from Holocene sediments of Lake Zeribar

Biologia 63/2: 162—166, 2008 Section Botany DOI: 10.2478/s11756-008-0025-z

Oospores of Chara tomentosa from Holocene sediments of Lake Zeribar (Iran) Andrzej Hutorowicz Department of Hydrobiology, Stanislaw Sakowicz Inland Fisheries Institute, ul. Oczapowskiego 10, PL-10-719 Olsztyn, Poland; e-mail: ahut@infish.com.pl

Abstract: Biometric measurements were performed on oospores of Chara tomentosa from Core 63-J from Lake Zeribar in Iran. The partially fossilized oospores examined did not differ significantly in dimensional measurements, number of ridges, or colour from oospores of modern specimens of C. tomentosa. Key words: Chara tomentosa; oospores; lake sediments; Lake Zeribar; Iran

Introduction Fossilized remnants of stoneworts (Characeae) attest to the earlier presence of an aquatic environment at the site at which they are found (Tobolski 2000). In lake sediments, the most commonly encountered fossils are deposited oospores and oosporangia of various stoneworts. Their characteristic morphology can be used to taxonomically identify the species of stoneworts occurring over time in a particular ecosystem (Krause 1986; Casanova 1991; Haas 1994). Identifying features are usually altered during the deposition and fossilization processes. Therefore, identification keys based on criteria for modern plants are often not reliable enough to ensure positive identification (Tobolski 2000). Research on stonewort oospores in lake-bottom sediments from the Holocene has been underway since the early 1900s, and several excellent treatises have been published (Krause 1986; Hass 1994). Nevertheless, positive identification of fossilized stonewort oospores still requires a great deal of material for comparison to be collected. Chara tomentosa Linnaeus 1753 is a cosmopolitan species. In Europe, C. tomentosa commonly occurs in lakes from Sweden and the Baltic coast to the Mediterranean Basin. C. tomentosa also occurs in north Africa and central Asia (Krause 1997; Ling et al. 2000). In central Europe, C. tomentosa grows in lakes and ponds, forming dense phytocoenoses most often in the zone of plants with floating leaves, just beyond the zone of rushes and reeds. In lakes with very clear water, C. tomentosa can also be found further out, in the zone of submerged plants (D˛ambska 1964; Tomaszewicz 1979). C. tomentosa can grow as deep as 30 m in the water (Hass 1994). Ongoing studies on cores from Lake Zeribar in Iran have shown that C. tomentosa oospores

can be present in great numbers in lake-bed sediments (Wasylikowa et al. 2006). This paper describes the biometrical and morphological variations in oospores of C. tomentosa from the Pleniglacial period from Lake Zeribar in northwest Iran.

Material and methods Oospores of Chara tomentosa were collected from Core 63-J of bottom sediments from Lake Zeribar in Iran (van Zeist & Wright 1963; Hutchinson & Cowgill 1963). Oospores from the core were selected for analysis and kept in hermetically sealed containers. Lake Zeribar is located in the Zagros Mts about 15 km from the border with Iraq, and 160 km northwest of Kermanshah (32◦ 32 N, 46◦ 07 E). The lake lies at an altitude of 1 300 m a.s.l., in a valley between mountains as high as 2 100 m (Stevens et al. 2001). The modern lake is about 5 km long and 1.5 km wide, and is completely surrounded by a marsh. Water level fluctuates between four and five meters, depending on the season (Wasylikowa 2005). A preliminary profile of the distribution of stonewort oospores in Core 63-J is presented elsewhere (Wasylikowa et al. in press). Oospores of C. tomentosa were found at core depths from 19.1 to 25.2 m, which corresponds to the time period from 16 200 to 25 500 years before the present (Wasylikowa & Walanus 2004) Oospores were identified using previously published descriptions of fossilized, partially fossilized and modern stonewort oospores (Krause 1986, 1997; Haas 1994; D˛ambska 1964; Hollerbach & Krasavina 1983). Altogether, more than 1 700 oospores were found in Core 63-J (Wasylikowa et al. in press). However, most of them were damaged. Biometric measurements were performed with the help of a stereomicroscope fitted with an image analyzer. Data recorded included longest polar axis (LPA), largest equatorial diameter (LED), isopolarity index (ISI = 100 LPA/LED), the width of the three adjacent fossules at the middle of the polar axis of the oospore and the number of

Brought to you of by Sciences | Instituto Federal Farroupilha IFFARROUPILHA c 2008 Institute of Botany, Slovak Academy Authenticated Download Date | 9/24/15 11:19 PM

Oospores of Chara tomentosa

163

1

100 mm

2

3

100 mm

4

100 mm

100 mm

Fig. 1. Lateral view of oospores of Chara tomentosa from Core 63-J from Lake Zeribar (Iran). Light microscopy (1–3), scanning electron microscopy (4).

ridges. Altogether, seventy-five well-preserved oospores were analyzed.

Results and discussion The oospores of Chara tomentosa examined in this study were large, with a narrow to wide ellipsoidal profile (Figs 1:1–4, Fig. 2). Some oospores were a little narrower at the apex than at the base. None of the oospores examined had a shoulder, the indentation in the lateral profile toward the apex of the oospore that is characteristic for other Chara species (Figs 1:1–4). The oospores were yellowish brown. They were very often empty, in which case they were transparent, but with well defined ridges. Oospore length (LPA) ranged from 795 to 1030 µm, with an average of 903 µm, and with most specimens falling between 860 and 980 µm in length (Fig. 3).

Equatorial diameter (LED) ranged from 500 to 655 µm, with an average of 572 µm, and with most specimens between 540 and 640 µm in diameter (Fig. 3). Isopolarity index ranged from 140 to 187, with an average of 158, and with most specimens having an isopolarity index of 150 to 170 (Fig. 3). The number of ridges ranged from 10 to 16, with an average of 13. The ridges were narrow and slightly wider toward the apex (Figs 4:1, 4:3–4). Fossules of equal width ran the entire length of the oospore. The width of the fossules at the equator ranged from 38 to 75 µm, with an average of 54 µm, and with most fossules having a width of 45 to 62 µm (Fig. 3). The fossa membrane was very finely granulated (Fig. 4:6). At the base of some specimens, the remnants of the cell wall of the ensheathing cell formed talon-shaped protrusions, sometimes joined together in a basket-like structure (Figs 1:3–4; Fig. 4:2). The basal pore was pentagonal and wide (Fig. 4:5).

Brought to you by | Instituto Federal Farroupilha IFFARROUPILHA Authenticated Download Date | 9/24/15 11:19 PM

A. Hutorowicz

164

Fig. 2. Correlation graph of length (LPA) versus equatorial diameter (LED) in seventy-five oospores of Chara tomentosa from Core 63-J from Lake Zeribar (Iran).

Fig. 3. Histograms of length (LPA), equatorial diameter (LED), isopolarity index (ISI) and width of fossa (F) in oospores of Chara tomentosa from Core 63-J from Lake Zeribar (Iran).

Oospores of modern specimens of C. tomentosa have dimensions similar to those of the oospores from Core 63-J (Migula 1909; D˛ambska 1964; Krause 1997). Most researchers have reported that oospore length ranges from 850 to 1050 µm, and equatorial diameter ranges from 600 to 700 µm (Migula 1909; D˛ambska

1964; Krause 1997). However, other researchers have reported somewhat lower values, with length ranging from 765 to 900 µm, and equatorial diameter ranging from 525 to 645 µm (Hollerbach & Krasavina 1983). The number of ridges in modern specimens is also similar to the number observed in the specimens from Lake


Oospores of Chara tomentosa

165

Fig. 4. Oospores of Chara tomentosa from Core 63-J from Lake Zeribar (Iran). Apical view (1, 4), basal view (2, 5), lateral view of the apical region (3), profile of the membrane in central part of oospore (6). Light microscopy (1,2), scanning electron microscopy (3–6).

Zeribar. In one report, the number of ridges ranged from 14 to 16 (Krause 1997). In another report, the number of ridges ranged from 13 to 14 (Hollerbach & Krasavina 1983). Modern specimens are also equally ellipsoidal, not flattened at the apex, almost always yellowish brown, and only very rarely black. The exterior wall of the oospore is thin, light yellow, and very delicately granulated. However, the granules may vary in size (Hollerbach & Krasavina 1983). The large variation in the dimensions of the oospores may be useful in determining changes in environmental conditions throughout the history of the lake. For example, oospores of Chara globularis Thuillier differ greatly in shape and size depending on whether they were collected from plants growing in lakes, peat bogs or ponds. The largest oospores were

found on plants growing in lakes, and the smallest on plants growing in ponds. Oospores from ponds also had the narrowest striations and the highest isopolarity indices (Boszke & Pelechaty 2006). Oospores of Chara aspera (Dech.) Willd. are longer in plants growing in freshwater than in plants growing in brackish water (Soulié-M¨ arsche 1991). The oospores of C. tomentosa differ from the oospores of other Chara species in their bigger size, their much lighter color, and their lack of a shoulder (Krause 1986). The most variable biometric parameter is the width of the fossa. Far less variation is observed in length and isopolarity index. In C. globularis, on the other hand, the most variable parameter is equatorial diameter, and the least variable parameter is the number of ridges (Boszke & Pelechaty 2006). SEM studies have shown that the external mor-


A. Hutorowicz

166 phology of the oospore wall is especially useful for identifying oospores of Nitella species (John & Moore 1987; Sakayama et al. 2005). This parameter is the least sensitive to environmental conditions (John & Moore 1987). The external morphology of the oospore wall may also prove useful in identifying Chara species, even though there is less variation in this parameter among Chara species than among Nitella species (Hollerbach & Krassavina 1983; Krause 1986). Acknowledgements This work has been carried out thanks to financial support by the State Committee for Scientific Research, Poland, grant No. 3 PO4F 089 23. References Boszke P. & Pelechaty M. 2006. Zmienno´s´ c morfologiczna oospor Chara fragilis Desv. w ró˙znych typach ekosystemów wodnych Wielkopolski (materialy Kolekcji Ramienic Polski profesor Izabeli D˛ambskiej). Ekologia i Technika 81: 118–122. Casanova M. 1991. An SEM study of developmental variation in oospore wall ornamentation of three Nitella species (Charophyta) in Australia. Phycologia 30: 237–242. D˛ambska I. 1964. Charophyta – Ramienice. Flora slodkowodna Polski. 13, Pa´ nstwowe Wydawnictwo Naukowe, 126 pp. Haas J.N. 1994. First identification key for charophyte oospores from central Europe. Eur. J. Phycol. 29: 227–235. Hollerbach M.M. & Krasavina L.K., 1983. Charavye Vodorosli – Charophyta. Oprodelitel Presnovodnych Vodoroslej SSSR. Izdatielstvo “Nauka”, Leningrad, 190 pp. Hutchinson G.E. & Cowgill U.W. 1963. Chemical examination of a core from Lake Zeribar, Iran. Science 140: 67–69. John D.M. & Moore J.A. 1987. An SEM study of the oospore of some Nitella species (Charales, Chlorophyta) with descriptions of wall ornamentation and an assessment of its taxonomic importance. Phycologia 26: 334–355.

Krause W. 1986. Zur Bestimmungsm¨ oglichkeit subfossiler Characeen-Oosporen an Beispielen aus Schweizer Seen. Vierteljahrsschrift der Naturforschenden Gesellschaft in Z¨ urrich 131: 295–313. Krause W. 1997. Charales (Charophycae). S¨ ußwasserflora vo Mitteleuropa. Band 18. Gustav Fischer, Jena, 202 pp. Ling Y.J., Xie S.L. & Langangen A. 2000. Charales of China. Nova Hedwigia 71: 69–94. Migula W. 1909. Kryptogamen-Flora von Deutschland, Deutsch¨ Osterreich und der Schweiz. Band II. Algen 2. Teil Rhodophyceae, Phaeiphyceae, Characeae. Verlag Friedrich von Zezschwitz, Gera, 383 pp. Sakayama H., Miyaji K., Nagumo T., Kato M., Hara Y. & Nozaki H. 2005. Taxonomic reexamination of 17 species of Nitella subgenus Tieffallenia (Charales, Charophyceae) based on internal morphology of the oospore wall and multiple DNA marker sequences. J. Phycol. 41: 195–211. Soulié-M¨ arche I. 1991. Charophytes as lacustrine biomarkers during the Quaternary in North Africa. J. Afri. Earth Sci. 12: 341–351. Stevens L.R., Wright H.E. Jr. & Ito E. 2001. Changes in seasonality of climate during the Late-glacial and Holocene at Lake Zeribar, Iran. The Holocene 11: 747–755. Tobolski K. 2000. Przewodnik do oznaczania torfów i osadów jeziornych. Pa´ nstwowe Wydawnictwo Naukowe, Warszawa, 508 pp. Tomaszewicz H. 1979. Ro´slinno´s´ c wodna i szuwarowa Polski. Wydawnictwo Uniwersytetu Warszawskiego, Warszawa, 324 pp. Wasylikowa K. & Walanus A. 2004. Timing of aquatic marshplant successions in different parts of Lake Zeribar, Iran, during the Late Glacial and Holocene. Acta Palaeobot. 44: 129– 140. Wasylikowa K. 2005. Palaeoecology of Lake Zeribar, Iran, in the Pleniglacial, Lateglacial and Holocene, reconstructed from plant macrofosils. The Holocene 15(5): 720–735. Wasylikowa K., Witkowski A., Walanus A., Hutorowicz A., Alexandrowicz S.W. & Langerat J.J. 2006. Palaeolimnology of Lake Zeribar, Iran, and its climatic implications. Quaternary Research 66: 477–493. van Zeist W. & Wright H. E. 1963. Preliminary pollen studies at Lake Zeribar, Zagros Mts, southwestern Iran. Science 140: 65–67. Received Aug. 31, 2006 Accepted Feb. 19, 2007
