Landscape fragmentation by urbanization in the Netherlands:optionsand ecological consequences

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Occurrence of bisphenol A in surface water and uptake in fish: evaluation of field measurements

In this study the actual presence of the suspected endocrine disrupter Bisphenol A (BPA) in water systems was studied in the Netherlands. BPA was shown to be present in Dutch surface water at levels up to 330 ng/l, and one occasional observation of 21 microg/l. During the three sampling periods, 60-80% of the samples, most from marine and estuarine locations, contained BPA levels below the limit of quantification (14-40 ng/l). At a selected number of locations the presence of BPA in fish was studied, which showed that BPA varied from 2 to 75 ng/g in the liver and 1 to 11 ng/g in the muscle. Based on present measured concentrations in surface water and on literature derived toxicity data it was concluded that ecotoxicological effects nor estrogenic effects are likely to occur in the field situation.     

Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats

Shell growth rate is an important component of fitness in bivalve molluscs. Using the parameter computed from the von Bertalanffy growth equation, we quantitatively compared rates of annual shell grwoth among the hard clams Mercenaria mercenaria, M. campechiensis, and their hybrids sampled from a variety of habitats in the Indian River lagoon, Florida, USA, a zone of species overlap and natural hybridization. Our results indicate that the classical paradigm describing hard clam growth, in which growth rate is fastest in M. campechiensis, intermediate in hybrids, and slowest in M. mercenaria is not supported in the Indian River lagoon. Instead, M. campechiensis has a growth advantage in deep-water habitats in the northern section of our study area. In the central and southern sections of our study area, hybrids have a growth advantage over M. mercenaria in shallow-water habitats, but M. mercenaria has a growth advantage over hybrids in deep-water habitats. In all other sampled habitats, either growth rate among genotype classes is equal, or M. mercenaria has a growth advantage. This complex relationship between genotype and habitat-specific growth provides a mechanism for selection to act on hard clams in the Indian River.     

Polycyclic aromatic hydrocarbons in weathered bottom ash from incineration of municipal solid waste

Polycyclic aromatic hydrocarbons (PAHs) were analysed in weathered bottom ash from different municipal solid waste incinerators. The sum of the 16 "USEPA" PAHs was found to vary from 480 to 3590 microg/kg. The amounts of carcinogenic PAHs were between 89 and 438 microg/kg ash. The maximum levels of carcinogenic PAHs exceed the Swedish generic guidelines for sensitive land use. The results showed that the amount of PAHs in fresh and weathered bottom ash are similar, indicating that the PAHs are strongly bound to the ash and only limited amounts are released to the surroundings.     

Changes in the cuticular hydrocarbons of incipient reproductives correlate with triggering of worker policing in the bulldog ant Myrmecia gulosa

In social insects, conflicts over male parentage can be resolved by worker policing. However, the evolution of policing behavior is constrained by the ability of individuals to identify reproductive nestmates, or their eggs. We investigated the occurrence of worker policing and its underlying chemical communication in the bulldog ant Myrmecia gulosa. Although workers have functional ovaries and can lay male-destined eggs, they do not reproduce in queenright colonies. To determine if their sterility is a consequence of worker policing, we experimentally induced worker reproduction in the presence of a queen. Some individuals were seized and immobilized by nestmates, and sometimes killed as a consequence. Although the ovarian development of immobilized individuals was variable, their cuticular hydrocarbon profiles were intermediate between reproductive and nonreproductive workers, indicating they were in the process of starting to reproduce. Approximately 29% of these incipient reproductive workers were successfully policed. To test for policing on eggs, we transferred viable worker eggs to queenright colonies and monitored their acceptance. Furthermore, we compared the surface hydrocarbons of the different types of eggs to determine whether these chemicals could be involved in egg recognition. We found that although there were differences in hydrocarbon profiles and discrimination between queen and worker-laid eggs, viable eggs were not destroyed. Our results strongly support the idea that cuticular hydrocarbons are involved in the policing of reproductive workers. A low level of worker policing appears sufficient to select for self-restraint in workers when few fitness benefits are gained by selfish reproduction. Policing of eggs may thus be unnecessary.     

Temporal changes in demand for and supply of nests in red bishops (Euplectes orix): dynamics of a biological market

The red bishop (Euplectes orix) is a highly polygynous and colonial weaverbird. Males construct several nests within their territories to which they try to attract females, and females are solely responsible for incubation and raising offspring. In this paper, we describe the characteristics of the red bishop’s mating system as a biological market and investigate the role of nests built by males as a traded commodity in a mating market. As timing of breeding in red bishops in arid and semi-arid zones depends on rainfall patterns which are often unpredictable, there are temporal changes in demand for and supply of nests within a breeding season, with breeding activities of males and females being highly synchronised. We found that males increased their nest-building speed with increased female breeding activity independently of rainfall, indicating that supply follows demand in this mating market. The supply of nests was always larger than the demand for nests. Construction costs for nests increased with demand for nests as indicated by shorter nest-building duration and shorter building delays between two consecutively built nests at times of high breeding activity. Males as a trading class are chosen according to the age of their nests offered, with young nests having a higher probability of being accepted by females. Furthermore, female choosiness with regard to nest age decreased when their own market value decreased, as predicted by biological market theory. The temporal changes of breeding activity together with the female preference for young and fresh nests require that males quickly adjust nest-building activity to varying female demand for new nests. However, males with a better adjustment of building speed to female breeding activity did not gain higher mating success.     

Colony founding,queen dominance and oligogyny in the Australian meat ant Iridomyrmex purpureus

Summary Field observations and laboratory experiments demonstrate that in the Australian meat ant, Iridomyrmex purpureus, the modes of colony founding are remarkably diverse. New colonies can originate from single foundresses (haplometrosis), or foundress associations (pleometrosis), or by colony budding, or the adoption of newly-mated queens that dig founding chambers next to mature nests (probably their natal nests, as workers protect them and may help them dig). Readoption of foundresses and pleometrosis lead to the coexistence of several queens in one nest. We discovered a striking antagonistic behavior among coexisting queens in young colonies, in the form of ritualized antennation bouts. These interactions result in a reproductive rank order in which dominant queens inhibit egg-laying by subordinates, but escalation into physical fighting is rare. Workers ignore queen dominance interactions and treat all queens equally. The first quantitative ethogram of dominance display behavior between multiple ant queens, and its reproductive consequences, is presented. As a colony grows, queens become intolerant of each other's presence and permanently separate within the nest. Once separated, queens appear to be equal in status, laying approximately equal numbers of eggs. All queens continue to be tolerated by workers, even when the colony has reached a size of several thousand workers and begun to produce reproductives. Such mature nests of I. purpureus fulfill the criteria of oligogyny, defined by worker tolerance toward more than one queen and antagonism among queens, such that a limited number of fully functional queens are spaced far apart within a single colony. Oligogynous colonies can arise in this species by pleometrotic founding (primary oligogyny) or by adoption of queens into existing nests (secondary oligogyny). The adaptive significance of the complex system of colony founding, queen dominance and oligogyny in I. purpureus is discussed.     

Substrate influence on epiphytic lichens

The origin of the presence of soil elements in the epiphytic lichen Lecanora conizaeoides was investigated in an area of heavily polluted soil (The Broekpolder The Netherlands). Analysis results of lichens, bark and tree rings of the supporting trees indicated that for As, Co, Cr, Cu, Fe, Hg, Sc and V the levels in lichens may be considered to originate from wet and dry deposition. The Cd, Mn and Zn levels in lichens might have originated from both wet and dry deposition and the substrate bark. For these three elements, in particular, accumulation characteristics in lichens should be further investigated.