Does sediment composition sort kinorhynch communities? An ecomorphological approach through geometric morphometrics

Diego Cepeda,Fernando Pardos,Nuria Sánchez,Dolores Trigo

doi:10.1038/s41598-020-59511-4

Diego Cepeda, Fernando Pardos + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-59511-4

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Abstract

Ecomorphology studies the relationship between organisms’ morphology and environment features. To better understand whether the shape of the body and the appendages involved in the movement is correlated to sediment composition in meiofaunal organisms, we study the evolved morphological adaptations to environment in selected taxa of the phylum Kinorhyncha: the allomalorhagid families Dracoderidae and Pycnophyidae, and the cyclorhagid genus Echinoderes. The selected taxa include the most diverse groups of Kinorhyncha worldwide, representing the 75.5% of the total phylum diversity. Widened, plump bodies and lateral terminal spines may be adaptive for species living in coarse, more heterogeneous sediments, as they could maintain a more powerful musculature to actively displace the sediment grains applying a greater force. Conversely, slender, vermiform bodies and lateral terminal spines would represent an adaptation of species inhabiting fine, more homogeneous sediments where there would not be much need to exert a high force to displace the sediment particles, and a more vermiform shape would even favour the burrowing of the animal through the smaller interstices. The studied kinorhynch taxa would also be adapted to the higher velocity of the sea-water and the intense erosion and transportation of heterogeneous sediments by possessing more robust bodies, avoiding getting laid off substratum under these conditions. These findings provide evolutionary evidence that body shape in the studied kinorhynch groups is adapted to environment.

Highlights

Morphological adaptations are frequently a response of ecological pressures and changes in environmental variables[1,2]
Most interstitial taxa are stouter and plumper in finer sediments where they need to dig through the sediment particles or live as sediment dwellers near the surface, whereas slender, vermiform species tend to inhabit in coarser sediments where they can move more through the interstitial space[12,13,14,15]
Meiofaunal organisms are tremendously dependent of sediment and reveal the effect of sediment structure and composition on morphology as crucial to better understand animals-habitat interactions

Summary

Introduction

Morphological adaptations are frequently a response of ecological pressures and changes in environmental variables[1,2]. Burrowing meiofauna (e.g. loriciferans, most kinorhynchs and ostracods, and some annelids, harpacticoid copepods and nematodes), that moves by active displacement of the sediment, is more frequent in finer sediments, and relationships between grain size and body shape are much more uncharted[16,17,18]. The hydrogen ion concentration (pH) is of relevance in meiobenthic ecology as it can induce morphological deformations and act as limiting factor for many organisms[8,23] In this regard, kinorhynchs are an ideal model to study morphology-sediment relationships since this phylum is mainly composed of burrowing meiofaunal species that inhabit a wide variety of oceanic soft sediments[24,25]. Primary spinoscalids are used by kinorhynchs to actively move through the sediment[24,25], whereas the LTS, of still unclear function, are in constant contact with the sediment, being very conspicuous and large in most of the groups and forced to move through the sediment particles

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