Search for: All records

To determine the historical dynamics of colonization and whether the relative timing of colonization predicts diversification rate in the species‐rich, murine rodent communities of Indo‐Australia.

Indo‐Australian Archipelago including the Sunda shelf of continental Asia, Sahul shelf of continental Australia, the Philippines and Wallacea of Indonesia.

Order Rodentia, Family Muridae.

We used a fossil‐calibrated molecular phylogeny and Bayesian biogeographical modelling to infer the frequency and temporal sequence of biogeographical transitions among Sunda, Sahul, the Philippines and Wallacea. We estimated diversification rates for each colonizing lineage using a method‐of‐moments estimator of net diversification and Bayesian mixture model estimates of diversification rate shifts.

We identified 17 biogeographical transitions, including nine originating from Sunda, seven originating from Sulawesi and broader Wallacea and one originating from Sahul. Wallacea was colonized eight times, the Phillipines five times, Sunda twice and Sahul twice. Net diversification rates ranged from 0.2 to 2.12 species/lineage/My with higher rates in secondary and later colonizers than primary colonizers. The highest rates were in the genusRattusand their closest relatives, irrespective of colonization history.

Our inferences from murines demonstrate once again the substantial role of islands as sources of species diversity in terrestrial vertebrates of the IAA with most speciation events occurring on islands. Sulawesi and broader Wallacea have been a major source of colonists for both island and continental systems. Crossings of Wallace's Line were more common than subsequent transitions across Lydekker's Line to the east. While speciation following colonization of oceanic archipelagos and large islands is consistent with adaptive radiation theory and ideas regarding ecological opportunity, we did not observe a strong signal of incumbency effects. Rather, subsequent colonists of landmasses radiated unhindered by previous radiations.

 

Sulawesi is the largest, most topographically complex island in the Wallacean biogeographic zone, and it has a rich fauna of endemic small mammals, dominated by rodents of the family Muridae. Among murids, the Bunomys division is the most species‐rich radiation on Sulawesi. In total, the division contains 11 genera and 32 species, five and 20 of which are endemic to Sulawesi. We combined a five‐locus phylogeny and linear cranial morphology to better understand the taxonomy and local scales of endemism within the Bunomys division on Sulawesi. Phylogenetic analyses of mitochondrial and nuclear DNA placedB. fratrorumamong other genera and inferredParuromysas sister to the type species ofTaeromys(T. celebensis). We resolve these issues by resurrectingFrateromys, a genus under whichB. fratrorumwas once placed, and returningParuromys dominatortoTaeromys. Within three species,F. fratrorum, T. callitrichus,andT. taerae, we recovered Pleistocene age divergences between populations sampled across the northern peninsula of Sulawesi; divergence between western and eastern populations ofF. fratrorummay reflect the existence of two species.

 

Arboreal locomotion allows access to above-ground resources and might have fostered the diversification of mammals. Nevertheless, simple morphological measurements that consistently correlate with arboreality remain indefinable. As such, the climbing habits of many species of mammals, living and extinct, remain speculative. We collected quantitative data on the climbing tendencies of 20 species of murine rodents, an ecologically and morphologically diverse clade. We leveraged Bayesian phylogenetic mixed models (BPMMs), incorporating intraspecific variation and phylogenetic uncertainty, to determine which, if any, traits (17 skeletal indices) predict climbing frequency. We used ordinal BPMMs to test the ability of the indices to place 48 murine species that lack quantitative climbing data into three qualitative locomotor categories (terrestrial, general and arboreal). Only two indices (both measures of relative digit length) accurately predict locomotor styles, with manus digit length showing the best fit. Manus digit length has low phylogenetic signal, is largely explained by locomotor ecology and might effectively predict locomotion across a multitude of small mammals, including extinct species. Surprisingly, relative tail length, a common proxy for locomotion, was a poor predictor of climbing. In general, detailed, quantitative natural history data, such as those presented here, are needed to enhance our understanding of the evolutionary and ecological success of clades.

 

Abstract Faunivorous mammals with simple guts are thought to rely primarily on endogenously produced enzymes to digest food, in part because they lack fermentation chambers for facilitating mutualistic interactions with microbes. However, variation in microbial community composition along the length of the gastrointestinal tract has yet to be assessed in faunivorous species with simple guts. We tested for differences in bacterial taxon abundances and community compositions between the small intestines and colons of 26 individuals representing four species of shrew in the genus Crocidura. We sampled these hosts from a single locality on Sulawesi Island, Indonesia, to control for potential geographic and temporal variation. Bacterial community composition differed significantly between the two gut regions and members of the family Mycoplasmataceae contributed substantially to these differences. Three operational taxonomic units (OTUs) of an unclassified genus in this family were more abundant in the small intestine, whereas 1 OTU of genus Ureaplasma was more abundant in the colon. Species of Ureaplasma encode an enzyme that degrades urea, a metabolic byproduct of protein catabolism. Additionally, a Hafnia–Obesumbacterium OTU, a genus known to produce chitinase in bat gastrointestinal tracts, was also more abundant in the colon compared to the small intestine. The presence of putative chitinase- and urease-producing bacteria in shrew guts suggests mutualisms with microorganisms play a role in facilitating the protein-rich, faunivorous diets of simple gut mammals. 

Although deer mice (Peromyscus spp.) are among the most studied small mammals, their species diversity and phylogenetic relationships remain unclear. The lack of taxonomic clarity is mainly due to a conservative morphology and because some taxa are rare, have restricted distributions, or are poorly sampled. One taxon, P. mexicanus, includes southern Mexican subspecies that have not had their systematic placement tested with genetic data. We analyzed the phylogenetic relationships and genetic structure of P. mexicanus populations using sequences of the mitochondrial gene cytochrome b. We inferred that P. mexicanus is paraphyletic, with P. m. teapensis, P. m. tehuantepecus, andP. m. totontepecus more closely related to P. gymnotis than to P. m. mexicanus. This highly divergent clade ranges from northeastern Oaxaca to northern Chiapas, including southern Veracruz, and southern Tabasco. In light of this group’s mitochondrial distinctiveness, cohesive geographic range, and previously reported molecular, biochemical, and morphological differences, we recommend it be treated as P. totontepecus. Our findings demonstrate the need for an improved understanding of the diversity and evolutionary history of these common and abundant members of North American small mammal communities. 

Abstract Deer mice (genus Peromyscus ) are among the commonest small mammals in the Nearctic zoogeographic region. Nevertheless, systematic relationships are only partially settled and numerous taxonomic questions await resolution. For instance, researchers have found that some members of the Peromyscus truei species group contain high levels of genetic divergence that could indicate the presence of cryptic species. We analyzed the systematics and phylogenetic relationships of the P. truei group using new and previously published mitochondrial cytochrome b sequences. Our analyses verify several earlier conclusions, but we also detected new clades that deserve recognition. Considering their mitochondrial distinctiveness, allopatric ranges, and previously reported molecular, biochemical, chromosomal, morphological, and ecological differences, we elevate three previously described taxa to species. We support the recognition of two subgroupings. The first comprises P. gratus , P. truei , and possibly P. cf. martirensis and P. cf.  zapotecae . The second contains to P. amplus , P. attwateri , P. collinus , P. difficilis , P. felipensis , P. laceianus , P. nasutus , P. ochraventer , and P. pectoralis. Placement of P. bullatus will likely remain unknown until genetic data are available. Further research could improve our understanding of the evolutionary history of Peromyscus , but in some cases taxonomic issues must be resolved first. 

Abstract Adaptive radiations are characterised by the diversification and ecological differentiation of species, and replicated cases of this process provide natural experiments for understanding the repeatability and pace of molecular evolution. During adaptive radiation, genes related to ecological specialisation may be subject to recurrent positive directional selection. However, it is not clear to what extent patterns of lineage-specific ecological specialisation (including phenotypic convergence) are correlated with shared signatures of molecular evolution. To test this, we sequenced whole exomes from a phylogenetically dispersed sample of 38 murine rodent species, a group characterised by multiple, nested adaptive radiations comprising extensive ecological and phenotypic diversity. We found that genes associated with immunity, reproduction, diet, digestion and taste have been subject to pervasive positive selection during the diversification of murine rodents. We also found a significant correlation between genome-wide positive selection and dietary specialisation, with a higher proportion of positively selected codon sites in derived dietary forms (i.e. carnivores and herbivores) than in ancestral forms (i.e. omnivores). Despite striking convergent evolution of skull morphology and dentition in two distantly related worm-eating specialists, we did not detect more genes with shared signatures of positive or relaxed selection than in a non-convergent species comparison. While a small number of the genes we detected can be incidentally linked to craniofacial morphology or diet, protein-coding regions are unlikely to be the primary genetic basis of this complex convergent phenotype. Our results suggest a link between positive selection and derived ecological phenotypes, and highlight specific genes and general functional categories that may have played an integral role in the extensive and rapid diversification of murine rodents.