOC and Fe sediment content. The correlations between metal concentrations in tubificid worms and chrinomid larvae were also rather poor, with coefficients of determinations ranging from 0.01 to 0.52. This indicates that understanding the chemistry of the environment does not suffice to predict the concentrations in organisms. Differences in the structural and functional organisation of the organisms, which among others determine the route of exposure, are at least equally important causes of variability in metal availability and accumulation.