Phylogenetic analysis of algal symbionts associated with four North American amphibian egg masses

PLoS One. 2014 Nov 13;9(11):e108915. doi: 10.1371/journal.pone.0108915. eCollection 2014.

Abstract

Egg masses of the yellow-spotted salamander Ambystoma maculatum form an association with the green alga "Oophila amblystomatis" (Lambert ex Wille), which, in addition to growing within individual egg capsules, has recently been reported to invade embryonic tissues and cells. The binomial O. amblystomatis refers to the algae that occur in A. maculatum egg capsules, but it is unknown whether this population of symbionts constitutes one or several different algal taxa. Moreover, it is unknown whether egg masses across the geographic range of A. maculatum, or other amphibians, associate with one or multiple algal taxa. To address these questions, we conducted a phylogeographic study of algae sampled from egg capsules of A. maculatum, its allopatric congener A. gracile, and two frogs: Lithobates sylvatica and L. aurora. All of these North American amphibians form associations with algae in their egg capsules. We sampled algae from egg capsules of these four amphibians from localities across North America, established representative algal cultures, and amplified and sequenced a region of 18S rDNA for phylogenetic analysis. Our combined analysis shows that symbiotic algae found in egg masses of four North American amphibians are closely related to each other, and form a well-supported clade that also contains three strains of free-living chlamydomonads. We designate this group as the 'Oophila' clade, within which the symbiotic algae are further divided into four distinct subclades. Phylogenies of the host amphibians and their algal symbionts are only partially congruent, suggesting that host-switching and co-speciation both play roles in their associations. We also established conditions for isolating and rearing algal symbionts from amphibian egg capsules, which should facilitate further study of these egg mass specialist algae.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ambystoma / physiology*
  • Animals
  • Base Sequence
  • DNA, Plant / genetics
  • DNA, Ribosomal / genetics
  • Genetic Variation / genetics
  • Molecular Sequence Data
  • North America
  • Ovum / physiology*
  • Phylogeny
  • RNA, Ribosomal, 18S / genetics
  • Ranidae / physiology*
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Symbiosis / physiology*
  • Volvocida / genetics
  • Volvocida / physiology*

Substances

  • DNA, Plant
  • DNA, Ribosomal
  • RNA, Ribosomal, 18S

Grant support

This study was supported by the Natural Sciences and Engineering Research Council of Canada - Discovery Grant to CB (http://www.nserc-crsng.gc.ca/professors-professeurs/grants-subs/dgigp-psigp_eng.asp). EK and RK were funded by startup grants by their respective institutions, which are intramural by definition. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.