Sex-dependent selection on an autosomal melanic female ornament promotes the evolution of sex ratio bias.

Sex-dependent selection often leads to spectacularly different phenotypes in males and females. In species in which sexual dimorphism is not complete, it is unclear which benefits females and males derive from displaying a trait that is typical of the other sex. In barn owls (Tyto alba), females exhibit on average larger black eumelanic spots than males but members of the two sexes display this trait in the same range of possible values. In a 12-year study, we show that selection exerted on spot size directly or on genetically correlated traits strongly favoured females with large spots and weakly favoured males with small spots. Intense directional selection on females caused an increase in spot diameter in the population over the study period. This increase is due to a change in the autosomal genes underlying the expression of eumelanic spots but not of sex-linked genes. Female-like males produced more daughters than sons, while male-like females produced more sons than daughters when mated to a small-spotted male. These sex ratio biases appear adaptive because sons of male-like females and daughters of female-like males had above-average survival. This demonstrates that selection exerted against individuals displaying a trait that is typical of the other sex promoted the evolution of specific life history strategies that enhance their fitness. This may explain why in many organisms sexual dimorphism is often not complete.

Selection on a eumelanic ornament is stronger in the tropics than in temperate zones in the worldwide-distributed barn owl.

Spatial variation in the pattern of natural selection can promote local adaptation and genetic differentiation between populations. Because heritable melanin-based ornaments can signal resistance to environmentally mediated elevation in glucocorticoids, to oxidative stress and parasites, populations may vary in the mean degree of melanic coloration if selection on these phenotypic aspects varies geographically. Within a population of Swiss barn owls (Tyto alba), the size of eumelanic spots is positively associated with survival, immunity and resistance to stress, but it is yet unknown whether Tyto species that face stressful environments evolved towards a darker eumelanic plumage. Because selection regimes vary along environmental gradients, we examined whether melanin-based traits vary clinally and are expressed to a larger extent in the tropics where parasites are more abundant than in temperate zones. To this end, we considered 39 barn owl species distributed worldwide. Barn owl species living in the tropics displayed larger eumelanic spots than those found in temperate zones. This was, however, verified in the northern hemisphere only. Parasites being particularly abundant in the tropics, they may promote the evolution of darker eumelanic ornaments.

Selection on a eumelanic ornament is stronger in the tropics than in temperate zones in the worldwide-distributed barn owl.

Spatial variation in the pattern of natural selection can promote local adaptation and genetic differentiation between populations. Because heritable melanin-based ornaments can signal resistance to environmentally mediated elevation in glucocorticoids, to oxidative stress and parasites, populations may vary in the mean degree of melanic coloration if selection on these phenotypic aspects varies geographically. Within a population of Swiss barn owls (Tyto alba), the size of eumelanic spots is positively associated with survival, immunity and resistance to stress, but it is yet unknown whether Tyto species that face stressful environments evolved towards a darker eumelanic plumage. Because selection regimes vary along environmental gradients, we examined whether melanin-based traits vary clinally and are expressed to a larger extent in the tropics where parasites are more abundant than in temperate zones. To this end, we considered 39 barn owl species distributed worldwide. Barn owl species living in the tropics displayed larger eumelanic spots than those found in temperate zones. This was, however, verified in the northern hemisphere only. Parasites being particularly abundant in the tropics, they may promote the evolution of darker eumelanic ornaments.

Proximate basis of the covariation between a melanin-based female ornament and offspring quality.

In contradiction to sexual selection theory, several studies showed that although the expression of melanin-based ornaments is usually under strong genetic control and weakly sensitive to the environment and body condition, they can signal individual quality. Covariation between a melanin-based ornament and phenotypic quality may result from pleiotropic effects of genes involved in the production of melanin pigments. Two categories of genes responsible for variation in melanin production may be relevant, namely those that trigger melanin production (yes or no response) and those that determine the amount of pigments produced. To investigate which of these two hypotheses is the most likely, I reanalysed data collected from barn owls ( Tyto alba). The underparts of this bird vary from immaculate to heavily marked with black spots of varying size. Published cross-fostering experiments have shown that the proportion of the plumage surface covered with black spots, a eumelanin composite trait so-called "plumage spottiness", in females positively covaries with offspring humoral immunocompetence, and negatively with offspring parasite resistance (i.show $132#e. the ability to reduce fecundity of ectoparasites) and fluctuating asymmetry of wing feathers. However, it is unclear which component of plumage spottiness causes these relationships, namely genes responsible for variation in number of spots or in spot diameter. Number of spots reflects variation in the expression of genes triggering the switch from no eumelanin production to production, whereas spot diameter reflects variation in the expression of genes determining the amount of eumelanin produced per spot. In the present study, multiple regression analyses, performed on the same data sets, showed that humoral immunocompetence, parasite resistance and wing fluctuating asymmetry of cross-fostered offspring covary with spot diameter measured in their genetic mother, but not with number of spots. This suggests that genes responsible for variation in the quantity of eumelanin produced per spot are responsible for covariation between a melanin ornament and individual attributes. In contrast, genes responsible for variation in number of black spots may not play a significant role. Covariation between a eumelanin female trait and offspring quality may therefore be due to an indirect effect of melanin production.

Ornament of Reason : an annoted english translation of rMa bya Byang chub brtson 'grus's : commentary to the Mūlamadhyamakakārikā

The present work contains an English translation of the Ornament of Reason (Tib. dBu ma'i rtsa ba shes rab kyi 'grel ba thad pa'i rgyan), an influential 12th century Tibetan commentary to a classic of Indian Buddhism, Nàgàrjuna's Root of the Middle Way (Skt. Mûlamadhyamaka-kârikâ Tib. dBu ma'i rtsa ba shes rab ces bya ba). The author, rMa bya byang chub brtson 'grus's, was among the first Tibetans to explicitly align themselves with the philosophical project of the 7th century Indian Madhyamaka teacher, CandrakTrti. With his stern revision and transformative re-employment of the epistemological framework that CandrakTrti otherwise scorns, rMa bya was however to develop an original and highly influential Madhyamaka interpretation.¦rMa bya's "topical outline" (Tib. sa bead) of his commentary is contained in the first appendix to the translation. The second appendix contains a digitalized version of the Rumtek edition of rMa bya's commentary, cross-referenced to the page numbers of the translation. The annotations contain concise explanatory remarks and suggestions for further reading, as well as identifications of the passages that rMa bya cites.

A female melanin ornament signals offspring fluctuating asymmetry in the barn owl.

Sexual selection theory predicts that males advertise quality by displaying extravagant ornaments. By contrast, whether phenotypic variation in females has a signalling function remains an open question. Here, to our knowledge, we provide the first evidence that a female plumage trait can signal fluctuating asymmetry in the offspring. We experimentally demonstrate in wild barn owls (Tyto alba) that the extent to which females display black spots on their plumage does not only signal offspring parasite resistance as shown in a previous study but also developmental homeostasis in the offspring. A greater number of spotted females produced offspring that had more symmetrical feathers during the period of growth. Males, that pair non-randomly with respect to female plumage spottiness therefore appear to gain substantial benefits by mating with heavily spotted females. Genetic variation in plumage spottiness is nevertheless maintained as the covariation between offspring body mass and mother plumage spottiness varies annually depending on environmental conditions.

Metaph’ornament and crime: the sequel to the delict of the centenary of Adolf Loos’ anti-ornament indictment

Ornamento: há cem anos, de que crime se tratava? Será ainda perseguido? Será ainda castigado? Será ainda um crime? No ano do centenário do ensaio «Ornamento e Crime» de Adolf Loos, uma digressão simultaneamente histórica, teórica, cultural e fenomenológica às raízes do ornamento, e a sua transformação, do dealbar do Movimento Moderno até hoje, em algo insondável e inesperado: a metáfora.

Croig Cave: a late Bronze Age ornament deposition and 3,500 years of coastal foraging in NW Mull, Scotland

Activity within caves provides an important element of the later prehistoric and historic settlement pattern of western Scotland. This contribution reports on a small-scale excavation within Croig Cave, on the coast of north-west Mull, that exposed a 1.95m sequence of midden deposits and cave floors that dated bewteen c 1700 BC and AD 1400. Midden analysis indicated the processing of a .... 950 BC, a penannular copper bracelet a discrete ritual episode within the cycle of otherwise potentially mundane activities. Lead isotope analysis indicates an Irish origin for the copper ore. A piece of iron slag within later midden deposits, dated to c 400 BC, along with high frequencies of wood charcoal, suggest that smithing or smelting may have occurred within the cave. High zinc levels in the historic levels of the midden c AD 1200 might indicate intensive processing of seaweed.

Sexually dimorphic legs in a neotropical harvestman (Arachnida, Opiliones): Ornament or weapon?

The evolution of sexually dimorphic traits has been the focus of much theoretical work, but empirical approaches to this topic have not been equally prolific. Males of the neotropical family Gonyleptidae usually present a strong fourth pair of legs armed with spines, but their functional significance is unknown. We investigated the putative functions of the leg armature in the harvestman Neosadocus maximus. Being a non-visual species. the spines on male legs can only be perceived by females through physical contact. Thus, we could expect females to touch the armature on the legs of their mates if they were to evaluate it. However, we found no support for this hypothesis. We did show that (1) leg armature is used as a weapon in contests between mates and (2) spines and associated sensilla are sexually dimorphic structures involved in ""nipping behavior"", during which a winner emerged in most fights. Finally, we demonstrate that five body structures directly involved in male-male fights show positive allometry in males. presenting slopes higher than 1, whereas the same structures show either no or negative allometry in the case of females. In conclusion, leg armature in male harvestmen is clearly used as a device in intrasexual contests. (C) 2008 Elsevier B.V. All rights reserved.