Mass-specific metabolic rate negatively co-varies with body mass from the whole-animal to the mitochondrial levels. Mitochondria are the mainly consumers of oxygen inspired by mammals to generate ATP ...or compensate for energetic losses dissipated as the form of heat (proton leak) during oxidative phosphorylation. Consequently, ATP synthesis and proton leak compete for the same electrochemical gradient. Because proton leak co-varies negatively with body mass, it is unknown whether extremely small mammals further decouple their mitochondria to maintain their body temperature or whether they implement metabolic innovations to ensure cellular homeostasis. The present study investigated the impact of body mass variation on cellular and mitochondrial functioning in small mammals, comparing two extremely small African pygmy mice (
, ∼5 g, and
, ∼7 g) with the larger house mouse (
, ∼22 g). Oxygen consumption rates were measured from the animal to the mitochondrial levels. We also measured mitochondrial ATP synthesis in order to appreciate the mitochondrial efficiency (ATP/O). At the whole-animal scale, mass- and surface-specific metabolic rates co-varied negatively with body mass, whereas this was not necessarily the case at the cellular and mitochondrial levels.
had generally the lowest cellular and mitochondrial fluxes, depending on the tissue considered (liver or skeletal muscle), as well as having more-efficient muscle mitochondria than the other two species
presents metabolic innovations to ensure its homeostasis, by generating more ATP per oxygen consumed.
Hybridization is often seen as a process dampening phenotypic differences accumulated between diverging evolutionary units. For a complex trait comprising several relatively independent modules, ...hybridization may however simply generate new phenotypes, by combining into a new mosaic modules inherited from each parental groups and parts intermediate with respect to the parental groups. We tested this hypothesis by studying mandible size and shape in a set of first and second generation hybrids resulting from inbred wild-derived laboratory strains documenting two subspecies of house mice, Musmusculus domesticus and Musmusculus musculus. Phenotypic variation of the mandible was divided into nested partitions of developmental, evolutionary and functional modules.
The size and shape of the modules were differently influenced by hybridization. Some modules seemed to be the result of typical additive effects with hybrids intermediate between parents, some displayed a pattern expected in the case of monogenic dominance, whereas in other modules, hybrids were transgressive. The result is interpreted as the production of novel mandible morphologies. Beyond this modularity, modules in functional interaction tended to display significant covariations.
Modularity emerges as a source of novel morphological variation by its simple potential to combine different parts of the parental phenotypes into a novel offspring mosaic of modules. This effect is partly counterbalanced by bone remodeling insuring an integration of the mosaic mandible into a functional ensemble, adding a non-genetic component to the production of transgressive phenotypes in hybrids.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Famennian (Late Devonian) started after and ended with two of the seven largest crises of the Phanerozoic, the Kellwasser and Hangenberg events, respectively. In between, global environmental ...trends have been identified, involving cooling and eustatic regression. Tropical and subtropical marine faunas were largely cosmopolitan. Overall, this suggests that the Famennian was marked by long-term environmental changes occurring in a relatively homogeneous manner despite being punctuated by several short-term events of limited faunal impact. How these trends were modulated according to geographic location is investigated in this study by comparing two continuous outcrops in the Montagne Noire (Col des Tribes section, France) and in Saxo-Thuringia (Buschteich section, Germany). Both were located in the subtropical area during this period and belonged to two former microcontinents bracketed between the closing Rheic Ocean and Gondwana. Sedimentary facies, oxygen isotopes, and the generic conodont composition (biofacies) were studied in a high resolution and in the same rock samples. Sedimentary facies provided an estimate of water depth and oxygen isotopes were used as paleotemperature proxy. Conodont biofacies were analyzed using a principal component analysis, allowing the expression of the variations in the two outcrops on the same axes, and a quantitative comparison with the other proxies. Sea-level and temperature variations were different between the two areas. Saxo-Thuringia displayed stable deep and warm conditions throughout. In contrast, the environment of the Montagne Noire was shallower and cooler during the Late and latest Famennian compared to the Early and Middle Famennian, congruent with the global change evidenced elsewhere. The location of Saxo-Thuringia, close to the first point of closure of the Rheic Ocean, might have favored active tectonics, causing a local departure from the eustatic trend. The stable temperatures at BU during the Late and latest Famennian may be due to the position of Saxo-Thuringia in the remnant Rheic Ocean, limiting water mass exchange with open seas, and favoring the persistence of warm conditions.
Offshore taxa persisted later at high abundance in the Saxo-Thuringian record. The two conodont biofacies records were otherwise very comparable. This suggests that other factors mitigated the water depth forcing on these conodont assemblages.
•Thuringia and Montagne Noire differed in sea-level and temperature trends during Late and latest Famennian.•Global cooling and regression are expressed in the Montagne Noire record.•The Thuringian record remained warm and deep throughout the Famennian.•Offshore conodont genera remained abundant for longer in warm and deep environments.
Recent extensive field prospecting conducted in the Upper Miocene of Lebanon resulted in the discovery of several new fossiliferous localities. One of these, situated in the Zahleh area (Bekaa ...Valley, central Lebanon) has yielded a particularly diverse vertebrate fauna. Micromammals constitute an important part of this assemblage because not only do they represent the first Neogene rodents and insectivores from Lebanon, but they are also the only ones from the early Late Miocene of the Arabian Peninsula and circumambient areas. Analyses of the murines from Zahleh reveal that they belong to a small-sized early Progonomys, which cannot be assigned to any of the species of the genus hitherto described. They are, thereby, shown to represent a new species: Progonomys manolo. Morphometric analyses of the outline of the first upper molars of this species suggest a generalist and omnivorous diet. This record sheds new light onto a major phenomenon in the evolutionary history of rodents, which is the earliest dispersal of mice. It suggests that the arrival of murines in Africa got under way through the Levant rather than via southern Europe and was monitored by the ecological requirements of Progonomys.
Early periods in Earth's history have seen a progressive increase in complexity of the ecosystems, but also dramatic crises decimating the biosphere. Such patterns are usually considered as ...large-scale changes among supra-specific groups, including morphological novelties, radiation, and extinctions. Nevertheless, in the same time, each species evolved by the way of micro-evolutionary processes, extended over millions of years into the evolution of lineages. How these two evolutionary scales interacted is a challenging issue because this requires bridging a gap between scales of observation and processes. The present study aims at transferring a typical macro-evolutionary approach, namely disparity analysis, to the study of fine-scale evolutionary variations in order to decipher what processes actually drove the dynamics of diversity at a micro-evolutionary level. The Late Frasnian to Late Famennian period was selected because it is punctuated by two major macro-evolutionary crises, as well as a progressive diversification of marine ecosystem. Disparity was estimated through this period on conodonts, tooth-like fossil remains of small eel-like predators that were part of the nektonic fauna. The study was focused on the emblematic genus of the period, Palmatolepis. Strikingly, both crises affected an already impoverished Palmatolepis disparity, increasing risks of random extinction. The major disparity signal rather emerged as a cycle of increase and decrease in disparity during the inter-crises period. The diversification shortly followed the first crisis and might correspond to an opportunistic occupation of empty ecological niche. The subsequent oriented shrinking in the morphospace occupation suggests that the ecological space available to Palmatolepis decreased through time, due to a combination of factors: deteriorating climate, expansion of competitors and predators. Disparity changes of Palmatolepis thus reflect changes in the structure of the ecological space itself, which was prone to evolve during this ancient period where modern ecosystems were progressively shaped.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In wild populations phenotypic differentiation of skeletal structures is influenced by many factors including epigenetic interactions and plastic response to environmental influences, possibly ...blurring the expression of genetic differences. In contrast, laboratory animals provide the opportunity to separate environmental from genetic effects. The mouse mandible is particularly prone to such plastic variations because bone remodeling occurs late in postnatal ontogeny, in interaction with muscular loading. In order to understand the impact of this process on mandible morphology, we investigated how change in the masticatory function affects the mandible shape, and its pattern of variation. Breeding laboratory mice on food of different consistencies mimicked a natural variation in feeding ecology, whereas mice affected by the murine analogue of the Duchenne muscular dystrophy provided a case of pathological modification of the mastication process.
Food consistency as well as dystrophy caused significant shape changes in the mouse mandible. Further differences were observed between laboratory strains and between sexes within strains, muscular dystrophy causing the largest morphological change. The directions of the morphological changes due to food consistency and muscular dystrophy were discrepant, despite the fact that both are related to bone remodeling. In contrast, directions of greatest variance were comparable among most groups, and the direction of the change due to sexual dimorphism was parallel to the direction of main variance.
Bone remodeling is confirmed as an important factor driving mandible shape differences, evidenced by differences due to both the consistency of the food ingested and muscular dystrophy. However, the resulting shape change will depend on how the masticatory function is affected. Muscular dystrophy caused shape changes distributed all over the mandible, all muscles being affected although possibly to a different degree. In contrast, the chewing function was mostly affected when the mice were fed on hard vs. soft food, whereas grinding likely occurred normally; accordingly, shape change was more localized. The direction of greatest variance, however, was remarkably comparable among groups, although we found a residual variance discarding age, sex, and food differences. This suggests that whatever the context in which bone remodeling occurs, some parts of the mandible such as the angular process are more prone to remodeling during late postnatal growth.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Deciphering the plastic (non-heritable) changes induced by human control over wild animals in the archaeological record is challenging. We hypothesized that changes in locomotor behaviour in a wild ...ungulate due to mobility control could be quantified in the bone anatomy. To test this, we experimented with the effect of mobility reduction on the skeleton of wild boar (
), using the calcaneus shape as a possible phenotypic marker. We first assessed differences in shape variation and covariation in captive-reared and wild-caught wild boars, taking into account differences in sex, body mass, available space for movement and muscle force. This plastic signal was then contrasted with the phenotypic changes induced by selective breeding in domestic pigs. We found that mobility reduction induces a plastic response beyond the shape variation of wild boars in their natural habitat, associated with a reduction in the range of locomotor behaviours and muscle loads. This plastic signal of captivity in the calcaneus shape differs from the main changes induced by selective breeding for larger muscle and earlier development that impacted the pigs' calcaneus shape in a much greater extent than the mobility reduction during the domestication process of their wild ancestors.
Do developmental systems preferentially produce certain types of variation that orient phenotypic evolution along preferred directions? At different scales, from the intra-population to the ...interspecific, the murine first upper molar shows repeated anterior elongation. Using a novel quantitative approach to compare the development of two mouse strains with short or long molars, we identified temporal, spatial and functional differences in tooth signaling center activity, that arise from differential tuning of the activation-inhibition mechanisms underlying tooth patterning. By tracing their fate, we could explain why only the upper first molar reacts via elongation of its anterior part. Despite a lack of genetic variation, individuals of the elongated strain varied in tooth length and the temporal dynamics of their signaling centers, highlighting the intrinsic instability of the upper molar developmental system. Collectively, these results reveal the variational properties of murine molar development that drive morphological evolution along a line of least resistance.
Island evolution may be expected to involve fast initial morphological divergence followed by stasis. We tested this model using the dental phenotype of modern and ancient common voles (Microtus ...arvalis), introduced onto the Orkney archipelago (Scotland) from continental Europe some 5000 years ago. First, we investigated phenotypic divergence of Orkney and continental European populations and assessed climatic influences. Second, phenotypic differentiation among Orkney populations was tested against geography, time, and neutral genetic patterns. Finally, we examined evolutionary change along a time series for the Orkney Mainland. Molar gigantism and anterior-lobe hypertrophy evolved rapidly in Orkney voles following introduction, without any transitional forms detected. Founder events and adaptation appear to explain this initial rapid evolution. Idiosyncrasy in dental features among different island populations of Orkney voles is also likely the result of local founder events following Neolithic translocation around the archipelago. However, against our initial expectations, a second marked phenotypic shift occurred between the 4th and 12th centuries AD, associated with increased pastoral farming and introduction of competitors (mice and rats) and terrestrial predators (foxes and cats). These results indicate that human agency can generate a more complex pattern of morphological evolution than might be expected in island rodents.
Identification of relevant taxonomic and evolutionary units is a recurrent issue in the fossil record, and all the more for ancient fossils devoid of modern equivalents such as conodonts. Extensive ...morphological variation has often led to the description of numerous species, subspecies or morphotypes, which may correspond to end-member morphologies reached through ontogeny. The platform elements of the Late Devonian conodont species
Icriodus alternatus
were characterized by rows of denticles coming into occlusion between opposite elements; each element grew by the incremental addition of lamellae and by the addition of successive triads during ontogeny. During the late Frasnian and the early Famennian, the important morphological variation within this species led to the description of three subspecies. An extensive sample of early Famennian
Icriodus alternatus
was quantified using 2D biometric measurements and denticle counts on 2D pictures, showing that the subspecies mainly differed in their size range but not in their general morphology. A 3D morphometric analysis was further performed on a subsample to characterize the shape of the ontogenetically older part of the elements. During ontogeny, early valleys between denticles tended to be filled, and the asymmetry between the inner and outer side of the element increased. These ontogenetic trends are responsible for the morphologies formerly described as the subspecies
Ic. alt. mawsonae
and
Ic. alt. helmsi
. Slight discrepancies between temporal ranges of the subspecies may be achieved through variations in range of size reached by the elements as a response to environmental changes. Disparity along ontogeny seems to follow an “hourglass model” suggesting a shift from relatively loose developmental constraints to a pattern of growth modulated by functional constraints during occlusion.
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