Developmental duration as an organizer of the evolving mammalian brain: scaling,adaptations, and exceptions

Neurodevelopmental duration plays a central role in the evolution of the retina and neocortex in mammals. In the diurnal primate eye and retina, it is necessary to scale the number of cones versus the number of rods with different exponents to defend their respective functions of spatial acuity and sensitivity in eyes of different sizes. The order of photoreceptor precursor specification, cones specified first, rods second, couples their respective cell numbers at maturity to the kinetics of embryonic stem cell proliferation. Different durations of retinogenesis change the ratio of rods to cones produced so as to defend both functions over a range of eye diameters. In the evolution of nocturnality, the same coupling of photoreceptor specification to neurogenesis is altered to fewer cones and many more rods in nocturnal eyes, by delaying the onset of retinogenesis. Similarly, the neocortex also shows coupling of the specification of laminar position with duration of neurogenesis. Overall, duration of neurogenesis directly predicts neocortex volume in most mammalian clades. In larger brains with longer neocortical neurogenesis, its organization changes progressively, differentiating the frontal pole from the occipital pole in volume of connectivity and number of neurons per unit column. This permits greater, hierarchically organized information abstraction with increasing neocortex volume. Exceptions do exist, however, in species of three separate taxa, marsupials, naked mole rats, and bats, which break the correlation of neurodevelopmental duration and brain size. Naked mole rats and bats both have small brains and unusual longevity, coupled with neurodevelopmental periods characteristic of much bigger‐brained animals, raising the possibility that developmental duration and lifespan have some genetic or mechanistic control in common. The role of duration of development in mediating between the mechanistic levels of construction of retinal and cortical organization, and the different life histories associated with larger brains, such as duration of parental care, learning and overall longevity are discussed.     

四川短尾鼩包皮腺的挥发性化学成分分析

哺乳动物的包皮腺分泌物对个体间性引诱及繁殖行为的信息交流和种群调节有着重要的作用。本研究以四川短尾鼩（Anourosorex squamipes）为研究对象对劳亚食虫目动物包皮腺挥发性化学成分和化学通讯功能进行报道。采用顶空固相微萃取—气质联用（HS-SPME-GC/MS）的方法,分析四川短尾鼩雄体包皮腺中挥发性物质的化学组成。结果表明：（1）四川短尾鼩雄体包皮腺的挥发性化学成分主要含烷烃类、醇类、酮类、醛类、醚类、酯类、酸类、芳香烃类等45种化合物;（2）成年雄性四川短尾鼩的包皮腺中挥发性成分有39种,幼年雄性含有28种,说明四川短尾鼩成年雄体的包皮腺中挥发性化学成分多于幼年雄体;（3）成年雄体的包皮腺分泌物中含有4种特有的挥发性化学成分,幼年雄体中特有成分仅为1种,表明四川短尾鼩包皮腺中的挥发性化学成分存在年龄差异;（4）四川短尾鼩包皮腺分泌物中不同化学成分相对含量不同,同种化学成分在不同个体间的相对含量存在差异。四川短尾鼩雄性包皮腺挥发性化合物种类丰富,个体、年龄差异明显。推测挥发性化合物中丁酸（Butanoicacid）、乙酸乙酯（Ethyl acetate）、苯酚（Phenol）为四川短尾鼩的信息素。本研究为进一步验证该物种的信息素成分及其传递机制提供了基础数据。     

Comparative skull osteology of Karsenia koreana (Amphibia,Caudata, Plethodontidae)

The recent discovery of a plethodontid salamander, Karsenia koreana, in Korea challenged our understanding of the biogeographic history of the family Plethodontidae, by far the largest family of salamanders, which otherwise is distributed in the New World with a few European species. Molecular studies suggest that Karsenia forms a clade with Hydromantes (sensu lato), which includes among its species the only other Old World plethodontids. We studied the skull of K. koreana and compared it with that of other plethodontid genera, especially members of the subfamily Plethodontinae, which it resembles most closely in general anatomy. The anatomy of its skull corresponds to the most generalized and apparently ancestral condition for plethodontids. No clearly autapomorphic states were detected, and no synapomorphies can be found that would link it to other genera. The Karsenia skull is cylindrical and well ossified, giving an impression of strength. In contrast, the skull of Hydromantes is highly derived; the skull is flattened and the bones are weakly ossified and articulated. Hydromantes and Karsenia share no unique anatomical features; differences between them are especially evident in the hyobranchial skeleton, which is generalized in Karsenia but highly modified in Hydromantes, which is well known for its highly projectile tongue. Plethodon and Plethodon‐like species, including Karsenia and to a lesser degree Ensatina, represent the more generalized and apparently ancestral plethodontid morphology. Specialized morphologies have evolved along only a few morphological axes within the Plethodontidae, resulting in a pattern of rampant homoplasy. Our analysis of the anatomy of the new Asiatic lineage illuminates some potential mechanisms underlying adaptive morphological evolution within the Plethodontidae. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

Attenuation of liver insoluble protein carbonyls: indicator of a longevity determinant?

Oxidative damage affects protein structure and function. Progressive accumulation of oxidized proteins is considered a putative mechanism of aging; however, empirical evidence supporting their role in aging is inconsistent. This inconsistency may reflect a failure to distinguish damage to particular cellular compartments. We found a significant reduction of protein carbonyls in the insoluble, but not in the soluble, fraction of liver tissues of long-lived compared with their short-lived counterpart. Of cellular components analyzed, only nuclear protein carbonyl level was uniformly reduced in long-lived compared with short-lived animals. This observation suggests that attenuated accumulation of protein carbonyls in the nucleus, where they can affect multiple aspects of gene expression and DNA repair, might contribute to the longevity in mammalian species.     

Effects of Road Crossings on Stream and Streamside Salamanders

Abstract: Salamanders are important members of faunal communities in Appalachian Mountain (USA) streams, and the use of salamanders as bioindicators is increasing. Roads are a part of the modern landscape, but effects of roads on stream and streamside salamander diversity and abundance is not clear. We sampled streams in central West Virginia, USA, using quadrats placed along transects in the flowing channel, dry channel, and stream bank to assess salamander diversity, richness, and abundance during 2004. We used Akaike's Information Criterion for model selection at reach (i.e., above and below culverts) and stream scales. Salamander diversity and richness was affected by elevation, stream gradient, canopy cover, and the presence of roads. Overall, stream and riparian habitat quality was the most important factor affecting salamander richness. The presence of roads, stream gradient, and elevation received the most empirical support for predicting species' abundances. Roads benefited disturbance-tolerant species but negatively affected other species. Impacts of roads and culverts on habitat should be considered by federal and state transportation agencies and natural resources agencies during the planning process and addressed through mitigation efforts. Managers should install culverts that are as wide as the stream channel, at grade with the streambed, and dominated by rubble substrate to provide maximum benefit for salamanders. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):760–771; 2008)     

Microsatellite primers for the African mole‐rat genus Cryptomys and cross‐species amplification within the family Bathyergidae

We report 11 microsatellite loci for the African mole‐rat genus Cryptomys (Rodentia: Bathyergidae), isolated from the Damaraland mole‐rat (Cryptomys damarensis) and the Common mole‐rat (C. hottentotus hottentotus). All loci are highly polymorphic in the source species, with between six and 13 alleles and observed heterozygosity ranging from 0.54 to 0.86. Two C. damarensis loci (DMR1 and 6) may be located on the X‐chromosome. Cross‐species amplification was investigated in 10 Bathyergid species, representative of the five genera. The majority of loci amplified polymorphic product in all Cryptomys species tested. Amplification was also widespread in the other genera, except in Heterocephalus.     

A tadpole-induced polyphenism in the salamander Hynobius retardatus

Abstract.— Larvae of the salamander Hynobius retardatus have two distinct morphs: normal and broad-headed, cannibal morphs. We performed three experiments to differentiate among the following hypotheses: The broad-headed morph is induced to allow: (1) feeding on nutritious conspecifics; (2) exclusion of strong competitors for food or space; or (3) feeding on large, tough prey when smaller prey items are unavailable. When newly hatched larvae were reared with a heterospecific, Rana pirica (an anuran amphibian) tadpoles, the broad-headed morph was induced more frequently compared with those reared with conspecifics. The phenotype expressed depended on the size of the tadpoles: The broad-headed morph occurred more frequently with small and the normal morph with large tadpoles. Metamorphosis occurred sooner in larvae fed conspecifics compared with those fed heterospecific tadpoles, and the mean growth rate of larvae fed conspecifics was significantly faster than that of those fed tadpoles, suggesting that the heterospecific tadpoles were less nutritive than the conspecifics. These results do not support the hypotheses that the broad-headed morph evolved for consuming conspecifics because of their better balance of nutrients or for excluding strong competitors for food or space. We tentatively conclude that the morph evolved to eat large, tough prey, including both conspecifics and heterospecific tadpoles. Because H. retardatus usually spawns very early in the spring in small ponds partially covered with ice and snow, newly hatched larvae may starve from the lack of proper food owing to extremely low water temperatures. Thus, the broad-headed morph of H. retardatus may represent a cold-habitat adaptation to overcome the severe circumstance when the only food items available are relatively large conspecifics or heterospecific tadpoles.     

Oxidized phospholipids as potential novel drug targets

The interactions of three therapeutic agents, viz. the antipsychotics HPD and CPZ, and the antineoplastic anthracycline DOX, with oxidatively modified phospholipids were studied by monitoring the quenching of fluorescence of an incorporated pyrene-labeled lipid derivative. All three drugs bound avidly to the two oxidized PCs bearing either an aldehyde or carboxylic function at the end of the sn-2 nonanoyl chain, with the highest affinity measured between CPZ and the latter oxidized lipid. Subsequent dissociation of the above drugs from the oxidized lipids by DNA, acidic phospholipids, and NaCl revealed the binding of these drugs with the aldehyde lipid to be driven by hydrophobicity similarly to their binding to lysophosphatidylcholine, whereas a significant contribution of electrostatics was evident for the lipid with the carboxylic moiety. These results connect to previous experimental data, demonstrating the induction by these drugs of oxidative stress and binding to membrane phospholipids. These issues are elaborated with reference to their clinical use and side effects.     

Differential effects of carotenoids on lipid peroxidation due to membrane interactions: X-ray diffraction analysis

The biological benefits of certain carotenoids may be due to their potent antioxidant properties attributed to specific physico-chemical interactions with membranes. To test this hypothesis, we measured the effects of various carotenoids on rates of lipid peroxidation and correlated these findings with their membrane interactions, as determined by small angle X-ray diffraction approaches. The effects of the homochiral carotenoids (astaxanthin, zeaxanthin, lutein, β-carotene, lycopene) on lipid hydroperoxide (LOOH) generation were evaluated in membranes enriched with polyunsaturated fatty acids. Apolar carotenoids, such as lycopene and β-carotene, disordered the membrane bilayer and showed a potent pro-oxidant effect (> 85% increase in LOOH levels) while astaxanthin preserved membrane structure and exhibited significant antioxidant activity (40% decrease in LOOH levels). These findings indicate distinct effects of carotenoids on lipid peroxidation due to membrane structure changes. These contrasting effects of carotenoids on lipid peroxidation may explain differences in their biological activity.     

Ectopic cervical thymi and no thymic involution until midlife in naked mole rats

Immunosenescence is a hallmark of aging and manifests as increased susceptibility to infection, autoimmunity, and cancer in the elderly. One component of immunosenescence is thymic involution, age‐associated shrinkage of the thymus, observed in all vertebrates studied to date. The naked mole rat (Heterocephalus glaber) has become an attractive animal model in aging research due to its extreme longevity and resistance to disease. Here, we show that naked mole rats display no thymic involution up to 11 years of age. Furthermore, we found large ectopic cervical thymi in addition to the canonical thoracic thymus, both being identical in their cell composition. The developmental landscape in naked mole rat thymi revealed overt differences from the murine T‐cell compartment, most notably a decrease of CD4⁺/CD8⁺ double‐positive cells and lower abundance of cytotoxic effector T cells. Our observations suggest that naked mole rats display a delayed immunosenescence. Therapeutic interventions aimed at reversing thymic aging remain limited, underscoring the importance of understanding the cellular and molecular mechanisms behind a sustained immune function in the naked mole rat.