Does polyxenous symbiosis promote sympatric divergence? A morphometric and phylogeographic approach based on Oxydromus okupa (Annelida, Polychaeta, Hesionidae)

Abstract

The polychaete Oxydromus okupa lives in association with the bivalves Scrobicularia plana and Macomopsis pellucida in the intertidal of Río San Pedro (CI = Cádiz Intertidal) and adjacent to CHipiona (CH) harbour, and in the subtidal of the Bay of Cádiz (CS = Cádiz Subtidal). We analyse these populations morphometrically, ecologically (including infestation characteristics) and genetically (intertidal populations, 16S and ITS-1 genes). We consider “host”, “environment” and the combined “host and environment” as possible factors of interpopulation variability. Morphometry revealed three well-defined clusters for CI, CH and CS, showing intergroup phenotypic differences ranging from 35 to 50%. Hosts shell lengths ranged between 26 and 36 mm for S. plana and 20 and 28 mm for M. pellucida. The infestation of small M. pellucida by juvenile O. okupa suggests they show an active size segregation behaviour. The intertidal seems to be less favourable (infestation rate <25% vs. up to 65% in the subtidal), and did not show recent bottleneck events. Overall, CI and CH were genetically homogeneous, but showed a significant divergence (one dominant haplotype in each host species), suggesting host shift as being a soft barrier to gene flow. Most characters related with host-entering varied among populations, suggesting symbiotic behaviour to play a key role in reducing panmixia and leading to the initial phases of a speciation process in sympatric symbiotic populations. Polyxeny and symbiotic behaviour in O. okupa seem thus to be underlying mechanisms contributing to its great phenotypic variety, marked ecological differences, and genetic divergence.

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.…”

“…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, ). It is also effective in other taxonomic groups such as amphipods (Bastos‐Pereira & Ferreira, ; García‐Dávila, Magalhães, & Guerrero, ) or isopods (KamilarI & Sfenthourakis, ).…”

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).…”

Sleeping with the enemy: unravelling the symbiotic relationships between the scale wormNeopolynoe chondrocladiae(Annelida: Polynoidae) and its carnivorous sponge hosts

“…Among them, for instance, is the scarce information available about behavioural observations based on living organisms (e.g. Martín et al, 2015), the nature of the trophic links between host and symbiont (see: Martín & Britayev, 1998, 2018, and the phylogeographic and colonization patterns of the symbiont, limited to the best of our knowledge to just two recent contributions (Lattig et al, 2017;Meca et al, 2019). Difficulties in obtaining all this information are directly linked to the inherent limitations of studying marine benthic organisms, which is particularly true for deep-water species, whose collection and investigation are particularly challenging.…”