Testicular melanization has evolved in birds with high mtDNA mutation rates

Differential investment in pre- and post-mating male sexual traits in response to prolonged exposure to ambient UVB radiation in a fish

Increasing UVB radiation (UVB) reaching earth's surface following stratospheric ozone depletion is linked to serious consequences for organisms. While studies have focused on direct cytocidal and immunomodulatory effects of UVB, indirect consequences for fitness-related life-history traits are largely unexplored, although knowledge is needed to understand organismal responses to climate change. The present study investigates the effects of developmental exposure to enhanced, but ecologically relevant, ambient UVB levels on growth (body size), parental behavior (nest-building), fitness-enhancing traits of pre-mating (sexual ornamentation) and post-mating (sperm traits) sexual selection as well as their interrelationships in male three-spined sticklebacks (Gasterosteus aculeatus). Moreover, potentially underlying direct UVB effects, testicular antioxidant capacity (TAC) and testes and skin melanization were quantified. Juvenile full-siblings were split into two groups and raised until adulthood in a semi-natural set-up under light conditions including either natural (UVB_normal) or elevated UVB levels (UVB_enhanced). When becoming reproductive, males were kept individually before data collection took place at their reproductive peak. The results showed that males from the UVB_enhanced-group were smaller than their brothers from the UVB_normal-treatment, whereas no treatment differences were observed for sexual ornamentation, sperm traits and TAC. Moreover, UVB-stressed males built their nests faster and the relationship between body size and nest size was negative for UVB_enhanced-males while being positive for UVB_normal-males. These results demonstrate that, depending on physical state, UVB-stressed males adjusted their behavior to some extent. Additionally, a trade-off between the investment in pre- and post-mating traits was found for UVB_enhanced-males, i.e. the intensity of their breeding coloration was negatively correlated with sperm number whereas this relationship was reversed for UVB_normal-males, thus showing an interaction between pre- and post-mating traits regarding exposure treatment. The interaction provides first experimental evidence that differential allocation to energetically demanding pre- and post-mating components of male fitness is triggered by a key environmental stressor of climate change.

Tissue-specific geometry and chemistry of modern and fossilized melanosomes reveal internal anatomy of extinct vertebrates

Recent reports of nonintegumentary melanosomes in fossils hint at functions for melanin beyond color production, but the biology and evolution of internal melanins are poorly understood. Our results show that internal melanosomes are widespread in diverse fossil and modern vertebrates and have tissue-specific geometries and metal chemistries. Tissue-specific chemical signatures can persist in fossils despite some diagenetic overprint, allowing the reconstruction of internal soft-tissue anatomy in fossil vertebrates, and suggest that links between melanin and metal regulation have deep evolutionary origins in vertebrates.

Recent discoveries of nonintegumentary melanosomes in extant and fossil amphibians offer potential insights into the physiological functions of melanin not directly related to color production, but the phylogenetic distribution and evolutionary history of these internal melanosomes has not been characterized systematically. Here, we present a holistic method to discriminate among melanized tissues by analyzing the anatomical distribution, morphology, and chemistry of melanosomes in various tissues in a phylogenetically broad sample of extant and fossil vertebrates. Our results show that internal melanosomes in all extant vertebrates analyzed have tissue-specific geometries and elemental signatures. Similar distinct populations of preserved melanosomes in phylogenetically diverse vertebrate fossils often map onto specific anatomical features. This approach also reveals the presence of various melanosome-rich internal tissues in fossils, providing a mechanism for the interpretation of the internal anatomy of ancient vertebrates. Collectively, these data indicate that vertebrate melanins share fundamental physiological roles in homeostasis via the scavenging and sequestering of metals and suggest that intimate links between melanin and metal metabolism in vertebrates have deep evolutionary origins.

Melanins and melanogenesis: from pigment cells to human health and technological applications

During the past decade, melanins and melanogenesis have attracted growing interest for a broad range of biomedical and technological applications. The burst of polydopamine-based multifunctional coatings in materials science is just one example, and the list may be expanded to include melanin thin films for organic electronics and bioelectronics, drug delivery systems, functional nanoparticles and biointerfaces, sunscreens, environmental remediation devices. Despite considerable advances, applied research on melanins and melanogenesis is still far from being mature. A closer intersectoral interaction between research centers is essential to raise the interests and increase the awareness of the biomedical, biomaterials science and hi-tech sectors of the manifold opportunities offered by pigment cells and related metabolic pathways. Starting from a survey of biological roles and functions, the present review aims at providing an interdisciplinary perspective of melanin pigments and related pathway with a view to showing how it is possible to translate current knowledge about physical and chemical properties and control mechanisms into new bioinspired solutions for biomedical, dermocosmetic, and technological applications.

Antibody selection for immunocytochemical characterization of the male reproductive system in Psittaciformes

The success of breeding programs is limited by the sparse knowledge about endocrine regulation and biochemical reactions in the psittacine male tract. The immunocytochemical analysis of parrots' testicular tissues provides an insight into their reproductive system but is often hampered by the lack of reliable antibodies. In the present study, we tested a large panel of antibodies raised against steroid receptors, steroidogenic enzymes, relaxin peptides including their receptors, and proliferation markers on paraffin sections of testicular tissue from eight psittacine genera representing three continents. All investigated species displayed the tested markers in somatic and germ cells of testis and epididymis, even though cell distribution was partly heterogenous and in species-specific patterns. The 17β-hydroxysteroid-dehydrogenase-2, 3β-hydroxysteroid-dehydrogenase, and smooth muscle actin allowed the cross-species differentiation between active and nonactive gonads. The remaining steroidogenic enzymes, steroid receptors, relaxin peptides, and Ki67 proved to be suitable to define reproductive activity depending on the parrot species. Adapting immunocytochemical methods to different psittacines was successful, though various cellular expression patterns do not allow the transfer of results among different parrot species. However, the availability of a reliable repertory of sexual markers is important to examine reproductive biology of psittacine birds.

Male reproductive traits of full-sibs of different age classes in three-spined sticklebacks (Gasterosteus aculeatus)

The process of ageing is associated with negative effects of mutations acting late in life, which range from those affecting cells to those affecting the whole organism. In many animal taxa, the deterioration of the phenotype with age also affects traits such as males’ primary and secondary sexual characteristics. In three-spined sticklebacks (Gasterosteus aculeatus), males usually reproduce at one or two years of age. To see whether sexual selection has the potential to differ between young and old males, full-sib brothers of different age classes were compared, which were bred and raised under standardised laboratory conditions. During two simulated, successive breeding seasons males were allowed to build their nest in single tanks either in the first (“young males”) or in the second (“old males”) breeding season. A comparison of reproductively active brothers of the first and second breeding season showed that older males produce more but smaller sperm, which might be of lower quality. The fact that older males stored more sperm is size dependent as the results show that larger males possess a greater absolute testis mass, which is inextricably linked to sperm number. However, independent of body size, old males had a lower intensity of red/orange and UV breeding coloration as well as a reduced testis melanisation, which might have consequences in female mate choice and sperm competition.