The cave bear’s hibernation: reconstructing the physiology and behaviour of an extinct animal

Abstract

When studying an extinct species such as the cave bear (Ursus spelaeus ROSENMÜLLER 1794), it is possible to apply a variety of molecular biology techniques such as the study of stable isotopes or mitochondrial DNA (mDNA) to infer patterns of behaviour or physiology that would otherwise remain concealed. Throughout Europe and along time, differences in the isotopic values (δ¹³C and δ¹⁵N) of cave bears arise from environmental differences and the Pleistocene climatic evolution. The climate determines the hibernation length, during which the cave bears undergo a particular physiology that can be related to an increase in δ¹⁵N during climate cooling. In order to verify whether hibernation affected the isotopic values, we compared cave bears in different ontogenetic stages. The results show that perinatal values reflect the values for mothers during hibernation, while juveniles show differences in maternal investment. A previous study in the literature based on complete mitochondrial DNA sequences of several individuals collected from closely situated caves showed that each cave housed, almost exclusively, a single lineage of haplotypes. This pattern suggests extreme fidelity to the birth site, or homing behaviour, and that cave bears formed stable maternal social groups, at least for the purpose of hibernation. Studies of this type offer unexpected data on the palaeobiology of this extinct animal.     

Was the ASN a Myelin Society?

Neurochemical Research -     

Hominid exploitation of the environment and cave bear populations. The case of Ursus spelaeus Rosenmüller-Heinroth in Amutxate cave (Aralar, Navarra-Spain)

Cave bears (Ursus deningeri and U. spelaeus) and hominids (Homo heidelbergensis, H. neanderthalensis, and H. sapiens) were potential competitors for environmental resources (subterranean and open air). Here, we examined the age at death of cave bear (Ursus spelaeus Rosenmüller-Heinroth) specimens from Amutxate cave in order to shed light on the effect of resource sharing between cave bears and hominids. After studying dental wear of the deciduous and permanent dentitions, the ontogenetic development of mandibles, and incremental layers of cement (annuli), we defined five age groups differentiated by marked development and size gaps. Our findings indicate that after hibernating, bears abandoned the den, thereby leaving the subterranean environment (caves) free for temporary hominid occupation-this would explain the subtle traces of hominid presence in many dens. However, a simple calculation based on age at death of subadult and adult cave bear specimens in Amutxate cave, extrapolated to the whole cave area, showed that the area surrounding this cave hosted bears for at least 9,000 years. This length of habitation, quite similar to the time-span derived from amino acid racemization and electron spin resonance, indicates that bear populations in the Amutxate cave constituted a serious constraint for hominid exploitation of the environment.     

Borrelia burgdorferi and the macrophage: routine annihilation but occasional haven?

Borrelia burgdorferi, the agent for Lyme disease, has a typical pattern of bacterial interaction with phagocytes: attachment, stimulation o f release o f inflammatory mediators and, in most cases, ingestion and killing. Spirochetes are killed extracellulorly by antibody plus complement via the classical pathway, as well as by phagocytes through apparently nonoxidative means. Yet rare persistent spirochetes (mutants?) have been identified both in patients' tissues and in cells grown in vitro. Ruth Montgomery and Stephen Malawista here ask: are some Borrelia wolves in sheeps' clothing, evading macrophage anti-microbial action?     

Function of the alternative oxidase: is it still a scavenger?

The alternative oxidase is a respiratory chain protein found in all higher plants, fungi, non-fermentative yeasts and trypanosomes. Its primary structure suggests that it is a new member of the di-iron carboxylate protein family. Recent sequence analysis indicates an evolutionary relationship between primitive members of this protein family and the alternative oxidase, suggesting that its early function was to scavenge di-oxygen. However, modelling of plant growth kinetics suggests a different function.     

Hovering sunbirds in the Old World: occasional behaviour or evolutionary trend?

The nectarivory of sunbirds in the Old World and hummingbirds in the New World evolved independently. While both groups are specialised in their feeding apparatuses, hummingbirds are moreover famous for their adaptations to sustained hovering flight. Recently, an example of a pollination system of the invasive plant Nicotiana glauca has been used to show that less adapted sunbirds also are frequently able to hover. Nevertheless, the question has remained why plants adapted to bird hovering pollination do not occur outside the New World. In this paper we show that the long‐peduncle Cameroonian Impatiens sakeriana is not capable of autonomous selfing and can be pollinated only by two often hovering sunbirds, the Cameroon sunbird Cyanomitra oritis and the northern double‐collared sunbird Cinnyris reichenowi. Our study revealed that this plant is highly specialised for pollination by C. oritis. Cinnyris reichenowi hovers less frequently and often thieves nectar by piercing the flower spur when perching. This study shows that pollination systems occurring in the Old World follow similar evolutionary trends as systems including hovering hummingbirds in the New World.     

Was the Late Ordovician mass extinction truly exceptional?

The Late Ordovician mass extinction event is the oldest of the five great extinction events in the fossil record. It has long been regarded as an outlier among mass extinctions, primarily due to its association with a cooling climate. However, recent temporally better resolved fossil biodiversity estimates complicate this view, providing growing evidence for a prolonged but punctuated biodiversity decline modulated by changes in atmospheric composition, ocean chemistry, and viable habitat area. This evolving view invokes extinction drivers similar to those that occurred during other major extinctions; some are even factors in the current human-induced biodiversity crisis. Even this very ancient and, at first glance, exceptional event conveys important lessons about the intensifying ‘sixth mass extinction’.     

Was the evolution of plastid genetic machinery discontinuous?

The plastid nucleoid consists of plastid DNA and various, mostly uncharacterized, DNA-binding proteins. The plastid DNA undoubtedly originated from an ancestral cyanobacterial genome, but the origin of the nucleoid proteins appears complex. Initial biochemical analysis of these proteins, as well as comparative genome informatics, suggest that proteins of eukaryotic origin replaced most of the original prokaryotic proteins during the evolution of plastids in the lineage of green plants.     

From a molecules’ perspective – contributions of ancient DNA research to understanding cave bear biology

Abstract

Few members of the Pleistocene megafauna have been as extensively studied as cave bears. Multidisciplinary research into cave bears has provided insights into their morphology, ecology, and evolution. Genetic studies have profited from the availability of large numbers of well-preserved remains. As a result, ‘ancient DNA (aDNA)’ from cave bears has provided significant insights into cave bear ecology, phylogeography and even potential causes of their extinction. Here I review the contributions that genetic research has made to our understanding of cave bear biology and evaluate the potential that new, genomic tools provide to shed further light onto how these iconic representatives of the Pleistocene megafauna lived and died.     

Was sind Artmerkmale?

Ohne Zusammenfassung     

Was istAcrosiphonia arcta?

No answer to this question is presented in this article. Two species, morphologically alike, differ in their life-cycles. One of these species has hitherto been found only once in a culture ofSpongomorpha aeruginosa, which was started using zoospores ofCodiolum petrocelidis. It has never been found in natural environments at Helgoland. This species has a heteromorphic life-cycle: a monoecious gametophyte which alternates with a unicellular sporophytical stage. Gametes do not develop parthenogenetically. The other species is a monoecious diplont, common at Helgoland and designated asAcrosiphonia arcta. It will not be possible to assign a name to these forms unless life-cycles of species from type-localities have been studied. In general, life-cycles are not significant for the characterization of units higher than genera. The order of Acrosiphoniales is characterized by operculate sporangia and gametangia respectively, as well as by the shape of the vegetative thallus.     

Was the initiation of translation in early eukaryotes IRES-driven?

The initiation of translation in eukaryotes generally involves the recognition of a 'cap' structure at the 5' end of the mRNA. However, for some viral and cellular mRNAs, a cap-independent mechanism occurs through an mRNA structure known as the internal ribosome entry site (IRES). Here, I postulate that the first eukaryotic mRNAs were translated in a cap-independent, IRES-driven manner that was then superseded in evolution by the cap-dependent mechanism, rather than vice versa. This hypothesis is supported by the following observations: (i) IRES-dependent, but not cap-dependent, translation can take place in the absence of not only a cap, but also many initiation factors; (ii) eukaryotic initiation factor 4E (eIF4E) and eIF4G, molecules absolutely required for cap-dependent translation, are among the most recently evolved translation factors; and (iii) functional similarities suggest the evolution of IRESs from spliceosomal introns. Thus, the contemporary cellular IRESs might be relics of the past.     

Was Aldo Leopold Right about the Kaibab Deer Herd?

In ecology textbooks prior to the 1970s, Aldo Leopold’s classic story of predator control, overpopulation of deer, and habitat degradation on the Kaibab Plateau during the 1920s epitomized predator regulation of herbivore populations. However, the story disappeared from texts in the late 20th century after several papers noted uncertainties in estimations of the deer population and provided alternative explanations. We re-examined the case study by determining the age structure of aspen (Populus tremuloides Michx.) on the plateau. Aspen comprises the majority of deer browse in the summer, and the absence of a normal cohort of aspen from the 1920s would indicate deer overpopulation. The number of aspen (at 1.4 m) dating to the 1920s was an order of magnitude lower than the null expectation. Other periods of unusual numbers of aspen included high numbers of aspen dating to the 1880s and 1890s (when regular surface fires ceased), few aspen dating from 1953 to 1962 (after a second irruption of the deer population), and very high numbers from 1968 to 1992 (coincident with widespread logging). These convergent lines of evidence support the idea of extreme deer herbivory in the 1920s, consistent with food limitation of deer at high populations (bottom–up control) and predation limitation at low deer populations (top–down control). Some uncertainty remains within the overall story, and this level of ambiguity is common in case studies that involve population ecology, land management, and people at the scale of 1,000 km² and 100 years. A complete version of the Kaibab deer story and its history would be a valuable, realistic case study for ecology texts.