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Based on molecular and morphological evidence, we describe a new species of murine rodent from Mt. Kampalili in easternmost Mindanao Island, Philippines. It is the third known species of Tarsomys , a genus endemic to Mindanao. The new species differs from congeners (T. apoensis and T. echinatus) in having smaller body size, shorter tail, smaller hind feet, soft and dense pelage of darker color, smaller skull with a broader zygomatic plate, shorter incisive foramina, and longer auditory bullae. The new species belongs to the " Tarsomys clade" of tribe Rattini that has diversified principally on Mindanao where, in addition to the 3 species of Tarsomys , it is represented by 2 species of Limnomys and 1 species of Baletemys. The Tarsomys clade also includes the Rattus everetti complex which is widespread throughout the oceanic portion of the Philippines and likely consists of at least 4 species. Molecular phylogenetic analysis strongly supports a sister relationship between this new species and T. apoensis , which diverged approximately 1.0 to 1.75 Ma. The phylogenetic position, morphological distinctness, and relatively ancient persistence of this species support within-island diversification as the most substantial contributor to existing species richness of small mammals in the Philippines. [ABSTRACT FROM AUTHOR]

Trabecular bone is modelled throughout an animal's life in response to its mechanical environment, but like other skeletal anatomy, it is also subject to evolutionary influences. Yet the relative strengths of factors that affect trabecular bone architecture are little studied. We investigated these influences across the Philippine endemic murine rodent clade Chrotomyini. These mammals have robustly established phylogenetic relationships, exhibit a range of well-documented substrate-use types, and have a body size range spanning several hundred grammes, making them ideal for a tractable study of extrinsic and intrinsic influences on trabecular bone morphology. We found slight differences in vertebral trabecular bone among different substrate-use categories, with more divergent characteristics in more ecologically specialized taxa. This suggests that the mechanical environment must be relatively extreme to affect trabecular bone morphology in small mammals. We also recovered allometric patterns that imply that selective pressures on bone may differ between small and large mammals. Finally, we found high intrataxonomic variation in trabecular bone morphology, but it is not clearly related to any variable we measured, and may represent a normal degree of variation in these animals rather than a functional trait. Future studies should address how this plasticity affects biomechanical properties and performance of the skeleton. [ABSTRACT FROM AUTHOR]

The Philippine archipelago hosts an exceptional diversity of murid rodents that have diversified following several independent colonization events. Here, we report the discovery of a new species of rodent from Mt. Kampalili on eastern Mindanao Island. Molecular and craniodental analyses reveal this species as a member of a Philippine "New Endemic" clade consisting of Tarsomys , Limnomys , and Rattus everetti (tribe Rattini). This new species of "shrew-mouse" is easily distinguished from its relatives in both craniodental and external characteristics including a long, narrow snout; small eyes and ears; short, dark, dense fur dorsally and ventrally; stout body with a tapering, visibly haired tail shorter than head and body length; stout forepaws; bulbous and nearly smooth braincase; narrow, tapering rostrum; short incisive foramina; slender mandible; and narrow, slightly opisthodont incisors. This new genus and species of murid rodent illustrates that murids of the tribe Rattini have exhibited greater species and morphological diversification within the Philippines than previously known and provides evidence that Mt. Kampalili represents a previously unrecognized center of mammalian endemism on Mindanao Island that is deserving of conservation action. [ABSTRACT FROM AUTHOR]

Island radiations represent unique evolutionary histories in unique ecological contexts. These radiations provide opportunities to investigate ecological diversification in groups that typically exhibit niche partitioning among their constituents, including partitioning of food resources. DNA metabarcoding produces finer levels of diet identification than traditional methods, allowing us to examine dietary niche partitioning in communities or clades in which species share superficially similar diets. Here, we use DNA metabarcoding to investigate dietary niche partitioning in an endemic radiation of mammals in the Philippines. Our data reveal niche partitioning as well as phylogenetically‐uncorrelated adaptive evolution in this small mammal community. Because 70% of the focal species belong to the tribe Chrotomyini, an endemic Philippine radiation of murid rodents that feed extensively on earthworms, this study sheds light on dietary adaptation and its role in the co‐occurrence of closely related species. Our results reveal fine‐scale resource partitioning within this community; our data provide compelling evidence for niche partitioning of diet that was masked by previous diet categories and will help in further dissecting the model adaptive radiation of endemic small mammals on Luzon. This study reinforces the notion that DNA metabarcoding can be a valuable tool for investigating both ecological relationships and evolutionary ecology at the community and phylogenetic level, respectively. [ABSTRACT FROM AUTHOR]

A lineage colonizing a geographic region with no competitors may exhibit rapid diversification due to greater ecological opportunity. The resultant species diversity of this primary-colonizing (incumbent) clade may limit subsequent lineages' ability to persist unless these non-incumbent lineages are ecologically distinct. We compare the diversity in diet-related mandibular morphology of two sympatric murid rodent clades endemic to Luzon Island, Philippines—incumbent Phloeomyini and secondary-colonizing Chrotomyini—to the mandibular morphological diversity of Sahul Hydromyini, the sister clade of Chrotomyini and the incumbent murid lineage on the supercontinent of Sahul. This three-clade comparison allows us to test the hypothesis that incumbent lineages can force persistent ecological distinction of subsequent colonists at the time of colonization and throughout the subsequent history of the two sympatric clades. We find that Chrotomyini forms a subset of the diversity of their clade plus Sahul Hydromyini that minimizes overlap with Phloeomyini. We also infer that this differentiation extends to the stem ancestor of Chrotomyini and Sahul Hydromyini, consistent with a biotic filter imposed by Phloeomyini. Our work illustrates that incumbency has the potential to have a profound influence on the ecomorphological diversity of colonizing lineages at the island scale even when the traits in question are evolving at similar rates among independently colonizing clades. [ABSTRACT FROM AUTHOR]

Existing radiations in a spatially limited system such as an oceanic island may limit the ecological opportunity experienced by later colonists, resulting in lower macroevolutionary rates for secondary radiations. Additionally, potential colonists may be competitively excluded by these incumbent (resident) species, unless they are biologically distinct (biotic filtering). The extant phenotypic diversity of secondary colonists may thus be impacted by lower rates of phenotypic evolution, exclusion from certain phenotypes, and transitions to new morphotypes to escape competition from incumbent lineages. We used geometric morphometric methods to test whether the rates and patterns of mandibular evolution of the Luzon "old endemic" rodent clades, Phloeomyini and Chrotomyini, are consistent with these predictions. Each clade occupied nearly completely separate shape space and partially separate size space. We detected limited support for decelerating and clade‐specific evolutionary rates for both shape and size, with strong evidence for a shift in evolutionary mode within Chrotomyini. Our results suggest that decelerating phenotypic evolutionary rates are not a necessary result of incumbency interactions; rather, incumbency effects may be more likely to determine which clades can become established in the system. Nonincumbent clades that pass a biotic filter can potentially exhibit relatively unfettered evolution. [ABSTRACT FROM AUTHOR]

Abstract: Diversity‐dependent cladogenesis occurs when a colonizing lineage exhibits increasing interspecific competition as it ecologically diversifies. Repeated colonization of a region by closely related taxa may cause similar effects as species within each lineage compete with one another. This may be particularly relevant for secondary colonists, which could experience limited diversification due to competition with earlier, incumbent colonists over evolutionary time. We tested the hypothesis that an incumbent lineage may diminish the diversification of secondary colonists in two speciose clades of Philippine “Old Endemic” murine rodents—Phloeomyini and Chrotomyini—on the relatively old oceanic island of Luzon. Although phylogenetic analyses confirm the independent, noncontemporaneous colonization of Luzon by the ancestors of these two clades, we found no support for arrested diversification in either. Rather, it appears that diversification of both clades resulted from constant‐rate processes that were either uniform or favored the secondary colonists (Chrotomyini), depending on the method used. Our results suggest that ecological incumbency has not played an important role in determining lineage diversification among Luzon murines, despite sympatric occurrence by constituent species within each lineage, and a substantial head start for the primary colonists. [ABSTRACT FROM AUTHOR]

The freshwater sculpin species Cottus gulosus and Cottus perplexus present a challenge to biologists because of their overlapping sympatric distributions, morphological similarity, and historical inconsistency regarding species limits and ranges. We applied linear morphometric analyses in conjunction with meristic and discrete character counts to 1) assess the validity of previously cited diagnostic characters, 2) test multivariate combinations of characters to elucidate novel diagnostic characters useful in distinguishing the 2 species, and 3) apply these diagnostic characters to identify previously unidentified specimens obtained from Washington streams, where the 2 species occur in sympatry. Our analysis of 270 Cottus specimens encompassing the range of both species uncovered little support for the diagnostic utility of previously cited characters, although significant differences between mean measurements for each group were detected in the proportion of individuals with palatine teeth and a median chin pore, as well as in mean mouth-width to body-width ratio. Additionally, we were unable to detect linear transformations of continuous measurements that could be used to reliably identify individuals of these 2 species. These results prevented us from confidently identifying the unknown Washington specimens and illustrate that multi-locus phylogenetic studies are needed to assess species boundaries for these morphologically similar fishes. [ABSTRACT FROM AUTHOR]