Inter-sexual differences in T-cell-mediated immunity of black-headed gull chicks (<Emphasis Type="Italic">Larus ridibundus</Emphasis>) depend on the hatching order

Hatching asynchrony in avian species leads to age and size differences between nestlings within a brood, handicapping last-hatched chicks in the sibling rivalry. Starvation due to this competitive disadvantage has been regarded as the primary cause of an increase in mortality with hatching order. However, for gulls it has also been suggested that disease is the cause of mortality for last-hatched chicks, possibly through reduced immunocompetence and thereby an enhanced susceptibility to infection. In addition, the male-biased mortality reported for several gull species may be related to a higher vulnerability to diseases in males compared to females. To determine the potential influence of the immune system on these mortality patterns, we investigated the T-cell-mediated immunity (CMI) of black-headed gull chicks in relation to hatching order and sex. We found a significant decrease in the CMI with hatching order. This result may be causally related to systematic changes in maternal yolk steroids and carotenoids within the laying sequence. For second-laid eggs, male CMI was significantly lower than female CMI. This is possibly linked to higher plasma levels of testosterone in male embryos which might have an immunosuppressive effect. If so, this effect is masked in eggs of either high (first egg) or low (last egg) quality. Chicks with low CMI showed enhanced mortality rates. Thus the differences in immune response are likely to contribute to the observed mortality patterns. However, hatching order significantly affected mortality independently of CMI, suggesting that competitive disadvantage due to hatching asynchrony is also important.Communicated by M. Webster     

Social stimulation,nuptial colouration,androgens and immunocompetence in a sexual dimorphic cichlid fish

The nature of the costs maintaining honesty of sexual signalling in inter- and intrasexual interactions remains a contentious issue. For carotenoid-based colour ornaments, it has been hypothesized that the honesty of the signal is enforced when carotenoid allocation to colour expression is traded off against carotenoid availability for immunocompetence. In addition, honesty is enforced if androgens required for colour expression are immunosuppressive. We tested whether there is a trade-off between colour expression and immunocompetence in a lek-breeding haplochromine cichlid fish, Pundamilia nyererei, from Lake Victoria with a carotenoid-based nuptial dress. First, we showed that expression of red nuptial colouration and social rank in a group were positively correlated. We then successfully manipulated the level of colour advertisement by socially stimulating individually housed males with a rival male: Stimulated males developed larger areas of red nuptial colouration and had higher levels of circulating 11-ketotestosterone (11-KT) than non-stimulated males. We subsequently tested the humoral immune response to a novel antigen (sheep red blood cells). There was no overall significant effect of social stimulation on antibody production, but in the stimulated males, the degree of red colouration and the antibody response were negatively correlated. This significant interaction between colour and treatment thus shows that the negative correlation between colouration and antibody production is dependent on the (manipulated) social environment. This study provides correlational and experimental evidence for a trade-off between expression of a sexual trait and one component of immune function in fish. We found no evidence for a direct effect of 11-KT on antibody production, and we discuss alternative mechanisms that could mediate the trade-off.     

The willingness to pay to remove billboards and improve scenic amenities

We use the contingent valuation method to measure the amount citizens are willing to pay to improve scenic mountain-view amenities through the removal of billboards. Our approach addresses both the perceived property rights as well as the perceptions of the status quo in the southern Appalachian Mountains. We find that individuals who retire to the mountains have different preferences for land use and mountain views than individuals who have ancestors who lived in Watauga County. In the aggregate, we find that citizens are willing to pay almost one-half million dollars to remove billboards from Watauga County roadsides. This study provides insights to the debate surrounding land use along public roads.     

Experimentally manipulated brood sex ratios: growth and survival in the black-headed gull (Larus ridibundus), a sexually dimorphic species

In sexually size dimorphic species, individuals of the larger sex often suffer from enhanced mortality during the nestling period. This has been attributed to higher nutritional requirements of the larger sex, which may render this sex more vulnerable to adverse food conditions. However, sex-biased mortality might not exclusively depend on the differences in food demand but also on other phenotypic differences, e.g., in competitiveness. Interference competition between the sexes and position in the laying sequence in particular may be essential components contributing to biased mortality.By creating synchronously-hatched unisex broods in the sexually size dimorphic black-headed gull, we specifically tested the effect of sex-specific food demand by excluding interference competition between the sexes as well as hatching asynchrony. To test the effect of egg quality, which varies with the position in the laying sequence, we composed each nest of chicks from eggs of all different positions in the laying sequence.All-male nests showed significantly enhanced mortality compared to all-female nests from the beginning of the development of the sexual size dimorphism onwards. This underlines the role of a higher food demand in biased mortality of the larger sex.In males but not females, asymptotic body mass and skeletal size were negatively associated with position in the laying sequence, while survival was not affected by position. As a consequence, sexual size dimorphism at the end of the nestling period was less pronounced compared to the natural situation. These data show that, although male growth is more sensitive to a decrease in egg quality, the higher mortality of last hatched chicks in natural nests is mainly due to hatching asynchrony and egg size but not egg content.     

Can male-male competition stabilize speciation? A test in Lake Victoria haplochromine cichlid fish

It has been suggested that sympatric speciation can be driven by sexual selection on male mating traits alone. However, a fundamental problem for this process is the lack of ecological differentiation that would stabilize the coexistence of incipient species through frequency-dependent selection. Such selection can also occur if male aggression is primarily directed towards similar rather than towards dissimilar phenotypes, so that rare male phenotypes would enjoy a negatively frequency-dependent fitness advantage. We experimentally tested such an aggression bias in two recently diverged, ecologically and anatomically similar sympatric cichlid species pairs of the genus Pundamilia from Lake Victoria. Territorial males of a pair of partially reproductively isolated species with red and blue nuptial coloration, respectively, studied in the laboratory were confronted simultaneously with both colour types enclosed in transparent tubes. Red males were more aggressive to red stimuli under white light but not when colour differences were masked under green light. Blue males were equally aggressive to both stimuli in both light conditions. Males of two apparently fully reproductively isolated species, again one with red and one with blue nuptial coloration, studied in the field, both directed more aggressive behaviour towards conspecific than towards heterospecific stimulus males. The differential allocation of aggression would create an advantage for males of the less abundant phenotype or species, thereby potentially supporting stable coexistence of the phenotypes. The finding that this effect was less clear in the partially reproductively isolated species pair than in the fully isolated species pair is discussed.     

An adaptive annual rhythm in the sex of first pigeon eggs

When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism.     

An experimental study on the causal relationships between (ecto-)parasites, testosterone and sexual signalling

Bird song is considered to have evolved via sexual selection and should as such honestly signal aspects of the quality of its bearer. To ensure honesty, the immunocompetence handicap hypothesis proposed a dual role of testosterone, having positive effects on sexual signalling but suppressive effects on immune function. However, recent studies showed that it is rather an immune activation that suppresses the androgen production. This reversed chain of causation may significantly alter the pathways, which translate the effects of parasites and pathogens into changes in the expression of male sexual traits. We infested male canaries with Ixodes ricinus tick nymphs to investigate the causal relationships between (ecto-)parasites, testosterone and sexual signalling, here singing behaviour. We focused on flexible song traits, which may quickly reflect changes in the infestation status, and tested whether these effects relate to changes in the plasma testosterone levels or health state. The experimental tick infestation altered the males’ song performance by reducing song consistency, a trait that had previously been identified to reflect male quality. The tick infestation lowered the plasma testosterone levels and had a negative effect on the health status in terms of a reduced hematocrit. Our pathway analysis then revealed that it is the parasite-induced reduction of the plasma testosterone levels but not of the health state that caused the changes in song consistency. Thus, our study supports the view that it is the effect of parasites and immune activation on plasma testosterone levels that generates the trade-off between immunocompetence and sexual signalling.     

印染行业清洁生产技术

论述了目前印染行业水污染的现状及原因，指出调整产业结构、应用新工艺、大力提倡节约用水、清沽生产将是印染行业实现可持续发展的必由之路。     

Direct male-male competition can facilitate invasion of new colour types in Lake Victoria cichlids

The possibility that disruptive sexual selection alone can cause sympatric speciation is currently a subject of much debate. The initial difficulty for new and rare ornament phenotypes to invade a population, and the stabilisation of the resulting polymorphism in trait and preference make this hypothesis problematic. Recent theoretical work indicates that the invasion is facilitated if males with the new phenotype have an initial advantage in male-male competition. We studied a pair of sympatric incipient species of cichlids from Lake Victoria, in which the red (Pundamilia nyererei) and blue males (P. pundamilia) vigorously defend territories. Other studies suggested that red phenotypes may have repeatedly invaded blue populations in independent episodes of speciation. We hypothesised that red coloration confers an advantage in male-male competition, assisting red phenotypes to invade. To test this hypothesis, we staged contests between red and blue males from a population where the phenotypes are interbreeding morphs or incipient species. We staged contests under both white and green light condition. Green light effectively masks the difference between red and blue coloration. Red males dominated blue males under white light, but their competitive advantage was significantly diminished under green light. Contests were shorter when colour differences were visible. Experience of blue males with red males did not affect the outcome of a contest. The advantage of red over blue in combats may assist the red phenotype to invade blue populations. The apparently stable co-existence of red and blue incipient species in many populations of Lake Victoria cichlids is discussed.Communicated by C. St. Mary     

Individualized water source as an indicator of attitudes about water management and conservation in humid regions

Public perceptions about water quantity and water as a common pool resource are understudied in humid regions. As water demand increases, the need to more closely manage water, even in humid areas, will increase, requiring better understanding how people perceive their water supply, how they view paying for water conservation and how water user characteristics influence attitudes. A survey finds correlations between utilizing an individual water source (e.g. well or spring) and attitudes toward water management and conservation. Compared to respondents with a shared water source, those with an individual source believe they are segregated from regional water concerns. They are less willing to pay for water management or conservation measures and less supportive of any government intervention in water management. These results suggest that planners and water managers may face resistance to conservation policies or any policy based on the idea of water as a common pool resource.