Asexual reproduction and heterozygote selection in an Antarctic demosponge (Stylocordyla chupachus, Suberitida)

M Carella,G Agell,M J Uriz

doi:10.1007/s00300-018-2436-9

M Carella, G Agell + Show 1 more

Open Access

https://doi.org/10.1007/s00300-018-2436-9

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Journal: Polar Biology	Publication Date: Nov 24, 2018
Citations: 2	License type: open-access

Affiliation: Centre d'Estudis Avançats de Blanes

Abstract

Antarctic bottoms harbor stable, benthic communities, subjected to low temperatures. Environmental stability may promote the asexual (clonal) reproduction of sponges to maintain adapted genotypes to those particular conditions. Stylocordyla chupachups forms patchy populations across the Antarctic continental shelf. Individuals are mostly similar in size without distinct cohorts, which indicates fast growth of the new recruits. Settlement of incubated (clonal?) functional sponges may accelerate sponge growth and success at early colonization phases. To analyze the weight of clonal reproduction in the species, a genetic study was performed on three close populations using eight polymorphic microsatellite loci that were designed from massive sequencing. The three study populations showed a relatively low genetic diversity and low loci polymorphism (from 2 to 6 alleles). The estimators of genetic structure, the Analysis of the Molecular Variance (AMOVA), and the presence of private alleles indicated low but significant structure between the populations. A relatively high rate of asexual reproduction (ca. 25% of the individuals) was detected. The program MLGsim found five identical multilocus genotypes (MLGs) with an asexual origin. An excess of heterozygotes (in five out of the eight loci genotyped) was found, which suggests a positive selection mechanism for heterozygotes. The relatively high rates of asexual reproduction may be the result of adaptation to the environmental stability, while heterozygote selection would help maintain some genetic diversity in the populations. S. chupachups has been reported to be one of the first sponge species recolonizing bare areas resulting from iceberg scouring, which indicates a high species fitness and adaptation to Antarctic bottoms. Two out of the three study populations showed bottleneck, which may indicate a recent founder effect and supports the pioneer nature of this species.

Highlights

Sponges are one of the most important taxa in terms of diversity and abundance in marine benthic ecosystems (Gili and Coma 1998)
We developed a set of microsatellite markers by sequencing from a part of the Stylocordyla chupachups genome, following the protocol in Guardiola et al (2016), analyzed their suitability for a population genetics’ study, and used these markers for assessing the extent of clonal reproduction in this sponge
Sequences were analyzed with the open-access program QDD v0.2.1 (Meglécz et al 2010), which is a useful tool for the discovery and selection of microsatellites, and for primer design

Summary

Introduction

Sponges are one of the most important taxa in terms of diversity and abundance in marine benthic ecosystems (Gili and Coma 1998) They are even more abundant in the Antarctic region, where sponges dominate many benthic communities between 100 and 200 m of depth, and account for ca. Global warming is weakening Antarctic barriers (Bromwich et al 2013; Duffy et al 2017; Griffiths et al 2017), the Antarctic continental shelf presents extreme low temperatures These features may have contributed to the biogeographic isolation of many Antarctic invertebrates such as sponges, promoting a high degree of species endemism in the area (Sarà et al 1992; McClintock 2005; Ríos 2006), which has been calculated to range from 43 to 68%, depending on the sponge Class (Downey et al 2012)

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