Anang S. Achmadi

Evolutionary novelty in a rat with no molars

Rodents are important ecological components of virtually every terrestrial ecosystem. Their success is a result of their gnawing incisors, battery of grinding molars and diastema that spatially and functionally separates the incisors from the molars. Until now these traits defined all rodents. Here, we describe a new species and genus of shrew-rat from Sulawesi Island, Indonesia that is distinguished from all other rodents by the absence of cheek teeth. Moreover, rather than gnawing incisors, this animal has bicuspid upper incisors, also unique among the more than 2200 species of rodents. Stomach contents from a single specimen suggest that the species consumes only earthworms. We posit that by specializing on soft-bodied prey, this species has had no need to process food by chewing, allowing its dentition to evolve for the sole purpose of procuring food. Thus, the removal of functional constraints, often considered a source of evolutionary innovations, may also lead to the loss of the very same traits that fuelled evolutionary diversification in the past.

Phylogeny, diversity, and biogeography of Southeast Asian spiny rats (Maxomys).

Abstract Knowledge of the diversity and relationships of species in many groups of plants and animals in Southeast Asia is severely limited, preventing an integrative understanding of evolutionary and ecological processes in island archipelagos. We generated a 3-locus DNA sequence data set to estimate phylogenetic relationships among species and populations of Maxomys, a genus of rodents endemic to Southeast Asia. Our inclusion of Crunomys as a potential outgroup supported the monophyly of Crunomys, but the genus was deeply nested within Maxomys. Because of the relatively ancient divergences (mean uncorrected p-distances up to 0.15 in cytochrome-b sequences) among species of Maxomys and short branch lengths among basal lineages of the phylogeny, we obtained little support for the oldest relationships in Maxomys + Crunomys. However, our analyses revealed unrecognized diversity in the form of divergent populations both between and within islands and the presence of 2 potentially undescribed species from Sulawesi. The Maxomys and Crunomys of Sulawesi belonged to 4 clades sister to extralimital species, suggesting that repeated overwater dispersal between Sundaland–Philippines and Sulawesi was an important isolating mechanism in the history of this group.

Repeated evolution of carnivory among Indo-Australian rodents

Convergent evolution, often observed in island archipelagos, provides compelling evidence for the importance of natural selection as a generator of species and ecological diversity. The Indo‐Australian Archipelago (IAA) is the worlds largest island system and encompasses distinct biogeographic units, including the Asian (Sunda) and Australian (Sahul) continental shelves, which together bracket the oceanic archipelagos of the Philippines and Wallacea. Each of these biogeographic units houses numerous endemic rodents in the family Muridae. Carnivorous murids, that is those that feed on animals, have evolved independently in Sunda, Sulawesi (part of Wallacea), the Philippines, and Sahul, but the number of origins of carnivory among IAA murids is unknown. We conducted a comprehensive phylogenetic analysis of carnivorous murids of the IAA, combined with estimates of ancestral states for broad diet categories (herbivore, omnivore, and carnivore) and geographic ranges. These analyses demonstrate that carnivory evolved independently four times after overwater colonization, including in situ origins on the Philippines, Sulawesi, and Sahul. In each biogeographic unit the origin of carnivory was followed by evolution of more specialized carnivorous ecomorphs such as vermivores, insectivores, and amphibious rats.

Local endemism and within‐island diversification of shrews illustrate the importance of speciation in building Sundaland mammal diversity

Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (i) little differentiation of terrestrial organisms among continental shelf islands and (ii) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well‐sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analysed nine unlinked loci from shrews of the genus Crocidura from seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognized Crocidura species from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species of Crocidura in the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra‐island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species‐level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within‐island diversification. Our results suggest that both between‐ and within‐island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the regions fauna is relictual and primarily governed by extinction.

Convergent evolution of aquatic foraging in a new genus and species (Rodentia: Muridae) from Sulawesi Island, Indonesia

The island of Sulawesi, in Indonesia, lies at the crossroads of the Indo-Australian Archipelago and has remained isolated from the Asian (Sunda) and Australian (Sahul) continental shelves for at least the last 10 million years. Of the 50 native species of rodents on Sulawesi, all are endemic and represent the evolution of a variety of ecological and morphological forms within the Muridae and Sciuridae. Carnivorous rodents have evolved, perhaps independently, in Muridae from the Philippines, Sulawesi, and Sahul, but semi-aquatic murids are only known from Sahul. Here we describe a new genus and species of insectivorous water rat from Sulawesi. Phylogenetic analyses demonstrate that it is related to the shrew rats of Sulawesi and represents an origin of aquatic carnivory that is independent from the evolution of water rats on Sahul. Many areas of Sulawesi have not been surveyed systematically and current lists of mammal species are likely to dramatically underestimate actual diversity.

A new genus and species of omnivorous rodent (Muridae: Murinae) from Sulawesi, nested within a clade of endemic carnivores

We document a new genus and species of rodent (Muridae) from the west-central region of Sulawesi Island, Indonesia. The new taxon is known only from the type locality at around 1,600 m elevation on Mt. Gandangdewata of the Quarles Range, in the district of Mamasa. With phylogenetic analyses of DNA sequences from 5 unlinked loci, we infer that the new taxon is sister to the Sulawesi water rat, Waiomys mamasae, and nested within a clade of rodents from Sulawesi that otherwise feed exclusively on invertebrates. The new species is distinguishable from other rodents of Sulawesi by the combination of its small, slender body; soft, gray–brown fur; small, rounded ears; long, sparsely haired tail; long, fine mystacial vibrissae; gracile cranium; short rostrum; pronounced lacrimal bone; prominent, sickle-shaped coronoid process; and pale orange enamel on labial surface of incisors. Unlike its closest relatives, the new species feeds on both plant and animal matter, and may represent a rare evolutionary reversal of traits associated with a carnivorous diet in murids.

A hog-nosed shrew rat (Rodentia: Muridae) from Sulawesi Island, Indonesia

We document a new genus and species of shrew rat from the north peninsula of Sulawesi Island, Indonesia. The new taxon is known only from the type locality at 1,600 m elevation on Mt. Dako, in the district of Tolitoli. It is distinguished from all other Indonesian murines by its large, flat, pink nose with forward-facing nares. Relative to other Sulawesi murines, the species has extremely large ears (∼ 21% of head and body length), very long urogenital hairs, prominent and medially bowing hamular processes on the pterygoid bones, extremely long and procumbent lower incisors, and unusually long articular surfaces on the mandibular condyles. Morphologically, the new taxon is most similar to a group of endemic Sulawesi rats known commonly as “shrew rats.” These are long faced, carnivorous murines, and include the genera Echiothrix, Melasmothrix, Paucidentomys, Sommeromys, and Tateomys. Our Bayesian and likelihood analyses of DNA sequences concatenated from 5 unlinked loci infer the new shrew rat as sister to a clade consisting of Melasmothrix, Paucidentomys, and Echiothrix, suggesting that Sulawesi shrew rats represent a clade. The Sulawesi water rat, Waiomys mamasae, was sister to the shrew rats in our analyses. Discovery of this new genus and species brings known shrew rat diversity on Sulawesi to 6 genera and 8 species. The extent of morphological diversity among these animals is remarkable considering the small number of species currently known. Kami mendokumentasikan genus dan spesies baru tikus cucurut dari bagian semenanjung utara pulau Sulawesi, Indonesia. Takson baru ini hanya diketahui dari lokasi spesimen tipe pada ketinggian 1,600 mdpl di Gunung Dako, Kabupaten Tolitoli. Ia dibedakan dari spesies tikus Indonesia lainnya berdasarkan ukuran hidung yang besar, datar, berwarna merah muda dengan moncong hidung menghadap ke arah depan. Jika dibandingkan dengan spesies tikus Sulawesi lainnya, spesies ini memiliki telinga yang sangat besar (∼ 21% dari panjang kepala dan badan), rambut urogenital yang sangat panjang, prosesus hamular yang jelas dan menonjol pada pertulangan pterygoid, gigi seri bagian bawah yang sangat panjang, dan penampang persendian yang panjang dan tidak biasa pada kondilus mandibula. Secara morfologi, takson ini lebih mirip dengan kelompok tikus endemik Sulawesi yang umumnya dikenal sebagai “tikus cucurut”. Kelompok ini dicirikan dengan mulut yang panjang, pemakan daging, dan termasuk didalamnya adalah genus Echiothrix, Melasmothrix, Paucidentomys, Sommeromys, dan Tateomys. Analisis Bayesian dan likelihood menggunakan sambungan sekuens DNA dari 5 lokus yang tidak terpaut menunjukkan spesies tikus cucurut baru ini berkerabat dekat dengan kelompok yang terdiri dari Melasmothrix, Paucidentomys, dan Echiothrix, memberi kesan tikus cucurut Sulawesi merepresentasikan suatu clade atau kelompok tersendiri. Tikus air Sulawesi, Waiomys mamasae, diketahui berkerabat dekat dengan tikus cucurut dalam analisis yang dilakukan. Penemuan genus dan spesies baru ini menambah keanekaragaman jenis tikus cucurut di Sulawesi yang telah diketahui menjadi 6 genera dan 8 spesies. Besarnya perbedaan morfologi di antara spesies-spesies tersebut merupakan sesuatu yang luar biasa mengingat sedikitnya jumlah spesies yang telah diketahui saat ini.

A new species of shrew (Soricomorpha: Crocidura) from West Java, Indonesia

Abstract We document the existence of a new species of shrew (Soricomorpha, Soricidae, Crocidura) in West Java, Indonesia, using both morphological and genetic data. Relative to other Southeast Asian Crocidura, the new species is medium-sized with a slender body and long tail, which together readily distinguish it from all other Javan shrews. Morphological differences between the new species and Crocidura paradoxura, another long-tailed shrew that is endemic to Sumatra, are subtle, but genetic differences suggest a long, independent evolutionary history. This description brings to 5 the total number of species of Crocidura recognized from Java. All 5 species are endemic to the island and as many as 4 occur in syntopy. Further investigation is needed to document geographical ranges of shrew species on Java, especially along the islands east–west climatic gradient, where previously proposed subspecies boundaries may be coincident with transitions in precipitation patterns.

Geographic isolation and elevational gradients promote diversification in an endemic shrew on Sulawesi

Phylogeographic research on endemic primates and amphibians inhabiting the Indonesian island of Sulawesi revealed the existence of seven areas of endemism (AoEs). Here, we use phylogenetic and population genetic analyses of one mitochondrial gene and 15 nuclear loci to assess geographic patterns of genetic partitioning in a shrew (Crocidura elongata) that is endemic to Sulawesi, but occurs across the island. We uncover substantial genetic diversity in this species both between and within AoEs, but we also identify close relationships between populations residing in different AoEs. One of the earliest divergences within C. elongata distinguishes a high-elevation clade from low-elevation clades. In addition, on one mountain, we observe three distinct genetic groups from low, middle, and high elevations, suggesting divergence along a single elevational gradient. In general, our results show that C. elongata, like several other Sulawesi endemic taxa, harbors extensive genetic diversity. This diversity is structured in part by known AoE boundaries, but also by elevational gradients and geographic isolation within AoEs.

Sperm morphology of the Rattini – are the interspecific differences due to variation in intensity of intermale sperm competition?

It is widely accepted that in mammals a causal relationship exists between postcopulatory sexual selection and relative testes mass of the species concerned, but how much it determines sperm size and shape is debatable. Here we detailed for the largest murine rodent tribe, the Rattini, the interspecific differences in relative testes mass and sperm form. We found that residual testes mass correlates with sperm head apical hook length as well as its angle, together with tail length, and that within several lineages a few species have evolved highly divergent sperm morphology with a reduced or absent apical hook and shorter tail. Although most species have a relative testes mass of 1-4%, these derived sperm traits invariably co-occur in species with much smaller relative testes mass. We therefore suggest that high levels of intermale sperm competition maintain a sperm head with a long apical hook and long tail, whereas low levels of intermale sperm competition generally result in divergent sperm heads with a short or non-existent apical hook and shorter tail. We thus conclude that sexual selection is a major selective force in driving sperm head form and tail length in this large tribe of murine rodents.