Another brick in the wall: population dynamics of a symbiotic species of Oxydromus (Annelida, Hesionidae), described as new based on morphometry

Abstract

Oxydromus humesi is an annelid polychaete living as a strict bivalve endosymbiont (likely parasitic) of Tellina nymphalis in Congolese mangrove swamps and of Scrobicularia plana and Macomopsis pellucida in Iberian saltmarshes. The Congolese and Iberian polychaete populations were previously considered as belonging to the same species, the latter showing regular distribution, intra-specific aggressive behaviour, and complex hostentering behaviour. The fresh Iberian samples enabled us to undertake consistent morphometric analyses, as well as to further analyse the characteristics of the association and the population dynamics of the Iberian population hosted by S. plana. Among the morphological differences between the Congolese and Iberian specimens, leading to the description of the latter as Oxydromus okupa sp. nov., the most important are: 1) longer cephalic appendages, 2) greater distance between the eyes, 3) larger dorsal cirrostyle in relation to the corresponding dorsal lobe and cirrophore. Moreover, dorsal and ventral lobes are similar in length, with the tip of the former reaching the tip of the latter in O. okupa sp. nov., while the dorsal lobe is much shorter than the ventral one in O. humesi. Mature adults of O. okupa sp. nov. occurred during the whole study period, with a higher percentage of ripe females in spring and, particularly, in summer. Numerous host specimens showed the symbiont’s most preferred shell length (>26 - 36 mm). However, the prevalence was very low (usually <5%) and showed a clear seasonal pattern, being lower during spring/summer. This suggests that males are able to leave their hosts during this period, most likely to improve fertilization by directly entering or approaching a host occupied by a ripe female, while females usually remain inside. Based on the new results, the current knowledge of symbiotic Hesionidae and their relationships with invertebrate hosts is updated and discussed.

Molecular and morphometric analyses identify new lineages within a large Eumida (Annelida) species complex

“…Previous morphometric studies among polychaetes have been used independently of molecular analyses to successfully resolve the taxonomy of several cryptic complexes or very similar species, often leading to the description of new species. A few extra steps to this type of methodology were first added by Ford and Hutchings () and more recently by Martin et al () and Meca et al () with the incorporation of statistical dissimilarities derived from the SIMPER routine of the PRIMER software (Clarke & Warwick, ) based on a matrix of morphometric measurements in order to distinguish between morphologically similar species. Our results succeeded in separating three of the four lineages through the PCA analysis.…”

“…WW and WWP were measured from the worm's widest part, usually from either segment 27 or 40 depending on the worm size. The distance between the eyes was measured from the centre of the eyespots to avoid possible different individual responses to fixation as is the case of hesionids in Martin et al ().…”

“…True cryptic species have no consistent morphological differences; however, some slight variations in the size and shape of key morphological characters can be further explored by quantitative morphometric analysis to complement the molecular data. Martin, Meca, Gil, Drake, and Nygren () were able to separate and delineate two distinct lineages from the symbiotic species Oxydromus humesi (Pettibone, 1961) (family Hesionidae) corresponding to Congolese and Iberian populations based on morphometric information alone. Other studies applied similar protocols in a variety of different polychaete groups (Coutinho, Paiva, & Santos, ; Ford & Hutchings, ; Lattig, San Martín, & Martin, ; Meca, Drake, & Martin, ).…”

Updating the current knowledge on the relationships between Haplosyllis chamaeleon Laubier, 1960 (Annelida, Syllidae) and Paramuricea clavata (Risso, 1826) (Cnidaria, Plexauridae) in the Mediterranean Sea

“…According to Lattig and Martin (2009), the main morphological traits were measured on well-preserved, complete polychaete specimens (from Portofino, Cap of Creus and the Chafarinas Archipelago); 36 specimens for body measurements and six specimens for dorsal cirri length pattern (as number of antennae and cirri articles) were placed on slides with glycerine and measured using a micrometric scale. The inter-population morphometric differences were analysed for size-independent data (by dividing all individual measurements by their respective body width) according to Martin et al (2017) and Meca et al (2019). All data were normalised prior to the analyses.…”

“…Data ordinations were performed by principal component analysis (PCA) and the significance of the obtained clusters was assessed by one-way analyses of similarity (ANOSIM) based on Euclidean distance resemblance matrices, both for the main body measurements and for the dorsal cirri length pattern. The morphometric characters most contributing to the average inter-population differences were estimated and shown as percentages according to Martin et al (2017) and Meca et al (2019). PCA and ANOSIM were executed with PRIMER, version 6.1.11, copyright by PRIMER-E Ltd. 2008 (Clarke and Warwick 2001;Clarke and Gorley 2006).…”