Chih-Han Chang

Belowground competition among invading detritivores

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.

Asian pheretimoid earthworms in North America north of Mexico: An illustrated key to the genera Amynthas , Metaphire , Pithemera , and Polypheretima (Clitellata: Megascolecidae)

The invasion of the pheretimoid earthworms in North America, especially the genera Amynthas and Metaphire, has raised increasing concerns among ecologists and land managers, in turn increasing the need for proper identification. However, the commonly used keys to this group are more than 30 years old with outdated taxonomic information and are based primarily on internal morphology. The requirement of significant amount of taxonomic expertise and dissection, even from the first entry of the key, has prevented broader use of these keys. As a result, many publications in the United States have used Amynthas spp. to represent the group without identifying the species. We present here a new key and diagnoses for the 16 pheretimoid earthworm species recorded in North America north of Mexico, including four genera: Amynthas (10), Metaphire (4), Pithemera (1), and Polypheretima (1). The descriptions were based on published records with modifications following inspection of specimens archived at the National Museum of Natural History, Smithsonian Institution, Washington, D.C. Photos of external and internal characters, including male pores, spermathecal pores, genital markings, spermathecae, prostate glands, and intestinal caeca, are presented to help identification. A summary of current knowledge about the ecology and historical context is provided for each species. We also highlight the previously overlooked and potentially common and widespread co-occurrence of three species-A. agrestis, A. tokioensis, and M. hilgendorfi-and point out that many recent claims of invasion of A. agrestis need to be re-evaluated for potential misidentification.

Molecular phylogeny and systematics of native North American lumbricid earthworms (Clitellata: Megadrili)

The family Lumbricidae is arguably the most well-known and well-studied earthworm group due to its dominance in the European earthworm fauna and its invasion in temperate regions worldwide. However, its North American members, especially the genus Bimastos Moore, 1893, are poorly understood. We revised the systematics of the genus Bimastos and tested the hypothesis of the monophyly of North American lumbricids using morphological characters and eight molecular markers. Phylogenetic analyses based on our extensive sampling of Bimastos and inclusion of Dendrodrilus and Allolobophoridella indicated a well-supported clade containing Bimastos and Eisenoides Gates, 1969, and provided the first evidence supporting that North American lumbricids are monophyletic. Assuming the available divergence time estimations and dating of land bridges are correct, it would suggest that the ancestor of this clade arrived North America through Beringia or the De Geer route during Late Cretaceous, and since then the clade has diverged from its Eurasian sister group, Eisenia. The peregrine genera Dendrodrilus and Allolobophoridella are nested within the Bimastos clade; we propose to treat them as junior synonyms of the genus Bimastos, and, contradictory to the commonly held belief of being European, they are indeed part of the indigenous North American earthworm fauna. Morphological characters, such as red-violet pigmentation, proclinate U-shaped nephridial bladders and calciferous diverticula in segment 10 further support this placement. The East Mediterranean–Levantine Spermophorodrilus Bouché, 1975 and Healyella Omodeo & Rota, 1989 are nested within the Dendrobaena sensu lato clade; therefore their close relationship with the North American Bimastos is refuted. Species fit the revised diagnosis of Bimastos are reviewed and keyed, and a new species, Bimastos schwerti sp. nov., is described.

Continuous 13C and 15N Labeling of Tree Litter using a Climate-Controlled Chamber

Substrates with a unique stable isotope signature provide researchers with the ability to trace nutrients through food webs. Plant material labeled with carbon (13C) can be produced by exposure to carbon dioxide (CO2) with an isotopic composition that differs from ambient conditions during photosynthesis. Labeling can occur continuously or be repeated over several “pulses.” Each method has a high cost either in the form of expensive control systems or significant time investments. In 2012, we built a large growth chamber and used an inexpensive, open-source ArduinoTM microcontroller to monitor and control interior conditions so that we could produce leaf litter dually enriched in 13C and nitrogen (15N) for future incubation experiments. We performed a labeling experiment on 73 saplings representing seven species in 2012 and repeated the labeling on 30 saplings of one species in 2013. We successfully produced over 1 kg of litter enriched in both isotopes; 15N-enrichment (δ15N: 759.2 ± 133.7‰) was much greater than 13C (δ13C: 11.2 ± 3.4‰). Roots (161.0 ± 8.6‰) were much more enriched in 13C than litter (11.2 ± 3.4‰), indicating significant translocation of newly fixed carbohydrates. Some species allocated more resources toward their leaves as trees with the most enriched litter had the least enriched roots. 13C litter enrichment in 2012 was at the lower end of the range reported by similar studies; however, litter from trees labeled over two seasons achieved a higher level of enrichment (401.4 ± 65.5‰).

Earthworms (Annelida: Clitellata) of Plummers Island, Maryland, U.S.A., with description of a new species

Abstract The earthworm fauna of Plummers Island, Maryland, U.S.A. was surveyed, recording a total of 12 species belonging to the families Lumbricidae, Acanthodrilidae, Megascolecidae, and Sparganophilidae. In addition to the well known peregrine lumbricids and megascolecids the island harbors four North American endemic species: Eisenoides lonnbergi (Michaelsen, 1894) (Lumbricidae), Sparganophilus tamesis Benham, 1892 (Sparganophilidae), Diplocardia caroliniana Eisen, 1899, and furthermore, a new species, Diplocardia zicsii sp. nov. (Acanthodrilidae).

Two new earthworm species of the genus Drawida (Oligochaeta: Moniligastridae) from southwestern Taiwan

This study describes two new species of earthworms belonging to the genus Drawida (Oligochaeta: Moniligastridae) from southwestern Taiwan. They are Drawida alishanensis sp. nov. and Drawida fenqihuensis sp. nov. The two species were found at elevations of 1407-1661 m in the Alishan area, Chiayi County. DNA barcodes from type specimens of the new species are reported. This is the first time that new species of Drawida are discovered from the island of Taiwan. In addition, Drawida keikiensis Kobayashi, 1938 from Korea is found to be synonymous with Drawida syringa Chen, 1933 from central China. The synonymy of Drawida glabella Chen, 1938 with Drawida barwelli (Beddard, 1886) is rejected.

Litter quality, dispersal and invasion drive earthworm community dynamics and forest soil development

In temperate deciduous forests of eastern USA, most earthworm communities are dominated by invasive species. Their structure and functional group composition have critical impacts on ecological properties and processes. However, the factors determining their community structure are still poorly understood, and little is known regarding their dynamics during forest succession and the mechanisms leading to these changes. Earthworm communities are usually assumed to be stable and driven by vegetation. In contrast, the importance of dispersal and ecological drift is seldom acknowledged. By analyzing a 19-year dataset collected from forest stands in eastern USA, we demonstrated that on a decadal timescale, earthworm community dynamics are shaped by the interplay of selection, dispersal, and ecological drift. We highlighted that forests at different successional stages have distinct earthworm species and functional groups as a result of environmental filtering through leaf litter quality. Specifically, young forests are characterized by soil-feeding species that rely on relatively fresh soil organic matter derived from fast-decomposing litter, whereas old forests are characterized by those feeding on highly processed soil organic matter derived from slow-decomposing litter. In addition, year-to-year species gains and losses are primarily driven by dispersal from regional to local species pools, and by local extinction resulted from competition and ecological drift. We concluded that with continued dispersal of European species and the recent “second wave” of earthworm invasion by Asian species from the surrounding landscape, earthworms at the investigated forests are well-established, and will remain as the major drivers of soil development for the foreseeable future.

Four new earthworm species of the genus Amynthas (Megascolecidae: Oligochaeta) from southwestern Taiwan with re-description of Amynthas tungpuensis Tsai, Shen and Tsai, 1999

ABSTRACT This study describes four new species of earthworms belonging to the genus Amynthas (Megascolecidae: Oligochaeta) from southwestern Taiwan. They are Amynthas quadriorbis sp. nov., Amynthas douliouensis sp. nov., Amynthas tsou sp. nov. and Amynthas dinghuensis sp. nov. The former three species are sexthecate with three pairs of spermathecal pores in 6/7–8/9 whereas A. dinghuensis is a small, octothecate earthworm with four pairs of spermathecal pores in 5/6–8/9. Amynthas quadriorbis and A. douliouensis were found in the foothills at elevations < 250 m near Douliou, Yunlin, whereas A. tsou and A. dinghuensis were from elevations of 1400–1664 m in the Alishan area, Chiayi. Amynthas quadriorbis has four large genital papillae in the male pore region. Amynthas douliouensis has paired genital papillae in presetal VIII–X and simple male pore structure. Amynthas tsou has paired genital papillae in presetal VIII–IX and male porophore with or without an anterior, posteromedial, or one anteromedial and one posteromedial papillae. Amynthas dinghuensis has two pairs of genital papillae medial to male porophores in postsetal XVII and presetal XIX. In addition, re-description of Amynthas tungpuensis, an endemic earthworm widely distributed in western Taiwan, is given. DNA barcodes (a 658-base-pair section of the mitochondrial cytochrome c oxidase subunit I gene) of the four new species and of A. tungpuensis are also reported.