Morphological Distinction of Three Ammonia Phylotypes Occurring Along European Coasts

Abstract

The high morphological variability observed in the genus Ammonia, together with its global distribution, led to the description of a plethora of species, subspecies, and varieties. Until now, many researchers used a limited number of (morpho-)species, and considered the numerous varieties as ecophenotypes. Recently, molecular studies show that these putative ecophenotypes are, in reality, well-separated genetically and should rather be considered as separate species. This study aims to investigate the morphological characteristics of three phylotypes (T1, T2, and T6) belonging to the genus Ammonia, encountered along European coasts. For this purpose, Ammonia specimens were sampled at 22 locations between 2014 and 2016 and were imaged using an environmental SEM (Scanning Electron Microscope). For 96 specimens, images of the spiral, umbilical, and peripheral sides were obtained and pore features were investigated using 1000x magnified images of the penultimate chamber on the spiral side. Sixty-one morphometric parameters were measured for each individual. To assign specimens to their respective phylotypes, we employed molecular analyses using SSU (Small Sub-Unit) rDNA fragments. A multivariate approach (Factorial Analysis of Mixed Data, FAMD), allowing the joint analysis of quantitative and qualitative measurements, was used to determine the most reliable morphometric parameters to discriminate the three phylotypes. Our results show that the use of only two morphological characteristics is sufficient to differentiate the three pseudocryptic species: the raised or flush character of the sutures on the central part of the spiral side and the mean pore diameter. These two criteria, which can be observed with a standard stereomicroscope, provide an efficient method to discriminate T1, T2, and T6 with at least 90% accuracy. We consider that there is still insufficient information to reliably assign previously defined formal scientific names to the three phylotypes, and therefore we recommend the continued use of phylotype designations T1, T2, and T6. Our results make it possible to study the distribution of these three pseudocryptic species (T1, T2, and T6) on the basis of stereomicroscope examination alone, which means these species can also be more easily recognized in dead/fossil assemblages. Among other things, this will allow verification in sediment cores of the putative recent introduction in European coastal areas of T6, which is often considered an exotic species originating from East Asia.

Scaling laws explain foraminiferal pore patterns

“…The range of pore radii measured on the spiral face (SEM images) shows that the three Ammonia sp. phylotypes T1, T2 and T6 39,40 are mixed in the present data set 41 .…”

“…As shown by Richirt et al . 41 , the phylotype T2 seems unable to attain a porosity higher than 20% and a mean pore radius larger than 0.7 µm (Figs 3–5, left cluster). T1 and T6 are able to attain higher overall porosity with upper limits of about 25% and 30% and a mean pore radius larger than 1.25 µm and 1.8 µm respectively (Figs 3–5, right cluster).…”

Foraminiferal community response to seasonal anoxia in Lake Grevelingen (the Netherlands)

“…Their sequences were deposited on GenBank (accession numbers MN190684 to MN190690) and Supplementary Figure 1 shows Scanning Electron Microscope (SEM) images of the spiral side and of the penultimate chamber at 1000x magnification for four individuals. A morphological screening based on the criteria proposed by Richirt et al (2019) confirmed that T6 accounts for the vast majority (>98 %) of Ammonia individuals, whereas T1, T2, T3 and Ammonia falsobeccarii are only present in very small amounts (Supplementary Table 3).…”

Checklist, assemblage composition, and biogeographic assessment of Recent benthic foraminifera (Protista, Rhizaria) from São Vincente, Cape Verdes

“…Darling et al, 2016). Once these characters are disclosed, they may be used to discriminate morphotypes representing a single OTU (Roberts et al 2016;Kucera et al 2017;Richirt et al 2019). We therefore attempted to discern the species up to a comprehensible level, in particular miliolids that were previously lumped as "Quinqueloculina spp.".…”