Robin S. Wilson

Commonness and rarity in the marine biosphere

Significance Tests of biodiversity theory have been controversial partly because alternative formulations of the same theory seemingly yield different conclusions. This has been a particular challenge for neutral theory, which has dominated tests of biodiversity theory over the last decade. Neutral theory attributes differences in species abundances to chance variation in individuals’ fates, rather than differences in species traits. By identifying common features of different neutral models, we conduct a uniquely robust test of neutral theory across a global dataset of marine assemblages. Consistently, abundances vary more among species than neutral theory predicts, challenging the hypothesis that community dynamics are approximately neutral, and implicating species differences as a key driver of community structure in nature. Explaining patterns of commonness and rarity is fundamental for understanding and managing biodiversity. Consequently, a key test of biodiversity theory has been how well ecological models reproduce empirical distributions of species abundances. However, ecological models with very different assumptions can predict similar species abundance distributions, whereas models with similar assumptions may generate very different predictions. This complicates inferring processes driving community structure from model fits to data. Here, we use an approximation that captures common features of “neutral” biodiversity models—which assume ecological equivalence of species—to test whether neutrality is consistent with patterns of commonness and rarity in the marine biosphere. We do this by analyzing 1,185 species abundance distributions from 14 marine ecosystems ranging from intertidal habitats to abyssal depths, and from the tropics to polar regions. Neutrality performs substantially worse than a classical nonneutral alternative: empirical data consistently show greater heterogeneity of species abundances than expected under neutrality. Poor performance of neutral theory is driven by its consistent inability to capture the dominance of the communities’ most-abundant species. Previous tests showing poor performance of a neutral model for a particular system often have been followed by controversy about whether an alternative formulation of neutral theory could explain the data after all. However, our approach focuses on common features of neutral models, revealing discrepancies with a broad range of empirical abundance distributions. These findings highlight the need for biodiversity theory in which ecological differences among species, such as niche differences and demographic trade-offs, play a central role.

Phylogeny of nereidids (Polychaeta, Nereididae) with paragnaths

A phylogenetic analysis was conducted of the Nereidinae — those members of the Nereididae (Polychaeta) with pharyngeal paragnaths. We had two objectives: to test the monophyly of currently accepted genera, subgenera and informal subgeneric groupings within the Nereidinae, and, if warranted, to propose a more natural classification of the Nereidinae. Parsimony analyses were undertaken, including 52 terminal taxa from all genera and informal groupings from the large heterogeneous genera Nereis, Ceratonereis, Neanthes and Perinereis. Analyses of a character set of 52 informative characters yielded more than 10 000 equally parsimonious trees with a length of 176 steps (consistency index [CI] = 0.34, retention index [RI] = 0.66). Reweighting three times resulted in 445 most parsimonious trees with length 54.62 (CI = 0.59, RI = 0.79). Many characters widely used in nereidid systematics were found to exhibit high levels of homoplasy. The most parsimonious trees could not be rooted such that the selected ingroup, ‘Nereididae with paragnaths’, was monophyletic, causing us to reject the monophyly of the Nereidinae as currently defined. The following genera were well supported by the parsimony analyses and are newly diagnosed: Alitta, Ceratonereis, Pseudonereis, Simplisetia, Solomononereis and Unanereis. Alitta succinea, Pseudonereis cortezi, Pseudonereis noodti and Pseudonereis pseudonoodti are proposed as new combinations. The parsimony analysis supported the monophyly of neither Composetia, Neanthes, Nereis and Perinereis nor of any new groupings of remaining species presently placed in those genera. It is these poorly supported genera that comprise most species of Nereididae.

Redescription of the Indo-Pacific polychaete Neanthes pachychaeta (Fauvel, 1918) n. comb. (Annelida, Phyllodocida, Nereididae) and its synonyms

Glasby C. J., Wilson R. S. & Bakken T. 2011. — Redescription of the Indo-Pacific polychaete Neanthes pachychaeta (Fauvel, 1918) n. comb. (Annelida, Phyllodocida, Nereididae) and its synonyms. Zoosystema 33 (3): 361–375. ABSTRACT Type specimens of three Indo-west Pacific nereidid polychaetes are redescribed: Ceratonereis pachychaeta Fauvel, 1918, Nereis (Ceratonereis) ramosa Horst, 1919 and Nereis (Lycoris) anchybchaeta Horst, 1924. No significant morphological differences were found between the three species. The latter two names are therefore relegated to junior synonymy with the oldest, C. pachychaeta. A lectotype is identified from among the syntypes of C. pachychaeta in order to stabilise the name and type locality of the species. Further, C. pachychaeta is newly transferred to the genus Neanthes, based on a comparison of generic level features, especially the presence of paragnaths on the oral ring. Newly collected specimens of Neanthes pachychaeta n. comb, from Indonesia, Philippines, northern Australia, Japan and French Polynesia are described and the living coloration reported for the first time. Apart from its striking red-orange colour, the species may be recognised by having paragnaths atop a plate-like basement and thick, hammer-headed fused falcigers in posterior parapodia. The new material and new synonymies give N. pachychaeta n. comb, a widespread Indo-Pacific distribution.

Clavadoce (Annelida: Phyllodocidae) from Australia.

The first records of the phyllodocid genus Clavadoce are provided from Australia, where the fifth species in the genus is now known: Clavadoce dorsolobata (Hartmann-Schröder, 1987) comb. nov. which is widely distributed in intertidal habitats in southeastern Australia. Clavadoce dorsolobata was described as Eumida (Sige) dorsolobata Hartmann-Schröder, 1987 and herein transferred to Clavadoce. Five species of Clavadoce are now known world wide, four of which are from different regions on the Pacific Ocean margin, while Clavadoce cristata is from the North Atlantic. The Australian species is the first record of Clavadoce for the southern hemisphere.