105 research outputs found
Pseudo-homeosis in avian feet: Response
No full textResponse from Galis, van Alphen and Metz: The letter by Feduccia [1] primarily concerns a semantic question: How does one define homeotic transformation and structural identity. It is tangential to the central theme of our review (F. Galis et al., Why five fingers? Evolutionary constraints on digit numbers, Trends Ecol. Evol. 16 (2001), pp.637-646)
Staat van het dier : Beschouwingen en opinies over de verschuivende relatie tussen mens en dier in Nederland
No full textDe positie van het dier in onze maatschappij verandert. De opstelling van de mens als heerser over dieren maakt geleidelijk plaats voor een houding die gekenmerkt wordt door betrokkenheid bij dieren en acceptatie van hun eigenheid. Inbreuken op dierenwelzijn worden steeds minder geaccepteerd. We bewegen naar een nieuw verbond tussen mensen en dieren. Dat stelt de Raad in zijn rapport 'De Staat van het Dier'
Divergent mating preferences and nuptial coloration in sibling species of cichlid fish
No full textMate choice by female cichlid fish from Lake Victoria plays an important role in speciation and the maintenance of species. Females are expected to select against males that are intermediate in their phenotype during the process of speciation driven by sexual selection. To test this, we hybridized two species of cichlids that differ in male nuptial coloration. Male hybrids were intermediate in nuptial coloration compared to the parental species. Hybrids had a comparable fitness to the parental species and did not suffer from inviability, sterility, skewed sex ratios, reduced survival or reduced growth rates. Females preferred males of their own species over males of the other species. This implies that female mate preference can drive speciation. Females of one species were able to distinguish between males of their own species and hybrid males; females of the other species however, were not able to see this difference. When there is hybridization in nature, for instance when coloration becomes invisible by an increase in turbidity of the water, there would be asymmetrical selection against hybrids. An understanding of these processes is crucial in speciation research and for the maintenance of biodiversity.NWO-ALW 810.64.011 Leids Universiteits Fonds Lucie Burgers Stichting Schure-Beijerinck-Popping FondsUBL - phd migration 201
No evidence for a genetic association between female mating preference and male secondary sexual trait in a Lake Victoria cichlid fish
No full textSexual selection by female mating preference for male nuptial coloration has been suggested as a driving force in the rapid speciation of Lake Victoria cichlid fish. This process could have been facilitated or accelerated by genetic associations between female preference loci and male coloration loci. Preferences, as well as coloration, are heritable traits and are probably determined by more than one gene. However, little is known about potential genetic associations between these traits. In turbid water, we found a population that is variable in male nuptial coloration from blue to yellow to red. Males at the extreme ends of the phenotype distribution resemble a reproductively isolated species pair in clear water that has diverged into one species with blue-grey mates and one species with bright red males. Females of the turbid water population vary in mating preference coinciding with the male phenotype distribution. For the current study, these females were mated to blue males. We measured the coloration of the sires and male offspring. Parents-offspring regression showed that the sires did not affect male offspring coloration, which confirms earlier findings that the blue species breeds true. In contrast, male offspring coloration was determined by the identity of the dams, which suggests that there is heritable variation in male color genes between females. However, we found that mating preferences of the dams were not correlated with male offspring coloration. Thus, there is no evidence for strong genetic linkage between mating preference and the preferred trait in this population [Current Zoology 56 (1): 57-64 2010]
Het smalle pad. Beperkingen van individuen en de evolutie van levensgemeenschappen
No full textPopulariserende publicati
Sexual selection and speciation: mechanisms in Lake Victoria cichlid fish
No full textThe several hundred species of cichlid fish endemic to Lake Victoria (East-Africa) are textbook examples of explosive speciation. This thesis evaluates the hypothesis that sexual selection by female mate choice has contributed to this process of divergence, by investigating the mechanisms that drive the evolution and divergence of mating preferences for colour patterns. I studied two representative model systems, the highly polymorphic species Neochromis omnicaeruleus and the species pair Pundamilia nyererei and P. pundamilia. I used observational and experimental approaches in both laboratory and field. My work indicates that the interaction between sexual selection and habitat heterogeneity, in terms of photic environment and parasite exposure, can promote population divergence in male nuptial coloration and female preferences. In contrast, predation pressure and water turbidity may constrain the evolution and persistence of conspicuously coloured morphs and species.Netherlands Foundation for the Advancement of Tropical Research (NWO-WOTRO, grant no. 82-243)UBL - phd migration 201
Co-evolution between parthenogenesis-inducing Wolbachia and its hosts.
No full textWolbachia are intracellular, symbiotic bacteria, known for their ability to manipulate the reproduction mechanism of their arthropod hosts, for example by inducing parthenogenesis. In this thesis, I studied the causes, consequences and dynamics of a parthenogenesis-inducing (PI) Wolbachia infection in two hosts, the parasitoid wasps Tetrastichus coeruleus (Hymenoptera: Eulophidae) and Asobara japonica (Hymenoptera: Braconidae). Interestingly, both T. coeruleus and A. japonica have Wolbachia-infected parthenogenetic populations and uninfected sexual populations. The main conclusions of this thesis are as follows. First, different scenarios may occur for the spread of PI-Wolbachia infection in different host species. Wolbachia has spread via vertical transmission through populations of T. coeruleus, whereas in A. japonica Wolbachia has spread via horizontal transmission. Second, different barriers may prevent migration and gene flow between Wolbachia-infected and uninfected populations in different host species. In T. coeruleus the different populations occur in different ecological environments, whereas in A. japonica there seems to be a geographical barrier between the different populations. Third, different ages of the PI-Wolbachia infection may have different consequences for the host species. The occasional male production by Wolbachia-infected A. japonica might be explained by the relatively young age of the infection. The Wolbachia infection in T. coeruleus seems to be older. Last, a PI-Wolbachia infection can have severe consequences for the sexual functionality of infected males and females. PI-Wolbachia seems to induce cytoplasmic incompatibility in infected A. japonica males. PI-Wolbachia-infected T. coeruleus females exhibited a degradation of receptivity to matings and of spermathecal morphology.LEI Universiteit LeidenNetherlands Organization for Scientific Research division Earth and Life Sciences (NWO-ALW), J.E. Jurriaanse Stichting Rotterdam.Dierenecologi
Mapping moving media: film and video
No full textMapping Moving Media is an inquiry into the specificity of film and video. In this study, I argue that mapping the specificity of these two media is indispensable in analyzing and understanding contemporary intermedial objects in which film and video are mixed or combined. Our understanding of the meanings and effects of moving images in contemporary society will increase when combinations of film- and video elements within moving image objects are taken into account. Contemporary (new) media theory offers a wide range of terms by which interrelations between media can be defined and conceptualized. However, although I take the wide variety of notions such as remediation and hypermediacy as helpful tools in analyzing the relationships between media, I argue that the starting point of an investigation into intermedial interactions should be the concept of medium specificity instead of the many notions which define forms of intermediality. This does not mean that we should return to some of essentialist ideas on medium specificity which have been attached to the concept. However, the rightful conclusion that essentialist ideas on medium specificity are rendered untenable by today’s mixed, multi-, and intermedia, too often overshadows the question of what is being mixed, expanded, remediated, refashioned, converged or combined. In this study I ask the questions “what is meant by video?” and “what is meant by film?” How are these two media (to be) understood? Can film and video be defined as distinct, specific media, and if so, how? I hold that in this era of mixed moving media, it is vital to ask these questions precisely and especially on the media of video and film.Modern and Contemporary Studie
Female mating preferences and male coloration covary with water transparency in a Lake Victoria cichlid fish
No full textRapid speciation in Lake Victoria cichlid fish of the genus Pundamilia may be facilitated by sexual selection: female mate choice exerts sexual selection on male nuptial coloration within species and maintains reproductive isolation between species. However, declining water transparency coincides with increasingly dull coloration and increasing hybridization. In the present study, we investigated the mechanism underlying this pattern in Pundamilia nyererei, a species that interbreeds with a sister species in turbid but not in clear water. We compared measures of intraspecific sexual selection between two populations from locations that differ in water transparency. First, in laboratory mate-choice experiments, conducted in clear water and under broad-spectrum illumination, we found that females originating from turbid water have significantly weaker preferences for male coloration than females originating from clear water. Second, both the hue and body coverage of male coloration differ between populations, which is consistent with adaptation to different photic habitats. These findings suggest that the observed relationship between male coloration and water transparency is not mediated by environmental variation alone. Rather, female mating preferences are indicated to have changed in response to this variation, constituting the first evidence for intraspecific preference-trait co-evolution in cichlid fish. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 398-406
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