Morphological and molecular identification of the dioecious "African species Volvox rousseletii (Chlorophyceae) in the water column of a Japanese lake based on field-collected and cultured materials.

Ryosuke Kimbara,Hiroko Kawai-Toyooka,Masanobu Kawachi,Hisayoshi Nozaki,Ryo Matsuzaki,Nanako Isaka,James G Umen

doi:10.1371/journal.pone.0221632

Ryosuke Kimbara, Hiroko Kawai-Toyooka + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0221632

Copy DOI

Abstract

Volvox rousseletii is a dioecious species belonging to Volvox sect. Volvox that has previously only been found in Africa. During field surveys in a large dam lake (Lake Sagami) in Kanagawa Prefecture, central Japan, we encountered a Volvox sect. Volvox species that produces dioecious sexual spheroids in the water column. Although sexual induction of this species in culture did not produce adequately well-developed sexual spheroids for species identification, molecular data directly obtained from field-collected sexual spheroids verified the identity of field-collected male and female sexual spheroids as well as cultured materials. Based on molecular and morphological data, the species was identified as V. rousseletii. This is the first record of a dioecious species of Volvox sect. Volvox in Japan.

Highlights

IntroductionVolvox is a morphologically interesting group of green algae due to the presence of thick cytoplasmic bridges between constitutive cells and spines on the zygote walls [1,2]
Mature asexual spheroids in culture were ovoid in shape with a broad posterior pole, measured 331–423 μm wide and 352–476 μm long, and contained 4700–11,800 cells embedded in individual sheaths at the periphery of the gelatinous matrix (Fig 1A and 1B)
The present combined data set from field-collected and cultured materials of a Volvox species distributed in a Japanese lake demonstrated the occurrence of V. rousseletii, which has previously only been reported from Africa [1,6]

Summary

Introduction

Volvox is a morphologically interesting group of green algae due to the presence of thick cytoplasmic bridges between constitutive cells and spines on the zygote walls [1,2]. This section of Volvox includes seven monoecious and three dioecious species [3,4,5]. Three of the monoecious species, V. globator, V. barberi, and V. capensis, are found on at least two different continents [1,3,4], records of the dioecious species of this section are not as frequent, and each has previously only been found in a small area of a single continent [1,5,6]. In Japan, at least two monoecious species of Volvox sect. Dioecious species of this section have not previously been recorded from Japan

Methods

Results

Discussion

Conclusion