Studies of life history of Gagea graeca (Liliaceae) based on morphological and molecular methods

Abstract

Background: We studied the life history of Gagea graeca (L.) A. Terracc. (sect. Anthericoides) by field surveys on the Greek island of Crete, including quantitative analyses of 405 individuals, estimation of resource allocation by measuring the nitrogen content of different plant organs, assessing seed set and recording genetic diversity via amplified fragment length polymorphism (AFLP) analyses. In contrast to most species of the genus G. graeca seems to be a short-lived perennial, developing several characters that are rather typical for annual plants.

Results: Although seed set varies largely, flowering plants produce many (68 ± 79) small, flattened seeds (mean weight 73 ± 22 µg) in comparison to a single bulbil. If measured as nitrogen content of the respective plant parts, investment in seeds (25%) is much higher than that in bulbils (4%). In addition, the threshold for flower formation (expressed as bulb size where 50% of the plants form the respective structure) is with 2.17 ± 0.05 mm lower than that for bulbils with 2.80 ± 0.16 mm. This is in accordance with AFLP analyses revealing predominantly sexual reproduction (only 9.1% of 110 investigated plants belonged to clones).

Conclusion: In the genus Gagea early, predominantly sexual reproduction seems to be characteristic for species from arid habitats, coupled with a low proportion of clonal plants.

Keywords: Amplified fragment length polymorphism (ALFP); Drought adaptation; Reproductive biology; Resource allocation; Seed set.

Fig. 1

a Distribution of Gagea graeca in the Mediterranean region (encircled regions). b Collecting sites for the four studied populations from the central part of the island of Crete (marked with an rectangle in a); map compiled using the geospatial conservation assessment tool GeoCAT (http://geocat.kew.org/)

Fig. 2

Growth sites for Gagea graeca. a, b Population I along a small gully in the phrygana of the Psilioritis Mts. c, d Population II at a temporarily wet fallow field. e, f Population III at former olive orchards, now invaded by holm oak, at a slope

Fig. 3

Morphology of Gagea graeca. a Strong flowering plant with two scapes and four basal leaves. b Closeup of a flower showing reddish veins (the color is even more pronounced at the outer side). c Longitudinal section through a flower, showing the blunt capsule. d Basal part of a flowering plant with one bulbil, showing the reddish tunics formed by the sheaths of basal leaves. e Three flowering plants showing variation in stolon length; the plant on the right comes close to the maximum. f Longitudinal section through a replacement bulb. Bar length indicates in a 1 cm, b–e 3 mm, f 2.5 mm

Fig. 4

Reproductive pattern of Gagea graeca, shown are cohorts of plants corresponding to classes of 0.25 mm diameter width of the replacement bulb (n = 405). a Proportions of plants forming flowers (black circles) and a basal bulbil (white circles, the latter are printed with a slight shift to the right to make overlaps with the black circles visible). Graphs were fitted against the equation y = 1/[1 + e^{−(x−xo)/b}] with xo as the threshold for the formation of the respective structure (indicated by a vertical dotted line). b Average numbers of basal bulbils (white circles) and flowers (black) per plant in the respective diameter classes. c Seed set. Bars for the latter two plots denote the standard error of means

Fig. 5

Seed set for Gagea graeca in dependence form the numbers of flowers (a); and the relation of capsules per flower (b). Most plants hat 1–3 flowers (these classes are represented by at least 40 plants each, black dots), whereas only eight plants had 4–7 flowers (white dots). Bars indicate the standard error of means

Fig. 6

Investment of carbon (a) and nitrogen (b) in different plant parts for three populations (I, II and IV) of Gagea graeca. Shown are mean ± SD of elementary contents (µg per mg dry weight) for bulbs (bulb, n = 3), seeds (seed, n = 6–10) and vegetative plant structures (veg, n = 3)

Fig. 7

Genetic diversity of two transects of Gagea graeca (populations I and II) comprising 27 and 28 pairs of plants, respectively. Grey rectangles without numbers represent plants with unique genotypes; white rectangles indicate plants belonging to clones which are numbered