Morphogenetic Observations on Monostroma

Occurrence, basic cultural characteristics, sex ratio and morphogenetics of Monostroma in Uranouchi Inlet and Ukibuchi of Tosa Bay, Pacific ocean. Felix bast , Usa Marine Biological Institute, 781-1161, Japan April-August 2006

Introduction to the habitat and life cycle

Introducing the genus Monostroma Class Ulvophyceae, Order: Codiolales - Morphology

Thalli can grow up to 20cm high and are irregularly undulate and folded.

Basal part has rhizoids to attach with the substratum.

Introducing the genus Monostroma – Cell structure

Multicellular thall us consists of single layer of cells.

Each cell has one cup shaped chloroplast with single pyrenoid

50µm 10µm

Introducing the genus Monostroma - Habitat

Monostroma grows attached to the inter-tidal rocks

Found in warm seas of temperate and subtropics

Introducing the genus Monostroma - Distribution

Arctic : Canada (Arctic) ( Taylor 1957 ).

Asia : Japan ( Yamada 1938 ) India ( G.Deshmukhe, 1998 ), Commander Islands ( Selivanova & Zhigadlova 1997 )

Europe : Britain ( Batters 1902 , Newton 1931 , Burrows 1991 , Hardy & Guiry 2003 ), Ireland ( Adams 1907 , Guiry 1978 , Morton 1994 ), Faroes ( Irvine 1982 , Nielsen & Gunnarsson 2001 ), France ( Feldmann 1954 , Coppejans 1995 ), Helgoland ( Bartsch & Kuhlenkamp 2000 ), Iceland ( Caram & Jónsson 1972 ), Ireland ( Batters 1902 , Adams 1907 , Cotton 1912 , Guiry 1978 , De Valéra et al. 1979 , Morton 1994 ), Italy ( Furnari , Cormaci & Serio 1999 ), Netherlands ( Stegenga & Mol 1983 , Stegenga et al. 1997 ), Norway ( Rueness 1997 ), Sweden ( Tolstoy & Österlund 2003 ).

Atlantic Islands : Azores ( Neto 1994 ).

North America : Alaska ( Lindstrom 1977 , Scagel et al. 1989 ), British Columbia ( Scagel et al. 1989 ), California ( Abbott & Hollenberg 1976 , Scagel et al. 1989 ), New Brunswick ( Taylor 1957 ), New York ( Taylor 1957 ), Oregon ( Hansen 1997 ), Quebec ( Taylor 1957 ), Washington ( Scagel et al. 1989 ).

South America : Chile ( Ramírez & Santelices 1991 ).

Africa : Morocco ( Benhissoune , Boudouresque & Verlaque 2001 ).

Antarctic and the subantarctic islands : Antarctica ( Papenfuss 1964 ).

Life cycle

Five different types of Life cycles have been observed

On the basis of life-cycle and thallus ontogeny there are some 14 subdivisions of Monostroma are classified

Dimorphic sexual

Alternation of generations

Macroscopic gametophyte,Microscopic sporophyte

Monostroma nititum

Monostroma latissimum

Dimorphic sexual

Macroscopic sporophyte

Microscopic gametophyte -discoid thalli

Monostroma zostericola

Dimorphic asexual

Mature thallus and cyst are asexual

Quadriflagellate swarmers and quadriflagellate zoospores

Monostroma undulatum

Monomorphic sexual

Gametophyte and sporophyte are identical

Monostroma grevillei

Monomorphic asexual

Bi/quadri flagellate asexual swarmers develops to thalli

No Alternation

Monostroma oxyspermum

Cultural characteristics

Study area, Usa Latitude = 33.436384 Longitude = 133.440371

Temperature

Temperature was measured with analogue thermometer, in-situ.

Usa Site 1, May 16

Temperature variation

Salinity Variation

24 Hrs change in ambient water temperature and salinity at sites on 07-28

Tidal graph showing sampling times 曇り気温（℃） 31 – 26 降水確率 30 ％）天気

Thalli collection

Seasonal changes in Thalli length: S1 and S2

Seasonal changes in Thalli length: S4 and S5

Study Area: Ukibuchi Lat 33.035678 , Long: 133.034445

Seasonal changes in Thalli length: Ukibuchi

Sex ratio at 4 sites

Salinity tolerance S1 S4

Standardization A1 A2 5 4 3 45 µmolphotons/m 2 /s Light Intensity S1 Thallus PES (S1) Media

Salinity tolerance S1 samples were found to be more tolerant to the salinity.

Morphogenetic observations in unidentified Monostroma islolated from Usa, Tosa.

Summary of findings

Unknown monostroma is observed to be having dimorphic diplo-haplontic life-cycle (alternation of generation) with microscopic sporophyte and macroscopic gametophyte (similar to M nitidum )

Thallus ontogeny appears to be different from M nitidum ( absence of saccate stage intermediate from erect filament to monostromatic membrane)

Summary of findings

Settled gametes undergo parthenogenesis which is morphogenetically identical to zygote development

A unique shunting-bypass is observed for a part of female gamete parthenogenesis , that has not been reported elsewhere.

Zygote development illustration

Fertilization

Anisogamy occurres between gametes released from dioicious thalli.

10 µm 10 µm

Plano zygotes 10 µm

Zygote development illustration

Zygote settlement and development 10µm 10µm In 48 hrs planozygotes lose flagella and settle down the substratum.

Zygote settlement and development 10µm 10µm Distal end swollen to form a new cell, in 7 days by taking various shapes.

Zygote settlement and development 10µm 10µm 10µm Pyrinoid In 1 month most are elliptical and starts forming cysts.

Sporophyte 10µm 10µm Complete maturation of sporophyte takes very long time, 6-8 months.

Sporophyte maturation 10µm 10µm S hape of sporophyte slightly elongate. Upon acquiring motility, zoospores swim away.

Zoospore release Have 4 flagella of same length. Does not have eye spots. 10 µm 10 µm

Zoospore development illustration

Settled zoospore and germination In about 10 Days, first transverse cell division happens. 10 µm 10 µm

Development of zoospore, 4 cell stage 15 days old culture. Thalli appears to have 3D structure 10µm 10µm

Development of zoospore, 8 cell stage 20 days old (after zoozpore release from sporophyte) culture 10µm 10µm

Further development of zoospore 3 dimensional erect filament. 30 days old culture 10 µm 10 µm

Formation of microscopic thalli Basal tissue (arrow head) develops into rhizoid. 60 days old culture. 100µm 10 µm

Parthenogenesis

Settled male and female gametes undergo parthenogenesis, exactly similar to the zygote maturation

A ratio of female gametes undergo shunting-bypass such that they directly develop into thalli with out sporophytic stage. This process have not been observed in male gametic parthenogenesis.

Limitations of this study