Notoryctes Research Articles

Therian origin of INSL3/RXFP2-driven testicular descent in mammals.

Introduction: During early development in most male mammals the testes move from a position near the kidneys through the abdomen to eventually reside in the scrotum. The transabdominal phase of this migration is driven by insulin-like peptide 3 (INSL3) which stimulates growth of the gubernaculum, a key ligament connecting the testes with the abdominal wall. While all marsupials, except the marsupial mole (Notoryctes typhlops), have a scrotum and fully descended testes, it is unclear if INSL3 drives this process in marsupials especially given that marsupials have a different mechanism of scrotum determination and position relative to the phallus compared to eutherian mammals. Methods: To understand if INSL3 plays a role in marsupial testicular descent we have sequenced and curated the INSL3 gene and its receptor (RXFP2) in a range of marsupials representing every order. Furthermore, we looked at single cell RNA-seq and qPCR analysis of INSL3 in the fat-tailed dunnart testis (Sminthopsis crassicaudata) to understand the location and timing of expression during development. Results: These data show a strong phylogenetic similarity between marsupial and eutherian orthologues, but not with monotreme INSL3s which were more similar to the ancestral RLN3 gene. We have also shown the genomic location of INSL3, and surrounding genes is conserved in a range of marsupials and eutherians. Single cell RNA-seq and qPCR data show that INSL3 mRNA is expressed specifically in Leydig cells and expressed at higher levels during the testicular descent phase in developing marsupials. Discussion: Together, these data argue strongly for a therian origin of INSL3 mediated testicular descent in mammals and suggests that a coordinated movement of the testes to the abdominal wall may have preceded externalization in marsupials and therian mammals.

Three Blind Moles: Molecular Evolutionary Insights on the Tempo and Mode of Convergent Eye Degeneration in Notoryctes typhlops (Southern Marsupial Mole) and Two Chrysochlorids (Golden Moles).

Golden moles (Chrysochloridae) and marsupial moles (Notoryctidae) are textbook examples of convergent evolution. Both taxa are highly adapted to subterranean lifestyles and have powerful limbs for digging through the soil/sand, ears that are adapted for low-frequency hearing, vestigial eyes that are covered by skin and fur, and the absence of optic nerve connections between the eyes and the brain. The eyes of marsupial moles also lack a lens as well as retinal rods and cones. Two hypotheses have been proposed to account for the greater degeneracy of the eyes of marsupial moles than golden moles. First, marsupial moles may have had more time to adapt to their underground habitat than other moles. Second, the eyes of marsupial moles may have been rapidly and recently vestigialized to (1) reduce the injurious effects of sand getting into the eyes and (2) accommodate the enlargement of lacrimal glands that keep the nasal cavity moist and prevent the entry of sand into the nasal passages during burrowing. Here, we employ molecular evolutionary methods on DNA sequences for 38 eye genes, most of which are eye-specific, to investigate the timing of relaxed selection (=neutral evolution) for different groups of eye-specific genes that serve as proxies for distinct functional components of the eye (rod phototransduction, cone phototransduction, lens/cornea). Our taxon sampling included 12 afrothere species, of which two are golden moles (Amblysomus hottentotus, Chrysochloris asiatica), and 28 marsupial species including two individuals of the southern marsupial mole (Notoryctes typhlops). Most of the sequences were mined from databases, but we also provide new genome data for A. hottentotus and one of the two N. typhlops individuals. Even though the eyes of golden moles are less degenerate than the eyes of marsupial moles, there are more inactivating mutations (e.g., frameshift indels, premature stop codons) in their cone phototransduction and lens/cornea genes than in orthologous genes of the marsupial mole. We estimate that cone phototransduction recovery genes were inactivated first in each group, followed by lens/cornea genes and then cone phototransduction activation genes. All three groups of genes were inactivated earlier in golden moles than in marsupial moles. For the latter, we estimate that lens/cornea genes were inactivated ~17.8 million years ago (MYA) when stem notoryctids were burrowing in the soft soils of Australian rainforests. Selection on phototransduction activation genes was relaxed much later (5.38 MYA), during the early stages of Australia's aridification that produced coastal sand plains and eventually sand dunes. Unlike cone phototransduction activation genes, rod phototransduction activation genes are intact in both golden moles and one of the two individuals of N. typhlops. A second marsupial mole individual has just a single inactivating mutation in one of the rod phototransduction activation genes (PDE6B). One explanation for this result is that some rod phototransduction activation genes are pleiotropic and are expressed in extraocular tissues, possibly in conjunction with sperm thermotaxis.

Evolution of the patella and patelloid in marsupial mammals.

The musculoskeletal system of marsupial mammals has numerous unusual features beyond the pouch and epipubic bones. One example is the widespread absence or reduction (to a fibrous “patelloid”) of the patella (“kneecap”) sesamoid bone, but prior studies with coarse sampling indicated complex patterns of evolution of this absence or reduction. Here, we conducted an in-depth investigation into the form of the patella of extant marsupial species and used the assembled dataset to reconstruct the likely pattern of evolution of the marsupial patella. Critical assessment of the available literature was followed by examination and imaging of museum specimens, as well as CT scanning and histological examination of dissected wet specimens. Our results, from sampling about 19% of extant marsupial species-level diversity, include new images and descriptions of the fibrocartilaginous patelloid in Thylacinus cynocephalus (the thylacine or “marsupial wolf”) and other marsupials as well as the ossified patella in Notoryctes ‘marsupial moles’, Caenolestes shrew opossums, bandicoots and bilbies. We found novel evidence of an ossified patella in one specimen of Macropus rufogriseus (Bennett’s wallaby), with hints of similar variation in other species. It remains uncertain whether such ossifications are ontogenetic variation, unusual individual variation, pathological or otherwise, but future studies must continue to be conscious of variation in metatherian patellar sesamoid morphology. Our evolutionary reconstructions using our assembled data vary, too, depending on the reconstruction algorithm used. A maximum likelihood algorithm favours ancestral fibrocartilaginous “patelloid” for crown clade Marsupialia and independent origins of ossified patellae in extinct sparassodonts, peramelids, notoryctids and caenolestids. A maximum parsimony algorithm favours ancestral ossified patella for the clade [Marsupialia + sparassodonts] and subsequent reductions into fibrocartilage in didelphids, dasyuromorphs and diprotodonts; but this result changed to agree more with the maximum likelihood results if the character state reconstructions were ordered. Thus, there is substantial homoplasy in marsupial patellae regardless of the evolutionary algorithm adopted. We contend that the most plausible inference, however, is that metatherians independently ossified their patellae at least three times in their evolution. Furthermore, the variability of the patellar state we observed, even within single species (e.g. M. rufogriseus), is fascinating and warrants further investigation, especially as it hints at developmental plasticity that might have been harnessed in marsupial evolution to drive the complex patterns inferred here.

Projected Global Loss of Mammal Habitat Due to Land-Use and Climate Change

Summary Human pressure on the environment is driving a global decline of biodiversity. Anticipating whether this trend can be reverted under future scenarios is key to supporting policy decisions. We used the InSiGHTS framework to model the impacts of land-use and climate change on future habitat availability for 2,827 terrestrial mammals at 15 arcmin resolution under five contrasting global scenarios based on combinations of representative concentration pathways and shared socio-economic pathways between 2015 and 2050. Mammal habitat declined globally by 5%–16% depending on the scenario. Africa (with declines up to 25%) and South America were the most affected regions. African insectivores, primates, Australian carnivorous marsupials and marsupial moles, and South American opossums declined the most. Tackling this loss would require a mix of actions across scales, including a global shift toward sustainability, addressing land-use change in sub-Saharan Africa, and helping endemic species track climate change in South America.

Projected Changes in Mammalian Habitat Under Contrasting Climate and Land Use Change Scenarios

Anthropogenic pressures on the environment are driving a global decline of biodiversity, and global change is projected to drive further decline. We used the InSiGHTS framework to model the impacts of climate change and land cover change on future habitat availability for 2827 terrestrial mammals at 15 arc minutes resolution, under five contrasting global change scenarios based on combinations of Representative Concentration Pathways (RCP) and Shared Socio-economic Pathways (SSP): SSP1-RCP2.6, SSP2-RCP4.5, SSP3-RCP6.0, SSP4-RCP6.0, SSP5-RCP8.5. Global habitat availability for mammals declined in all five scenario combinations from 2015 to 2050, and median declines ranged from 5% under SSP1-RCP2.6 to 16% under SSP5-RCP8.5. Africa (with median declines up to 25% under SSP5-RCP8.5), South America and Oceania were the most impacted regions. Afrosoricida (southern African golden moles and Madagascan tenrecs), Primates, Dasyuromorphia (Australian carnivorous marsupials), Notoryctemorphia (Australian marsupial moles), and Didelphimorphia (South American opossums) were amongst the taxa that lost more habitat under all scenarios. The preservation of mammalian habitat under global change will require a mix of actions at different scales, including shifting towards sustainability globally, addressing land-use change in sub-Saharan Africa, and helping endemic mammals track climate change in Oceania and South America.

Trophic ecology of marsupial predators in arid Australia following reshaping of predator assemblages

The extirpation of marsupial predators and their replacement by eutherian carnivores are likely to have cascading ecological impacts on the trophic structure of arid Australia. Here, we assessed the diet and characterized the trophic role of the 3 largest remaining carnivorous marsupials (< 200 g body mass) in arid Australia: cresttailed mulgaras (Dasycercus cristicauda), kowaris (Dasyuroides byrnei), and brush-tailed mulgaras (Dasycercusblythi). The species show a high level of trophic connectivity; each is highly interactive, being predator or prey of numerous species across multiple phyla. The prey base of each of the predator species was broad and included vertebrates, invertebrates, and plants. Crest-tailed mulgaras consumed the most vertebrates including prey up to the size of the southern marsupial mole (Notoryctes typhlops). Kowaris consumed prey up to the size of the European rabbit (Oryctolagus cuniculus). Although capable of capturing or scavenging vertebrates, the diet of each species was dominated by arthropods < 2 g in body mass.

Analysis of Phylogenomic Tree Space Resolves Relationships Among Marsupial Families.

A fundamental challenge in resolving evolutionary relationships across the tree of life is to account for heterogeneity in the evolutionary signal across loci. Studies of marsupial mammals have demonstrated that this heterogeneity can be substantial, leaving considerable uncertainty in the evolutionary timescale and relationships within the group. Using simulations and a new phylogenomic data set comprising nucleotide sequences of 1550 loci from 18 of the 22 extant marsupial families, we demonstrate the power of a method for identifying clusters of loci that support different phylogenetic trees. We find two distinct clusters of loci, each providing an estimate of the species tree that matches previously proposed resolutions of the marsupial phylogeny. We also identify a well-supported placement for the enigmatic marsupial moles (Notoryctes) that contradicts previous molecular estimates but is consistent with morphological evidence. The pattern of gene-tree variation across tree-space is characterized by changes in information content, GC content, substitution-model adequacy, and signatures of purifying selection in the data. In a simulation study, we show that incomplete lineage sorting can explain the division of loci into the two tree-topology clusters, as found in our phylogenomic analysis of marsupials. We also demonstrate the potential benefits of minimizing uncertainty from phylogenetic conflict for molecular dating. Our analyses reveal that Australasian marsupials appeared in the early Paleocene, whereas the diversification of present-day families occurred primarily during the late Eocene and early Oligocene. Our methods provide an intuitive framework for improving the accuracy and precision of phylogenetic inference and molecular dating using genome-scale data.

Craniomandibular Anatomy of the Subterranean MeridiolestidanNecrolestes patagonensisAmeghino, 1891 (Mammalia, Cladotheria) from the Early Miocene of Patagonia

ABSTRACT Among the collections made during the 1896–1899 Princeton Expeditions to Patagonia are three specimens with partial crania and postcrania of Necrolestes patagonensis Ameghino, 1891, from Santa Cruz Province, Argentina. Necrolestes has anatomical specializations found in extant subterranean mammals, and other features identifying Necrolestes as a late Miocene member of the South American Meridiolestida, a non-therian clade that otherwise is limited to the Cretaceous and Paleocene. Anatomical aspects of the three Princeton specimens have been reported previously but they are more fully described here after additional preparation. The most novel discoveries concern specializations of the snout that help identify Necrolestes as a head-lift digger, as are the extant African golden moles and Australian marsupial moles. As in other meridiolestidans and most non-therian mammals, Necrolestes has a septomaxilla at the external nasal aperture. However, the septomaxilla of Necrolestes has structures that but...

Surface foraging in Scapanus moles

Abstract Some mole genera, including Scapanus of western North America, are usually considered to be fully fossorial. I present data showing that surface foraging is used by adults of all four Scapanus species, and evidence that such foraging is not a particularly rare behavior. Scapanus moles forage on the surface when leaf litter is wet and does not produce much noise; they also move slowly, remain within a small area, and usually forage in places with dense cover. These adaptations decrease the risk of predation and make surface foraging behavior difficult to detect for human observers. Numerous unpublished and a few published observations suggest that many, if not all, species in other “fully fossorial” mole genera forage on the surface at least occasionally. This is true not just for true moles (Talpidae), but also for unrelated, but convergently similar golden (Chrysotalpidae) and marsupial (Notoryctidae) moles. Apparently, surface foraging is too important for fossorial insectivores to be completely lost even in the most fossorial taxa.

Going underground: postcranial morphology of the early Miocene marsupial mole Naraboryctes philcreaseri and the evolution of fossoriality in notoryctemorphians

We present the first detailed descriptions of postcranial elements of the fossil marsupial mole Naraboryctes philcreaseri (Marsupialia: Notoryctemorphia), from early Miocene freshwater limestone deposits in the Riversleigh World Heritage Area, northwestern Queensland. Qualitative functional analysis of these elements suggest that Na. philcreaseri was very well-adapted for burrowing, albeit somewhat less so than the living marsupial moles Notoryctes typhlops and N. caurinus. Quadratic discriminant analysis of limb measurements suggests that Na. philcreaseri was subterranean, and its Index of Fossorial Ability is almost identical to that of Notoryctes species, being among the highest known for any mammal. These results suggest that notoryctemorphians evolved their specialised, “mole-like” subterranean lifestyle prior to the early Miocene. Given that forested environments predominated in Australia until the middle-late Miocene, this transition to subterranean behaviour may have occurred via burrowing in forest floors, in which case fossorial mammals that live in tropical rainforests today (such as the placental golden moles Chrysospalax trevelyani and Huetia leucorhina) may represent reasonable living analogues for early notoryctemorphians. However, alternative scenarios, such as a cave-dwelling or semi-aquatic ancestry, should be considered. Phylogenetic analysis using a Bayesian total evidence dating approach places Naraboryctes as sister to Notoryctes with strong support (Bayesian posterior probability = 0.91), and indicates that Naraboryctes and Notoryctes diverged 30.3 MYA (95% HPD: 17.7-46.3 MYA). The age and known morphology of Na. philcreaseri does not preclude its being ancestral to Notoryctes. Using estimates of divergence times and ratios of nonsynonymous to synonymous substitutions per site, we infer that the nuclear gene “Retinol-binding protein 3, interstitial” (RBP3), which plays a key role in vision, became inactive in the Notoryctes lineage ~5.4 MYA (95% HPD: 4.5-6.3 MYA). This is much younger than previous published estimates, and postdates considerably the age of Na. philcreaseri, implying that RBP3 was active in this fossil taxon; hence, Na. philcreaseri may have retained a functional visual system. Our estimate for the inactivation of RBP3 in the Notoryctes lineage coincides with palaeobotanical evidence for a major increase in the abundance of grasses in Australia, which may indicate the appearance of more open environments, and hence selection pressure on notoryctemorphians to spend less time on the surface, leading to relaxed selection on RBP3. Ultimately, however, a fuller understanding of the origin and evolution of notoryctemorphians-including when and why they became “mole-like”-will require improvements in the Palaeogene fossil record of mammals in Australia

Backfilled tunnels provide a novel and efficient method of revealing an elusive Australian burrowing mammal

Abstract Itjaritjari, the southern marsupial mole (Notoryctes typhlops), is an extreme fossorial species that is very rarely encountered on the surface and has been regarded as a sand swimmer that leaves no reliable trace of its passage through the sand. Like many extreme fossorial species on other continents, itjaritjari is poorly known and is considered rare and threatened. In this study, surface tracks known to have been made by itjaritjari were followed underground where they became clearly defined, circular, sand-filled tunnels with a mean diameter of 39 mm. Trenches dug to expose vertical sections of dune revealed that backfilled tunnels of similar appearance and dimensions were common on dunes in the study areas, averaging 3.2 backfilled tunnels per vertical square meter. Loose sand, and thus opportunities for sand swimming, is confined to the surface in the Australian dune fields, which are well vegetated and characterized by lightly bonded sand. Rather than sand swim, itjaritjari carves tunnels a...

Surfacing behaviour and ecology of the marsupial mole (Notoryctes typhlops) at Uluru-Kata Tjuta National Park

Little is known about the distribution and ecology of the cryptic and unique marsupial mole. In this paper we report on the habitat preferences and surfacing behaviour of marsupial moles on the basis of surface sign surveys conducted in Uluru-Kata Tjuta National Park and Ayers Rock Resort over a 12-month period by Uluru-Kata Tjuta National Park staff and traditional owners. A key aim of the study was to assess the potential viability of using surface sign as a rapid, non-intrusive alternative to traditional survey methods. We found that surfacing occurred widely across the study area, but that it was highly variable both across survey sites and over time. Significant relationships existed between surface sign counts and environmental variables, including fire age, timing of significant rainfall events, presence of infrastructure and the cumulative rainfall received in the preceding three months. We concluded that the use of marsupial mole surface sign is likely to be a useful method for monitoring the distribution, abundance and habitat requirements of this cryptic species.

Diet and prey selection of the southern marsupial mole: an enigma from Australia's sand deserts

AbstractThe two marsupial moles are the sole extant members of the order Notoryctemorphia, an ancient Australian lineage, with extreme adaptations for fossoriality. We tested whether the order conforms to the expectation that the low productivity of subterranean environments results in subterranean mammals being generalist feeders. To do this, we examined diet, invertebrate availability in foraging areas and prey selection by the southern marsupial mole or Itjaritjari Notoryctes typhlops, which occupies the sand deserts of southern and central Australia. Because the species is so infrequently encountered, we examined digestive tracts from museum specimens which themselves are rare; we obtained access to ∼12% of all specimens available in Australia's museums. Our invertebrate sampling protocol was based on a novel survey method, which, for the first time, enables quantification of the distribution and habitat use of N. typhlops. We sampled topographic positions on sandridges and areas of the soil profile (0–70 cm) where marsupial moles forage. Rarefaction methods indicated our sample size was sufficient to record the majority of prey items. Material in digestive tracts of 16 specimens consisted of five insect orders (Coleoptera, Hymenoptera, Isoptera, Lepidoptera and Orthoptera), scorpions, spiders and plant material. N. typhlops consumed two main prey types: social insects (ants and termites) and the larvae of beetles. Ants, termites and beetle larvae were also the main invertebrates captured in soil cores on sandridges; other invertebrates combined contributed &lt;5% to abundance. Prey selection assessment using Jacobs' index and Bonferroni confidence intervals indicated an active avoidance of termites (D = −0.61), whereas ants (D = −0.13) and beetle larvae (D = 0.57) and all other prey categories were taken in proportion to availability. Our results show that N. typhlops is best classed as a dietary generalist despite its specialized adaptations for a subterranean lifestyle.

Cross‐cultural systematic biological surveys in Australia’s Western Desert

Summary We describe small‐scale biological surveys conducted by a collaboration of biologists and Traditional Owners designed to build scientific knowledge of the biota in remote desert regions of Western Australia. Importantly, while science driven (including systematic survey methods), the project also incorporated Indigenous Ecological Knowledge (IEK). In doing so, it has assisted with cross‐generational transfer and preliminary documentation of IEK in this region. Here, we describe a case study of surveys conducted with the Pila Nguru (Spinifex People) in the Spinifex Native Title Determined Area of the Great Victoria Desert. A total of 185 native plant species were recorded (representing 37 families and 94 genera). Only one individual of a weed species was recorded. Three plant species are new to science; Grevillea ilkurlka ms. Dicrastylis sp. ‘Ilkurlka’ and Gnephosis sp., with the first two of these species of conservation interest. The survey recorded 148 species of vertebrates; 72 birds, 21 mammals (of which six were introduced), 54 reptiles and one frog. Many animal names used by the Spinifex People were documented. The following animals that are of conservation interest were recorded: Itjarri‐itjarri (Southern Marsupial Mole, Notoryctes typhlops), Nganamarra (Malleefowl, Leipoa ocellata), Murrtja (Brush‐tailed Mulgara, Dasycercus blythi), and Princess Parrot (Polytelis alexandrae). We concur with previous authors that biological surveys, when cross‐cultural, can not only build scientific knowledge, but contribute to broader social goals of assisting Aboriginal people with cross‐generational transfer and documenting of IEK.

Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely ‘transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these—the dental morphology known as zalambdodonty—was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages—marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene.

Petrosal anatomy in the fossil mammal Necrolestes: evidence for metatherian affinities and comparisons with the extant marsupial mole

We present reconstructions of petrosal anatomy based on high-resolution X-ray computed tomography scans for the fossil mammal Necrolestes and for the marsupial mole Notoryctes sp. Compared with other mammals, Necrolestes exhibits a mosaic of plesiomorphic and derived characters, but most of the evidence supports its metatherian status. We revised previous descriptions and report on features of phylogenetic or functional significance. Necrolestes exhibits features that support metatherian affinities, such as the presence of a short and lateral prootic canal, and the loss of the stapedial artery in adults. A deep groove at the anterior pole of the promontorium is present in front of the cochlear housing, a variant on the extrabullar pathway of the internal carotid artery. The promontorium is laterally bordered by a large bony projection resembling the eutherian tegmen tympani [De Beer GR (1937) The Development of the Vertebrate Skull, Oxford, Clarendon Press, p. 391]. Posteromedial to the secondary facial foramen and anterolateral to the fenestra vestibuli is a pronounced fossa for the tensor tympani muscle. On the medial part of the pars canalicularis there is a great inflation of the medial side of the caudal tympanic process, a structure of unknown function. The internal acoustic meatus exhibits a broad transverse septum and is bordered laterally by a broad prefacial commissure. The cochleae of Necrolestes and of Notoryctes have fewer spiral turns (1.1 and 1.6, respectively) than most marsupials. The lateral semicircular canal is more expanded than the posterior semicircular canal in Necrolestes but not in Notoryctes. Both Necrolestes and Notoryctes have a second crus commune, i.e. the lateral semicircular canal opens into the ampulla of the posterior semicircular canal. A stylomastoid foramen enclosed anterodorsally by both the pars cochlearis and pars canalicularis is present in Dasyuridae, Dromiciops gliroides and Notoryctes.

Environmental Correlates of Physiological Variables in Marsupials

We analyzed body temperature (T(b)), basal metabolic rate (BMR), wet thermal conductance (C(wet)), and evaporative water loss (EWL) of marsupials by conventional and phylogenetically corrected regression. Allometric effects were substantial for BMR, C(wet), and EWL but not T(b). There was a strong phylogenetic signal for mass and all physiological traits. A significant phylogenetic signal remained for BMR, C(wet), and EWL even after accounting for the highly significant phylogenetic signal of mass. T(b), BMR, C(wet), and EWL allometric residuals were correlated with some diet, distribution, and climatic variables before and after correction for phylogeny. T(b) residuals were higher for marsupials from arid environments (high T(a) and more variable rainfall). The fossorial marsupial mole had a lower-than-expected T(b) residual. The allometric slope for BMR was 0.72-0.75. Residuals were consistently related to distribution aridity and rainfall variability, with species from arid and variable rainfall habitats having a low BMR, presumably to conserve energy in a low-productivity environment. The nectarivorous honey possum had a higher-than-expected BMR. For C(wet), the allometric slope was 0.55-0.62; residuals were related to diet, with folivores having low and insectivores high C(wet) residuals. The allometric slope for EWL was 0.68-0.73. EWL residuals were consistently correlated with rainfall variability, presumably facilitating maintenance of water balance during dry periods.

Combined Mitochondrial and Nuclear DNA Sequences Resolve the Interrelations of the Major Australasian Marsupial Radiations

Australasian marsupials include three major radiations, the insectivorous/carnivorous Dasyuromorphia, the omnivorous bandicoots (Peramelemorphia), and the largely herbivorous diprotodontians. Morphologists have generally considered the bandicoots and diprotodontians to be closely related, most prominently because they are both syndactylous (with the 2nd and 3rd pedal digits being fused). Molecular studies have been unable to confirm or reject this Syndactyla hypothesis. Here we present new mitochondrial (mt) genomes from a spiny bandicoot (Echymipera rufescens) and two dasyurids, a fat-tailed dunnart (Sminthopsis crassicaudata) and a northern quoll (Dasyurus hallucatus). By comparing trees derived from pairwise base-frequency differences between taxa with standard (absolute, uncorrected) distance trees, we infer that composition bias among mt protein-coding and RNA sequences is sufficient to mislead tree reconstruction. This can explain incongruence between trees obtained from mt and nuclear data sets. However, after excluding major sources of compositional heterogeneity, both the "reduced-bias" mt and nuclear data sets clearly favor a bandicoot plus dasyuromorphian association, as well as a grouping of kangaroos and possums (Phalangeriformes) among diprotodontians. Notably, alternatives to these groupings could only be confidently rejected by combining the mt and nuclear data. Elsewhere on the tree, Dromiciops appears to be sister to the monophyletic Australasian marsupials, whereas the placement of the marsupial mole (Notoryctes) remains problematic. More generally, we contend that it is desirable to combine mt genome and nuclear sequences for inferring vertebrate phylogeny, but as separately modeled process partitions. This strategy depends on detecting and excluding (or accounting for) major sources of non-historical signal, such as from compositional non-stationarity. [Base composition; combined data; marsupial; mitochondrial genome; phylogeny.].

Locking Yourself Out: Diversity Among Dentally Zalambdodont Therian Mammals

We review the evolution of dental zalambdodonty across therian mammals. Among zalambdodonts, there is little or no occlusion between the protocone and talonid basin and one of the central cusps of the upper molars (metacone or paracone) and the talonid basin of the lower molars are lost or reduced. Over two dozen genera of therian mammals show zalambdodont molars, including tenrecids, chrysochlorids, Solenodon, the marsupial mole Notoryctes, the extinct placentals Apternodus, Oligoryctes, Parapternodus, and Koniaryctes, and the extinct marsupials Necrolestes and Yalkaparidon. The chiropteran Harpiocephalus is nearly zalambdodont. Transformation series provided by paleontological or ontogenetic data, plus occlusal relationships, can be used to determine the homology of molar cusps in zalambdodont taxa. Zalambdodont dental specialization does not appear to have led to ecological specialization. With the important exception of golden moles and tenrecs, dentally zalambdodont taxa are less speciose than their nonzalambdodont sister taxa.

Relationships Among the Families and Orders of Marsupials and the Major Mammalian Lineages Based on Recombination Activating Gene-1

Controversies remain over the relationships among several of the marsupial families and between the three major extant lineages of mammals: Eutheria (placentals), Metatheria (marsupials), and Prototheria (monotremes). Two opposing hypotheses place the marsupials as either sister to the placental mammals (Theria hypothesis) or sister to the monotremes (Palimpsest or Marsupionta hypothesis). A nuclear gene that has proved useful for analyzing phylogenies of vertebrates is the recombination activation gene-1 (RAG1). RAG1 is a highly conserved gene in vertebrates and likely entered the genome by horizontal transfer early in the evolution of jawed vertebrates. Phylogenetic analyses were performed on RAG1 sequences from seven placentals, 28 marsupials, and all three living monotreme species. Phylogenetic analyses of RAG1 sequences support many of the traditional relationships among the marsupials and suggest a relationship between bandicoots (order Peramelina) and the marsupial mole (order Notoryctemorphia), two lineages whose position in the phylogenetic tree has been enigmatic. A sister relationship between South American shrew opossums (order Paucituberculata) and all other living marsupial orders is also suggested by RAG1. The relationship between the three major groups of mammals is consistent with the Theria hypothesis, with the monotremes as the sister group to a clade containing marsupials and placentals.