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Plant Species Biology (2007) 22, 125­128

doi: 10.1111/j.1442-1984.2007.00184.x

NOTES AND COMMENTS

Sex ratios in populations of Geranium sylvaticum in European Russia
POLINA A. VOLKOVA,* VERA S. RUDAKOVA and ALEXEY B. SHIPUNOV *Moscow State University, Biological Department, Vorobyevy Gory, Moscow, 119899 Russia, Moscow Medicine Academy, Trubetskaya Street,8-2, Moscow, 119992 Russia, and College of Natural Resources, University of Idaho, Idaho 83844-1133, United States of America

Keywords: European Russia, Geranium, gynodioecy, sex ratio. Received 10 July 2006; accepted 15 February 2007

Introduction
Flowers of Geranium sylvaticum L. are normally hermaphroditic and have 10 stamens. Some flowers have reduced non-functional anthers or do not have anthers at all; these flowers are called female flowers. Flowers with 1­9 functional anthers are classified as intermediate (Asikainen & Mutikainen 2003). Such a reduction probably prevents self-fertilization and lets female flowers produce more seeds, or seeds with greater nutrient stores, which increases the population's fitness (Asikainen & Mutikainen 2003, 2005; Ramula & Mutikainen 2003). A negative correlation has been found between the frequency of female flowers and seed production of hermaphroditic flowers in G. sylvaticum populations (Asikainen & Mutikainen 2003). Given the importance of sex ratio to the reproductive biology of this species, this pattern warrants further investigation. Finnish researchers have investigated the frequency of female flowers in 23 Geranium sylvaticum populations in Finland (Asikainen & Mutikainen 2003). The proportion of female flowers in these populations varied from 0.4 to 27.2% (11.5% on average) and was apparently dependent on habitat conditions; female flowers are less frequent in southern populations (Asikainen & Mutikainen 2003). Low numbers of `intermediate' flowers were found in very low frequency (less then 1%) in less than half of the Southern Finland populations, and only one population had 42% of intermediate-type flowers. Northern populations, in contrast, showed higher frequencies of intermediate flowers. Sex ratio variation among populations may also be explained by ecological factors that affect the relative seed fitness of the two gender morphs (Asikainen & Mutikainen 2003).
Correspondence: Polina A. Volkova Email: avolkov@orc.ru

As G. sylvaticum is widely distributed in Europe and Asia, we decided to investigate other populations of this species to determine whether the latitudinal distribution pattern of flower type observed in Finland is a general pattern. We also attempted to check whether sex ratio variation between populations is caused by habitat conditions.

Materials and methods
The investigations were carried out during June and July 2003­2005 in the northern part of the Tver region (N 58°15, E 34°30; 564 plants from 21 populations, Fig. 1) and in the northern part of the Murmansk region on the Barents Sea shore (N 69°10, E 36°00; 274 plants from four populations, Fig. 1). During this project, we followed the ecological definition of populations, as described in Waples and Gaggiotti (2006). We counted the number of fertile stamens for one flower from each flowering plant in the population. It was important to investigate flower buds instead of open flowers because anthers easily drop from the stamen filaments in the latter stages of flower development and this could cause an erroneous count of fertile stamen number. In addition, we inferred some characteristics of habitat conditions (light intensity, moisture, soil acidity and degree of soil mineralization) from modified Ellenberg tables (Hill et al. 1999), using lists of the most frequent vascular plant species in the locality. The statistical analysis of our data was carried out in R statistical environment (R Development Core Team 2004). We used the standard deviation (SD) of the mean to show data variance around mean values.

Results
The regions investigated in the present study have obvious differences in the values of some edaphic factors

© 2007 The Authors Journal compilation © 2007 The Society for the Study of Species Biology


126 P. A. VOLKOVA ET AL. The proportion of `intermediate' flowers in the population varies from 9 to 84% in the Tver region (43 6% in average) and from 0 to 4% (1.5 1%) in the Murmansk region (Table 1).

Discussion
In general, our data on the sex ratio in different populations of G. sylvaticum in European Russia corresponds poorly with the published data of Asikainen and Mutikainen (2003) on Finnish populations. Female flowers were much rarer in our study than was reported by Asikainen and Mutikainen (2003) for southern Finland. The proportion of hermaphroditic flowers was much more lower in the temperate region than in the arctic region, which is contrary to Asikainen and Mutikainen's (2003) findings. The Murmansk region is the only area where our results resemble the Finnish data (Asikainen & Mutikainen 2003) with respect to the low frequency of `intermediate' flowers. These differences could perhaps be explained by the different sizes of the populations (the Russian populations investigated in the present study are much smaller than the Finnish populations) because it is known from other plant species that variance in sex ratio increases inversely with population size (Plantago maritima investigations by Nilsson & Agren 2006). We may also have encountered temporal (Agren & Willson 1991) or longitudinal variation in the frequency of female flowers in populations of G. sylvaticum. Finally, the bias in the sex ratio in the populations could be explained if the Finnish researchers examined open flowers instead of flower buds (some anthers can drop from the stamen filaments leading to inflated estimates of intermediate and female flowers). However, Eija Asikainen (pers. comm. 2006) stated that in their investigations all stamens were accurately counted several times during flowering. Thus, the geographical variation in female flower frequency in populations of G. sylvaticum seems to have more complex patterns than has been previously reported (Asikainen & Mutikainen 2003, 2005; Ramula & Mutikainen 2003). The frequency of female plants in gynodioecious populations may vary widely over relatively short distances (Couvet et al. 1990). Some stochastic processes could influence the sex ratio in small gynodioecious populations (Nilsson & Agren 2006). We hope that further investigations throughout the range of G. sylvaticum, with due attention to the stages of flower development, will provide further information on sex in G. sylvaticum populations.

Fig. 1 Map of the investigated area. Crosses mark the investigated populations: 1, Tver region; 2, Murmansk region.

calculated from the Ellenberg tables. We observed low soil mineralization in the Murmansk region (2.0­3.0 points on the Ellenberg tables) compared to medium or high mineralization in the Tver region (3.5­7.5 points). Soil was moderately acid in the Murmansk region (3.0­5.0) and weakly acid or neutral in the localities from the Tver region (5.0­7.5). We found no female flowers in any of the investigated populations in the Tver region; and we found only one female flower in the four investigated populations in the Murmansk region (Table 1). The proportion of hermaphroditic flowers in the temperate Tver region is lower on average (mean SD: 57 6%) than in the arctic Murmansk region (97 0.5%) (Table 1). The proportion of hermaphroditic flowers in the Tver region depends on edaphic factors: we found a significant positive association between the proportion of hermaphroditic flowers in the population and moisture (Multiple r-squared = 0.21, F = 5.18, P = 0.034; Fig. 2), and a significant negative association between the frequency of hermaphroditic flowers and soil pH (multiple r-squared = 0.35, F = 10.34, P = 0.005; Fig. 3).

Acknowledgments
All fieldwork was carried out during summer excursions of the Moscow South-West High School under Dr
Plant Species Biology 22, 125­128

© 2007 The Authors Journal compilation © 2007 The Society for the Study of Species Biology


SEX RA TIOS IN GERANIUM POPULA TIONS
Table 1 Frequency of plants of different sexes Population number 1 2 3 4 5 6 111 201 202 203 204 205 206 207 208 209 210 211 212 213 214 221 222 223 224 No. plants 6 18 20 16 18 40 17 26 36 28 59 14 31 18 9 8 61 33 28 23 61 108 108 41 18

127

Region Tver region

Female 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0) (0.9) (0) (0) (0)

No. plants of a given sex `Intermediate' Hermaphroditic 4 15 15 11 12 15 7 5 5 4 18 3 7 6 0 1 7 0 0 2 0 3 2 0 0 (66.7) (83.3) (75) (68.8) (66.7) (37.6) (41.2) (19.2) (13.9) (14.3) (30.5) (21.4) (22.6) (33.3) (0) (12.5) (11.5) (0) (0) (8.7) (0) (3.7) (1.9) (0) (0) 2 3 5 5 6 25 10 21 31 24 41 11 24 12 9 7 54 33 28 21 61 104 106 41 18 (33.3) (16.7) (25) (31.2) (33.3) (62.5) (58.8) (80.8) (86.1) (85.7) (69.5) (78.6) (77.4) (66.7) (100) (87.5) (88.5) (100) (100) (91.3) (100) (96.3) (98.1) (100) (100)

Murmansk region

Number of plants of a given sex (ratio of the number of plants of a given sex to the total plant number in the population [%]).

Fraction of hermaphroditic flowers (%)

Fraction of hermaphroditic flowers (%) 4.0 4.5 5.0 5.5 6.0 Moisture degress (Ellenberg points) 6.5

100

80

60

40

20

20

40

60

80

100

4

5 6 Soil pH (Ellenberg points)

7

Fig. 2 Correlation between the proportion of hermaphroditic flowers in the population and the moisture level in the Tver' region. The dashed line is a linear regression (y = 17x - 23.5).

Fig. 3 Correlation between the proportion of hermaphroditic flowers in the population and soil pH in the Tver' region. The dashed line is a linear regression (y =-14x + 152.5).

S. Glagolev. We thank O. Aleksandrova, N. Guryanova, E. Kost, O. Kostereva, O. Kudina, K. Markvichyova, D. Mordvinkin, E. Peskova and P. Tsesarskij for their essential help in the field and Cort Anderson for English improvement.
Plant Species Biology 22, 125­128

References
Agren J. & Willson M. F. (1991) Gender variation and sexual differences in reproductive characters and seed production in gynodioecious Geranium maculatum. American Journal of Botany 78: 470­480.

© 2007 The Authors Journal compilation © 2007 The Society for the Study of Species Biology


128 P. A. VOLKOVA ET AL.
Asikainen E. & Mutikainen P. (2003) Female frequency and relative fitness of females and hermaphrodites in gynodioecious Geranium sylvaticum (Geraniaceae). American Journal of Botany 90: 226­234. Asikainen E. & Mutikainen P. (2005) Preferences of pollinators and herbivores in gynodioecious Geranium sylvaticum. Annals of Botany 95: 879­886. Couvet D., Atlan A., Belhassen E., Gouyon P. H., Gliddon C. J. & Kjellberg F. (1990) Coevolution between two symbionts: the case of male-sterility in plants. In: Futuyma D. & Antonovics J. (eds). Oxford Surveys in Evolutionary Biology, Vol. 7. Oxford University Press, New York, pp. 225­249. Hill M. O., Mountford J. O., Roy D. B. & Bunce R. G. H. (1999) Ellenberg's indicator values for British plants. ECOFACT, Technical Annex. Vol. 2. Nilsson E. & Agren J. (2006) Population size, female fecundity, and sex ratio variation in gynodioecious Plantago maritima. Journal of Evolutionary Biology Online early. [Cited 14 May 2006.] Available from URL: http://www.blackwellsynergy.com/doi/abs/10.1111/j.1420-9101.2005.01045.x. Ramula S. & Mutikainen P. (2003) Sex allocation of females and hermaphrodites in the gynodioecious Geranium sylvaticum. Annals of Botany 92: 207­213. R Development Core Team (2004) R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna. Waples R. S. & Gaggiotti O. (2006) What is a population? An empirical evaluation of some genetic methods for identifying the number of gene pools and their degree of connectivity. Molecular Ecology 15: 1419­1439.

© 2007 The Authors Journal compilation © 2007 The Society for the Study of Species Biology

Plant Species Biology 22, 125­128